무전해 Ni-P 두께와 Assembly Process가 Solder Ball Joint의 신뢰성에 미치는 영향

Abstract

The ability of electronic packages and assemblies to resist solder joint failure is becoming a growing concern. This paper reports on a study of high speed shear energy of Sn-4.0wt%Ag-0.5wt%Cu (SAC405) solder with different electroless Ni-P thickness, with <TEX>$HNO_3$</TEX> vapor's status, and with various pre-conditions. A high speed shear testing of solder joints was conducted to find a relationship between the thickness of Ni-P deposit and the brittle fracture in electroless Ni-P deposit/SAC405 solder interconnection. A focused ion beam (FIB) was used to polish the cross sections to reveal details of the microstructure of the fractured pad surface with and without <TEX>$HNO_3$</TEX> vapor treatment. A scanning electron microscopy (SEM) and an energy dispersive x-ray analysis (EDS) confirmed that there were three intermetallic compound (IMC) layers at the SAC405 solder joint interface: <TEX>$(Ni,Cu)_3Sn_4$</TEX> layer, <TEX>$(Ni,Cu)_2SnP$</TEX> layer, and <TEX>$(Ni,Sn)_3P$</TEX> layer. The high speed shear energy of SAC405 solder joint with <TEX>$3{\mu}m$</TEX> Ni-P deposit was found to be lower in pre-condition level#2, compared to that of <TEX>$6{\mu}m$</TEX> Ni-P deposit. Results of focused ion beam and energy dispersive x-ray analysis of the fractured pad surfaces support the suggestion that the brittle fracture of <TEX>$3{\mu}m$</TEX> Ni-P deposit is the result of Ni corrosion in the pre-condition level#2 and the <TEX>$HNO_3$</TEX> vapor treatment.