ABSTRACT
ABSTRACT This chapter discusses the mechanism of corrosion of leadfree solders in harsh environments, such as marine environments or acid rain. Lead-free solders are susceptible to galvanic corrosion in the presence of humidity, resulting from the presence of dissimilar elements in their microstructure. The mechanism of galvanic corrosion is explained in terms of electrochemical migration, with potentiodynamic polarisation being the main mode of investigating the mechanism of corrosion. A few case studies
CONTENTS
8.1 Lead-Free Solders ....................................................................................... 150 8.2 Corrosion of Lead-Free Solders ................................................................ 152
8.2.1 Types of Corrosion ......................................................................... 152 8.2.2 Galvanic Corrosion ........................................................................ 153 8.2.3 Electrochemical Migration ........................................................... 154 8.2.4 Potentiodynamic Studies for Corrosion Investigation ............. 154 8.2.5 Selected Case Studies on Corrosion Resistance of Lead-
Free Solders ..................................................................................... 157 8.2.5.1 Case Study 1: Sn-3.5Ag and Sn-0.8Cu .......................... 157 8.2.5.2 Case Study 2: Sn-3.0Ag-0.5Cu (SAC 305)/Sn-1.0Ag-
0.5Cu (SAC 105) Solder ................................................... 158 8.2.5.3 Case Study 3: Doped SAC Solder Alloys ..................... 158 8.2.5.4 Case Study 4: Impact of Salt Exposure on Package
Reliability ........................................................................ 158 8.2.5.5 Case Study 5: Role of Passivation Layer on
Material Surface .............................................................. 159 8.2.6 Experimental Methodologies to Investigate Corrosion ........... 159
8.2.6.1 Water Drop Test ............................................................... 159 8.2.6.2 ECM Investigation Using Voltage-Biased
Microchannel ................................................................... 161 8.3 Impact of Corrosion on Lead-Free Solder Performance ....................... 162 8.4 Conclusion .................................................................................................. 163 References ............................................................................................................. 164
on the corrosion behaviour of different lead-free solders are illustrated. In addition, some experimental methods to investigate corrosion behaviour are elaborated. Finally, a discussion on industrial standards in microelectronics packaging subjected to harsh environmental conditions is presented, in terms of performance, reliability and functionality.
