THERMO-MECHANICAL RELIABILITY OF LEAD-FREE SOLDER JOINTS IN FLIP CHIP PACKAGE FOR HIGH-TEMPERATURE APPLICATIONS
Emeka H. Amalu N. N. Ekere Musa T. Zarmai
AbstractFlip chip (FC) is a package used to assembly electronic device for high-temperature applications. The operating conditions at high-temperatures support the formation and growth of intermetallic compound (IMC) in a flip chip joints which contain tin as an alloying element of the package solder ball and copper in the bond pad of the printed circuit board (PCB). High-temperature applications coupled with the presence of IMC accelerate the degradation of the solder joints in the package which consequently results in assembly failure. The damage mechanism of these solder joints is studied whilst the magnitude of the damage was quantitatively evaluated to determine the impact of the thickness of intermetallic compound (IMC) layer on the reliability of the joints. Finite element modelling utilising Anand’s plasticity model was employed to simulate the visco-plastic response of the solder joints of five virtual test vehicle assemblies of the FC package to an induced temperature cycle load. The assemblies have different IMC layer thickness and these geometries were subjected to the same accelerated high-temperature cycles utilising, in parts, the IEC standard 60749-25. The results demonstrate that the thickness of IMC layer impact the reliability of the FC solder joints. The results also show that the magnitude of the average accumulated visco-plastic energy density per cycle ( ) depends on the volume percentage of solder and IMC in the joints. The dependency is proposed as the reason why the existing life prediction models based on are not sufficient in predicting the damage in solder bump joints.