Bridging
Bridge connection is one of the common defects in SMT production. It will cause short circuit between components, and it must be repaired when it meets bridge connection. There are many reasons for bridge connection
1) Quality problems of solder paste
① The metal content in solder paste is high, especially if the printing time is too long, it is easy to increase the metal content, resulting in IC pin bridging;
② The solder paste has low viscosity and overflows to the outside of the solder pad after preheating;
③ The drop of solder paste tower is poor, and it overflows outside the solder pad after preheating;
Solution: adjust the proportion of solder paste or use high quality solder paste.
2) Printing system
① The repeated accuracy of printing machine is poor, and the alignment is not even (steel plate alignment is not good, PCB alignment is not good), which causes solder paste to be printed outside the pad, especially the fine pitch QFP pad;
② The size and thickness of template window are not designed correctly, and the Sn Pb alloy coating of PCB pad design is not uniform, which leads to excessive solder paste.
Solution: adjust the printer and improve the PCB pad coating.
3) It is a common reason in production that solder paste is full flow after being pressed due to excessive pressure. In addition, if the placement accuracy is not enough, the components will shift and the IC pins will deform.
4) The reflow furnace heating rate is too fast, the solvent in solder paste has no time to volatilize.
Solution: adjust the height of Z axis of SMT and the heating rate of reflow furnace.
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Post time: Sep-15-2020