Investigation of IMC growth and solder joint reliability on new surface finish-ENEPIG

As the semiconductor technology advancing, the component size is gradual miniaturizing, so either busless design or electroless plating process should be used to meet the requirement of high routing density. Between these two solutions, electroless plating process has another advantage-lower cost. In electroless plating process, ENIG is popular in the industries, but it easily causes solder joint problems due to potential black pad issue. Therefore, a new surface finish- E'less nickel E'less Palladium immersion Gold (ENEPIG) is developed to overcome this problem by introducing a Pd layer between Ni and Au. In this paper, we studied the solder joint reliability for ENEPIG after multiple reflow times ( 1x, 3x, 6x ) by using conventional ball shear test, cold-ball pull test. High speed ball shear test was also applied to simulate high strain rate loading, such as drop test. Failure mode and micro analysis were carried out by the analytical tools, including SEM and EDX. From the SEM imagines, it is founded that the IMC thickness of electrolytic Ni/Au was thicker than ENEPIG under identical reflow times. From the ball shear test results, it seems no obvious difference between different reflow times for Electrolytic Ni/Au and ENEPIG. The failure mode of Electrolytic Ni/Au and ENEPIG were both broken at solder. Cold-ball pull test showed Electrolytic Ni/Au and ENEPIG have same failure mode distribution. In the high speed ball shear test, the behavior of broken interface was quite different between Electrolytic Ni/Au and ENEPIG. The broken interface of electrolytic Ni/Au ususlly happened at IMC phase, but the ENEPIG usually happened at solder phase. It could be deduced that ENEPIG has better solder joint quality.