Reason analysis:

1. If the top and bottom of the easy pcb are not evenly heated, the last in and the first out, the PCB board is prone to bending and warping defects;

2. When entering the tin furnace, the liquid tin on the solder pad will be arc shaped by the surface tension of the liquid, resulting in uneven tin thickness on the solder pad. In addition, due to the blowing force of hot air and the action of gravity, the lower edge of the solder pad will produce a tin sag, which will make the welding of SMT surfacemount parts difficult to stick firmly, resulting in tombstoning or tombstoning of the parts after welding;

3. The smaller the easy pcb pad, the more obvious the tin arc on the surface of the pad, and the worse the flatness.

The solution:

For the BGA package plate less than 14MIL solder pad or the board with high flatness requirements, considering the hidden dangers of tin spraying, it is not recommended to make tin spraying plate, you can change to heavy gold, gold plating, if the customer must make tin spraying circuit board, it is necessary to clarify the customer’s requirements for flatness.