How to avoid the Parts Falling on the First Side During the Second Reflow Soldering of SMT (Part 4)

4. Adopt the method of mixing high and low solder paste

In fact, XPCB Limited does not recommend this method, because the solder strength of low-temperature solder paste is not good, so please go through a strict reliability evaluation before use. Moreover, there are solder pastes of different temperatures in the factory, and there is a risk of using the wrong solder paste. The method is to print high-temperature solder paste when reflow on the first side, and low-temperature solder paste when reflow on the second side, so that you don’t have to worry about the parts on the first side being dropped by the second reflow. For example, SAC305 solder paste is printed on the first side of the board, the melting point is 217°C, and the peak value of Reflow is 250°C. Then on the second side of the solder paste Sn42Bi58 low temperature solder paste, the melting point is 138°C, and the maximum Reflow peak is recommended not to exceed 220°C (recommended to be controlled below 200°C), so that the first side that has been laid uses SAC305 tin There will be no chance to remelt the tin at all.

5. Re-welding after returning to use (machine welding, manual welding)

Calculate the cost of post-re-welding and the cost of parts falling, and compare the cost-effectiveness. Sometimes blindly pursuing automation when the time is not ripe may not save costs. It is better to compare and calculate whether the calculation is cost-effective. . In addition to manual welding for post-re-welding, robot welding can also be considered. After all, the quality of manual welding is more doubtful.

As a professional FPC soft board manufacturer, XPCB Limited is so honored to have worked together with many of you. At XPCB Limited we are always more than ready to assist our new customers in any way we can.  Please feel free to contact us at any time if you have any questions.