Effects of Component Rework on Reliability rev02 Khaw Mei Ming - Keysight HDP User Group Project Meeting 2 nd June 2016 © HDP User Group International, Inc.

Background Current rework guidelines regarding the number of allowable reworks for a component site need to be upgraded or better understood with solid research. Most companies say a component can be reworked 2 or 3 times. Maybe only 1 or 2 for a BGA. Can we allow >1/2x rework for BGA/QFN located very far apart to another BGA/QFN? © HDP User Group International, Inc. 2

Goal © HDP User Group International, Inc. Establish a limit for the number of reworks that can occur for BGAs on an assembly without impacting the overall reliability

Learnings from previous studies: Source: iNemi’s adjacent component rework project. -Use a lead-free rework profile that keeps the adjacent CBGA solder joints below liquidus (217°C) while keeping the reworked uBGA within J- STD-020D (260°C peak for rework). -Heat shields (Al and Ceramic) only helped to reduce temperature at adjacent component by 2-4°C, based on TV spacing of 500 mil (13mm). -Well formed joints on adjacent components -> no secondary reflow. -Thicker IMC on adjacent components but is not a reliability concern. -No change in electrical continuity testing. -No change in voids. Source: CALCE Solder Joint Reliability of Reworked SMT Assemblies -Durability of SAC solder reduces with increase in number of rework, based on mechanical bend test. -Copper pad dissolution in reworked BGAs with SAC solder is more significant compared to those with SnPb solder.

Study on Microstructure of VIPPO Designed PCB in Pb-Free Rework Via-in-pad Cu cap thickness is a very critical factor for soldering and rework. Lesser Cu cap thickness resulted in more pad damage/dissolution and caused voids in joint. Minimum 1mil Cu cap thickness is preferred on bare board to ensure reliability after further rework operations. Voids in epoxy could impact Cu cap plating process, causing big voids in the solder joint during the reflow soldering process More thermal cycles may cause bigger risk to VIPPO pad damage VIPPO dimple could cause voids formation after soldering and rework. by Cisco Systems at SMTA China East 2014

Keysight-CM Evaluation on adjacent parts at different distances with different localize method U18 U17 U19 U13 Localize Heating Location Measure surrounding Location No significant heat reduction on the neighboring components using either method. However, neighboring component at less than 10mm (400 mil) from the rework location will still be exposed to temperature above 200°C.

100 mil Case study example: 2 BGAs can be placed and reworked 100 mils apart from each other. Will each undergo secondary reflow with reliability risk with more than 1x rework?

Variables, PCB design:Proposed metrology to measure the variables Expected outcomeTest vehicle consideration Layer count/thickness8L, 16L, 24L, etc.Higher layer count help to absorb and spread heat 20L only Cu weight on outer layer½ oz, 1 oz.Higher cu weight, > tendency for delamination ½ oz only Surrounding ground planeShield tracksIncreases heat spread to neighboring components Yes Trace width2mils, 3mils, 4mils, etc.Bigger trace width enables higher heat conduction to surrounding components, trace degradation? Mix of 3-5 mils Laminate materialFR4, medium loss, low loss Material degradationR1755V Types, size and density of via in pad Open microvia, epoxy filled via, cu filled via, multiple FHS Via degradationVIPPO epoxy filled uvia, dogbone vias, 0.25mm DHS Surrounding via – types, sizes and density Open microvia, epoxy filled via, cu filled via, through holes, multiple FHS Via degradationVIPPO epoxy filled uvia, dogbone vias, 0.25mm DHS

Variables, component Proposed metrology to measure the variables Expected outcome Test vehicle consideration Component packaging Plastic, ceramic, metal IMC growthMix Component typeHeat sensitiveVoids, IMC growthYes Component sizeµBGA/QFN, large BGA/QFN (1mm pitch, 0.8mm pitch, 100 I/O 0.5mm pitch) Voids, IMC growthlarge & small BGA (1mm pitch, 0.8mm pitch, 0.5mm pitch) Distance to rework site Different distances starting at 100 mil (2.54 mm) Smaller voids on component further from rework site, IMC growth Mix Heat shieldsCeramic non- woven fiber, aluminum foil, kapton tape, etc. IMC growthIgnore

Scope: -Components -High density large BGAs -Large and small BGAs -Various distances to rework site -Some ground planes Test method: -Cross-section to check for IMC thickness, grain structure and evidence of secondary reflow -Cross-section on PCB copper pad to check for dissolution -CSAM/Thru scan to check for PCB delamination on inner and outer layers -Voids in BGA balls via 5DX -Electrical resistance/continuity test -ATC testing 0-100C, 1000 cycles -Shock / Drop Evaluation per Jedec standards

Project IS / IS Not This Project IS:This Project IS NOT: Evaluation of thermal dispersion using localized heating rework Evaluation of thermal dispersion using hand repair Evaluation of a typical PCA with large, high density BGAs/BTCs Evaluation of different PCB designs Assessment of different distances to rework site Evaluation of rework equipment Assessment of mechanical drop/shock reliability and accelerate thermal cycling reliability after multiple rework Assessment of solder joint reliability under other stress/temperature conditions Impact on voids at adjacent components Assessment of acceptable voids%.

HDPUG FCBGA Package Warpage Project – NOT APPLICABLE

HDPUG Pad Cratering Project – NOT APPLICABLE

HDPUG Microvia in Pad (VIP) Impact on Pb-free Solder Joint Reliability Project – NOT APPLICABLE 6L, 0.125” (3.175mm) thick, 7.0 x 6.5” (177.8 x 165.1mm), ImmAg. 16 boards, totaling 64 components of each type were tested, 32 with microvia-in-pad (laser drilled 6 mils) and 32 without microvia-in-pad.

Proposed test vehicle design #1

Proposed test vehicle design #2

Proposed parts to use A-PBGA mm-40mm-DC-LF-305 (PN 31313) SAC305 & Daisy Chained Die Size = mil sq 21 per Tray / 2 Tray Minimum U$18.85 each 8 week lead time A-CTBGA84-.5mm-7mm-DC-LF-305 (PN 31317) SAC305 & Daisy Chained Die Size = 200mil sq 476 per Tray / $7.00 Tray Charge will apply if full tray qty is broken U$2.80 each 8 week lead time A-CVBGA97-.4mm-5mm-DC-LF-305 SAC305 & Daisy Chained Die Size = 125mil sq 360 per Tray / $7.00 Tray Charge will apply if full tray qty is broken U$3.30 each 8 week lead time

Proposed parts to use LP5907-YKE mm x 0.6mm, 0.35mm pitch Texas Instrument 4 pin DSBGA DFN1010B mm x 1.0 mm, 0.35 mm pitch NXP 6+2 pin plastic DFN 1NG mm x 41mm, 1mm pitch Keysight Technologies Ceramic FCBGA 1594 balls *Temp sensitive component: Do not exceed a peak package body temperature of 245°C. P/N: 1NG Component size: 35 x 35 mm, Pitch: 1 mm Keysight Technologies Metal EBGA, 538 balls NBB-402-T1 from RF micro devices Size: 3.28 x 3.28 mm (max) Pitch: 1.02 mm (max) Ceramic BGA, 9 balls Optional parts