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The relationship between PCB process COB and SMT patch

736 Published by FASTPCBA 11月 21,2018

The relationship between PCB process COB and SMT patch

Perform before COB process, it is necessary to finish SMT processing work, this is because the SMT process need to use the steel plate (font) to print solder paste, and steel plate must be flat in empty PCB circuit boards (bare PCB) above, can use template to imagine spray paint, spray paint to paint, however, if you want to paint walls have high up, then the template cannot be appressed at metope, highlighting to paint is not smooth;Steel plate is equivalent to the template, if PCB circuit boards have other above the surface of the parts above, the steel plate can’t stick in the PCB circuit boards, flat that printed solder paste thickness will be uneven, and the thickness of the solder paste will affect the subsequent parts of solder, too much solder paste can cause short circuit parts (solder short), solder paste too little will cause an empty welding solder (skip);A spatula is used to print the solder paste and pressure is applied. If the PCB is already on board, it may break down.

pcb smt

 If the COB is completed first, will form a class on PCB circuit board round hill, so it can’t be used in the steel plate to solder paste printing, also cannot turn other welding in PCB circuit boards, electronic components and PCB circuit boards of screen printing have to after the high temperature of 240 ~ 250 ℃ soldering furnace, general COB sealant (epoxy) most cannot afford such a high temperature embrittlement, finally cause instability in quality.

Therefore, COB process is usually a process after SMT patch processing.After COB sealing, it is usually an irreversible process, that is, it cannot be repaired again. Therefore, it will be the last step of all PCB assembly, and the process of COB will be executed only when the electrical characteristics of the board are ok.

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