Wafer level packaging of MEMS devices using microalloyed lead-free solders

Date

2023-12

Author

Sevinç, Mertcan

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The growing popularity of MEMS devices makes packaging methods and processes essential. The need for packaging and lower costs push wafer-level packaging to be more appealing for several applications such as microbolometers, resonators, and micromirrors. Cu-In-Sn gains attraction among various wafer-level packaging methods. due to its low bonding temperature compared to other transient liquid phase bonding systems. Ternary alloy allows improvement upon the lacking aspects of binary TLP bonding. Bonding at temperatures below 200°C becomes possible with the combination of In-Sn. Reducing the thermal stress and combining with low temperature bonding makes Cu-In-Sn system suitable candidate for CMOS packaging. In this regard, the applicability of the system was studied in this thesis for wafer-level packaging. Throughout this study, the possibility of Cu-In-Sn bonding has been examined in detail. Bonding methods showed promising results. Sputtered Cu and thermally evaporated Sn and In layers were used on both device and cap wafers. Bonding attempts at 200°C and 250°C yielded inadequate outcomes. Examination after annealing revealed that sluggish diffusion due to incorrect processing parameters were the reason, such as bonding temperature. Process optimizations were performed and the resulting mechanical properties and final melting temperatures of wafers bonded between 200-350°C were investigated in detail. Bonds that have melting temperatures up to and higher than 550°C were obtained with bonding procedures that take place at 250°C and 350°C. It was observed that bonding at higher temperatures yielded higher mechanical strength. An average shear strength of 19.1 MPa was obtained when processed at 350°C and an average shear strength of 8.5°C was obtained with a processing temperature of 250°C.

Subject Keywords

Wafer-level packaging, Cu-In-Sn ternary alloy, MEMS packaging, TLP bonding, SLID bonding

URI

https://hdl.handle.net/11511/107720

Collections

Graduate School of Natural and Applied Sciences, Thesis