Lead-free Solder Joint Electromigration Induced Interface Compound Growth And Failure Research

As the development of microelectronic packaging continues to be miniaturization and high performance package density, electro-migration is becoming an important failure mechanism of interconnects, The Roadmap for Semiconductors(ITRS) regard electro-migration failure mechanism as the key bottleneck of high density packaging technology development. In this paper, the problem of lead-free solder microstructure compounds evolution and crack expansion under the thermal and electric coupling is studied, the main works and results are as follows:(1) The lead-free solder interconnect electro-migration test platform was build, and design test equipment to carry out electro-migration experiments. Electro-migration tests were carried out tests on three aspects: the chip has been tested for different Ambient temperature and current density of the chip surface temperature; the chip has been tested for the compounds growth evolution of lead-free solder at ambient temperature of 150℃ and the current density under 1.8×104A/cm2. After test, the sample was observed under SEM compound structure evolution electron microscope; Finally, the chip has been tested for crack formation and expansion of lead-free solder at ambient temperature of 150℃ and the current density under 1.5×104A/cm2. After test, observe the crack structure of the test sample under SEM electron microscope.(2) The electro-migration experiments are summarized and analyzed. Based on actual chip temperature measurement, the temperature variation was summaried and chip thermal convection coefficient of chip chip surface is determined by the finite element analysis.The electro-migration induced solder compounds growing were analyzed,and the relationship between compounds growth angle change rate with cut-off voltage, the compounds growth rate with cut-off voltage were studied, wherein: the left solder growth rate is 6.2%/10 mv, to the right solder growth rate was 12.6%/10 mv. The left side of the solder joint angle change rate of compounds is 6.5degrees/10 mv, the right side of the solder joint angle change rate is 12.75degrees/10mv; the test of crack were analyzed, and there are two kind of crack formations, one is the continuous integration smooth rounded crack formation, one is due to the internal stress caused by the expansion of brittle cracks.(3) The test vehicle was modeled by finite element software ANSYS, and combined with experimental test results, the thermoelectric coupling analysis is carried. The experimental results and the temperature distribution ANSYS simulation results is relatively consistent. Based on atomic density integration method(ADI), the predict failure position of critical joints and SEM results were compared. The results showed that: ADI method can predict the location of solder electro-migration failure accurately.