IPC/JEDEC-9704A 2012 - January Printed Circuit Assembly Strain Gage Test Guideline Supersedes IPC/JEDEC-9704A June 2005
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IPC/JEDEC-9704A ®
Printed Circuit Assembly Strain Gage Test Guideline
Developed by the JEDEC Reliability Test Methods for Packaged Devices Committee (JC-14.1) and the SMT Attachment Reliability Test Methods Task Group (6-10d) of the Product Reliability Committee (6-10) of IPC
Supersedes: IPC/JEDEC-9704 - June 2005
Users of this publication are encouraged to participate in the development of future revisions. Contact: IPC 3000 Lakeside Drive, Suite 309S Bannockburn, Illinois 60015-1219 Tel 847 615.7100 Fax 847 615.7105
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IPC/JEDEC-9704A
Acknowledgmentt Acknowledgmen Members of the JEDEC Reliability Test Methods for Packaged Devices Committee (JC-14.1) and the SMT Attachment Reliabili Reli ability ty Test Methods Task Task Group (6-10d) of the IPC Produ Product ct Reli Reliabili ability ty Commi Committee ttee (6-10) have worke worked d toge together ther to develop this document. We would like to thank them for their dedication to this effort. Any document involving a complex technology draws material from a vast number of sources. While the principal members of the SMT Attachment Reliability Test Methods Task Group are shown below, it is not possible to include all of those who assisted in the evolution of this standard. To each of them, the members of JEDEC and IPC extend their gratitude. Product Reliability Committee
JEDEC Reliability Test Methods for Packaged Devices Committee
SMT Attachment Reliability Test Methods Task Group
Chair Reza Ghaffarian, Ph.D. Jet Propulsion Laboratory
Chair Jack McCullen Intel Corporation
Chair Reza Ghaffarian, Ph.D. Jet Propulsion Laboratory
Technical Liaisons of the IPC Board of Directors
Dongkai Shangguan Flextronics International Shane Whiteside TTM Technologies SMT Attachment Reliability Test Methods Task Group
Neil Adams, Circuit Check Inc. Mudasir Ahmad, Cisco Systems Inc. Aileen Allen, Hewlett-Packard Company Michael Azarian, University of Maryland Anurag Bansal, Cisco Systems Inc.
Christopher Hunt, National Physical Laboratory
John M. Radman, Trace Laboratories - Denver
Anna Lifton, Cookson Electronics
Paul Reid, PWB Interconnect Solutions Inc.
Anne Lomonte, Draeger Medical Systems, Inc. Rachel Matthews, Vanguard EMS, Inc.
Elizabeth Benedetto, Hewlett-Packard Company
Alan McAllister, Intel Corporation
Trevor S. Bowers, Adtran Inc.
Keith Newman, Hewlett-Packard Company
Nicole Butel, Avago Technologies
David Nelson, Raytheon Company
Rosa Reinosa, Hewlett-Packard Company Martin Scionti, Raytheon Missile Systems Russell S. Shepherd, Microtek Laboratories Julie Silk, Agilent Technologies
Michael Paddack, Boeing Company
Mark Trahan, Texas Instruments Inc.
Deepak Pai, General Dynamics Info. Sys., Inc
Vasu Vasudevan, Intel Corporation
Glenn Dody, Dody Consulting Harold Ellison, Quantum Corporation
Satish Parupalli, Intel Corporation
Melissa Warner, Itron Inc.
Dennis Fritz, MacDermid, Inc.
John H. Quick, IBM Corporation
Phil Geng, Intel Corporation
Jagadeesh Radhakrishnan, Intel Corporation
Anthony Wong, National Semiconductor Corp.
Beverley Christian, Research In Motion Limited
David D. Hillman, Rockwell Collins
Bill R. Vuono, Raytheon Company
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Table of Contents 1
SCOPE ........................................................................ 1
4
DAT DA TA ANAL ANALYSI YSIS S AND REPO REPORTIN RTING G ..................... 15
1.1
Purpose Purp ose ......... .................. ................... .................... .................... ................... ................. ........ 1
4.1
Analys Ana lysis is Req Requir uireme ements nts ........ ............ ........ ........ ........ ........ ........ ........ ...... .. 15
1.2
Background Backg round .......... ................... ................... .................... .................... ................... ......... 1
4.2
Test Freq Frequency uency .......... .................... ................... ................... .................... ............ .. 16
1.3
Term ermss and Defi Definit nition ionss .... ........ ........ ........ ........ ........ ........ ........ ........ ........ ...... 3
4.3
Strain Str ain Gag Gagee Test Rep Report ort Temp emplat latee .... ........ ........ ........ ........ .... 16
1.3.1
Area Array Compo Component nent ......... .................. ................... .................... ............ 3
4.3.1
Abstract Abstr act ................ .......................... .................... ................... ................... ................. ....... 16
1.3.2
Component Comp onent ......... ................... .................... ................... ................... .................... ............ 3
4.3.2
Introduct Intr oduction ion ............. ....................... .................... ................... ................... .............. .... 16
1.3.3
Interconn Inte rconnect ect .......... ................... ................... .................... .................... ................... ......... 3
4.3.3
Test Appar Apparatus atus and Setup ................. ........................... ................. ....... 16
1.3.4
Non-Area Non-A rea Array Compo Component nent ....................... ............................... ........ 3
4.3.4
Results Resul ts ............. ....................... .................... ................... ................... .................... ............ .. 16
1.3.5 1.3 .5
Diagon Dia gonal al Str Strain ain (εd) .......... ................... ................... .................... ................ ...... 3
1.3.6
Microstra Micr ostrain in ................. ........................... .................... ................... ................... ............. ... 3
1.3.7 1.3 .7
Princi Pri ncipal pal Str Strain ain (eP) .......... .................... ................... ................... ................ ...... 3
1.3.8
Rosette Roset te .......... ................... ................... .................... .................... ................... ................. ........ 3
1.3.9
Pad Crate Cratering ring .................... ............................. ................... .................... ................ ...... 3
5
CONC CO NCLU LUSI SION ONS S ...................................................... 17
6
FUTU FU TURE RE ST STUD UDIE IES S .................................................. 17
APPENDIX APPE NDIX A
ICT DESI DESIGN GN CONSI CONSIDERA DERATION TIONS S ....... 18
APPE AP PEND NDIX IX B
ACRO AC RONY NYMS MS ........................................ 21
1.3.10 Stac Stacked ked Rosette Rosette Strain Strain Gage ........................... ............................... .... 3 Figures
1.3.11 1.3.1 1 Stra Strain in .......... .................... .................... ................... ................... .................... ................... ......... 3 1.3.12 Stra Strain in Guidance Guidance ......... ................... .................... ................... ................... ............. ... 3
Figure Fig ure 1-1
Examples Exampl es of of Solder Solder Joi Joint nt Damag Damage e (top: (top: pad pad cratering, crater ing, bottom left: bulk solder joint failu failure, re, bottom right: solder solder interfacial interfacial fracture) .......... ............ 2
Figure Figur e 1-2
Area Array Compo Component nent ............. ....................... ................... .............. ..... 3
Figure Fig ure 1-3
Diagonal Diagon al strai strain n metri metric c is the the maxim maximum um of of e2 or e4, whichever strain is greater along these two directions, directions, relative relative to the component. component. ....... 3
Figure Fig ure 3-1
Example Exampl e Board Board Ass Assemb embly ly Proce Process ss Steps Steps for Strain Measurement Measurement ......... ................... ................... ................... ............. ... 5
Figure Fig ure 3-2
Example Exampl e Syste System m Asse Assembl mbly y Proces Process s Steps Steps for Strai Strain n Measur Measurement ement ......... ................... ................... ................. ........ 5
Figure Fig ure 3-3
PCA wit with h SMT Com Compon ponent ents s Only Only (Afte (Afterr SMT SMT Reflow) .............................................................. 6
Figure Fig ure 3-4
PCA wit with h Both Both SMT SMT and and Thr Throug ough-H h-Hole ole Components Compon ents (After Wave Solder) Solder) ......... ................... ............ 7
Figure Fig ure 3-5 3-5
ICT Fixtu Fixture re Strai Strain n Gage Gage Test Test Setup Setup ........... ............... ...... .. 7
Figure Figur e 3-6
Stacked Stacke d Rosett Rosette e Strai Strain n Gage .......... ................... ................. ........ 9
Figure Fig ure 3-7 3-7
Strain Str ain Gage Gage Dime Dimensi nsions ons (Inc (Inches hes)) .... ........ ........ ........ ........ .... 9
Figure Fig ure 3-8
Recommend Recomm ended ed Gage Gage Pla Placem cement ent for BGA Components Compon ents .......... ................... ................... .................... ................... ............ ... 10
1.3.13 Stra Strain in Metric Metric ......... ................... .................... .................... ................... ................. ........ 3 1.3.14 Stra Strain-Ra in-Rate te ......... ................... .................... ................... ................... .................... ............ 3 1.3.15 Stra Strain in Gage .......... .................... ................... ................... .................... ................... ......... 3 1.3.16 Stra Strain in Gage Element Element ........................... .................................... ................. ........ 4 1.4 2
Revisi Rev ision on Lev Level el Cha Change ngess ........ ............ ........ ........ ........ ........ ........ ........ ...... .. 4 .................. ................... .................. ........ 4 APPLI AP PLICAB CABLE LE DOC DOCUME UMENTS NTS .........
2.1
IPC (No (Norm rmati ative) ve) .......... .............. ........ ........ ........ ........ ........ ........ ........ ........ ........ .... 4
2.2
ASTM AST M (Inf (Inform ormati ative) ve) .... ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ .... 4
2.3
Other Oth er Pub Public licati ations ons (I (Info nform rmati ative) ve) .... ........ ........ ........ ........ ........ ...... 4
3
GENERAL GENE RAL REQU REQUIREM IREMENTS ENTS/GUI /GUIDELI DELINES NES ............ 4
3.1
Boards Boar ds .......... ................... ................... .................... .................... ................... ................. ........ 6
3.2
Compon Com ponent entss and Dev Device icess .......... .............. ........ ........ ........ ........ ........ ...... .. 8
3.2.1
Area Array Compo Components nents .............. ........................ .................... .............. .... 8
3.2.2
Non-Area Non-A rea Array Compo Components nents ......... ................... .................... ............ 8
3.3
Strain Str ain Gag Gagee .... ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ...... .. 9
3.3.1 3.3 .1
Strain Gage Strain Gage Plac Placeme ement nt of Are Areaa Arra Array y Component Comp onentss ......... ................... ................... ................... .................... ................. ....... 10
Figure Fig ure 3-9
Interfe Inte rferen rence ce Due Due to BGA BGA Pus Pushdo hdown wn Block Block .... 11
Figure Figur e 3-10
Interference Interfe rence Due to ICT ICT Probe Probe ......... .................. .............. ..... 11 11
3.3.2
Strain Stra in Gage Gage Place Placement ment for Non-Ar Non-Area ea Arra Array y Componentss ......... Component ................... ................... ................... .................... ................. ....... 12
Figure Figur e 3-11 3-11
Centroid of Gage Centroid Gage Placeme Placement nt Above Corner Land Pad .......... ................... ................... .................... ................... ................. ........ 12
3.4
Gagee Att Gag Attach achmen mentt .... ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ....... ... 12
Figure Figur e 3-12 3-12
3.5
Lead Wi Wires res ......... ................... .................... ................... ................... ................... ......... 13
Component Removal Component Removal to Facilitate Facilitate Gage Placement ....................................................... 12
3.6
Measur Mea sureme ement nt Equ Equipm ipment ent ...... .......... ........ ........ ........ ........ ........ ........ ...... 14
Figure Figur e 3-13
Uni-Axial Strain Uni-Axial Strain Gage Gage Placeme Placement nt for MLCC MLCC packages (within 1.0 mm of solder fillets) ...... 12
3.7
Measurem Meas urement ent Calib Calibrati ration on .......... .................... ................... ............... ...... 14
Figure Figur e 3-14 3-14
Lead Wire Routin Routing g Example Example ......... ................... ................. ....... 13
3.8
Manual Manu al Simu Simulati lation on .......... .................... .................... ................... ............... ...... 14
Figure Figur e 3-15
Example Exampl e Gage Gage Correlatio Correlation n Tool Tool ......... ................... ............ .. 14
3.9
Strain Str ain Met Metric ric ......... ............. ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ...... 15 15
Figure Fig ure 4-1 4-1
Time Ti me Histo History ry of the the Strai Strain n Limit Limit Crite Criteria ria ......... ......... 15
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Figure A-1
Illustration of Suppo Illustration Support rt ‘‘ska ‘‘skate’’ te’’ when a UUT’s Support is Overloaded with Upward Pressure, Causing it to Collide with a Compo Component. nent. .......... ................... ................... ................... ............ ... 18
Figure Fig ure A-2
Illustrati Illustr ation on of of UUT Sup Suppor portt Area Areas s and Keep-out Areas Areas aroun around da BGA component component ......... .................. ................... .................... ................. ....... 19
Figure Fig ure A-3
Illustrati Illustr ation on of of Compon Component ent to to Suppo Support rt Clearance and Proper Support Alignment ........................................................ 20
Tables Table 4-1
vi
Example Strain Example Strain Repor Reportt for a Strain Strain Gaged Component that went through Various Handling Handl ing and Assembly Processes Processes ......... .................. ......... 17
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Printed Circuit Assembly Strain Gage Test Guideline 1 SC SCOP OPE E
This document is meant to be used as a methodology for strain gage placement and subsequent testing of Printed Circuit Assemblies (PCAs) using strain gages. The method describes specific guidelines for strain gage testing of PCAs during the printed board manufacturing process, including assembly, test, system integration, and other types of operations that may induce board flexure. The sugge suggested sted procedure procedure enabl enables es print printed ed board assemblers assemblers to condu conduct ct stra strain in gage testing independently independently,, and provi provides des a quantitative method for measuring board flexure, and assessing risk levels. The topics covered include: • Test setup and equipment requirements • Strain measurement • Report format This document assumes the methodology is being used to test a surface mount device such as Ball Grid Array (BGA), Small Outline Outli ne Packa Package ge (SOP) (SOP),, Chip Scale (Siz (Size) e) Packa Package ge (CSP) (CSP),, and area area-arra -array y surf surface ace mount (SMT) conne connectors ctors/sock /sockets. ets. In certain cases, the described test approach may be used for non-area-array discrete (SMT) devices such as capacitors or resistors. 1.1 Pur Purpose pose Strai Strain n gage testing testing allows objective objective analysis analysis of the strain and strain rate levels levels to which a surf surface ace mount
component may be subjected during PCA assembly, test, and operation. Characterization of worst-case PCA strain is critical due to the susceptibility of component interconnects to strain-induced failures. Excessive strain can result in various failure modes for different solder alloys, package types, surface finishes, or laminate materials. Such failures include solder ball cracking, trace damage, laminate related adhesive failure (pad lifting) or cohesive failure (pad cratering) and package substrate cracking (see Figure 1-1). Board flexure control using strain gage meas measurem urement ent has prove proven n benefi beneficial cial to the electronics electronics industry industry, and continues to gain acceptance as a method to identify and improve manufacturing operations that can pose a high risk for interconnect damage. However, with the rapid transition to lead-free assembly technology, increased interconnect densities, and new laminate materials, the potential for flexure-induced damage has increased. Many board assemblers are now required to operate under strain levels specified by their customers or component suppliers. 1.2 Backgr Background ound
As strain measurement technology has matured, different methodologies have developed. Variations in strain gage methodology inhibit reliable data collection and prevent data comparison across the industry. This document provides a standardized set of guidelines to address variations in gage mounting, gage placement, experiment design, data acquisition system variables, and strain metrics. PCA strain measurement includes application of strain gages to the printed board near specified components, followed by subjecting the instrumented board to various test, assembly, and handling operations. Steps which exceed strain limits are deemed excessive and are identified so that corrective actions can be made. Strain limits may come from the customer, component supplier or internal best known practices. Examples of strain measurement criteria are shown in the www.ipc.org/ IPC-WP-011 white paper. By identifying areas sensitive to manufacturing variation, strain gage testing provides insight into the effects of a production ramp. Strain gage measurements become the baseline for future process improvement activities, and quantify the effectiveness of adjustments. Manufacturing steps that are typically characterized are listed below: 1. SMT assembly assembly process: process: • Printed board depanelization processes • All manual handling processes • All rework and retouch processes • Connector installation • Component installation 1
IPC/JEDEC-9704A
January 2012
Solder Ball
IPC-9704a-1-01
Figure 1-1 Examp Examples les of Solder Joint Damage Damage (top: pad cratering, cratering, bottom left: bulk solder solder joint failure, bottom right: solder interfacial fracture)
2. Prin Printed ted board test proce processes: sses: • In-Circuit Test (ICT), or equivalent ‘‘shorts and opens’’ type test • Board Functional Test (BFT), or equivalent functional test 3. Mechanical assembly: assembly: • Heat sink assembly • Printed board support/stiffener assembly • System board integration, or system assembly • Peripheral Component Interconnect (PCI) or daughter card installation • Dual In-line Memory Module (DIMM) installation 4. Ship Shipping ping and Handling Handling Assembly processes for different printed boards and assemblers vary. Tests such as ICT and BFT are referred to generically in this document; nomenclature can vary at different manufacturing sites. In such cases, apply the same requirements to the equivalent test processes. However, the goal is to characterize all assembly steps involving mechanical loading. Do not constrain testing to the steps listed above, or only to perceived high risk areas. The data from these tests can serve as a baseline for future reference.
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1.3 Terms and and Definitions The definition definition of all terms used herein shall herein shall be be in accordance with IPC-T-50 and as defined
below. A component component that has terminations terminations arranged in a grid on the bottom of the package and contained within the component outline (See Figure 1-2). 1.3.1 Area Array Array Component Component
Any device or mechanical interconnect interconnect structure which is affixed to the printed circuit board. 1.3.2 Compone Component nt
Conductive element used for elect Conductive electrical rical interconnecinterconnection, e.g., solder ball, lead, etc. 1.3.3 Interco Interconnect nnect
1.3.4 1.3. 4 Non-Ar Non-Area ea Arra Array y Compo Component nent A comp componen onentt that has term termina ination tionss
arranged around the periphery of the package in either a leaded or leadless configuration. This includes components with end-cap terminations such as chip capacitors or resistors. IPC-9704a-1-02
1.3.5 1.3 .5 Diag Diagonal onal Strain Strain ( εd )
The directional directional strain aligned aligned with e 2 of the the strain str ain gag gagee or ort orthog hogona onall to thi thiss dir direct ection ion,, e 4 (where (where e4 = e1 + e3 - e2) whichever is greater:
Figure Figu re 1-2 Are Area a Array Array Compone Component nt
εd = Max ( | e2 |, | e1 + e3 - e2 | )
e4
as shown in Figure 1-3 1.3.6 Micros Microstrain train
e1
e2 e3
Dimensionless unit, 106 x (change in length) ÷ (original
length).
e4 The maximum maximum and mini minimum mum normal normal strains in a plane, always perpendicular to each other and oriented in directions for which the shear strains are zero. 1.3.7 Princip Principal al Strain (eP )
e p p =
e 1 + e 3 1 (e 1 − e 2)2 + ( e 2 − e 3)2 ± 2 √2
√
IPC-9704a-1-03
Strain gage cont Strain containin aining g two or more independent independent grids for making measurements of strain along each of their axes about a common point. 1.3.8 Rosette
Figure 1-3 Diagona Diagonall strain strain metric metric is the maximum of e2 or e4, whichever strain is greaterr along these two direct greate directions, ions, relative to the component.
The formation formation of a cohes cohesive ive dielectri dielectricc crack or fracture underneath the pad of a surface mount component. 1.3.9 Pad Cratering Cratering
1.3.10 Stacked Rosette Rosette Strain Gage Strai Strain n gage rosette constructe constructed d of grid gridss stacked one above the other about a com-
mon point. 1.3.11 Strain
Dimensionless unit, (change in length) ÷ (original (original length).
1.3.12 Strain Guidance Guidance The limit for the magnitude magnitude of a chose chosen n strain metric. metric.
The defined strain parameter parameter sele selected cted as a crit critical ical measuremen measurementt crit criterio erion. n. Diago Diagonal nal strain and principal strain are two possible strain metrics. 1.3.13 Strain Metric Metric
1.3.14 StrainStrain-Rate Rate
Changee in stra Chang strain in divided by the time interval interval during which this change is measured. measured.
Planar metallic foil pattern pattern that is adhered to an underlying surface and exhibits a change in resistance when subjected to a strain. 1.3.15 Strain Gage
3
IPC/JEDEC-9704A
January 2012
1.3.16 Strain Gage Gage Element Sensi Sensing ng area of strain gage defined by the serpentine serpentine metallic metallic grid pattern. 1.4 Rev Revisio ision n Lev Level el Chan Changes ges Chang Changes es that were incorporate incorporated d into the curre current nt revi revision sion of this standard standard are indicated indicated
throughout by gray shading of the relevant subsection(s). Changes to a figure or table are indicated by gray shading of the figure caption or table header. The following sections have been removed from this document revision: • 1.4, Future Studies • 3.8, Manual Simulation, paragraphs 8 and 9 referring to optional recommendations for simulating in-process handling. • 3.9, Shipping Package Test (now covered in IPC-9703). • Appendix A (Strain Limits) and appendix B (Reference for Rate Limited Guidance), both of which have been transferred to the IPC-WP-011 white paper for revision (www.ipc.org/IPC-WP-011) . 2 APPLIC APPLICABLE ABLE DOCUMENT DOCUMENTS S
The following normative documents are applicable and constitute a part of this specification to the extent specified herein. Subsequent issues of, or amendments to, these documents will become a part of this specification. Informative documents listed list ed below are for reference reference only only.. Docum Documents ents are grou grouped ped under categories categories as IPC, Joint Elect Electron ron Device Engin Engineeri eering ng Council (JEDEC), American Society for Testing and Materials (ASTM) and others depending on the source. 2.1 IPC (Normati (Normative) ve)1
IPC-T-50 Te Terms rms and Definitions for Interconnecting and Packaging Electronic Circuits IPC-D-279
Design Guidelines for Reliable Surface Mount Technology Technology Printed Board Assemblies Assemblies
IPC-7095
Design and Assembly Assembly Process Implementation Implementation for BGAs
IPC-9701
Performance Test Test Methods and Qualification Requirements for Surface Mount Solder Attachments Attachments
IPC/JEDEC-9702
Monotonic Bend Characterization Characterization of Board-Level Interconnects Interconnects
IPC/JEDEC-9703
Mechanical Shock Test Test Guidelines for Solder Joint Reliability
IPC/JEDEC-9707
Spherical Bend Test Test Method for Characterization of Board Level Interconnects
IPC-9708
Test Te st Methods for Characterization of Printed Board Assembly Pad Cratering
2.2 ASTM (Informa (Informative) tive)2
ASTM E1561-93
(Reaffi (Reaf firmed rmed 2003) Standard Practices for Analysis Analysis of Strain Gage Rosette Data
2.3 Other Publications Publications (Informativ (Informative) e)
Code of Practice, for installation of electrical resistance strain gauges, British Society of Strain Measurement
3
IPC-WP-011 Guidance for Strain Gage Limits for Printed Circuit Assemblies 4 3 GENERA GENERAL L REQUIREMENTS/GUI REQUIREMENTS/GUIDELINES DELINES
Figure 3-1 and Figure 3-2 illustrate examples of process steps where strain gage measurements are recommended. Figure 3-1 shows the steps for printed circuit assembly and Figure 3-2 for system assembly. Example manufacturing assembly and test steps where strain measurements should typically be taken are depicted by the strain measurement icon in Figure 3-1 and Figure 3-2. Multiple iterations or actuations of each process step can help characterize the associated process variance. This can also provide insight into situations where there is complex bending. 1. 2. 3. 4.
4
www.ipc.org www.astm.org www.bssm.org www.ipc.org/IPC-WP-011
January 2012
IPC/JEDEC-9704A
= Strain Measurement
Wave Solder
DIMMs etc.
Post-SMT
ICT #1
Board Assembly
CPU
CPU
HS
HS
ICT #2
HS
Packaging
Functional Test Disassembly
HS
MEM
MEM
Functional Test
Functional Test Preparation
Component Hardware Assembly IPC-9704a-3-01
Figure 3-1 Examp Example le Board Assembly Assembly Process Process Steps for for Strain Measurement Measurement
CPU
HS MEM MEM
System Board Assembly = Strain Measurement
MEM
PC Packaging
PC System Assembly
IPC-9704a-3-02
Figure 3-2 Examp Example le System Assembly Assembly Process Process Steps for Strain Strain Measurement Measurement
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Due to the limited mechanical strain applied prior to SMT reflow, reflow, and more importantly because solder joints are formed only after reflow, strain characterization is required only for operations following SMT reflow. 3.1 Boar Boards ds
Typically, a minimum of two test boards are instrumented. They are not required to be electrically functional but must mechanically represent the latest design. At a minimum, evaluate the following two board types: • Printed boards with SMT components only (after SMT reflow) • Printed boards with both SMT and through-hole components (after wave solder) These are the minimum requirements. Characterization of the system assembly process might require additional test boards. If a device under test is strained to a point where damage may have occurred, the system should be evaluated to ensure that accurate data can still be assessed using this test board. The first instrumented printed board should reflect a printed circuit assembly (PCA) that has been through SMT reflow, just prior to wave solder. An example is shown in Figure 3-3. At this stage, the board contains only SMT components. As can be seen in Figure 3-3, appropriate wire management is important for these boards. Bundling and securing the wires with heat resistant tape or ties is important when preparing these boards. The wires should be run between components, where they will not interfere with any process steps. The objective at this stage is to characterize the strain/strain rate during manual handling, insertion/removal of connectors and other through-hole components, and any electrical testing conducted prior to wave solder. This printed board should not be used for the characterization of assembly steps after wave solder.
Example gage location
Wires bundled and secured
9704a-3-03
Figure 3-3 3-3
PCA with with SMT Components Components Only Only (After SMT SMT Reflow)
The second instrumented printed board should be similar to PCAs that have completed wave solder. An example is shown in Figure 3-4. As with the previous board (Figure 3-3), appropriate wire management practices should be followed. This printed board contains all SMT and through-hole components and is used to characterize all assembly steps after final reflow including (where applicable): • Depanelization/r Depanelization/routing outing
• Daughter card insertion/removal
• Board support/stiffener assembly
• Heat sink attachment
• Final system assembly
• Test operations (ICT, BFT)
• PCI card insertion/removal
• BGA and through-hole component rework
• DIMM module insertion/removal 6
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Wires bundled and secured
Example gage location
9704a-3-04
Figure 3-4 PCA with with Both SMT and Through-Hole Through-Hole Components Components (After (After Wave Solder) Solder)
Although ICT and BFT are typical high strain/strain rate operations, damage is possible in any other step. A typical ICT strain gage test setup is illustrated in Figure 3-5.
Wires bundled and secured away from hold-down posts
9705a-3-05
Figure 3-5 3-5
ICT Fixture Fixture Strain Strain Gage Test Test Setup Setup
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All assembly steps should be characterized. Attention should also be paid to processes where mechanical fixtures are used, e.g., support fixtures, press fit fixtures, thumbscrew fixtures, etc. Where racks or trays are used, process steps such as storage and board transfer, should also be considered. It is strongly recommended that any manual handling between assembly steps, with or without fixtures, be characterized. If the manual handling steps are similar, combining the handling test into one test run, representative of worst-case handling, is acceptable. Details of this manual handling simulation must be documented in the test report. Simulations should also be conducted to quantify the associated variability. There may be unique manufacturing processes that require alternative configurations. For example, through-hole components typically require wave solder. Wave solder conventio conve ntionally nally follows follows conve convectio ction n reflow (one or two passes depending depending on board layou layout). t). However, However, a PCA could have inductor coils manually inserted before SMT reflow and not require wave solder. In cases where assembly characterization prior to wave solder is required, the test board shall shall be mechanically representative of boards prior to SMT reflow. In such instances, alternative set-ups are acceptable as long as all mechanical loading characterization requirements are met. The following components must be also present on the printed board: • Components of large physical size and/or mass • Components which mechanically constrain the printed board, e.g., bus bars, long connectors, etc. It is recommended that test boards be inspected for excessive warpage prior to instrumentation. Another possible consideration would be the effect of solder aging, i.e., solder joints on instrumented test boards that would have aged significantly longer than production boards. This should be considered when interpreting the results. 3.2 Comp Componen onents ts and Devi Devices ces The supplier supplier and user user shall agree on components that should be strain gaged and tested. shall agree
3.2.1 and 3.2.2 list recommendations for strain gage testing. It is recom recommend mended ed that any area array array device with a packa package ge body size equal to or larger than 27 x 27 mm or finer pitch components (0.8 mm pitch and below) with body size > 10 mm should be evaluated. If there are several fine pitch components, then, at a minimum, the three worst case locations should be tested based on engineering judgment, history of damage, or finite element analysis. 3.2.1 Area Array Array Components Components
The above represents one of the methods that may be employed as a criterion for characterization. Alternative criteria to determine strain gage placement include observed failure locations, historical failure rates, finite element analysis, assembly/ test fixture configuration, printed board design, and BGA package design. Printed board and package design considerations include geometry, materials, and configuration. Failure locations may be identified using dye (Dykem® or equivalent) penetration and component removal (‘‘dye-and-pry’’) techniques. For printed boards with a large number of BGA components (i.e., six or above) it is acceptable to rely first on a Finite Element Analysis (FEA) model, or other analytical and computation methods, to predict the areas of highest risk for gage location. However, if initial testing identifies areas of high strain, this should be followed up with more comprehensive testing CAUTION: Where such methods are employed, it is important to recognize that one may not fully in the area of concern. CAUTION: Where understand all the loads that will be applied, to all locations, at all loading operations. In all cases, it is recommended that the four package corners be strain gaged unless space constraints make this impossible. For CPU sockets, strain gages should be placed in proximity to corner solder joints of the BGA, so that the perpendicular grids of the tri-axial strain gage are parallel to the solder joint rows/columns. Differences between socket designs make consistent strain gage placement impractical. In general, strain gages will be placed between 6 mm and 10 mm from the BGA corner solder joints. Strain gages should only be placed at customer or vendor specified locations and orientations when measurements are being directly compared to customer or vendor specified strain guidance. The interconnect interconnectss in non-area array components components with smal smaller ler solder joints and stif stiff f bodies (i.e., Multilayer Ceramic Capacitor (MLCC)) are also susceptible to strain induced solder joint failures. By evaluating the strain generated during these processes, and ensuring they remain within acceptable limits, failures such as solder joint cracking, device fracture, pad lifting, pad cratering, and printed board conductor damage can be significantly minimized/eliminated. See the www.ipc.org/IPC-WP-011 www.ipc.org/IPC-WP-011 IPC white paper for additional information. 3.2.2 Non-Are Non-Area a Array Components Components
Selection of components on which to place gages should be evaluated on a case-by-case basis. MLCC packages (1210 size and larger) on thin boards (< 2.36 mm [0.093 in] thick) are most susceptible and should be considered for measurement.
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Details of the recommended strain strain gage are
as follows: • Three elem element ent stac stacked ked rect rectangul angular ar (0/45 (0/45/90) /90) rose rosette tte strai strain n gage • 1.0 to 2.0 mm2, nominal, gage sensor size • 120 or 350 Ω strain gages • Lead wire attach pads located at or lead wires attached on one side of strain gage Examples of such gages are illustrated in Figure 3-6 and Figure 3-7. The gage length should be as small as possible to minimize effects of non-uniform PCA strain gradients. Howeverr, str eve strain ain gages sho should uld be lar large ge eno enough ugh so tha thatt sma small ll features such as conductors and vias do not affect the strain reading.
IPC-9704a-3-06
Figure 3-6 Stack Stacked ed Rosette Rosette Strain Gage
IPC-9704a-3-07
Figure 3-7 3-7
Strain Gage Dimensio Dimensions ns (Inches) (Inches)
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For strain measurements at varying temperatures, the Coefficient of Thermal Expansion (CTE) of the strain gage is not critical so long as the gage factor is stable in the temperature range. However, if this is not the case, the CTE of the strain gage should be matched to the printed board substrate. Strain gages with or without pre-attached lead wires can be used. Selection should be based on preference and specific applications. Strain gages with pre-attached lead wires have the advantage of not requiring lead wire soldering, but it can be more difficult to maintain a high quality bond line during strain gage attachment. Lead wires can be re-soldered but the bond line cannot be re-done. Conversely, manually soldered lead wires could result in electrical shorts. Lead wire soldering is best performed under a 20 - 50X optical inspection microscope. Local bending near components will create variations in gage readings. For this reason gage placement must be precise. Wherever feasible the gages should be placed as described below. If the preferred location cannot be used, then strain guidance developed using the preferred location is not applicable. In this case, additional risk evaluation methods (i.e., destructive failure analysis) should be used in addition to strain monitoring in the alternate gage location. 3.3.1 3.3. 1 Str Strain ain Gage Pla Placem cement ent of Are Area a Arr Array ay
Unless a dif Unless differe ferent nt placement placement is agreed agre ed upon between between user and sup supplie plier, r, the preferred placement is recommended. Components
The pre prefer ferred red gage pla placem cement ent for gag gages es is to have strain gages, on the surface of the PCA, on all four corners of the selected component, with the centers of the rosette (not the rosette backing backi ng matr matrix) ix) located at the inte intersect rsection ion of lines offset from the package edge 3.56 ± 0.25 mm [0.14 ± 0.01 in], as shown in Figure 3-8. To ass assess ess str strain ain ris risk k on are area-a a-arra rray y soc socket kets, s, gages gag es sho should uld be pla placed ced rel relati ative ve to the sol solder der joint interconnects, rather than the plastic housing.
e3
e2
9704a-3-08 e1 Grid strains e1 and e3 in Figure 3-8 should be oriented orien ted parallel to the edges of the package. Figure 3-8 Recom Recommended mended Gage Gage Placement Placement for for BGA Components Components Grid strain e2 in Figure 3-8 should be oriented diagonally away from package, with respect to the edges of the package. The consistent and precise placement of gages is critical to correlation of data between test location and samples.
The distance between the gage and the BGA components might vary at each corner due to varying constraints. In such instances, gages should be placed as close to the preferred placement as possible. This information should be indicated in the test report, including photographic documentation. Gage placement should be precise and consistent. In the event that another component, hole, or other obstruction interferes with the preferred placement, a single strategy should be employed as an alternative. Examples are discussed in the following paragraphs. There may be situations where strain gages are not necessary on all corners of a device, such as when two or more devices are immediately adjacent or banked. In such instances, employ analytical techniques or computational models to identify the locations of the highest strain, thereby reducing the number of required strain gages. All supporting assumptions and analysis must be clearly documented in the test report. It is recommended to provide a keepout area around components, where possible, to allow for strain gage placement and to reduce board flexure near components. However, there may be situations where strain gage placement is limited mechanically. For example, ICT fixtures have ICT probes, pushdown pins and BGA pushdown blocks which prevent strain gage placement in desired locations. Examples of such situations are illustrated in Figure 3-9 and Figure 3-10. In such instances, removal of part of the component may be considered as an alternative of last resort. In this case, when removing the corner of any component, the gage should be placed so that its centroid is placed on top of the corner land pad on the PCA. The alignment of the strain gage rosette should be such that grid sensing element directions e1 and e3 are 10
January 2012
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ICT Fixture Top Mold Removed BGA Corner Section
Removed BGA Corner Section
Periphery BGA Support Block Centroid
BGA Gage
Gage
PWB FR4
IPC-9704a-3-09
Figure 3-9 3-9
Interference Interfe rence Due Due to BGA Pushdo Pushdown wn Block
ICT Fixture Top Mold Test points or pushdown pins
Removed BGA Corner
Flat BGA Support
Removed BGA Corner
BGA Gage
Gage
PWB FR4
IPC-9704a-3-10
Figure 3-10 Interf Interference erence Due to to ICT Probe Probe
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oriented parallel to the edges of the package. Grid sensing element direction e2 should be oriented along the package diagonal. This alternate placement is illustrated in Figure 3-11. It is important to note that corner cutting changes the package geometry and mechanics and does not represent typical boundary conditions. If this method is used, additional evaluation methods are needed (such as destructive failure analysis) to fully assess the risk.
Place the centroid of the stacked rosette on top of the corner land pad on the PCB
Removal of the BGA section should be limited to fit the rosette
BGA
BGA
e1 e2
Corner land pad
e3 Rosette BGA Edges
Periphery BGA Support Block
Test Points
IPC-9704a-3-11
Figure 3-11 3-11 Centro Centroid id of Gage Placemen Placementt Above Corner Corner Land Pad Pad
The removal of the component should be limited to what is necessary neces sary to faci facilita litate te the placement placement of the strain gage. An example is illustrated in Figure 3-12. In the event that two gages at the corners of adjacent components would overlap, the test should be conducted using multiple PCAs. It is suggested that all corners of the component be gaged on the same PCA. 3.3.2 3.3. 2 Str Strain ain Gag Gage e Pla Placem cement ent for Non-Area Non-Area Arr Array ay Comp Compoo-
Unless a different Unless different placement placement is agreed upon between user and supplier, the preferred placement is recommended. nents
To asse assess ss the risk to chipchip-level level non-leaded non-leaded ceram ceramic ic comp compoonents, uni- or tri-axial strain gages may be used. The preferred placement is with the gage substrate edge no more than 1.0 mm away from each end of the component, aligned along the compon com ponent ent len length gth.. An exa exampl mplee of thi thiss is sho shown wn in Fig Figure ure 3-13.
Figure 3-12 3-12 Compon Component ent Removal Removal to Facilita Facilitate te Gage Placement
Board preparation is is a critical part of the instr instrumenta umentation tion process. Proper board prepar preparation ation will help ensure the proper bonding of strain gages; this will, in turn, improve the accuracy of the readings. 3.4 Gage Attachm Attachment ent
Strain gage attachment Strain attachment should also be perf performed ormed in accor accor-dance with instructions provided by the strain gage and adhesive suppliers. Note that strain gages require the use of specially cial ly form formulate ulated d adhes adhesive ive syste systems. ms. For detai details, ls, check with your strain gage supplier.
Within 1 mm Figure 3-13 3-13 Uni-Ax Uni-Axial ial Strain Strain Gage Placem Placement ent for MLCC MLCC packages (within 1.0 mm of solder fillets)
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Recommendation for board preparation and attachment of the strain gages is as follows: Prior to strain gage placement, prepare the surface to ensure proper adhesion. 1. The surface surface shall be prepared per the strain gage manufacturer’s instructions, taking care to not damage the printed board shall be material (the surface to which the gage is being adhered should be flat): a. Desol Desolder der small components components and discrete components components that interfere interfere with gage place placement. ment. b. Clean the surface surface with a solvent, such as Isopr Isopropyl opyl alcohol. alcohol. Solvents used shall shall be chemically clean. 2. Once the surf surface ace has been prepared, prepared, attach the stra strain in gages usin using g the appropriate appropriate adhesive adhesive system. 3.5 Lea Lead d Wires Wires
Actuall selection Actua selection of lead wires may vary depending depending on the specific applicat application. ion.
Details of the suitable lead wires are as follows: • 30 American Wire Gage (AWG) lead wire preferred; • Poly (vinyl chloride) PVC or Kynar insulation, or single solid copper wire with polyurethane enamel coating is preferred for ICT fixturing • Three-wire configuration (allows lead wire resistance compensation) is preferred over conventional two-wire configuration. • 1.5 to 2.5 meter lead wire length is recommended, but wire length should be no longer than needed. A two-wire quarter bridge doubles the desensitization of the strain gage, can introduce a significant amount of temperature sensitivity due to leads, and creates a potential balancing issue for the instrumentation. For the most stable static measurements, a three-wire system should be used. As lead wire routing is typically most constrained in ICT fixtures, lead wires must be routed in such a way as to avoid interference with supports and push-down posts when the fixture is engaged. An example of lead wire routing is illustrated in Figure 3-14.
Figure 3-14 Lead Wire Routin Routing g Example Example
If the same test board is used for both ICT and BFT, lead wire routing must accommodate the footprint of the mechanical support and pins for both fixtures. Single solid copper wires can help facilitate routing in ICT fixtures, and also help minimize vacuum leakage. Alternatively, ICT fixtures can also be designed to better accommodate the routing of lead wires. Some considerations are presented in Appendix A. Reinforce the lead wire attachment at each strain gage with epoxy or tape. Use adhesive-backed polyimide film or fiberglass cloth. 13
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3.6 Measur Measurement ement Equipment Equipment Stra Strain in measurements measurements are sensitive sensitive to scan frequ frequency ency,, data signal bit width, and stra strain in sig-
nal limits (gain). All sampling must be simultaneous, as sequential sampling may result in miscalculated strain values. The following guidelines are recommended: • For high strain rate events, such as ICT or other bed-of-nails type of testers, it is recommended to set the scan frequency to 2000 Hz. In cases where this is not possible, a minimum scan frequency of 500 Hz is recommended. • For general low strain rate assembly processes, such as mechanical assembly, a minimum scan frequency of 500 Hz is recommended. A minimum sampling resolution of 12 to 16 bits is recommended. Adjust signal amplifier gain for optimum use of dynamic range (that is, maximize the gain, but set it low enough to prevent clipping of peak strain values). It is a good practice to use a data acquisition system that has built-in low pass filtering to remove noise during strain gage data collection. If the data appears truncated, the measurement frequency should be increased to verify there is not a high frequency dynamic event occurring. Additionally, the number of available monitoring channels limits the number of measurements in any one pass. While multiple passes are allowable if there are insufficient channels, all three gages in any stacked rosette must be monitored at the same loading. Since the printed board material has low thermal conductivity, gages are more likely to heat up due to the electrical current passing through them. While making use of a three lead-wire setup and quarter bridge will reduce this effect, the excitation voltage should be balanced with the signal/noise ratio. If the strain value drifts significantly while the PCA is at rest, the voltage should be reduced until this effect either disappears, or the signal/noise ratio becomes acceptable. In general, an excitation level of 2V should provide satisfactory performance. 3.7 Measur Measurement ement Calibration Calibration It is important to calibrate the strain gage measurement equipment per the manufacturer’s
specifications and within the manufacturer’s recommended schedule. As many of the procedures above can lead to errors in measuring the PCA strain, proper calibration of equipment will ensure the accuracy of the readings. One method of calibration is the use of a simple calibration jig. Such jigs can be use used d to find and eli elimin minate ate many errors errors due to gag gagee pla placem cement ent,, gag gagee attachment, data acquisition system setup, and lead wires. One example is shown in Figure 3-15. In this jig, a coupon board is deflected in steps by the insertion of shims. The strain for each shim is recorded and can be compared against expected variation. The fixture is only meant to check for basic errors in gage attachment and measurement. It cannot be used to capture dynamic (sampling rate) errors, nor does it check for errors associated with the actual manufactur manuf acturing ing equip equipment, ment, i.e., therm thermal al ef effects fects,, or wire inter interfere ference nce with manufacturing equipment. 3.8 Manual Simulation Simulation Apart from mechanically mechanically actuated test operations, operations,
most other assembly steps are manually simulated. This is an integral part of strain stra in gage testing. testing. It is impo important rtant that in-process in-process handl handling ing is adequ adequatel ately y characterized. This can be achieved by carefully replicating observed handling processes, and the simulation of worst case handling.
IPC-9704a-3-15
Figure 3-15 Examp Example le Gage Gage Correlati Correlation on Tool
Such tests are intended to help identify weaknesses in the printed board, and to help optimize handling practices and fixture design. Where possible, proper handling procedures should be followed in order to minimize printed board flexure and appropriate fixturing should be used to handling boards between various process steps. The results from these simulations can be grouped into two general categories: • Observed handling • Excursionary handling Observed hand Observed handling ling represents represents handl handling ing that printed boards would typically typically exper experience ience during assem assembly bly and test test.. Strai Strains ns imposed would be representative of nominal loads exerted during manufacturing, assembly, and test. Excursionary handling, on the other hand, represents extreme or worst case events. While these events are unlikely, they represent a real and potential risk and should be understood, e.g., improper handling, etc. Such testing is important as it will determine if the PCA is susceptible to such excitations. 14
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Good judgment must be exercised to ensure that simulations are representative of the worst-case assembly strain profile. Simulation of manual handling and failure analysis steps should be based on observation of actual work practices, not on a volunteer assembler assembler.. Repeat each step a minimum of three times to capture the natural variation of the subject assembly step. Do the same for mechanically actuated test steps. For instance, to simulate through-hole connector insertion prior to wave solder, press the actual connector to simulate the insertion process. In all applications, exercise judgment to identify additional simulations. Unless strict procedures absolutely prevent occurrence, all possible worst case handling processes should be simulated. Particular attention should be paid to the characterization of manual handling with unintended hand-hold locations, e.g., heat sinks, board stiffeners, supports, etc. When monitoring strain levels during process steps (such as manufacturing, manufacturing, ICT, assembly), the strain metric should be the one that was used to derive strain guidance (such as in IPC/JEDEC-9707). 3.9 Str Strain ain Metric Metric
4 DATA ANALYSIS ANALYSIS AND REPORTI REPORTING NG
Generate a test report once data collection is complete. The recommended report format is represented in 4.3. 4.1 Analys Analysis is Requirements Requirements The details of the analysis analysis will vary with the particular particular strain limit criteria criteria being employed. employed.
Depending on the criteria, at a minimum, the peak values (maximum and minimum) of the principal or diagonal strain, depending on what is being evaluated, should be given for each step monitored. It is recommended to measure both diagonal and maximum and minimum principal strains. Other strain limit criteria may require calculation of the strain rate. Strain rate calculations may use a least squares fit or similar technique over the range of interest to avoid sampling errors. For further information regarding the computation of strain and strain rates, please consult with your equipment vendor. For operations that contain multiple steps (i.e., system assembly) it is recommended that the time history of the strain limit criteria be plotted as in Figure 4-1. This will assist in making any needed changes to the operation. Analysis data must highlight high risk operations that exceed the strain limit criteria. Any high-risk areas, as defined in this section, should be further analyzed.
DIMM Insertion
Video 2-pin RM
PCI Connectors
HD Connectors Peripheral connectors (i.e.. monitor, mouse, keyboard, etc...)
Figure 4-1 4-1
Time History History of the the Strain Strain Limit Criteria Criteria
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4.2 Test Frequenc Frequency y Conduct strain gage testing in the following following events:
• Before any test or assembly fixture is brought online • Whenever there are modifications to a test fixture that might alter the strain profile • Whenever there are modifications to an assembly process that might alter the strain profile • In-process fixture design evaluation • Enclosure design validation prior to hard-tooling In addition, strain gage tests should be conducted as part of the routine Preventative Maintenance (PM) process. It is strongly recommended that a PM program be developed to ensure that the strain profiles are within specified limits at all times. All test fixtures, including spares and backups, should be evaluated using strain gages. Fixtures of identical design can possess different strain and strain rate profiles. 4.3 Strain Gage Gage Test Report Report Template Test Reports Reports shall be in the following format: shall be 4.3.1 Abstra Abstract ct
A one parag paragraph raph executive executive summary summary of results. Use a pass pass/fail /fail table to summ summarize arize the results. results.
4.3.2 Introdu Introduction ction A one paragraph paragraph explanation explanation of test purpose, purpose, and gener general al description description of test. 4.3.3 Test Apparatus Apparatus and Setup Setup
A detailed description, description, using words and photographs, of the test equipment.
If experiments are used to determine the optimal setup or design, clearly define the experimental process and analysis outline. The detailed description should list the following: • Date of test • Test board (Include information on components characterized, i.e., package type, solder ball pitch, etc., and printed board thickness) • Strain gage specification (Include gage factor) • Strain gage placement information, i.e., the distance of the X-Y offset from subject component • Strain measurement equipment • Details of each assembly process (such as revision and serial number of fixtures, if applicable) • Test events should be performed multiple times with multiple personnel to assess variability 4.3.4 4.3. 4 Res Results ults A detailed detailed summary summary of test results results including including the item itemss listed below:
• Graph of applicable diagonal or principal strain on critical components over time (see Figure 4-1 for an example) • Table of peak strain & strain rate values for each strain gage for each event being evaluated (handling, assembly, ICT, etc.), see Table 4-1. A, B, C and D are the strain and strain rate limits set by the user • Steps taken to reduce unacceptable levels of strain – Graph and tables demonstrating strain reductions This sample report contains the measured strain and strain rate values and the user strain guidance. This format may not apply if the user does not have strain guidance. The example reports both diagonal and principal strain metrics since supplier guidance may be provided in either metric.
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Table 4-1 Examp Example le Strain Report Report for a Strain Strain Gaged Component Component that went through Various Various Handlin Handling g and Assembly Processes Processes
Measured peak strain
Measured strain rate at peak strain value
Strain Guidance (where A, B, C are absolute numeric limits defined by the user). These values may be dependent on the measu measured red strain rate
Measured peak strain as a % of strain guidance
Pass/Fail (pass if within required limits)
PCA Handling
Max Principal Strain
| A | µε
% of A
Pass/Fail
Min Principal Strain
| B | µε
% of B
Pass/Fail
Diagonal Strain
| C | µε
% of C
Pass/Fail
Assembly Part 1 (Heat sink attach)
Max Principal Strain
| A | µε
% of A
Pass/Fail
Min Principal Strain
| B | µε
% of B
Pass/Fail
Diagonal Strain
| C | µε
% of C
Pass/Fail
Assembly Part 2 (Plug in DIMMs)
Max Principal Strain
| A | µε
% of A
Pass/Fail
Min Principal Strain
| B | µε
% of B
Pass/Fail
Diagonal Strain
| C | µε
% of C
Pass/Fail
Assembly Part 3 (Screw down covers)
Max Principal Strain
| A | µε
% of A
Pass/Fail
Min Principal Strain
| B | µε
% of B
Pass/Fail
Diagonal Strain
| C | µε
% of C
Pass/Fail
5 CONCLUS CONCLUSIONS IONS
A detailed summary describing the most important experimental results and list of recommendations for either changes in printed board assembly procedures, design changes for the system or test fixture, or further testing. Clearly explain justification for the recommendations. 6 FUTURE STUDI STUDIES ES
A one paragraph description of recommended future testing.
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APPENDIX A ICT DESIGN CONSIDERATIONS ICT is often determined to be the most significant strain event that is experienced by a printed circuit assembly. Consequently the following section presents best practices in ICT design to minimize component damage. To ensure a properly designed fixture, a Computer-Aided Design (CAD) file of the Unit Under Test (UUT) nomenclature is necessary. The CAD file is created from a printed board design package (it is recommended to use the printed board design output since it typically will have more detailed information than photo plot files, such as Gerber files). The CAD file is used by the test fixture manufacturer to accurately place UUT supports, pockets for UUT components, and placement of strain gages. Output from printed board design packages can vary. The output results depend on the input of board and component information. Because of this, and because of the number of design packages used throughout the industry, it would be difficult to standardize the parameters of the output file. As a general guide, the more detailed the input information is, the better the output file will be. When designing the test fixture’s board support system the number one priority is to keep the UUT planar. Attention must be paid to the placement and quantity of board supports in densely probed areas to offset the probe forces. Too low a number of board supports may lead to excessive strain on the UUT and cause the support to ‘‘skate.’’ Support ‘‘skate’’ is when a UUT’s support is over loaded with upward pressure causing it to buckle under its load and slide along the surface of the UUT, often stopping as it collides with a component, as illustrated in Figure A-1.
Board support buckles under excessive pressure and skates into adjacent component
Top Plate
Probe Plate
IPC-9704a-a-01
Figure A-1 Illustr Illustration ation of Support ‘‘skate’ ‘‘skate’’’ when a UUT’s Support Support is Overloaded with with Upward Pressure, Causing it to Collide with a Component.
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Avoid placing board supports closer than a 10 mm radius to BGA corners to provide sufficient clearance for the strain gage rosette. See Figure A-2.
Preferred placement: Centerline of rosette located at intersection of lines offset from the component edge 3.56 mm ± 0.25 mm [0.14 in ± 0.01 in] See Detal A. 90º(Typ)
3.56 mm ± 0.25 mm [0.140 in ± 0.01 in]
R10 [0.393 in] from corner of component
Recommended board support keep out area for rosette placement
Component
90º(Typ)
90º(Typ)
Keep out area: Equal to 10% of component length Recommended UUT support: 80% of component length if and where possible
Detail A
3.56 mm ± 0.25 mm [0.140 in ± 0.01 in] Component
Centerline of strain gages, not “rosette package” is offset from component edge. IPC-9704a-a-02
Figure A-2 A-2
Illustration Illustr ation of UUT Support Support Areas and Keep-out Keep-out Areas Areas around a BGA compone component nt
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January 2012
Whenever possible, place top and bottom board supports as closely in-line with each other as possible to provide a solid stack up of material to further reduce strain on the UUT. When placing board supports it is recommended a clearance of 1.3 mm be maintained between the board support and component edge. See Figure A-3. Additionally the placement of support blocks over heavily probed PTH connectors is permissible.
Top support clearance 1.3 mm [0.50 in] from component edge 1.3 mm [0.050 in] Top board support
Bottom board support Top Plate Dead stop
Probe Plate
Keep boards supports in-line to reduce strain on UUT IPC-9704a-a-03
Figure A-3 Illustr Illustration ation of Component Component to Support Clearance Clearance and Proper Support Alignment Alignment
Strain gage rosettes should be placed where required on the UUT per vendor specification. If available, use the Finite Element Analysis as a guide for placement and for anticipated strain limits for each rosette. Lead wires can be damaged and test results may fluctuate greatly if placed under board supports. To properly place rosettes and lead wires it is recommended to use a clear plot of the test fixture’s board supports. If necessary, remove smaller components (capacitors and resistors) located under or near the desired rosette location. Carefully fasten the lead wires to the UUT avoiding contact with the fixture supports. Again, if necessary, smaller components can be removed for routing of the lead wires without affecting the stain gage test results.
20
January 2012
IPC/JEDEC-9704A
APPENDIX B ACRONYMS ASTM AST M
Americ Ame rican an Soc Societ iety y for Test esting ing and Mat Materi erials als
AWG
Amer Am eric ican an Wir iree Ga Gage ge
BGA
Ball Grid Array
BFT BF T
Boaard Fu Bo Fun nct ctio ion nal Tes estt
C SP
Chip Scale Package
CTE CT E
Coef Co efffic icie ient nt of Th Ther erma mall Ex Expa pans nsio ion n
CAD CA D
Comp Co mput uter er-A -Aid ided ed De Desi sign gn
DIMM DI MM
Dual Du al In In-l -lin inee Me Memo mory ry Mo Modu dule le
FEA FE A
Fini Fi nite te El Elem emen entt An Anal alys ysis is
ICT
In-Circuit Test
JEDEC JED EC
Joint Joi nt Ele Electr ctron on Dev Device ice Eng Engine ineeri ering ng Cou Counci ncill
MLCC MLC C
MultiMul ti-Lay Layer er Cer Cerami amicc Cap Capaci acitor tor
PCA PC A
Prin Pr inte ted d Ci Circ rcui uitt As Asse semb mbly ly
PCII PC
Peri Pe riph pher eral al Co Comp mpon onen entt In Inte terc rcon onne nect ct
PVC PV C
Poly Po ly--Viny nyll Ch Chlo lorrid idee
PM
Prev Pr eveent ntat ativ ivee Mai aint nten enan ance ce
SOP SO P
Smaall Ou Sm Outtli line ne Pa Pack ckaage
SMT
Surface Mount
UUT
Unit Under Test
21
ANSI/IPC-T-50 Terms and Definitions for Interconnecting and Packaging Electronic Circuits Definition Submission/Approval Sheet The purpose of this form is to keep current with terms routinely used in the industry and their definitions. Individuals Indiv iduals or compa companies nies are invited to comment. Please complete this form and return to:
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Standard Improvement Form The purpose of this form is to provide the Technical Committee of IPC with input from the industry regarding usage of the subject standard.
Individuals or companies are invited to submit comments to IPC. All comments will be collected and dispersed to the appropriate committee(s).
IPC/JEDEC-9704A If you can provide input, please complete this form and return to: IPC 3000 Lakeside Drive, Suite 309S Bannockburn, IL 60015-1249 Fax: 847 615.7105 E-mail:
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1. I recommend changes changes to the following: Requirement, Requirem ent, paragra paragraph ph number Test Met eth hod number
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