At present, heat-resistance is given to a soldered joint by using a Pb-based single-alloy solder. In order to achieve Pb-free soldering, a reliability test was conducted using a composite type solder paste to solder joints. From this test it was found that joints made using a composite-type solder paste were equal to or stronger than joints made using the Pb-free single-alloy solder. It was also confirmed that the high-melting-point intermetallic compounds (IMC) were bonded continuously, forming a heat-resistant joint. The composite-type paste was prepared by mixing solder powder, Cu powder, and flux. This paper reports on the strength of the formed IMC of the joint after it is allowed to stand at a high temperature, the strength after a temperature cycle test, and the features observed in the structure of the soldered part before and after the test.