High-temperature fatigue life of flip chip lead-free solder joints at varying component stand-off height

摘要

The recent uses of microelectronics as sensors or control devices at high-temperature ambient increase the rate of visco-plastic degradation of solder joints of their components. The response of solder bumped joints to the induced thermal load culminates in plastic strain which over many cycles may accumulate damage in the joints, subsequently leading to their fatigue failures. Finite element modelling is employed to investigate the impact of static structural factors of flip chip (FC) assembly on its solder joint damage at high-temperature excursions. This paper discusses results of a modelling study focused on effects of component stand-off height (CSH) and intermetallic compound (IMC) on static structural integrity of lead-free solder joints in a flip chip FC48D6.3C457 package which is cycled between -38 ℃ and 157 ℃ temperatures. The result analysis is based on accumulation of damage indicators such as stress, strain and plastic work density in the solder joints. The accumulated damage was used to predict the thermo-fatigue life of different architectures of the FC assembly. It was found that the fatigue life of the joint assemblies decrease exponentially as the component stand-off height decreases in a cubic function. Based on our research results, it is proposed that the size of diameter of bond pad defined by solder mask on printed circuit board (PCB) should not exceed 110% of the size of diameter of bond pad at the chip side.