How to set the temperature of lead-free reflow soldering

The temperature curve of lead-free reflow soldering refers to the curve of the temperature at the test point on the surface assembly device of PCB with time. Therefore, lead-free reflow temperature curve is an important factor to determine welding defects. Setting the temperature of lead-free reflow soldering is the top priority in reflow soldering process. Jeenoce electronics here to share how to set the lead-free reflow temperature.

For lead-free solder paste, the temperature difference between components must be as small as possible. This can also be achieved by adjusting the reflow temperature. Using the traditional temperature curve, although the temperature difference between elements is inevitable when the plate forms the peak temperature, it can be reduced by several methods:

1、 Extend the warm-up time. This greatly reduces the temperature difference between the peak and the return elements. Most convection reflux furnaces use this method. However, because the flux may evaporate too fast through this method, it may cause poor wetting due to the oxidation of pins and pads.

2、 Increase the preheating temperature. The traditional preheating temperature is generally 140 ~ 160 ° C, which may be increased to 170 ~ 190 ° C for lead-free solder. Increasing the preheating temperature reduces the required peak formation temperature, which in turn reduces the temperature difference between elements (pads). If the flux cannot accept a higher temperature level, it will evaporate again, resulting in poor wetting due to oxidation of pad pins.

3、 Trapezoidal temperature curve (extended peak temperature). Prolonging the peak temperature time of elements with small heat capacity will allow the elements and elements with large heat capacity to reach the required reflux temperature and avoid overheating of smaller elements.