Bridging is one of the common defects in SMT production, it will cause short circuit between components, and it must be repaired when encountering bridging. There are many reasons for bridging, including:

4.1 Solder paste quality problems 

4.1.1 The metal content in the solder paste is too high, especially if the printing time is too long, the metal content is prone to increase, resulting in the bridge connection of IC pins;

4.1.2The viscosity of the solder paste is low, and it flows out of the pad after preheating;

4.1.3 The drop of solder paste tower is poor, and it flows out of the pad after preheating；

Solution: Adjust the solder paste ratio or use a good quality solder paste.

4.2printing system

4.2.1 The repeatability of the printing machine is poor, and the alignment is uneven (the steel plate is not aligned well, the PCB alignment is not good), so that the solder paste is printed outside the pads, especially the fine-pitch QFP pads;

4.2.2 The size and thickness of the stencil window are not designed correctly, and the Sn-pb alloy plating layer of the PCB pad design is not uniform, resulting in too much solder paste.

Solution: Adjust the printer to improve the PCB pad coating.

4.3 Excessive placement pressure and full flow of solder paste after being pressed are common reasons in production. In addition, if the placement accuracy is not enough, the components will be displaced and the IC pins will be deformed.

4.4The heating rate of the reflow soldering furnace is too fast, and the solvent in the solder paste has no time to volatilize。

Solution: Adjust the Z-axis height of the placement machine and the heating speed of the reflow furnace.