Thermal Cycling Reliability Study of Ag–In Joints Between Si Chips and Cu Substrates Made by Fluxless Processes

Abstract

The purpose of this research is to assess the reliability of Ag-In joints in thermal cycling (TC) environment. Si chips and Cu substrates were bonded using silver (Ag) and indium (In) multilayer structure without applying any flux. After bonding, the samples were annealed in air at 250 °C for 190 h to convert the joint into an alloy of small intermetallic grains and solid solution (Ag). The resulting joint has a melting temperature higher than 800 °C. Si-Cu pair was chosen because of the large coefficient of thermal expansion mismatch, i.e., 2.7 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-6</sup> /°C of Si versus 17 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-6</sup> /°C of Cu. Two TC tests were performed. All 10 samples passed 100 cycles of initial TC test between -40 °C and 85 °C. They were then subjected to 5000 cycles of TC test between -40 °C and 200 °C. Seven of ten samples survived beyond 5000 cycles. Three samples broke at 850, 2600, and 3000 cycles, respectively. The early failure was probably caused by imperfections and defects in the joints. Based upon these results, it seems that our Ag-In joints compare favorably with sintered silver joints. The Ag-In joints not only have high-melting temperature but also survive harsh TC environment.