2023-07-25 17:33:18
After the PCB is printed, various electronic components need to be welded to fixed positions as required to form a PCBA with certain functions, and the welding positions of the components must be accurate and firm. In this step, the factory generally uses wave soldering and reflow soldering, but before performing the soldering operation, the electronic components need to be fixed to the fixed position of the PCB by glue, so the dispensing technology needs to be applied. So what are the requirements for the PCB dispensing technology?
1. Dispensing Amount
The diameter of the glue point should be half of the pad pitch, and the diameter of the glue point after placement should be 1.5 times the diameter of the glue point. This can ensure that there is enough glue to bond the components and avoid too much glue from dipping the pads. The amount of dispensing is determined by the length of dispensing time. Before the actual dispensing operation, the dispensing parameters should be selected according to the production situation, room temperature and glue viscosity, etc.
2. Dispensing Pressure
The dispensing machine applies a pressure to the dispensing needle rubber cylinder to ensure that the glue can be squeezed out of the dispensing nozzle. If the pressure is too high, it will easily cause too much glue, but if the pressure is too low, there will be discontinuous glue dispensing, which will cause defects. The pressure should be selected according to the glue of the same quality and the temperature of the working environment. A high ambient temperature will make the viscosity of the glue smaller and the fluidity better. At this time, it is necessary to lower the pressure to ensure the supply of glue.
3. Dispensing Nozzle Size
In actual operation, the inner diameter of the dispensing nozzle should be 1/2 of the diameter of the dispensing point. During the dispensing process, the dispensing nozzle should be selected according to the size of the pad on the PCB. For example, the size of the pads of 0805 and 1206 is not much different, and the same needle can be selected, but for pads with a large difference, different dispensing nozzles must be selected. This can not only ensure the quality of glue points, but also improve production efficiency.
4. The distance between the dispensing nozzle and the PCB board
Different dispensing machines use different needles, and the dispensing nozzle has a certain degree of stop. At the beginning of each operation, ensure that the stop lever of the dispensing nozzle touches the PCB.
5. Glue Temperature
Generally, epoxy resin glue is stored in the refrigerator, and it should be taken out in advance before use, so that the glue is fully consistent with the working temperature. If the ambient temperature is too low, the glue point will become smaller, resulting in wire drawing, so the ambient temperature should be controlled. At the same time, the humidity of the environment should also be ensured. If the humidity is low, the glue point will tend to dry out, affecting the bond.
6. Flue Viscosity
The viscosity of glue will directly affects the quality of dispensing. If the viscosity is high, the glue points will become smaller and even drawn; If the viscosity is low, the glue point will become larger, which may infiltrate the pad. During the dispensing process, a reasonable pressure and dispensing speed should be selected for glues of different viscosities.
7. Curve of Curing Temperature
For the curing of glue, the general manufacturer has given the temperature curve. In practice, a higher temperature should be used to cure as much as possible, so that the glue has sufficient strength after curing. In actual operation, a higher temperature should be used for curing as much as possible, so that the glue has sufficient strength after curing.
8. Bubble
The glue must not have bubbles. A small bubble can cause many pads to have no glue. Every time the glue is filled, the air in the glue bottle should be emptied to prevent empty punching.
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