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Codification of Flip Chip Knowledge

Antonio Prats

March 2002

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ObjectiveFacilitate practical applications of research results

• Design optimization• Specs• Materials selection• Product specific process development• Trouble shooting

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Two PartsYield Prediction Software

• “Placement Yield” – in-plane variations• “Assembly Yield” – out-of-plane variations

Codification Documents• “Underfill Codification” – Materials evaluation and

underfill process design• “Reflow Encapsulant Codification” – Materials

evaluation and reflow encapsulant process design

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Placement Yield SoftwareGoal

• Conservative estimate of defect levels associated with in-plane (primarily substrate) tolerances

Defect• A solder bump not in contact with its pad

User Input• Substrate layout, pad shapes and sizes, variations in

size and location, mask thickness, bump dimensions, machine accuracy

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Example Pad Design Screen

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Example Thickness Consideration Screen

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Assembly Yield SoftwareGoal

• Conservative estimate of defect levels associated with warpage, bump height variations, and solder collapse

Defect• A solder bump not in contact with its pad/paste• Solder Bridging (New for 2001)

User Input• Bump locations and variations in bump height, pad

diameters and thicknesses, paste volume, component and board warpage

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Assembly Yield Software Screen

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Underfill Codification Manual

• Discussion of issues important to the underfill process

• Establishment of a materials knowledge base to save time during process development

• Procedures for process development

• Troubleshooting (to be expanded in 2002)

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Table of Contents1 INTRODUCTION2 DISPENSER EVALUATION

2.1 Specific Flip Chip Issues3 MATERIALS SELECTION4 DATA BASE

4.1 Thaw4.2 Flow & 'Gel' Times4.3 Life4.4 Flow Time Optimization4.5 Fillet Thickness Dependence4.6 Cure4.7 Automatic Fillet Formation4.8 Proximity Test4.9 Bakeout Requirements4.10 Diagnostic Tests (Reference

Performance)5 MATERIALS SPECIFIC

EQUIPMENT CHARACTERIZATION

6 MATERIALS HANDLING6.1 Substrates6.2 Chips6.3 Underfill Materials

7 PRODUCT SPECIFIC PROCESS7.1 Underfill Process7.2 Bake7.3 Standoff7.4 Substrate Temperature7.5 Preferred Fillet Thickness7.6 Volumes7.7 Dispensing7.8 Final Flow Optimization7.9 Footprint & Keep Out7.10 Curing7.11 Wetting & Voiding7.12 SMT Process Integration

8 TROUBLESHOOTING9 REFERENCES

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Typical Correlation Between Nominal Dispensed Volume and Fillet Thickness

Johnson & Matthey 8802, 3 mil Gap

0

4

8

12

16

0 2 4 6 8 10 12

Nominal Dispense Value (mg)

Fille

t Thi

ckne

ss (m

il)

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Taper Flow Experimental Setup

ClampClamp

0 mil5 mil

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Different Dispense Patterns

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Reflow Encapsulant Codification Manual

• Discussion of issues important to assembly with reflow encapsulants, with emphasis on differences from underfill process

• Establishment of a materials knowledge base to save time during process development

• Procedures for process development

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Table of ContentsINTRODUCTIONDISPENSER EVALUATION

• Board Handling• Ease of programming, calibration (offsets)• Vision System• Pump Type• Dispense Volume Control• Uniformity and Precision• Heating• Cleaning• Technical support• Potential Alternatives: Stencil Printing

MATERIAL EVALUATION• Life• Bakeout• Dispensing

• Needle Size and Type• Volume

• Dispense Voids• Due to Substrate Features• From High Shear Rate• Absorption of Voids

• Placement• Wetting• Placement Force and Hold Time• Placement Voiding

• Reflow Soldering Window• Post Curing• Statistics

PROCESS DEVELOPMENT• Dispensing

• Repeatability of Volume/Fillet Thickness• Dispense Pattern

• Bakeout• Placement• Reflow Soldering Window• Post Curing

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Reflow Profiles for Testing Reflow Process Window

0

50

100

150

200

250

0 60 120 180 240 300Seconds

Tem

pera

ture

(°C

)

No-Flow #1 No-Flow #2No-Flow #3 No-Flow #4No-Flow #5 No-Flow #6No-Flow #7 No-Flow #8No-Flow #9 No-Flow #10

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Some Possible Dispense Patterns

Dot Full Square

Small Square X Small Squarewith Arms

AsteriskDotDot Full SquareFull Square

Small SquareSmall Square XX Small Squarewith Arms

Small Squarewith Arms

AsteriskAsterisk

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SummaryDefect Prediction Programs

• Design optimization• Specs

Codification Documents• Equipment and materials evaluation• Rapid product specific process design• Troubleshooting