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Pad Crater ProjectPad Crater Project““Definition StageDefinition Stage””
Thilo Sack
Celestica
Update for Member Meeting
9/21/2011
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The The issue(sissue(s))
• Pad Cratering defects are a significant challenge
with Pb-free PCB materials and/or Pb-free solders,
particularly associated with large BGA devices
• Pad Pull or Ball shear testing has not shown to
consistently represent the actual propensity for pad
cratering of a material and in some cases can give
misleading and/or opposite results from what
actually occurs in real assemblies
• A way is needed to rank order materials that is
directly related to actual pad cratering
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Project OverviewProject Overview
• Create a relatively simple test vehicle with a single large BGA assembled in the middle– 6 layers, 0.093” thick
• Fabricate the bare boards from multiple different materials– Include a significant variety of materials, filled and unfilled
– Include materials that have also done “well” in HDPUG Pb-free materials projects
– Don’t test materials that have done poorly in HDPUG Pb-free materials projects
– Other materials as suggested by members
• Perform bend to break testing to rank order the materials– Design TV to virtually ensure trace breaks simultaneous with
laminate (Electrical break)
– Spherical bend testing
– Will need to include some amount of strain gage measurements (CLS to support a limited subset)
– Both Single Bend to Break and Repeated Load to Break
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Project Overview (contProject Overview (cont’’d)d)
• On the same boards ALSO perform Cold Ball Pull testing for
a correlation to actual pad cratering
– Intel will support this
• On the same boards – ALSO perform Charpy Impact testing
(May or may not track with fracture toughness/pad
cratering).
– Bob Nevis (Microtek) and Shengyi have both offered to
support this testing.
– Need to understand how to quantify these results
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What this Project will ProvideWhat this Project will Provide
• Rank order of materials (based on
electrical failure) in
– Single bend to break
– Repeated bend to break
– Cold Ball Pull (CBP Testing)
– Charpy Impact & Surface Impact Testing
– Limited strain data
• Correlation of the results (if possible)
between tests
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Bend to Break TestingBend to Break Testing
• Meadville to support Bend to Break testing
– Spherical bend to be used
– 3000-3500 uε/sec is the sweet spot to
minimize scatter in the results ...
• 1000 and lower introduces a different failure mode,
6000-7000 exhibits twice the scatter in the results ...
this is typical of behavior seen in a brittle material.
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Spherical Bend Fixture
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Key IssuesKey Issues
• Define the materials to be tested
– Compare filled vs. unfilled, FR4 – brominated and HF,
Selected High speed materials
– Look at “cap” technologies – such as Zeta
– Select “good” materials (HDPUG Pb-free Materials 1
and 2)
• Material suppliers need to supply the materials at no cost
– First Draft/Proposed Material List follows
• Define the required sample size
– 10? Single Bend to Break
– 20? Repeated Bend to Break
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ComponentComponent
• Practical Components A-PBGA680-1.0mm-35mm-DC-LF-305
• PBGA 680 35x35mm Perimeter+ BGA, 1mm pitch
• 689 x 689 mil die size
• Quote of 1000 for $10,700.00
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Test Vehicle DesignTest Vehicle Design
Topside of
board
shown.
Bottom side
of board is
identical
with a
footprint
change
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Rough Proposed Rough Proposed StackupStackup –– To be refined To be refined
to specify exact glass stylesto specify exact glass styles
6 layer board - rough stackup
Prepreg - 106 or 2113 (Hi vs. Low Resin)- Cap for those specific constructions
Prepreg - 106 or 2113 (Hi vs. Low Resin)- Cap for those specific constructions
.093" over laminate
PrepregL4 1 ounce Cu Plane
LaminateL5 1/2 ounce Cu
L6 1/4 ounce Cu
L1 1/4 ounce Cu
L2 1/2 ounce Cu
LaminateL3 1 ounce Cu Plane
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Test Vehicle (continued)Test Vehicle (continued)
Top - NSMDBottom – NSMD
except for corners as shown are SMD
• “Bend to break” of Cu trace feature• 3 mil traces off the corner pads
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CBP Standard Coupon
16 mil
18 mil
15 mil
17 mil
14 mil
0.125” tooling holes1.75” apart
10 x 10 pad arrays on 1 mm centers
14 mil pad with 24 mil soldermask clearance
15 mil pad with 25 mil soldermask clearance
16 mil pad with 26 mil soldermask clearance 17 mil pad with 27 mil soldermask clearance
18 mil pad with 28 mil soldermask clearance
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Charpy Impact Test
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Surface Impact Test
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Surface Impact Test (cont’d)
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Proposed Panelization
16 mil
18 mil
15 mil
17 mil
14 mil
Surface Impact
Coupon
Cold Bump Pull
Coupon
CharpyImpact Test
Coupon
Charpy and Surface Impact Test Coupons will be free of all copper in the inner layers.
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Repeated Bend to Break
• What was the correct limits ??
– current proposal for 2 levels 60% and 80% of
“single bend to break value” ??
• Select a small subset of materials (ie.
370HR and a higher modulus) material to
perform initial larger range of “repeated
bend to break” values to better establish
practical limits
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Considerations for Pad Considerations for Pad CrateringCratering TestTest
• Materials
– Filled vs Unfilled Hi Tg Phenolic Resin
– Halogen Free
– Dicy
– Mid Tg
– High Speed
– Cap Layers
• Resin Content/Glass style effect on outer layers
– 106 vs. 2116 between L1-2 and N-N-1
• Pad Size
– Normal vs. enlarged solder mask defined pads,
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PreliminaryPreliminary Material List (part 1) Material List (part 1)
• High Tg Filled Phenolic FR4s– Isola 370HR– EMC EM-827– Panasonic R1755V – Shenzen Pacific (PIC) FL-170 (Possibly replace with Hitachi MCL-E-75G)– ITEQ IT-180i– Panasonic R2125– Grace GA-170LE– Shengyi S1190
• High Tg Non-filled Phenolic FR4s– Isola 370 Turbo– Shengyi S1170– TUC TU-722
• High Tg Halogen Free FR4s– Grace GA-HF-17– ITEQ IT-170GRA – EMC EM-370(D) or EMC-370 (one but not both)– Panasonic R1577 (Megtron 2) – Shengyi S1165– Ventec VT-447– TUC TU-862HF– Hitachi MCL-HE-679G
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PreliminaryPreliminary Material List (part 2) Material List (part 2)
• Mid-Tg FR4s
– ITEQ IT-158
– EMC EM-825
– Isola 254 - This a dicy FR4 -OK in low layer count Pb-free
• High Speed Materials
– Isola FR-408HR
– Panasonic Megtron 4
– TUC TU-872LK or SLK
– EMC EM-828
– MGC FL-700
– Panasonic Megtron 6
• Cap Materials (over Isola 370HR)
– Zeta
– Shengyi S1160F
– Hitachi KS-6600
– Hitachi CUTE
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Proposed Process Flow
Impact Tests
DMA Test
Bend TestMonotonic or
Spherical Bend(Meadville)
Ship to Assembler
Precondition Bake 4hrs 120C
& Cool
PCB Fabrication
Precondition Bake 8hs 120C
& Cool
Procure Components
Ship to Assembler
Mark Lot Codes & SN
on PCBs
Kit PCBs, Components & Materials
Assemble & Test
Ship to Test Lab
Divide & Kit Test
Specimens
Precondition Bake 4hrs 120C
& Cool
DMA
Cold Bump Pull(Intel)
Charpy & Surface Impact
(Shengyi)
Modulus 25-200CGlass Transition
Variables at Fail
Document Post Impact Conditions
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What this Project WILL NOT DO What this Project WILL NOT DO
(as currently planned)(as currently planned)
• It will not provide data that necessarily correlates to
pad cratering occurring by thermo-mechanical
stresses – such in reflow/cool-down as material
properties above Tg will be very different from those
at room temperature.
• If Charpy Impact correlates to pad cratering – can
possibly repeat on hot boards comparatively easily
(Phase 2 – using same boards built as same time in
this project?)
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Where are we on this Project?Where are we on this Project?
• Need to resolve– Materials list/sample sizes
• Current funding for 500 parts only
• Either we increase the funding to get 1000 parts or decrease either
– Samples size per material
– Number of materials/options
• Need to finalize
– Stackup
– Material stackup options
– Material supplier commitments (to provide materials)
– Fabricators to build
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Project MilestonesProject Milestones
• Define the full extent of the Project - Team
• Define the test vehicle – Team - complete– Component
– Board (layers, thickness, size, etc.)
• Design the Test Vehicle – ALU - complete
• Determine materials to test – Team – in progress
• Determine the required sample sizes - Team
• Material suppliers provide materials at no cost in return for rank ordering (coded)
• Fabricators to build the test vehicle – TBD - Multiple
• Procure components – Oracle +?
• Assemble Test vehicles – Celestica/Flextronics?
• Limited strain gauge testing - Celestica
• Bend testing- Meadville
• Cold Ball Pull testing – Intel
• Charpy & Surface Impact testing - Shengyi
• Data analysis and reporting