Solder joint reliability of surface mount chip resistors/capacitors on insulated metal substrates

For enhanced heat transfer, insulated metal substrates are attractive alternatives to the FR-4 printed circuit boards which have been conventionally used in automotive engine controllers. Although appealing from the viewpoint of enhanced thermal performance, the high coefficient of thermal expansion of aluminum relative that of FR-4 boards leads to a increased probability of fatigue failures of surface mount solder connections subjected to thermal cycling. In this work, the thermal fatigue life and reliability of solder joints used to attach components to insulated metal substrates has been studied using finite element modeling and actual life testing. In particular, this investigation has examined the reliability of solder connections for ceramic chip resistors and chip capacitors. Several two-dimensional (plane stress and plane strain) and three-dimensional nonlinear finite element models have been prepared and executed for both chip resistors and chip capacitors on insulated metal substrates. Several common sizes of the resistors/capacitors have been modeled including 1206, 0805, 0603, and 0402. Attributes of the finite element models included elastic-plastic solder constitutive behavior, large deformations, and thermal cycling. Initiation of solder joint fatigue cracking was estimated using the predicted plastic strains within a Coffin-Manson type fatigue model. The fatigue life predictions of the finite element analyses have been correlated with solder joint crack initiation and life measurements for actual components under thermal cycling. A broad matrix of test configurations with various substrate materials, resistor/capacitor sizes, and encapsulants has been considered.<>