Abstract
High flexibility is one of the key requirements on die attach materials for most MEMS packages as temperature changes during the assembly process and application lead to thermo-mechanical stress as a consequence of thermal mismatch, i.e. dissimilar coefficients of thermal expansion of substrate, chip and adhesive. A distortion of the signal characteristics of the extremely stress-sensitive MEMS device may be the consequence of this thermo-mechanical stress. For the first time, 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 a patented mCD chemistry with Young's modulus values down to 5 MPa (0.725 ksi) at room temperature. DMTA measurements show that temperature storage at +120 °C (+248 °F) does not cause adhesive embrittlement that could negatively affect the reliability of the MEMS package. The curing temperatures of these adhesives are extremely low down to +100 °C (+212 °F), which reduces stress development during the assembly process. In addition, the adhesives have very process-friendly properties and allow processing times of one week. The option of dual curing enables preliminary light fixation of the chip within just seconds.
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