Thermal fatigue endurance of Sn3Ag0.5Cu0.5In0.05Ni and Sn2.5Ag0.8Cu0.5Sb solders in composite solder joints of LTCC/PWB assemblies

Abstract

Purpose -The purpose of this paper is to investigate the thermal fatigue endurance of two lead-free solders used in composite solder joints consisting of plastic core solder balls (PCSB) and different solder materials, in order to assess their feasibility in low-temperature cofired ceramic (LTCC)/printed wiring board (PWB) assemblies. Design/methodology/approach -The characteristic lifetime of these joints was determined in a thermal cycling test (TCT) over a temperature range of 240-1258C. Their failure mechanisms were analyzed after the TCT using scanning acoustic and optical microscopy, scanning electronic microscope, and field emission scanning electronic microscope investigation. Findings -The results showed that four different failure mechanisms existed in the test assemblies cracking in the mixed ceramic/metallization zone; or a mixed transgranular/intergranular failure occurred at the low temperature extreme; whereas an intergranular failure within the solder matrix; or separation of the intermetallic layer and the solder matrix occurred at the high temperature extreme. Sn3Ag0.5Cu0.5In0.05Ni was more resistant to mixed transgranular/intergranular failure, but had poor adhesion with the Ag3Sn layer. On the other hand, cracking in the mixed ceramic/metallization zone typically existed in the joints with Sn2.5Ag0.8Cu0.5Sb solder, whereas the joints with Sn3Ag0.5Cu0.5In0.05Ni were practically free of these cracks. The characteristic lifetimes of both test joint configurations were at the same level (800-1,000) compared with joints consisted of Sn4Ag0.5Cu solder and PCSB studied earlier.Originality/value -The study investigated in detail the failure mechanisms of the Sn3Ag0.5Cu0.5In0.05Ni and Sn2.5Ag0.8Cu0.5Sb solders under harsh accelerated test conditions. It was proved that these solders behaved similarly to the ternary SnAgCu solders in these conditions and no improvement can be achieved by utilizing these solders in the non-collpasible solder joints of LTCC/PWB assemblies.

Power Module Interconnection Reliability in BTS Applications

“…Voids themselves present an easy fracture path for a propagating crack, but they also concentrate stresses in their vicinity. This results in more severe strain and the formation of a recrystallized area [13,14]. This behavior was also observed in SnAg joints, as shown in Figure 10.…”

Effect of ENIG deposition on the failure mechanisms of thermomechanically loaded lead‐free 2nd level interconnections in LTCC/PWB assemblies

“…The primary failure of the joints of assembly B was located within the solder matrix, as shown in Figure 8(b). The observations of FE-SEM analysis (Figures 10 and 11) proved that a mixture of transgranular (fatigue) and intergranular (creep) failures formed in the SAC387 and SAC-InNi joints at the low-temperature extreme, similar to the joints of AgPtmetallized modules (Nousiainen et al, 2007b(Nousiainen et al, , 2010. Considering the width of the striations on the fracture surface, the growth rate of the transgranular (fatigue) crack in SAC-InNi was identical with the similar joint of AgPtmetallized modules (Nousiainen et al, 2010), whereas the SAC387 joints showed better fatigue endurance compared with Sn4Ag0.5Cu alloy (Nousiainen et al, 2007b).…”

“…The observations of FE-SEM analysis (Figures 10 and 11) proved that a mixture of transgranular (fatigue) and intergranular (creep) failures formed in the SAC387 and SAC-InNi joints at the low-temperature extreme, similar to the joints of AgPtmetallized modules (Nousiainen et al, 2007b(Nousiainen et al, , 2010. Considering the width of the striations on the fracture surface, the growth rate of the transgranular (fatigue) crack in SAC-InNi was identical with the similar joint of AgPtmetallized modules (Nousiainen et al, 2010), whereas the SAC387 joints showed better fatigue endurance compared with Sn4Ag0.5Cu alloy (Nousiainen et al, 2007b). The SEM and FE-SEM analyses (Figures 8(b), 10 and 11) also confirmed that intergranular (creep) failure was the dominant mechanism at the inner edge of the joint, not separation between the IMC layer and the lead-free solder matrix.…”

“…Porosity may result in excessive dissolution of the metallization layer and the glass phase may deteriorate the wettability of the solder lands (Bochenek et al, 2001;Nousiainen et al, 2007a). It was also shown that the inadequate adhesion strength of the interface between the Ag 3 Sn layer and Sn-based lead-free solders (Sn4Ag0.5Cu and Sn3Ag0.8Cu0.5In0.05Ni) degraded the reliability of the 2nd level interconnection in TCTs (Nousiainen et al, 2007b(Nousiainen et al, , 2010.…”