Page 11 - Wire Bonding in Microelectronics

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Section 6B Ni-Based Platings Used in
Electronics Packaging . . . . . . . . . . . . . . . . . . . . . . . . . 200
6B.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . 200
6B.2 Electroless Plating Processes . . . . . . . . . . . . . 202
6B.2.1 Ni Plating . . . . . . . . . . . . . . . . . . . . . . 203
6B.2.2 Pd Plating . . . . . . . . . . . . . . . . . . . . . 205
6B.2.3 Au Plating . . . . . . . . . . . . . . . . . . . . . 206
6B.3 Wire Bond Process Window and Reliability
on Plated Bond Pads . . . . . . . . . . . . . . . . . . . 208
6B.3.1 Ni/Au . . . . . . . . . . . . . . . . . . . . . . . . 208
6B.3.2 Ni/Pd/Au . . . . . . . . . . . . . . . . . . . . . 212
6B.3.3 Ni/Pd . . . . . . . . . . . . . . . . . . . . . . . . . 216
6B.4 Plasma Cleaning . . . . . . . . . . . . . . . . . . . . . . . 220
6B.5 Direct Cu Bonding . . . . . . . . . . . . . . . . . . . . . 221
Chapter 6B References . . . . . . . . . . . . . . . . . . . . . . . . 222
7 Cleaning to Improve Bondability and
Reliability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 225
7.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . 225
7.1.1 Molecular Cleaning Methods to Enhance
Bondability and Reliability . . . . . . . . 228
7.1.2 Ultraviolet-Ozone Cleaning . . . . . . . 229
7.1.3 Plasma Cleaning . . . . . . . . . . . . . . . . . 232
7.1.4 Plasma Cleaning Mechanism . . . . . . 235
7.1.5 Discussion and Evaluation of
Molecular and Solvent Cleaning
Methods . . . . . . . . . . . . . . . . . . . . . . . . 237
7.1.6 Problems Encountered in Using
Molecular Cleaning Methods . . . . . . 238
7.1.7 Burnishing . . . . . . . . . . . . . . . . . . . . . . 240
7.2 The Sensitivity of Different Bonding
Technologies to Surface Contamination . . . . . 242
Appendix 7A Circuit Damage Caused by Plasma
Cleaning During Packaging . . . . . . . . . . . . . . . 244
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245

8 Mechanical Problems in Wire Bonding . . . . . . . . . 249
8.1 Cratering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 249
8.1.1 Introduction . . . . . . . . . . . . . . . . . . . . 249
8.1.2 Bonding Machine Characteristics and
Setup Parameters . . . . . . . . . . . . . . . . 254
8.1.3 Bonding Force . . . . . . . . . . . . . . . . . . . 256
8.1.4 Tool Wire-Pad Impact Force . . . . . . . 258
8.1.5 Causes of Cratering—Materials . . . . 258
8.1.6 Intermetallic Effects on
Cratering . . . . . . . . . . . . . . . . . . . . . . . 260