Highly flexible die attach adhesives for MEMS packages

Key requirements on die attach materials for most MEMS packages include high flexibility. The reason for this is that temperature changes during the assembly process and application may lead to thermo-mechanical stress as a consequence of thermal mismatch (dissimilar coefficients of thermal expansion of substrate, chip and adhesive). Distortion of the signal characteristics of the extremely stress-sensitive MEMS device is the consequence of this thermo-mechanical stress. The newly developed adhesives provide an outstanding combination of high flexibility and high die shear strength, giving them a competitive edge over the currently used MEMS die attach adhesives. This paper describes highly flexible heat-curing adhesives on the basis of acrylates and the patented mCD chemistry with a Young's modulus down to 5 MPa at room temperature. DMTA measurements show that temperature storage at +120 °C does not cause adhesive embrittlement, which would have a negative effect on the MEMS package's reliability. The curing temperatures of these adhesives are extremely low down to +100 °C, which reduces stress development during the assembly process. In addition, the adhesives have very process-friendly properties with processing times of one week. The option of dual curing enables preliminary light fixation of the chip within just seconds.