SMD process

Patch process is divided into:

Solder paste printing, SMT chip (by hand and machine), the middle inspection, reflow soldering, furnace inspection, performance testing, aging test (some do not need), packaging

 

1, printing solder paste.

After the solder paste to warm after the first mixing, and then put a small amount of steel in the printing press, the amount of scraper to go when the solder paste to the scraper 3/2 better. After the first test printing should pay attention to observe the solder paste on the PCB pad position is full, there is no less tin or tin, but also pay attention to whether there is a short circuit, open the case. This is a crucial point, which can lead to poor quality behind. On the stencil

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Board direction

Try to convey the same direction with the machine Each printing three PCB board must be cleaned with a toothbrush once the stencil, to prevent plugging leakage of solder paste PCB; unprinted PCB board solder paste is prohibited on the docking station to prevent the empty paste; each time When the line, stencil must be promptly returned to the warehouse.

 

2, patch.

Put the printed PCB on the fixture, and send it to the Mounter through the automatic board feeder. Mounter program is prepared in advance, the machine identifies a board when it will start automatically pick-up placement. The first board affixed to the first piece must be checked first check the main components of the specification, placement, polarity of the components, with or without missing paste, paste and solder paste printing is appropriate. Patch staff must pay attention to the machine throw material, strict control of the material caused by the material, the strict control of the patch room temperature, humidity and so on.

 

3, the middle check.

Need to pay attention to check the polarity of the components (with or without reverse), there is no offset mounting, with or without short circuit, with fewer pieces, pieces, with or without tin.

 

4, reflow soldering.

Check the good circuit board after reflow soldering will be carried out automatically, the principle is through the heating element heating, and then mining

With hot air circulation so that the temperature in different temperature ranges remain within the set temperature range, to the circuit board for uniform heating, so that the paste after preheating, heating, reflow, automatic melting after cooling welding. It should be noted here is the temperature of the reflux must be controlled well, too low the solder paste can not melt, there will be cold welding; PCB is too easy to foaming, the components will burn out. Paste personnel must pay attention before the reflow temperature is correct, the preheating temperature is appropriate, too low flux incomplete evaporation, residue after reflow, affecting the appearance; too high will cause the flux premature volatilization, resulting in reflow Weld Phenomenon, at the same time may produce tin beads.

 

5, after the furnace inspection.

Here you need to check the appearance of the product to see if there are poor soldering, ie, solder, solder ball, short circuit, component offset, component erection

(Commonly known as monument), floating components, the wrong polarity, the wrong parts, missing parts and so on. Mass production (greater than or equal to 100), mount 15

The block must be reflow soldered to confirm the solderability of the component.