Effect of Polyethylene Glycols with Different Polymer Chain Lengths on the Bonding Process Involving In Situ Formation of Silver Nanoparticles from Ag2O

The need for lead-free alternatives to conventional solders for metal-bonding processes has prompted the development of processes based on metal nanoparticles. In this study, the low-temperature bondability of silver oxide (Ag2O) pastes containing polyethylene glycols (PEGs) with different polymer chain lengths was investigated. Bonding was achieved because of the low-temperature sinterability of silver nanoparticles that form in situ through redox reactions between Ag2O and PEGs. It was found that PEGs with shorter chain length provide superior bondability at low bonding temperatures. Thermogravimetric-differential thermal analysis and thermomechanical analysis showed that shorter PEGs resulted in less residual organic material in the sintered silver layer and contributed to form a larger amount of silver nanoparticles. Therefore, pastes with shorter PEGs afforded well-sintered, high-density silver joints and exhibited superior bondability even at lower temperatures. Using ethylene glycol, which has the shortest chain length, the tensile strength achieved was 11 MPa for bonding at 150 degrees C.