In the dispensing machine industry, the following problems are prone to occur in production, such as mismatching of glue dot size, drawing, glue dipping pads, and easy to drop due to poor curing strength. To solve these problems, we should study the technical parameters of the whole to find a solution to the problem.
So how to solve these problems of the dispenser in the industry? There are the following points to solve the problems of the dispenser.
1 dispensing volume
According to working experience, the size of the glue dot diameter should be half of the pad spacing, and the diameter of the glue dot after the patch should be 1.5 times the diameter of the glue dot. This can ensure that there is sufficient glue to bond the components and avoid excessive glue from dipping the pads. The amount of dispensing is determined by the rotation time of the screw pump. In practice, the rotation time of the pump should be selected according to the production situation (room temperature, viscosity of the glue, etc.).
2 Dispensing pressure (back pressure)
At present, the dispensing machine uses a screw pump to supply the dispensing needle hose. It takes a pressure to ensure that sufficient glue is supplied to the screw pump (taking the US CAMALOT5000 as an example). Too much back pressure can easily cause glue overflow and excessive glue volume; too little pressure will cause intermittent dispensing and leak points, which will cause defects. The pressure should be selected according to the glue of the same quality and the working environment temperature. High ambient temperature will make the glue viscosity smaller and fluidity better. At this time, the back pressure needs to be reduced to ensure the supply of glue, and vice versa.
3 needle size
In practice, the inner diameter of the needle should be 1/2 of the diameter of the dispensing point. During the dispensing process, the dispensing needle should be selected according to the size of the pad on the PCB: for example, the pad sizes of 0805 and 1206 are not much different. You can choose the same kind of needle, but for different pads, you need to choose different needles. This can not only ensure the quality of the glue point, but also improve production efficiency.
4 the distance between the needle and the PCB
Different dispensers use different needles, and some needles have a certain stop (such as CAM / A LOT 5000). At the beginning of each work, the distance between the needle and the PCB should be calibrated, that is, the Z-axis height calibration.
5 glue temperature
Generally epoxy resin glue should be stored in the refrigerator at 0--5 ℃, and it should be taken out 1/2 hour in advance to make the glue fully consistent with the working temperature. The use temperature of the glue should be 23 ℃ --25 ℃; 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 the stringing phenomenon will occur. A difference of 5 ° C in ambient temperature will cause a 50% change in the amount of dispensing. Therefore, the ambient temperature should be controlled. At the same time, the temperature of the environment should also be guaranteed. The glue point with low humidity is easy to dry and affect the adhesion.
6 viscosity of glue
The viscosity of the glue directly affects the quality of the dispensing. If the viscosity is large, the glue point will become smaller or even drawn; if the viscosity is small, the glue point will become larger, which may infiltrate the pad. During the dispensing process, a reasonable back pressure and dispensing speed should be selected for glues of different viscosities.
7 curing temperature curve
For the curing of glue, temperature curves have been given by general manufacturers. In practice, the higher temperature should be used to cure as much as possible, so that the glue has sufficient strength after curing.
There must be no bubbles in the glue. A small gas will cause many pads to be free of glue; every time the hose is replaced midway, the air at the connection should be evacuated to prevent runaway. For the adjustment of the above parameters, the method of point and surface should be used. Changes in any one parameter will affect other aspects. At the same time, the generation of defects may be caused by multiple aspects. The possible factors should be checked one by one, and then exclude. In short, the parameters should be adjusted according to the actual situation in production, both to ensure production quality and improve production efficiency.
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