PCB News - What is PCBA dispensing and what equipment is used for PCBA dispensing?

What is PCBA dispensing and what equipment is used for PCBA dispensing?
The dispensing process is mainly used in a mixed placement process where through-hole insertion (THT) and surface mount (SMT) coexist. Throughout the production process, we can see that from the distribution and curing to the end, a component of the printed circuit board(PCB) can be soldered by wave soldering. During this period, the interval is very long, and there are many other processes, so the curing of the components is particularly important.

The dispensing process is mainly used in a mixed placement process where through-hole insertion (THT) and surface mount (SMT) coexist.

Process control in the dispensing process. The following process defects are prone to occur in production: unqualified glue dot size, wire drawing, dipping pad, poor curing strength and easy chip drop. Therefore, this is a solution to control the technical parameters of dispensing.

1. Dispensing amount

According to work experience, the size of the glue dot diameter should be half of the pad spacing, and the glue dot diameter should be 1.5 times the diameter of the glue dot after the patch. This will ensure that there is enough glue to bond the components and prevent too much glue from contaminating the pads. The distribution amount is determined by the distribution time and the distribution amount. In fact, the distribution parameters should be selected according to the production conditions (room temperature, glue viscosity, etc.).

2. Distribution pressure

Currently, the company's dispensers apply pressure to the dispensing syringe to ensure that there is enough glue to squeeze out the dispensing nozzle. If the pressure is too high, it will cause too much glue; if the pressure is too low, it will cause intermittent dispensing and leakage, which will cause defects. The pressure should be selected according to the same quality of glue and the temperature of the working environment. If the ambient temperature is high, the viscosity of the glue will decrease and the fluidity will be improved. At this time, the pressure can be reduced to ensure the supply of glue, and vice versa.

3. The size of the dispensing nozzle

In fact, the inner diameter of the dispensing nozzle should be 1/2 of the diameter of the glue dispensing point. In the dispensing process, the dispensing nozzle should be selected according to the size of the pad on the PCB: for example, the pad size of 0805 and 1206 is not different, you can choose the same needle, but you should choose a different dispensing nozzle for the difference of the pad. Large, not only can ensure the quality of glue dots, but also improve production efficiency.

4. The distance between the dispensing nozzle and the PCB board

Different dispensers use different needles, and the dispensing nozzle has a certain degree of stop. At the beginning of each work, please make sure that the stop rod of the dispensing nozzle is in contact with the PCB.

5. Glue temperature
Generally, epoxy resin glue should be stored in a 0-50c refrigerator, and should be taken out 1/2 hour in advance to make the glue fully meet the working temperature. The use temperature of the glue should be 230c-250c; the ambient temperature has a great influence on the viscosity of the glue. If the temperature is too low, the glue point will become smaller and wire drawing will occur. A 50c difference in ambient temperature will result in a 50% change in the dispensing volume. Therefore, the ambient temperature should be controlled. At the same time, it should also ensure that the ambient temperature and humidity are low, and the glue spots are easy to dry, which affects the adhesion.
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