FCBGA Package Warpage Definition Stage Project Kirk Van Dreel - Plexus HDP User Group Member Meeting Host: Ericsson Stockholm, Sweden May 28, 2013 Presented by Bob Smith © HDP User Group International, Inc.

© HDP User Group International, Inc. Purpose Mitigate Area Array solder joint quality defects generated by package and/or board warpage during SMT reflow © HDP User Group International, Inc.

© HDP User Group International, Inc. Background Package/board Warpage increasing trends Driven by thinner package substrates and thinner die   Package/Board contacts getting smaller and closer thereby reducing ability to overcome increased Warpage. Solder Joint Quality Impact of increasing Package and Warpage. With advent of lead free soldering, the assembly temperatures have increased and the warpage impact has been exacerbated. © HDP User Group International, Inc.

Examples of Warpage Induced Defects Package Substrate Die Board Head-on-Pillow Open Non –Wet Open Stretched joint Head on pillow Various Solder Joint Defects can occur during SMT Reflow Soldering due to Excessive BGA component and/or Board Warpage © HDP User Group International, Inc.

© HDP User Group International, Inc. Goal Establish a limit for dynamic package warpage that can be mitigated during board assembly without impacting solder joint quality Need to set a baseline for today, and set what the limit is for all gaps. It will be non-package or non-PCB related © HDP User Group International, Inc.

© HDP User Group International, Inc. Project Objectives Identify mitigation paths for solder joint yield loss caused during the SMT reflow soldering process specifically due to the excessive warpage of package and/or boards Evaluate these mitigation paths for their effectiveness in increasing solder joint yield despite high levels of package and/or board warpage © HDP User Group International, Inc.

Technical Discussion Potential Mitigation Paths Alternate solder paste and package solder ball metallurgies, i.e., low temperature solders Alternate solder temp profiles (steep ramp, soak, spike reflow profile, for instance) Alternate package termination geometries (instead of balls) Optimized solder paste printing geometries  New solder paste formulations Tacky Fluxes, applied by dipping   © HDP User Group International, Inc.

© HDP User Group International, Inc. Project Scope - What is IN FCBGA Package just as its entering the SMT Reflow Oven Die FC BGA Package Substrate Package Substrate Project Focus Area Printed Circuit Board Reflow Process Temperature –Time Profile Oven Atmosphere Solder Paste Rheology Wetting Metallurgy Activator chemistry Volume printed on land Surface Finish OSP/ENIG/ImAg/ENEPIG/ etc Package Termination Geometry (ball, pillar, column, etc) Metallurgy (SAC, low Ag SAC, BiSnAg, other) © HDP User Group International, Inc.

© HDP User Group International, Inc. Project Scope - What is OUT Package Warpage Mitigation Laminate Type Stack-up Die Thickness Die Size Package Warpage Measurement Metrologies Specifications Die FC BGA Package Substrate Package Substrate Printed Circuit Board Board Warpage Mitigation Laminate Type Stack-up Board Warpage Measurement Metrologies Specifications © HDP User Group International, Inc.

© HDP User Group International, Inc. Project Structure Phase 1 - Test Method Development This phase will establish a test method which will enable the team to compare and contrast the effects of the mitigation techniques Phase 2 - Characterization Of Mitigation Methods and Max Package Warp Specifications This phase will leverage phase 1’s output to establish the maximum warp an optimized process can accommodate and characterize the contribution of the mitigation techniques on the process yield. © HDP User Group International, Inc.

© HDP User Group International, Inc. Phase 1 Project Plan Project Development / Planning Test Method Development Process HoP Mitigation Study Rework Test Method Resourcing of equipment, materials, and response characteristics measurements. Reflow Test Method Baseline Process Characterization Complete In-Process Not started © HDP User Group International, Inc.

© HDP User Group International, Inc. Phase 1 Status Project Scope, Objectives, and Flow defined Key Variables Identified to Control and Monitor during SMT Reflow Soldering Selected the Metrologies to vary and monitor the gap between Ball and paste during the reflow soldering process Drafted Experimental Plans and Resources Needed for initial Objectives Defined Test Substrate /Board Requirements Plexus has taken over from Intel as Team leader Revising the project management Plan 19-21 22-29 30-33 34 © HDP User Group International, Inc.

© HDP User Group International, Inc. Phase 1 - Near Term Develop Modified Cisco Rework Method Metrology: Run the designed experiments to confirm the feasibility of using Hot Air Rework machine to control the gap between solder ball and solder paste with temperature with a full array package instead of a single solder ball at a time Develop Modified Plexus Reflow Method Metrology: Confirm proof of concept for using the expansion of a high CTE adhesive to vary ball-to-paste gap in the pre-reflow zone of an in-line reflow soldering oven Confirm proof of concept of solder preform wetting into multiple PTHs in the board for sharply decreasing ball-to-molten paste gap in the reflow zone of an in-line reflow soldering oven Develop Real Time Monitoring: Confirm the capability for real time monitoring of ball-to-paste gap and solder joint formation mechanisms of high dynamic warpage area array packages during the reflow process and of the Malcom RCA-1 Observation Monitor Video Camera in an in-line reflow oven the VDS-1 Video Monitoring System in a Reflow Simulator Batch Oven © HDP User Group International, Inc.

© HDP User Group International, Inc. Team Members –to date Agilent Fujitsu Panasonic Akrometrix H3C ParkElectro Alcatel-Lucent Huawei Phillips Arlon Hitachi Plexus ASE Hitachi-Chemical Rockwell Celestica IBM Sytech Ciena Indium TTM Tech Cisco Intel Viasystems Curtiss-Wright IST Group Ventec Elite Materials Juniper Zestron Emerson Kyzen ZTE Ericsson Medtronic Fiberhome Nihon-Superior Flextronics Oracle © HDP User Group International, Inc.

© HDP User Group International, Inc. Back-up © HDP User Group International, Inc.

Effect of Typical Dynamic Warpage Characteristics of FCBGA packages on Solder Joint Formation Post Solder Ball Collapse Point Maximum Ball-Board Separation Point Temp Start of Significant Pull Way of Ball from Board reflow Cool down soak `Flat Package` Point Ramp up Post Solidification Point Room Temperature Head-on-Pillow Open Time The typical Dynamic Warpage of a FCBGA package entails For a corner solder joint…….contact first, then separation between the solder ball and the solder paste For a center solder joint……separation first, then contact between the solder ball and the solder paste This contact + separation or vice versa sequence creates solder joint defects © HDP User Group International, Inc.

Gap in Center joint of Package Gap in Corner Joint of Package Variation of Gap between Bottom of Solder Ball and Top of Solder Paste (when solid or molten) `Flat Package` Point Start of Significant Pull Away of Ball from Board Temp Maximum Ball-Board Separation Point Post Solder Ball Collapse Point Post Solidification Point Gap in Center joint of Package Gap in Corner Joint of Package Gap Sharp Decrease in Gap due to collapse of central solder joints Room Temperature Time Besides first contact , then separation for the corner ball, there is a sharp decrease in the gap as the solder balls melt and collapse in the reflow zone within the reflow soldering oven This sharp drop and gap can facilitate coalescence of the molten solder ball and molten solder paste if paste flux is still active © HDP User Group International, Inc.

© HDP User Group International, Inc. Key Points Any method of simulating BGA package warpage during reflow soldering needs to address the following to simulate the conditions for corner solder joints Initial Contact of the BGA solder ball with the solder paste and subsequent separation before or during the soak zone or ramp region Sharp drop in the gap between the molten solder ball and molten paste when the solder balls melt and collapse in the reflow zone region Any method of simulating BGA package warpage during reflow soldering needs to address the following to simulate the conditions for central solder joints No contact between the BGA solder ball and solder paste before or during the ramp zone or soak zone until the flat package point is reached Contact developed between the solder ball and solder paste later in the soak zone © HDP User Group International, Inc.

Simulation for the Corner and Outer Row Solder Joints of the BGA Requirements Initial Contact of the BGA solder ball with the solder paste and subsequent separation before or during the soak zone or ramp region Sharp drop in the gap between the molten solder ball and molten paste when the solder balls melt and collapse in the reflow zone region SAC Solder Pre-form and Solder Paste or Flux Package Room Temp ~20C Adhesive Gap < 0 Initial set up entails amount (thickness) of adhesive adjusted to ensure negative gap between the solder balls and the paste; Board Soak Zone Temp ~160C Gap > 0 Expansion of the adhesive in its thickness direction raised the balls from the paste and creates a positive gap Board Melting of solder preforms in the reflow zone and the subsequent flow of the molten solder into PTH will dramatically drop the stand-off height of the package and eliminate the gap Reflow Zone Temp ~240C Gap < 0 Board The amount of gap and rate at which it is created in the ramp zone of the profile is controlled by the expansion coefficient of the adhesive in its thickness direction © HDP User Group International, Inc.

© HDP User Group International, Inc. One Proposal to Simulate Gap Variation between the BGA Solder Ball and the Solder Paste on the PCB Land BGA Package BGA Solder Balls Adhesive Solder Paste Gap > 0 Board Solder Preform Function of Adhesive: To simulate the increase in the gap by changing its length with increasing temperature due to its coefficient of thermal expansion Function of Solder Preform: To melt at reflow temperature and flow into the PTH it is placed over and simulate the sudden decrease in the gap that occurs when the balls collapse after becoming molten © HDP User Group International, Inc.

Balls and solder paste melt while in contact 4/26/2017 Simulation for the Central Solder Joints of the BGA Requirements No contact between the BGA solder ball and solder paste before or during the ramp zone or soak zone until the flat package point is reached Contact developed between the solder ball and solder paste later in the soak zone Low Temp Solder Pre-form and Solder Paste or Flux Package Adhesive Initial set up entails a gap between the solder balls and the paste; gap amount controlled by amount (thickness) of adhesive Room Temp ~20C Gap at RT > 0 Soak Zone Temp ~160C When the low temp solder pre-form melts balls lowered and touch SAC solder paste Gap < 0 Reflow Zone Temp ~240C Gap < 0 Balls and solder paste melt while in contact The temperature at which the solder ball and paste make contact can be varied by using different solders with different melting points in the SAC profile soak zone Intel Confidential

Requirements for Adhesive Under Component to Simulate the Gap between the Ball and the Paste during SMT Reflow Soldering Adhesive Gap > 0 Expansion of the adhesive in its thickness direction raises the balls from the paste and creates a positive gap Minimum Gap to simulate problematic warpage is 150 microns Board High Coefficient of Linear Expansion after Cure; Sufficient Hardness/Modulus/Rigidity to push the package up as the adhesive expands Survive temperatures up to 250C after cure Dispensable or screen printable Key question: What is the range of Linear Expansion that is needed for the adhesive? © HDP User Group International, Inc.

Cisco’s SRT Rework Equipment Method for Head-on-Pillow Testing BGA rework equipment was also used to reflow the solder ball and the solder paste, while controlling the movement of the solder ball with respect to the solder paste on the pad. The purpose of controlling the movement is to mimic the movement of the corner balls of a BGA as they warp during the reflow process. © HDP User Group International, Inc.

Conditions for Cisco’s Method C1: Initially there is no initial contact between the solder ball and the paste. Then at 200 ° C during the cooling down phase, the solder ball is pulled down slowly (1 mil/second) so that it makes contact with the solder paste. C2: Initially there is no initial contact between the solder ball and paste. Then at 190 °C during the cooling down phase, the solder ball is pulled down slowly so that it makes contact with the solder paste. This condition is similar to C1 but there is less contact time before solidification. C2 Note: When initial contact is made between ball and paste, no H-o-P defects were formed © HDP User Group International, Inc.

Photo’s of Cisco’s Method for Evaluating H-o-P defects Before Solder Paste Reflow After Solder Paste Reflow Aspects of Actual Reflow Soldering of high warpage BGAs NOT Simulated in this Test Lifting up of the solder ball from the solder paste during initial temperature ramp (though this can be done with the equipment) Un-constrained Ball Collapse when the solder melts Temperature Profile simulated with hot air rework machine instead of a reflow oven © HDP User Group International, Inc.

Malcom RCA-1 Observation Monitor Observes and Records the components on a PCB as it goes through the Reflow Oven © HDP User Group International, Inc.

Summary of Obj. # 3 Experimental Plans Experiment Name Phase Description of Experiment High CTE Adhesive Development A Feasibility of ME-280+ silicone fillers adhesive Sample Preparation and its expansion effect on gap variation between BGA ball and PCB land through the reflow oven B effect of adhesive volume on gap variation and package tilting during reflow soldering C Explore other materials with higher CTE than that of ME-580+silicone fillers Solder Preform Development Proof of Concept Validation using off-the-shelf preform Preform Design Plated Through Hole Design D Preform Fabrication at Indium Corp E Board Fabrication at Member PCB Fabricator Combined Adhesive and Solder Preform Validation Using Developed Adhesive and solder preform with substrate and boards, conduct test runs with printed solder paste © HDP User Group International, Inc.

Summary of Obj. # 3 Experimental Plans Experiment Name Phase Description of Experiment Development of Modified Cisco Hot Air Rework Machine Method A Exploratory Experimental Runs to confirm the method works Comprehensive Factors DOE, using critical process variables from screening DOE results and including material Variables and ball pitch/ ball size to determine main effects and 2 factor interactions B Screening DOE using Process Variables to determine main effects and 2 factor interactions C © HDP User Group International, Inc.

Resources Needed for Initial Objectives Experiment Resources Potential Source Modified Cisco Hot Air Rework Method Test Substrate Laminate Panasonic Fabrication of Test Substrate and Boards Member PCB Fabricator, to be identified Solder Balls Senju Solder Paste Senju/Indium/Alpha/Shenmao Stencils for solder printing Non-member Supplier Running Experiments with Hot Air Rework Machine Intel/Celestica/A.P.E Failure Analysis including Dye and Pry Intel / other members to be identified High CTE material Lord Corp / Panasonic / Other yet to be identified Solder Preforms Indium Corp SMT Reflow Oven Flextronics / Intel Designers for Solder Preform and Boards Members, to be identified © HDP User Group International, Inc.

Resources Needed for Initial Objectives Experiment Resources Potential Source Modified Plexus Method usign High CTE Material and Solder Preform High CTE material Lord Corp / Panasonic / Other yet to be identified Solder Preforms Indium Corp SMT Reflow Oven Flextronics / Intel Designers for Solder Preform and Boards Members, to be identified Flextronics / Intel / Other Real Time Monitoring of Ball-to-Paste Gap Camera for In-line Reflow Oven and In-line SMT Oven Intel / Other Member(s) to be identified Batch Reflow Oven with Video Camera Nihon Superior / Other Member(s) to be identified © HDP User Group International, Inc.

Test Substrates Proposal Ball Pitch Ball Size Body Size Quantity of Substrates (Approx) Quantity of Balls per Substrate (Approx) 0.5 mm 0.3 mm 7 mm 150 600 0.8 mm 15 mm 800 1.0 mm 0.6 mm 35 mm 300 1000 Thickness: 400 microns w/two copper layers, on each side of the core Panasonic labs to build the substrate using low warpage materials Substrate / Board Fabrication to be done at a PCB supplier member Ball Attach to be done at Outside sub-contractor

Proposed Schedule