Mechanical Simulation and Characterization of Flexural Fracture of Stacked Die Memory Package

Memory packages for mobile applications are getting thinner in body and higher in capacity, which brings up a challenge for package strength, especially for flexural strain of MCP (Multiple Chip Package). Finite Element Analysis (FEA) demonstrates that bending strain is highly dependent on package configuration and molding compound material. It has been observed that molding compound behaves with a distinct elastic-plastic property, while silicon dies fractures in a brittle mode, which is unable to withstand excessive strain [1]. In addition, based on simulation and experimental observations, three failure modes with the corresponding failure locations have been identified as molding compound cracking first, die cracking first, and interfacial delamination first. Simulation prediction capability of package break strain has been established based on the three failure modes. The simulation results agree well with testing measurements using strain gauge. It also is demonstrated that the dominant failure mode can change when package structure changes. Molding compound effect on package break strain also has been studied. It is shown that the selection of molding compound for high break strain should take failure modes into accounts, generally, high ductility molding compound is beneficial to obtain a better bending strain at the package surface.