The impact of thermal cycling regime on the shear strength of lead‐free solder joints

Abstract

Purpose -The purpose of this work is to undertake a comparison of accelerated test regimes for assessing the reliability of solder joints, in particular those made using lead-free solders. Design/methodology/approach -Identical samples of 1206, 0805 and 0603 resistors were subjected to six different cycling regimes to investigate the effect of thermal excursions, ramp rates and temperature dwells. Findings -The most damage to joints was found to be caused by thermal cycling between 255 and 1258C, with a 108C/min ramp rate and 5 min dwells. Large thermal excursions were shown to give faster results without compromising the failure mode.Research limitations/implications -Similar degrees of damage in the lead-free solder joints were experienced from thermal shock regimes with ramp rates in excess of 508C/min. However, these regimes, although faster to undertake, appeared to cause different crack propagation modes than observed with the thermal cycling regimes. However, these differences may be small and thermal shock testing may still be used to differentiate between, or enable ranking of, the effects of changes to materials or processes on the reliability of the solder joints. Hence, it is envisaged that if a wide range of conditions are to be tested a first sift can be completed using thermal shock, with the final work using typical thermal cycling conditions. Practical implications -The difference between the SAC (95.5Sn3.8Ag0.7Cu) and SnAg (96.5Sn3.5Ag) solder alloy results across all types of cycles showed very little difference in the rates of joint degradation. Originality/value -This paper compares relative reliability (remaining shear strength) of three chip components soldered with two lead-free alloys based on various thermal cycling conditions.

Investigating the thermomechanical properties and intermetallic layer formation of Bi micro-alloyed low-Ag content solders

“…Then, intermetallic layer thickness measurements and mechanical characterisations have been performed on each type of samples. By analysing the crosssections of the samples after the TS cycles, it can firstly be said that the path of cracks inside the solder joints is in agreement with the literature [23]; the cracks propagate next to the metallisation of the chip components (Fig. 11).…”

Finite element analysis of lead-free surface mount devices

“…On the other hand, a structure comprising components of different materials can demonstrate thermal stresses even in the case of uniform thermal conditions and absence of external constraints due to the difference in levels of coefficients of thermal expansion (CTEs). Usually electronic assemblies are manufactured from a range of materials with varying CTEs [2]. Since these assemblies experience temperature/power changes during their use (e.g.…”

“The measurement of creep rates and stress relaxation for micro-sized lead-free solder joints”

“…An accelerated testing regime is typically thermocycling [9] or power cycling, during which stress is accumulated due to localised CTE material mismatches. The relatively weak solder joints are the most compliant materials in the assembly (Figure 1), and hence any stress due to localised CTE mismatches (i.e.…”