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FCBGA Package Warpage Definition Stage Project Raiyo Aspandiar - Intel HDP User Group Member Meeting Host: Oracle Santa Clara, CA. Feb. 26. 2013 © HDP.

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Presentation on theme: "FCBGA Package Warpage Definition Stage Project Raiyo Aspandiar - Intel HDP User Group Member Meeting Host: Oracle Santa Clara, CA. Feb. 26. 2013 © HDP."— Presentation transcript:

1 FCBGA Package Warpage Definition Stage Project Raiyo Aspandiar - Intel HDP User Group Member Meeting Host: Oracle Santa Clara, CA. Feb © HDP User Group International, Inc.1

2 2 Purpose

3 © HDP User Group International, Inc.3 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.

4 © HDP User Group International, Inc.4 Examples of Warpage Induced Defects for Area Array Solder Joints Stretched joint Head on pillow Head-on-Pillow Open Die Board Non –Wet Open Various Solder Joint Defects can occur during SMT Reflow Soldering due to Excessive BGA component and/or Board Warpage

5 Real Time Videos will be shown for two cases – `Bad` Solder Paste causing Non-Wet Open Defects – `Good` Solder Paste resulting in acceptable solder joints 5 Real Time Videos of Solder Joint Formation Video Camera Set up Malcolm Tech Video camera Reflow Oven Belt or Rail FCBGA Package Solder Balls Solder Paste Camera fixture

6 © HDP User Group International, Inc Cooling Real Time Videos of Solder Joint Formation Time Temperature

7 © HDP User Group International, Inc.7 Two Real Time Videos of Solder Joint Formation of a FCBGA package with high dynamic warpage will now be shown

8 © HDP User Group International, Inc. 8 Project Scope Project Scope - What is IN the Scope Die Package Substrate Printed Circuit Board Project Focus Area FC BGA Package Substrate Solder Paste Rheology Wetting Metallurgy Activator chemistry Volume printed on land Package Termination Geometry (ball, pillar, column, etc) Metallurgy (SAC, low Ag SAC, BiSnAg, other) FCBGA Package just as its entering the SMT Reflow Oven Reflow Process Temperature –Time Profile Oven Atmosphere Surface Finish OSP/ENIG/ImAg/ ENEPIG/ etc

9 © HDP User Group International, Inc. 9 Project Scope Project Scope Die Package Substrate Printed Circuit Board FC BGA Package Substrate Package Warpage Mitigation Laminate Type Stack-up Die Thickness Die Size - What is OUT of the Scope Package Warpage Measurement Metrologies Specifications Board Warpage Mitigation Laminate Type Stack-up Board Warpage Measurement Metrologies Specifications

10 Goal 10 © HDP User Group International, Inc. Establish a limit for dynamic package warpage that can be mitigated during board assembly without impacting solder joint quality

11 Project Objectives 1.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 2.Evaluate these mitigation paths for their effectiveness in increasing solder joint yield despite high levels of package and/or board warpage 11 © HDP User Group International, Inc.

12 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 Each mitigation path can comprise a separate project proposal or all can be combined into one project 12 © HDP User Group International, Inc.

13 What has been Done to Date Project Scope, Objectives, and Flow defined Key Variables Identified to Control and Monitor during SMT Reflow Soldering o Gap between Ball and Paste Selected the Metrologies to vary and monitor the gap between Ball and paste during the reflow soldering process Modified Plexus Method of Adhesive and Solder Pre-form under Package Ciscos Rework Equipment Use Method Real Time observation of Solder Joint Formation using Malcom Tech Cameras and overs Drafted Experimental Plans and Resources Needed for initial Objectives Defined Test Substrate /Board Requirements © HDP User Group International, Inc

14 What is Planned For the Near Future Develop Modified Cisco Rework Method Metrology: o 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 Cisco Rework Method Metrology: o 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 o 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: o 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 1.the Malcom RCA-1 Observation Monitor Video Camera in an in-line reflow oven 2.the VDS-1 Video Monitoring System in a Reflow Simulator Batch Oven © HDP User Group International, Inc.14

15 What is Planned Beyond the Near Future Brainstorm Mitigation paths: for excessive warpage of package and/or boards induced SMT solder joint yield loss and select potential candidates for assessment Select Mitigation Path: Obtain Components and Design and Procure Boards for Evaluation of Mitigation Paths Assess Effectiveness of Mitigation Path: Design and Run Experiments to evaluate present capability of materials and processes and feasibility of the Warpage-induced Defects Mitigation Paths © HDP User Group International, Inc.15

16 © HDP User Group International, Inc.16 Proposed Project Flow

17 © HDP User Group International, Inc.17 Team Members –to date Akrometrix Alcatel-Lucent Arlon ASE Celestica Ciena Cisco Curtiss-Wright Emerson Ericsson Fiberhome Flextronics Fujitsu H3C Huawei Hitachi Hitachi-Chemical IBM Indium Intel IST Group Juniper Medtronic Multek Nihon-Superior Panasonic Phillips Plexus Rockwell Sytech TTM Tech Ventec Zestron ZTE

18 Back-up © HDP User Group International, Inc.18

19 Temp Effect of Typical Dynamic Warpage Characteristics of FCBGA packages on Solder Joint Formation © HDP User Group International, Inc. 19 Head-on-Pillow Open Room Temperature `Flat Package` Point Start of Significant Pull Way of Ball from Board Maximum Ball-Board Separation Point Post Solder Ball Collapse Point Post Solidification Point Time Ramp up soak reflow Cool down 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

20 Variation of Gap between Bottom of Solder Ball and Top of Solder Paste (when solid or molten) © HDP User Group International, Inc. 20 Time `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 Room Temperature Sharp Decrease in Gap due to collapse of central solder joints 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

21 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.21

22 Simulation for the Corner and Outer Row Solder Joints of the BGA © HDP User Group International, Inc. 22 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 Gap < 0 Package Adhesive Board Gap > 0 Room Temp ~ 20C Soak Zone Temp ~ 160C Board Reflow Zone Temp ~ 240C Gap < 0 Initial set up entails amount (thickness) of adhesive adjusted to ensure negative gap between the solder balls and the paste; SAC Solder Pre-form and Solder Paste or Flux Expansion of the adhesive in its thickness direction raised the balls from the paste and creates a positive gap 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 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

23 One Proposal to Simulate Gap Variation between the BGA Solder Ball and the Solder Paste on the PCB Land © HDP User Group International, Inc.23 Gap > 0 Board Adhesive Solder Preform BGA Package BGA Solder Balls Solder Paste 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

24 Simulation for the Central Solder Joints of the BGA Gap < 0 When the low temp solder pre-form melts balls lowered and touch SAC solder paste Balls and solder paste melt while in contact Gap at RT > 0 Gap < 0 Package Adhesive Room Temp ~ 20C Soak Zone Temp ~ 160C Reflow Zone Temp ~ 240C Low Temp Solder Pre-form and Solder Paste or Flux Initial set up entails a gap between the solder balls and the paste; gap amount controlled by amount (thickness) of adhesive 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 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

25 Requirements for Adhesive Under Component to Simulate the Gap between the Ball and the Paste during SMT Reflow Soldering © HDP User Group International, Inc.25 Gap > 0 Board 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 Adhesive 1)High Coefficient of Linear Expansion after Cure; 2)Sufficient Hardness/Modulus/Rigidity to push the package up as the adhesive expands 3)Survive temperatures up to 250C after cure 4)Dispensable or screen printable Key question: What is the range of Linear Expansion that is needed for the adhesive?

26 Ciscos SRT Rework Equipment Method for Head-on-Pillow Testing © HDP User Group International, Inc.26 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.

27 Conditions for Ciscos Method © HDP User Group International, Inc.27 C1 C2 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. Note: When initial contact is made between ball and paste, no H-o-P defects were formed

28 Photos of Ciscos Method for Evaluating H-o-P defects © HDP User Group International, Inc. 28 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

29 Malcom RCA-1 Observation Monitor © HDP User Group International, Inc.29 Observes and Records the components on a PCB as it goes through the Reflow Oven

30 Summary of Obj # 3 Experimental Plans © HDP User Group International, Inc.30 Experiment NamePhaseDescription 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 Beffect of adhesive volume on gap variation and package tilting during reflow soldering CExplore other materials with higher CTE than that of ME- 580+silicone fillers Solder Preform Development AProof of Concept Validation using off-the-shelf preform BPreform Design CPlated Through Hole Design DPreform Fabrication at Indium Corp EBoard Fabrication at Member PCB Fabricator Combined Adhesive and Solder Preform Validation A Using Developed Adhesive and solder preform with substrate and boards, conduct test runs with printed solder paste

31 Summary of Obj # 3 Experimental Plans © HDP User Group International, Inc.31 Experiment NamePhaseDescription 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 BScreening DOE using Process Variables to determine main effects and 2 factor interactions CComprehensive 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

32 Resources Needed for Initial Objectives © HDP User Group International, Inc.32 ExperimentResourcesPotential Source Modified Cisco Hot Air Rework Method Test Substrate LaminatePanasonic Fabrication of Test Substrate and Boards Member PCB Fabricator, to be identified Solder BallsSenju Solder PasteSenju/Indium/Alpha/Shenmao Stencils for solder printingNon-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 materialLord Corp / Panasonic / Other yet to be identified Solder PreformsIndium Corp SMT Reflow OvenFlextronics / Intel Designers for Solder Preform and Boards Members, to be identified

33 Resources Needed for Initial Objectives © HDP User Group International, Inc.33 ExperimentResourcesPotential Source Modified Plexus Method usign High CTE Material and Solder Preform High CTE materialLord Corp / Panasonic / Other yet to be identified Solder PreformsIndium Corp SMT Reflow OvenFlextronics / Intel Designers for Solder Preform and Boards Members, to be identified SMT Reflow OvenFlextronics / 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

34 Test Substrates Proposal 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 Ball PitchBall SizeBody Size Quantity of Substrates (Approx) Quantity of Balls per Substrate (Approx) 0.5 mm0.3 mm 7 mm mm0.5 mm 15 mm mm 0.6 mm35 mm

35 Proposed Schedule


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