Green mould compounds: Impact on second level interconnect reliability

The change-over from conventional to so-called green moulding compounds has gradually taken place in the last five years. These green mould compound materials have a lower thermal expansion and higher elastic modulus. As a consequence of the modified thermal and mechanical properties, an impact on the thermo-mechanical behaviour of the package-board assembly is expected (so-called Package Board Interaction: PBI). The CTE difference between the package and the board increases introducing the green mould compounds. This paper discusses the impact of the use of green moulding compounds to the second level solder joint fatigue cracking. The comparison with non-green mould compounds used in the past is done by experiments for TSOP´s and by finite element modelling studies for a wide range of packages. The study reveals that the impact of the transition to green mould compound is substantial and can lead to early solder joint fatigue failures in applications. The paper also shows that tests on flexible PCB´s underestimate the impact. In particular for assembly on rigid boards the mean life time may reduce to 20% of the life time obtained for non-green moulded packages.