SMT is the electronic components on PCB with SMT machine, involved in the process including solder paste printing, SMT, reflow soldering, visual inspection and testing
COB are machine use IC and PCB are bond wire bond, including scanning board, some red glue, paste IC, the vinyl, a pretest, sealing, baking process, after the test.
PCBA processing, use the machine or manual insert plug-in components to the circuit boards and welding, which is on the PCB bare board through SMT parts, repass DIP the entire process of the plugin.
Perform before COB system will finish SMT, this is because the SMT need to use the steel plate to solder paste printing, and steel plate must be flat in empty on the PCB.
Can imagine to use template spray paint, spray paint to paint, however, if you want to paint walls have high up, then the template cannot be flat at metope, highlighting to paint is not smooth;
Steel plate is equivalent to the template, if the circuit board has other above the surface of the parts above, the steel plate can't stick in the circuit board, the printed solder paste thickness will be uneven.
Solder paste thickness will affect the subsequent parts of solder, too much solder paste can cause short circuit parts, solder paste too little will cause empty welding;
Coupled with the printing pressure on the solder paste need scraper and will, if have parts on printed circuit boards, and may be broken.
If you finish the COB, 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 can't to other electronic parts welded on the circuit board, and solder paste printing circuit board have to after the high temperature of 240 ~ 250 ℃ soldering furnace back, general COB binding sealant was mostly cannot afford such a high temperature embrittlement, finally cause unstable quality.
So COB process is usually placed in SMT processing after a process, plus the COB sealant after generally belongs to the irreversible process, is also unable to rework repair.
So at the end of the circuit board assembly process, but also to determine the electrical properties of the board have no problem to perform the COB process.
SMT materials mainly for SMT components, such as mobile phone on the surface of the internal resistor, capacitor, single-chip microcomputer, etc. , the surface mount technology welding.
DIP material mainly into components, such as computer motherboard electrolytic capacitor, the power part of the transformer, triode, etc.
Plug-in components or wave soldering process mainly through manual welding processing, relative to the SMT materials, processing technology, and a much higher cost is the patch.
At present most is given priority to with SMT welding material, welding industry has a small DIP components, some special product will also basically all use DIP components, such as power supply, etc.
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