The effect of melting time on lead-free solder strength

In this test, the effect of melting time on reflow soldering of lead-free solder was investigated. Lead-free solders, which had been qualified in a previous test, were used. The production window for the melting time was investigated. As is known, the melting time for solder joints should not be too short since this may cause cold joints. On the other hand, solder time should not be too long, either, because this may cause brittle intermetallic weakened solder joints. Also, components cannot withstand too long a period in the elevated temperature needed to melt the lead-free solder. In the test, samples of copper rod 3 mm in diameter were used and soldered together on their ends. The melting time in the reflow oven was set to be that recommended by manufacturers. The variations in the time were adjusted to be about 30% shorter than the recommended time and also two times longer as well as about four times longer than recommended. Using a universal pulling test machine, the effect of the melting time on the solder strength was tested. The pulling force needed to break the joint was measured and compared. The strength of a normal tin-lead soldered joint was tested and used as a reference level