Accelerated life time measurement with in-situ force and displacement monitoring during thermal cycling on solder joints

Abstract

The challenges to select materials for the development of electronic modules are aligned with the product requirements, like load condition during operation time, and economic aspects, like processing costs. Often these requirements based on different load types are contradictory, which makes the selections very difficult. This paper is focused on the thermally-induced thermo-mechanical load in the solder connections. In order to improve of the material selection, the authors have developed a setup enabling a cost-efficient material characterization. By testing electronic devices it is not possible to separate the ageing of the solder material from degradation of the incorporated plastic materials. The current setup significantly reduces the order of the influencing materials. Further advantage of this equipment is to design an acceleration level not by the increase of the temperature stroke, but by adaption of the displacement level. The principle of the setup is focused on the accelerated thermally induced mechanical load imposed onto specimen during thermal cycling. The load frame placed in a conventional temperature chamber consists of two metals, frame and core. This construction causes a thermal mismatch which is either induced onto the specimen and onto the incorporated force sensor as well, because this is connected in series. The intensity of the force signal represents the mechanical resistance of the specimen against the enforced displacement. Simultaneously, two contactless displacement sensors integrated into the system close to specimen measure the relative frame-core deformations in directions in- and out-of-plane. The novel measurement setup was developed by focus on homogeneous temperature distribution and stress free specimen assembly. Further, the setup enables to incorporate an adapted realistic BGA-like solder joint configuration. Since the specimen is connected to the setup with an adhesive, it was necessary to prove a long-term stability of the adhesive connections. The paper will present the setup calibration steps necessary for understanding the unique force-deformation behaviour of the system as function of temperature. Finally, degradation measurements on the BGA-like solder joint specimens for various environmental conditions will be presented