A fast crack-free bonding method for glass and silicon using laser transmission welding with a defocused beam

This paper presents a novel fast crack-free bonding method for glass and silicon based on the defocused beam laser transmission welding technique (LTW). The bonding and crack formation mechanisms during LTW are discussed in detail in this paper. It was shown that the LTW technique using a defocused beam could effectively reduce the temperature gradient during the process to avoid crack formation. Meanwhile, the defocused beam could increase the bonding width of a single scan, reducing the number of scans for large-area bonding and further improving the efficiency of the bonding process. To find the welding conditions for different dimension requirements, a regression model was developed to determine the width of the weld. The crack-free bonding conditions were found by using the support vector machine (SVM). The regression model and the boundaries for the crack-free bonding conditions were both validated under randomly selected processing parameters. Finally, a 7.54 mm x 12.5 mm large crack-free bonded area was fabricated using this technique to demonstrate the feasibility of this technique. The crack-free bonded part was fabricated within 2 min, which is 8 times faster than the conventional anodic bonding. This study showed that the defocused beam LTW is a much more efficient and competitive alternative to the conventional bonding methods for silicon and glass, holding a huge potential in applications like semiconductor packaging and MEMS fabrication.