fcbga package warpage definition stage project raiyo aspandiar - intel hdp user group member meeting...
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FCBGA Package Warpage Definition Stage Project
Raiyo Aspandiar - IntelHDP User Group Member
MeetingHost: Oracle
Santa Clara, CA.
Feb. 26. 2013© HDP User Group International, Inc. 1
© HDP User Group International, Inc. 2
Purpose
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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.
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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
• 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 TechVideo camera
Reflow Oven Belt or Rail
FCBGA Package
Solder BallsSolder Paste
Camera fixture
6
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1 2 3 4 5 6 7 8 9 10 Cooling
Real Time Videos of Solder Joint Formation
Time
Tem
pera
ture
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Two Real Time Videos of Solder Joint Formation of a FCBGA package with high dynamic warpage
will now be shown
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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
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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
Goal
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Establish a limit for dynamic package warpage
that can be mitigated during board assembly
without impacting solder joint quality
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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
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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
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What has been Done to Date
• Project Scope, Objectives, and Flow defined• Key Variables Identified to Control and Monitor during SMT Reflow
Solderingo 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 Cisco’s Rework Equipment Use Method Real Time observation of Solder Joint Formation using Malcom Tech Camera’s
and overs
Drafted Experimental Plans and Resources Needed for initial Objectives
Defined Test Substrate /Board Requirements© HDP User Group International, Inc. 13
19-21
22-29
34
30-33
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 oveno 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
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
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Proposed Project Flow
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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
Back-up
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Temp
Effect of Typical Dynamic Warpage Characteristics of FCBGA packages on Solder Joint Formation
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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
reflowCool 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
Variation of Gap between Bottom of Solder Ball and Top of Solder Paste (when solid or molten)
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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 PointGap 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
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 regionSharp 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 reachedContact developed between the solder ball and solder paste later in the soak zone
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Simulation for the Corner and Outer Row Solder Joints of the BGA
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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
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
One Proposal to Simulate Gap Variation between the BGA Solder Ball and the Solder Paste on the PCB Land
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Gap > 0
Board
Adhesive
Solder Preform
BGA PackageBGA 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
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
Requirements for Adhesive Under Component to Simulate the Gap between the Ball and the Paste during SMT Reflow
Soldering
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Gap > 0
Board Expansion of the adhesive in its thickness direction raises the balls from
the paste and creates a positive gapMinimum 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 expands3) Survive temperatures up to 250C after cure4) Dispensable or screen printable
Key question: What is the range of Linear Expansion that is needed for the adhesive?
Cisco’s SRT Rework Equipment Method for Head-on-Pillow Testing
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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.
Conditions for Cisco’s Method
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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 timebefore solidification.
Note: When initial contact is made between ball and paste, no H-o-P defects were formed
Photo’s of Cisco’s Method for Evaluating H-o-P defects
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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
Malcom RCA-1 Observation Monitor
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Observes and Records the components on a PCB as it goes through the Reflow Oven
Summary of Obj # 3 Experimental Plans
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Experiment Name Phase Description of Experiment
High CTE Adhesive Development
AFeasibility 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
A Proof of Concept Validation using off-the-shelf preform
B Preform Design
C Plated Through Hole Design
D Preform Fabrication at Indium CorpE Board 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
Summary of Obj # 3 Experimental Plans
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Experiment Name Phase Description of Experiment
Development of Modified Cisco Hot Air Rework
Machine Method
A
Exploratory Experimental Runs to confirm the method worksComprehensive 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 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
Resources Needed for Initial Objectives
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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
Resources Needed for Initial Objectives
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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
SMT Reflow Oven 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
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 Pitch Ball Size Body SizeQuantity of Substrates
(Approx)
Quantity of Balls per Substrate
(Approx)
0.5 mm 0.3 mm 7 mm 150 600
0.8 mm 0.5 mm 15 mm 150 800
1.0 mm 0.6 mm 35 mm 300 1000
Proposed Schedule