using mlo’s to build vertical contact space …mlo aligned and placed on pcb 5. reflow the...
TRANSCRIPT
Presentation toSouthwest Test Workshop 2002
Using MLOs to Build Vertical Technology Space Transformers
Bill Fulton and Bill PardeeWentworth
Laboratories
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Overview1. Terminology2. Benefits of MLOs vs MLCs3. MLO Basics4. MLO Variables5. MLO Manufacturing Challenges6. Processing MLO for Use as Space Transformer7. Test Verification 8. Reliability9. Performance Data10. Conclusions
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Terminology/Acronyms 1. ST – Space Transformer2. MLO – Multi Layered Organic3. MLC – Multi Layered Ceramic4. BGA – Ball Grid Array5. FR4 – Fiber Glass6. ePTFE – Expanded Polyetraflouroethylene7. CRES – Contact Resistance8. C4 – Controlled-Collapse Chip Connection 9. CTE – Coefficient of Thermal Expansion10. OSP – Organic Solderability Perservative
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Benefits of MLO vs MLC
1. Design/Manufacturing Time
i. MLO – customer supplied at time of order
ii. MLC – lead time of up to three months
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Benefits of MLO vs MLC2. Cost
i. Typical MLO package – $15 - $50ii. Custom designed MLC – NRE $10,000 -
$15,000, $5,000 – $10,000 each (10 piece minimum)
3. Tighter Pitches (BGA side)i. Minimum pitch MLC 1.0 mm (typical)ii. Minimum pitch MLO 0.6 mm (typical)
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MLO BasicsApplication “Flip Chip” Packaging for1. Microprocessors2. ASICs3. DSPs4. Memory –
Flash and DRAM
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MLO Basics1. Design: Determined by customer’s
packaging group2. Vendors
i. 3M (W.L. Gore)ii. IBMiii. Fujitsuiv. Ibidenv. Kyoceravi. NTK
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MLO Basics
3. Compositioni. FR4 – most commonly used fiberglass-type materialii. ePTFE – newer material
1. resin composite – uniform structure throughout2. better machinability with laser3. better CTE matching4. ideal for dense arrays, tighter pitch size – device
side
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Typical MLO Assembly
Underfill
MLOSolder paste and spheres
PCB
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MLO Variables
1. Thickness2. BGA Pitch3. Pad Composition4. Solder Mask Opening5. Metal Stiffener Rings6. C4 Pitch7. Flatness
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MLO Manufacturing ChallengesStructural integrity
Problem - BGA pattern voids under C4 areaSolution - Underfill on BGA side
BGA PitchProblem - Accommodate smaller pitch requirements
• 1.27 mm – past• 1.00 mm – today• 0.80 mm – soon• 0.60 mm – future Solution - Create custom fine pitch solder stencils
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MLO Manufacturing ChallengesPad Composition
Problem – OSP and solder on padsSolution – Remove and plate with nickel and gold
Solder Mask OpeningProblem – Solder mask opening too smallSolution – Remove solder mask (proprietary process)
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MLO Manufacturing ChallengesMetal Stiffener Ring
Problem – C4 pads recessed below stiffener Solution – Stepped Cobra® head
Stiffener
C4 pad
area
Step
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MLO Manufacturing ChallengesC4 Pitch
No issue with current fine pitch contact technology
FlatnessProblem – Warping of extra-thin MLOs Solution – Custom lap at assembly
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Processed C4 Pad
Solder mask
C4 pad
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MLO Processing
Unprocessed MLO –soldermask still on
pad area
Processed MLO –solder mask
cleared from PAD area
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MLO Processing Preparation1. Remove solder
2. Remove solder mask exposing pad3. Nickel and gold plate
Solder Solder Mask
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Post-Processing Inspection
1. Visually inspect C4 pads for damage2. Verify alignment of C4 pads within .0003”
in true position3. Measure flatness of C4 area – .0005”or
less4. Measure flatness on entire MLO – .0015”
or less5. Test for allowable leakage <5 nA @5VDC
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Bonding MLO on Probe CardBGA Attach1. Equipment:
i. Solder Stencil Printer –apply solder to BGA pads
ii. Programmable Reflow Oven
2. Fixturing: i. BGA Alignment
Placement Tool– align and place
MLO to PCB
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Bonding MLO on Probe CardBGA Attach Techniques1. Apply solder paste and solder spheres to
BGA pads2. Reflow solder 3. Apply solder paste to PCB4. MLO aligned and placed on PCB5. Reflow the assembly in programmable oven 6. Apply underfill to MLO7. Inspect
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Completed Space Transformer
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Verification of Probe Card
Final Assembly Test1. Leakage2. Bulk Planarity3. Overdrive leakage4. Alignment5. Full planarity & CRES
6. Wire Check7. Components
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Performance Data
Typical Pad Wear
1 million touchdowns
Initial condition
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Performance Data
MLO Lifetime Performance as Measured by Path Resistance and Planarity
0
0.5
1
1.5
2
0 200000 400000 600000 800000 1000000
Touchdowns
CRes ohms Planarity Values mil
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ConclusionMLO/ST technology benefits:1. Fast turnaround as compared to custom-
designed MLC2. Lower cost probe card cost due to lower ST
costs3. Closer match to actual “real world” application
due to similarity of materials 4. Performance equal to more expensive MLCs5. Ideal, cost-effective solution for short-runs of
ASICs and other specialty devices