1 Reporter : 黃一軒 Advisor : 莊承鑫 老師 Institute of Mechanical Engineering Southern Taiwan University Southern Taiwan University, Tainan Taiwan

2 Outline Motivation Simulation Design and Boundary conditions Results and Discussions - Influence of cap on PWB’s thermal deformation - Influence of adhesive material and thickness What is Buffer Layer? - Discussion on buffer layer effect Conclusions

Solder paste printing ↓ Pick and Place machine ↓ Reflow(260 ℃ ) ↓ Complete 3 Motivation (b) SMT (Surface Mount Technology) (a) COB (Chip on Board) Advantage: Cost down, Small size, Simple design, etc. Shortcomings : molding difficult. Advantage: Automation. Shortcomings : Reflow temperature is higher. ECM Reflow(260 ℃ ) MEMS Microphone Solder paste printing Pick and Place machine Reflow

4 What is problem of MEMS Microphone ? PWB Heating of chip from SMT. 260 ℃ High temperature Cap effect PWB PWB effect Chip E Adhesive CTE Soft Cap Rigid

5 Simulation Design and Boundary conditions Heating process Total element :  2000 Hinge Sliding end Simulation Cases

6 Material properties 2025D > 3140RTV  DA RTV  DA6501 > 2025D Metal Cap > PWB > LCP Cap LCP Cap > PWB > Metal Cap

Results and Discussions 7

8 Buffering effect No Buffering effect Low EHigh E

9 Conclusions low Young’s modulus A low Young’s modulus adhesive materials, such as 3140RTV and DA6501, effectively isolates the silicon chip with less influence of thermal deformation from bottom PWB as the buffer layer effect. the adhesive thickness at 30um According to the simulations result when the adhesive thickness at 30um is at the minimum of stress and deformation on the diaphragm. controlled in a low level However, the thickness of soft adhesive needs to be controlled in a low level to prevent the thermal stress in the diaphragm rising with thickness.

Thank you for your attention 10