Assembly challenges for low modulus die attach material for MEMS devices

Packaging technique for MEMS devices such as selection of appropriate materials, proper process steps and approaches are crucial to meet the end product requirement in terms of overall package functionality and performances. Packaging MEMS devices requires low modulus die attach material due to their delicate intrinsic properties against interfacial mismatch as a result of thermo-mechanical stresses. Silicone based adhesives are good candidates as they exhibit properties of low modulus, 100 to 1000 times lower than conventional silica filled die attach epoxy. Manufacturability of such low modulus material often pose challenges at die attach in terms of bond line thickness, die attach material coverage, fillet height and planarity control. This paper discusses the impact of silicone based adhesive on wire bond ability. Material characterization through the use of thermo-gravimetric analyzer (TGA) and differential scanning calorimeter (DSC) to understand the adhesive curability and weight loss will also be discussed. Process robustness study through comprehensive DOE and optimization is important to meet the desired process capability index, Cpk. In addition, this paper will also explain the importance of staging duration from commence of die attach to curing process to assure the second wire bond strength is capable of meeting reliability requirement. The approaches used in this study are some of the challenges faced in producing a robust die attach material capable of meeting the various MEMS devices performance requirement.