Page 7 - Wire Bonding in Microelectronics

vi Co n t e n t s

2.7 Variations of Fine-Wire Bonding Technology . . . 38
2.7.1 Ribbon Wire Bonding . . . . . . . . . . . . . 38
2.7.2 Parallel Gap and Tweezer Welding . . . 39
2.8 Major Chip Interconnection Alternatives to
Wire Bonding (Flip Chip and TAB) . . . . . . . . 42
2.8.1 Flip Chip . . . . . . . . . . . . . . . . . . . . . . . . 42
2.8.2 Tape-Automated Bonding . . . . . . . . 44
2.9 Wire-Bonding Technology: A Comparison and
Future Directions . . . . . . . . . . . . . . . . . . . . . . . . 45
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

3 Bonding Wire Metallurgy and Characteristics That
Can Affect Bonding, Reliability, or Testing . . . . . . 51
3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
3.2 Stress-Strain Characteristics of Bonding
Wires . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
3.3 The Shelf-Life Aging of Bonding Wires . . . . . 53
3.4 General Discussion of Gold
Bonding Wire . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
3.5 Aluminum Wire for Ultrasonic
Wedge Bonding . . . . . . . . . . . . . . . . . . . . . . . . . 61
3.6 Wire and Metallization Hardness . . . . . . . . . . 62
3.7 The Effect of EFO Polarity on Gold
Wire and Its Metallurgy . . . . . . . . . . . . . . . . . . 63
3.8 Metallurgical Fatigue of Bonding Wires . . . . 63
3.9 Copper Wire for Ball Bonding . . . . . . . . . . . . . 67
3.10 Conductor Burn Out (Fusing) . . . . . . . . . . . . . 68
3.10.1 Bonding Wires . . . . . . . . . . . . . . . . . . 68
3.10.2 The Maximum Allowable Current
for PCB and MCM Conductors . . . 72
Appendix 3A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
Appendix 3B . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
4 Wire Bond Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
4.2 The Destructive Bond Pull Test . . . . . . . . . . . . 80
4.2.1 Variables of the Bond Pull Test . . . . . 80
4.2.2 Peeling (Tweezer Pulling) for “Quality
Tests” and Troubleshooting of Wedge
Bonds and Crescent (Tail) Bonds . . . 83
4.2.3 Failure Predictions That Are Based
on Pull Test Data Must Have

Confirmed Normality . . . . . . . . . . . . . 85