Grain orientations and failure mechanism of isothermal aged nano Sn-3Ag-0.5Cu/Cu solder joints by microwave hybrid heating and shear mechanical strength

Abstract

The application of microwave hybrid heating (MHH) technique in low-temperature joining presents a notable benefit of delivering both selective and uniform heating, a characteristic that is not typically found in traditional welding techniques. This experimental investigation aimed to evaluate the reliability of joints under a uniform temperature condition compared to those formed through the reflow soldering method. The present study successfully achieved joint formation through the utilization of the reflow soldering technique, utilizing a maximum temperature of 250 degrees C and a reflow time of 600 s. EBSD characterization, revealed the occurrence of recovery and recrystallization at the joint. Moreover, as the duration of aging increases, the crystallographic orientation of Sn and Cu6Sn5 becomes more prominent, with Cu6Sn5 exhibiting growth predominantly along a specific direction [0 0 1]. In addition, the MHH technique was employed, using specific parameters of 900 W and 195 s, to achieve successful joint production. Empirical findings revealed that reflow joints saw a significant drop of 34.2 % in their shear strength after being aged for 7 days. Likewise, the shear strength of MHH joints decreased by 28.9 % under the same aging conditions. During the aging process spanning 21-28 days, the decrease in shear strength proportion gradually diminishes. More precisely, the reflow soldering head experiences a reduction of merely 7.6 %, while MHH demonstrates a decrease of only 2.5 %. The joint's fracture pattern shifted from primarily ductile to a combination of mixed fracture after a duration of 28 days for both soldering methods, which contrasts with the previously observed timeframe of 7-21 days.