Study On The Key Processes Of Silicon Microphone Assembly

Silicon Microphone,which base on MEMS technology, is more and more popular in consumable electronic filed. But low assembly yield and high failure rate in application were met in Silicon Microphone assembly process due to the special MEMS structure, PCB material and different working principle from common IC package. This project’s purpose is to choose proper material and optimize the parameters in Silicon Microphone assembly key process to improve its assembly yield and the reliability in application. In final a proper assembly process specification is setup.Epoxy fluidity and the connection strength are varied with the different epoxy viscosity. The proper epoxy viscosity is selected and the parameter of dispensing and die bonding is optimized to make the die shear strength improved from 450gf to 1200gf, MEMS leakage rate is reduced from 956ppm to 0ppm and controlled the epoxy creep height between 40% ~ 80% of MEMS height.Wire bonding process is separated to two steps to improve the bondability on MMES, IC and PCB. Bondability on MEMS is improved by depositing one layer gold on MEMS pad. Non-stick rate on MEMS pad is reduced from 8000ppm to 420ppm by further optimizing the bonding parameter. Bondability on IC is improved by bonding a bump on IC pad and parameter optimization as well.Bondability on PCB was improved by plasma cleaning. Non-stick rate on PCB was reduced from 5700ppm to 800ppm after optimizing the plasma cleaning parameter. Proper bonding capillary is selected and the bonding parameter is optimized to get proper bump-ball shape in PCB bond pad to reduce the wire stress in 2nd bond point, thereby reduce the wire broken rate in 2nd bond point. Smooth bump ball with 3~3.5 times of golden wire diameter was got by finally and it reduced the wire broken rate from 800ppm to 30ppm.