Alternative lead free die attach for power module packaging

Inhalt:
The next review of exemption 8(e) about lead in high melting temperature type solders (i.e. lead based alloys containing 85% by weight or more lead) will be take place in 2014. An alternative to lead base alloy has to be defined before this dead line in order to comply with lead free regulation for automotive high power electronics. Lead free soldering is known to generate more voids than the current high lead content solder. Therefore, new processes, such as vacuum or forming gas reflow soldering, have been investigated in order to reduce the void within the solder joint and to improve the packaging reliability. First, this paper focuses on the lead free die attachment process optimization by using a die laser soldering technology, second on the reliability evaluation of the different test samples, and third onto a reliability simulation procedure for characterizing future assemblies. Several commercial lead free alloys have been evaluated throughout Design of Experiments considering the following quality criteria: porosity rating of the solder joints, thermal shock and power cycling tests withstanding. An acceptable lead-free solder solution is proposed for highly constrained power application. It satisfies both process requirements and reliability objectives compared to standard high lead solders.