A study of interfacial reaction between molten Sn-Ag solder and Te substrate

• Main Authors: Huang, Yen-Chun, 黃彥鈞
• Other Authors: Liao, Chien-Neng
• Format: Others
• Language: zh-TW
• Published: 2009
• Online Access: http://ndltd.ncl.edu.tw/handle/76539270100174568164

碩士 === 國立清華大學 === 材料科學工程學系 === 97 === Telluride-based thermoelements can react with Sn-contained solders and form SnTe intermetallic compounds that may deteriorate electrical and mechanical properties of soldered junctions. In addition to the diffusion barrier approach, chemical composition of the solder alloys could be adjusted to suppress or decrease the rate of SnTe formation. In this study the effects of Ag addition (0.1, 1, 3.5, 5 wt.%) in pure Sn on the interfacial reaction between molten solder and Te substrate is explored. It is found that the thickness of SnTe compound is reduced after soldering reaction when more than 1 wt.% Ag is added into Sn solder. For an identical time of 300 minutes, the SnTe thickness is decreased from 570 �慆 for a pure Sn and Te reaction to only 11 �慆 for a Sn-Ag alloy and Te reaction. The suppression of SnTe compound formation is associated with the presence of Ag3Te2 and Ag2Sn3Te5 ternary compounds that are located in between the SnTe compound and the Te substrate. However, the rate at which SnTe initially forms is enhanced as the formation of SnTe originates from two different sources: byproduct of molten solder and Te substrate (Ag3Te2 and SnTe) and excess SnTe when Ag3Te2 further reacts with Sn in the solder (Ag2Sn3Te5 and SnTe). When the thickness of SnTe remains essentially constant, SnTe undergoes a conservative ripening, resulting in surface roughening. Based on top-view scanning electron microscopy micrographs, it is calculated that SnTe particles size increase approximately with the cube root of reaction time.