Common defects and solutions in the dispensing process
1. The common causes are that the inner diameter of the adhesive nozzle is too small, the dispensing pressure is too high, the distance between the nozzle and PCB is too large, the chip glue is expired or the quality is not good, the chip glue viscosity is too good, the temperature can not be restored to room temperature after being taken out of the refrigerator, and the dispensing amount is too large.
Solutions: change the nozzle with larger inner diameter; reduce the dispensing pressure; adjust the "stop" height; change the glue, select the glue with appropriate viscosity; after the patch adhesive is taken out of the refrigerator, it should return to room temperature (about 4h) before putting into production; adjust the dispensing amount.
2. The amount of glue from the nozzle is too small or no glue spots come out. The causes are generally that the pinhole is not completely cleaned; impurities are mixed into the patch glue, resulting in hole plugging; and insoluble glue is mixed.
Solution: change the clean needle; change the high-quality patch adhesive; the brand of the patch adhesive should not be wrong.
3. But there is no dispensing. The reason is that the patch glue mixed with bubbles and the glue nozzle is blocked.
Solution: the glue in the syringe should be de bubbled (especially the self filled glue); the glue nozzle should be replaced.
4. When the adhesive is cured, the components move, and the pins of the components are not on the pad. The reason is that the glue output is not uniform, for example, one of the two glue points of the chip component is more than one; the component is displaced or the initial adhesion of the chip adhesive is low; the PCB is placed too long after dispensing, and the glue is half cured.
Solution: check whether the glue nozzle is blocked and eliminate the uneven phenomenon of glue output; adjust the working state of the Mounter; change the glue; the PCB should not be placed too long after dispensing (less than 4h).
5. The chip will fall off after wave soldering
After curing, the bonding strength of the components is not enough, which is lower than the specified value, and sometimes the chip will fall off when touching by hand. The reason is that the curing process parameters are not in place, especially the temperature is not enough, the component size is too large, and the heat absorption is large; the light-curing lamp is aging; the amount of glue is not enough, and the components / PCB are contaminated.
Solution: adjust the curing curve, especially increase the curing temperature. Generally, the peak curing temperature of thermal curing adhesive is about 150 ℃. If the peak temperature is not reached, it is easy to cause flake off. For the UV curing adhesive, it is necessary to observe whether the curing lamp is aging and whether the lamp tube is blackened; the quantity of glue and whether the components / PCB are contaminated should be considered.
6. Floating/shifting of component pins after curing
The phenomenon of this kind of fault is that the component pin floats or shifts after solidification, and the solder will enter under the pad after wave soldering, and short circuit and open circuit will occur in serious cases. The main reasons are uneven adhesive, too much glue or component offset.
Solution: adjust dispensing process parameters; control dispensing amount; adjust patch process parameters.
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