Properties of solders with low melting point

The aim of the work is to analyse thermal properties and microstructure of solders, which should be suitable for application in electronics. The solders must have low enough working temperature to avoid thermal damage of the assembly and uniform microstructure in whole bulk. For solders presented in this work the required temperatures are less than 150 °C. They represent alternative, for example, to the conductive adhesives, which are in use. Five types of solders have been studied. They were created from the metals: Sn, In, Bi, Cd. The solder on the basis of Bi/Sn, has the composition of 58 wt.% Bi and 42 wt.% Sn of eutectic point of the alloy and the melting point of 141 °C. The second solder of the composition of 53 wt.% Bi, 26 wt.% Sn and 21 wt.% Cd proved the melting temperature of 103 °C. The next both solders are on Sn/In basis. The solder with composition of 70 wt.% In and 30 wt.% Sn has the melting point temperature of 126 °C. The second solder of nearly eutectic composition, 50 wt.% Sn and 50 wt.% In has lower melting temperatures about 117 °C. The last one is ternary solder with composition of 53 wt.% Sn, 37 wt.% Bi and 10 wt.% In with the melting point between 100 and 123 °C. Differential scanning calorimetry (DSC) was used to determine the thermal properties of these solders. For the study of microstructure light microscopy and X-ray diffraction analysis were used. The analysis of solders microstructure show that almost all solders have homogenous distribution of two or three phases in the microstructure.