What are the factors affecting the bonding of PCB?

- Mar 14, 2019-

For the bonding of components on the surface of a printed circuit board, there are three factors that affect the bonding effect. So what about the factors affecting PCB manufacturing by FASTPCBA Electronics below?

1. The amount of glue

The amount of glue required for bonding is determined by many factors. Some users have developed some internal application guidelines based on their own experience. These guidelines can be consulted when selecting the most suitable amount of glue. However, due to the differences in rheology of PCB manufacturing sheet glue, it is unrealistic to completely copy, so it is absolutely necessary to adjust the amount of glue used. The strength of the bond and the ability to resist wave soldering are determined by the strength and bonding area of the bond. In general, the height of the glue dot should be greater than the gap between the SMD and the PCB, and the glue has at least 80% contact area with the SMD component after deployment. A qualified dispensing process has strict limits on the shape and size of the dots. For example, the size of the dots should be smaller than the distance between the pads, and the accuracy of the dispensing position and the distance between the pads and the pads should be considered. The margin, too large an area will make rework very difficult. It is recommended to use double dispensing. For example, PCB manufacturing and assembly of 1206 components, first analyze the distance between the pads (2mm), and then take into account the accuracy of the pad and dispensing position and the expansion of the glue after placing the chip capacitor. The maximum allowable diameter of the glue point is 1.2mm, and the typical height of the glue point is 0.1mm. By analogy, the patch is equipped with 0805 components, the pad pitch is 1mm, and the glue dot size is 0.8mm. The amount of different SMD patch glue applied. When the pad is too high or the gap under the SMD component is too large, first place a spacer between the pads, then place the patch glue on it.

SMD component

2. The impact of SMD components

SMD does not consider the problem of bonding when designing. Fortunately, the bonding of most components is not a problem. But you must also be aware of some individual and error-prone places. SMD is usually made of epoxy resin, but it is also made of glass ceramic and aluminum. Epoxy resin has good adhesion, but ceramic and glass diodes usually have low adhesion.

3. The impact of PCB

The PCB is usually a reinforced glass fiber epoxy board with copper wires and pads on it. There is no essential difference in surface roughness between a general PCB and a PCB with a solder mask. On a PCB with a solder mask, the bonding is done on a protective film. Usually, the adhesion of the protective film is not problematic. When the shear strength is tested, it is seen that the protective film is first destroyed. However, some protective films may also have insufficient bonding strength, which may be caused by contamination of the protective film before curing or partial curing of the film.

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