Wearout Evaluation of Soldered Interconnections for Surface Mounted Leadless and Leaded Components

Abstract

The wearout characteristics were investigated for soldered interconnections of surface mount technology (SMT) chip resistors, chip capacitors and a 44 I/O ceramic leaded chip carrier (CLCC) package. Four double‐sided test vehicles were subjected to accelerated thermal cycling in the — 10°C to + 110°C range; 30°C/min ramp rate; and 1 minute dwell time at each temperature extreme. The test was interrupted at initially 500 cycle and later at 1000 cycle intervals to perform visual inspection of all soldered interconnections, functional performance verification for the test vehicles, and resistance measurement on leaded SMT joints. Metallographic examinations and fractographic studies were also performed after 0, 4500 and 13000 cycles to characterise the micromechanisms of soldered joint strength degradation and failure. The wearout thresholds for soldered joints of chip resistors and capacitors on side 1 were respectively 2500 and 4500 cycles. The greater thermal fatigue resistance of the latter joints was attributed to a lower device‐substrate coefficient of thermal expansion (CTE) mismatch and a more favourable device geometry compared with chip resistors. These passive components on side 2, however, showed a virtually identical soldered joint wearout threshold of 6500 cycles. The constraints imposed by the applied mounting adhesive were primarily responsible for this behaviour. No correlation appeared to exist among various failure criteria used to determine the onset of failure for leaded SMT soldered connections. The concurrent monitoring of electrical resistance and the applied tensile load showed a modest relationship between the load drop and resistance increase, however. The test vehicles continued to pass the functional performance verification, even after 13000 thermal cycles. Nonetheless, the joint wearout thresholds were considered to be 2500, 4500 and 4500 cycles for chip resistor, chip capacitor and CLCC components, respectively. A 50% soldered joint strength drop was considered as the wearout threshold for the CLCC device. Metallographic examination showed limited barrel wall cracking of the vias and no evidence of cracks with the through‐hole soldered joints, even after 13000 thermal cycles.