Page 10 - Wire Bonding in Microelectronics

Co n t e n t s ix

5.3.7 Au-Au, Al-Al, Au-Ag, and Some
Less-Used Monometallic Bonding
Systems . . . . . . . . . . . . . . . . . . . . . . . . . 164
Appendix 5A Rapid Bond Failure in
Poorly Welded Au-Al Wire Bonds . . . . . . . . . 168
Appendix 5B Thermal Degradation in Au-Al
Ball Bonds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170
Effect of Manufacturing & Service
Conditions . . . . . . . . . . . . . . . . . . . . . . 173
Appendix 5C Various Bond-Related
Corrosion Reactions . . . . . . . . . . . . . . . . . . . . . 174
Halogen-Aluminium Corrosion Reactions . . . 174
Sulfur-Copper-Chlorine Corrosion
Reactions . . . . . . . . . . . . . . . . . . . . . . . 176
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176
6 Introduction to Plating, Section A (Gold) and
Section B (Nickel-Based) Bond Pad
Technology and Reliability . . . . . . . . . . . . . . . . . . . . 183
Section A Bond Failures Resulting from
Gold-Plating Impurities and Conditions . . . . . . . . 184
6A.1 Gold Plating . . . . . . . . . . . . . . . . . . . . . . . . . . 184
6A.2 Specific Plating Impurities . . . . . . . . . . . . . . 186

6A.3 Hydrogen Gas Entrapments in
Plated Films . . . . . . . . . . . . . . . . . . . . . . . . . . . 188
6A.3.1 Failure Symptoms that Appear
Similar to Gas Entrapments:
Resistance Drift . . . . . . . . . . . . . . . . 189
6A.4 Failures from Metallic Impurities in or
on Gold Films that Are Not an Intentional
Part of Plating Baths . . . . . . . . . . . . . . . . . . . . 190
6A.4.1 Introduction . . . . . . . . . . . . . . . . . . . 190
6A.4.2 Nickel . . . . . . . . . . . . . . . . . . . . . . . . . 192
6A.4.3 Copper . . . . . . . . . . . . . . . . . . . . . . . . 193
6A.4.4 Chromium . . . . . . . . . . . . . . . . . . . . . 194
6A.4.5 Titanium . . . . . . . . . . . . . . . . . . . . . . 194
6A.4.6 Tin . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195
6A.5 Gold Plating Standards . . . . . . . . . . . . . . . . . 195
6A.5.1 Recommendations for Reliable
Gold-Plated Films . . . . . . . . . . . . . . 196
6A.6 Electroless Autocatalytic Gold . . . . . . . . . . . 197
6A.7 Nongold Platings Used in Electronics
Packaging . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197
Chapter 6A References . . . . . . . . . . . . . . . . . . . . . . 198