Effect of addition with epoxy polymer to Sn-Bi solder paste

Eutectic tin-bismuth (58Bi42Sn) alloy is commonly used in low-temperature soldering because of its low melting temperatures, superior wettability, and low thermal expansion coefficients. The structure created using Sn-Bi solder paste has low strength due to the brittleness of the Bi phase, which prevents a good solder connection. This circumstance limits the applications of Sn-Bi solder paste. To overcome this disadvantage, a new solder paste was created by combining epoxy resin with Sn-Bi solder paste. We got the reflow profile by evaluating the melting parameters of the solder paste and the epoxy system's hardening reaction using differential scanning calorimetry (DSC). By these means, the solder paste was soldered at the optimal temperature. This new solder paste was tested for contact angle, spreading area, and drop test. The findings revealed that when the epoxy resin content was optimal, the mechanical characteristics of the solder improved, and a considerable improvement in the spreading area was observed with a higher contact angle when compared to Sn-Bi solder paste. In the study, it was observed that the solder made with epoxy addition was much more durable than normal solder in drop tests. The solder with 5 wt.% content, which we consider ideal, performed 2.6 times better than the epoxy-free solder. For this reason, the use of epoxy-added solders in vehicles sent to space or structures that will be exposed to high vibration will provide a significant advantage in terms of solder strength. In addition, covering the exterior surface of Sn-Bi solder paste with epoxy polymer provides a protective layer against external influences. Epoxy's ability to stick to diverse surfaces allows solder paste to be soldered on a variety of surfaces.