RF MEMS technology shows great promise for wireless communication and other RF applications. However, the packaging of RF MEMS devices becomes one of the most important issues in MEMS device fabrication and presents challenges due to the unique requirements. Special precautions are not only required to allow assembly processes after releasing the delicate structures but also to ensure the structures to operate in a stable atmosphere during its entire lifetime. These requirements come on top of the other wellknown requirements for cell phone components: cost, size and height. NXP Semiconductors has developed an efficient packaging technology for RF-MEMS devices in close cooperation with the Fraunhofer Institute in Itzehoe (ISiT). This paper presents a summary of several major aspects of our development activities in order to generate this new packaging technology.
Transferring molding process is widely used in the plastic IC packaging. Die cracking failures due to transfer molding process may occur. In this paper, an investigation on the die fracture and its failure probability is conducted. The approaches and results of die strength characterization, FE modeling on the laminate-based packages, and simulation-based prediction of the die fracture probability rate are presented. Weibull statistics model was used to describe the probability distribution. Model parameters were obtained by fitting to the test results. 3D parametric FE models were established to conduct numerical simulations to predict the stress field and die fracture probability caused during the transfer molding process. For a BGA package, the influence of the solder mask opening under the die on the fracture probability was investigated. For the capped MEMS, high stress levels are induced in the cap and the MEMS die during the molding process. The cavity size, cap thickness, the molding pressure, and the wafer surface finishing process have significant influences on the fracture failure probability. It shows that improvement of die fracture probability can be achieved by changing the designs or the die surface finishing process to meet the reliability requirements.
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