Codification of Flip Chip Knowledge

Antonio Prats March 2002 1

Objective

Facilitate practical applications of research results • Design optimization • Specs • Materials selection • Product specific process development • Trouble shooting 2

Two Parts Yield 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 3

Placement Yield Software Goal

• 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 4

Example Pad Design Screen

5

Example Thickness Consideration Screen

6

Assembly Yield Software Goal

• 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 7

Assembly Yield Software Screen

8

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) 9

Table of Contents 1 INTRODUCTION 2 DISPENSER EVALUATION

2.1 Specific Flip Chip Issues

3 MATERIALS SELECTION 4 DATA BASE

4.1

Thaw 4.2

4.3

4.4

4.5

Flow & 'Gel' Times Life Flow Time Optimization Fillet Thickness Dependence 4.6

4.7

4.8

4.9

Cure Automatic Fillet Formation Proximity Test Bakeout Requirements 4.10 Diagnostic Tests (Reference Performance)

5 MATERIALS SPECIFIC EQUIPMENT CHARACTERIZATION 6 MATERIALS HANDLING

6.1

6.2

6.3

Substrates Chips Underfill Materials

7 PRODUCT SPECIFIC PROCESS

7.1

7.2

Underfill Process Bake 7.3

7.4

7.5

7.6

Standoff Substrate Temperature Preferred Fillet Thickness Volumes 7.7

7.8

Dispensing Final Flow Optimization 7.9

Footprint & Keep Out 7.10 Curing 7.11 Wetting & Voiding 7.12 SMT Process Integration

8 TROUBLESHOOTING 9 REFERENCES

10

Typical Correlation Between Nominal Dispensed Volume and Fillet Thickness Johnson & Matthey 8802, 3 mil Gap

16 12 8 4 0 0 2 4 6 8

Nominal Dispense Value (mg)

10 12 11

Taper Flow Experimental Setup

Clamp Clamp 0 mil 5 mil 12

Different Dispense Patterns

13

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

14

Table of Contents INTRODUCTION DISPENSER 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 15

Reflow Profiles for Testing Reflow Process Window 250 200 150 100 50 0

0 60 No-Flow #1 No-Flow #3 No-Flow #5 No-Flow #7 No-Flow #9 120 180

Seconds

No-Flow #2 No-Flow #4 No-Flow #6 No-Flow #8 No-Flow #10 240 300 16

Some Possible Dispense Patterns

17

Summary Defect Prediction Programs

• Design optimization • Specs

Codification Documents

• Equipment and materials evaluation • Rapid product specific process design • Troubleshooting 18