Failure analysis method to study solder wicking phenomena in modern microelectronic devices

Many plastic encapsulated multi chip module (MCM) devices are prone to delamination due to lack of adherence between the materials that compose the package. The problem can get worse if there is a moisture sensitivity level (MSL) violation. When there is a poor adherence between ceramic passive components like capacitors or resistors and plastic molding compound delamination can occur on top of the components and a path for solder to flow is created. When a delaminated MCM device is submitted to lead free solder reflow above 250 °C peak temperature, the solder contained inside the package can flow through any void or empty space inside the package. This could affect the performance and reliability of the system. Package level reliability tests can be performed to assure that good adherence of the materials that compose the device package exists. A solder heat resistance (SHR) test is commonly performed to validate that a specific device package can withstand the worst moisture–solder reflow scenarios during the final assembly process. In this work experiments were carried out in order to replicate the solder wicking failure mechanism. Two groups of MCM, 77 devices were subjected to SHR test using moisture sensitivity level MSL2A and MSL3 conditions and a 250 °C peak reflow temperature. The electrical failures that occurred after the experiment were analyzed according to a specific failure analysis method in order to detect the failure mechanism. Special attention was paid on leakage current and continuity failures since these are the main failure modes associated with solder wicking on ceramic passive components assembled in MCM devices.