Novel Materials for MEMS Packaging: MEMS Die Attach and ASIC Die Coating and Encapsulation

In a lot of MEMS-based devices, stress decoupling is of highest importance in order to avoid temperature-induced stress, i.e. on the membranes of pressure sensors or microphones. DELO's latest generation of MEMS die attach (DA) adhesives reaches Young's moduli lower than e.g. those of silicones at room temperature. The patented mCD chemistry also allows for an optional light pre-fixation of the dispensed adhesive in order to avoid unwanted spreading or bleeding during placement of the MEMS chip and/or the final heat curing step (b-stage process). In addition, DELO has developed new materials for ASIC die coating and ASIC encapsulation. Exposing the ASIC die to e.g. IR radiation leads to unwanted signal noise, especially in MEMS microphones. The bare ASIC die is exposed to the back volume ambience on all five sides. Hence, all five surfaces of the die need to be shielded (five face coating) against IR. DELO has developed materials with tailored dispensing and flow properties for this application. These adhesives are optimized for jet dispensing, still leaving the freedom to adjust the layer thickness to the needs of the application. The coating covers all five surfaces very well while minimizing the spread on the substrate, keeping the footprint small. This paper describes the new possibilities for MEMS packaging arising from MEMS DA adhesives based on DELO's patented mCD chemistry featuring a Young's modulus of <; 1MPa at room temperature, which is lower than that of silicones. A further benefit of this class of adhesives is its screen- or stencil-printability for a fast and precise production process. Bondlines of about 50 μm are achievable, improving stress decoupling significantly.