The dispensing machine itself is a device to control the amount and time of glue vomiting. So before using dispensing machine, we must solve the glue problem that affects the quality of electrocolloid. What problems do we usually have? Let's have a look with the two-component glue maker.
In glue dispensing machine, glue must not have bubbles, a small bubble will form a lot of pads without glue, forming the phenomenon of air beating, resulting in unqualified products, so every time when changing the rubber pipe in the middle, it must empty the joint. As for the solidification of glue, ordinary consumer manufacturers have given the temperature curve. In practice, high temperature should be used as far as possible to make the glue strong enough after curing.
Viscosity of glue directly affects the quality of dispensing. If the viscosity is high, the adhesive point will become smaller, even wire drawing; if the viscosity is low, the adhesive point will become larger, and then the pad may be stained. In the process of dispensing, we should select reasonable back pressure and dispensing speed for different viscosity glue.
In addition to the influence of glue and external environment, as for the dispensing machine itself, usually the dispensing machine used by enterprises is to supply dispensing needles with a screw pump, so a constant pressure is needed to ensure that enough glue is supplied to the screw pump. If the pressure is too high, it is easy to form glue overflow and excessive glue content; if the pressure is too small, it will present the phenomenon of intermittent dispensing and leakage points, thus forming defects. Therefore, the pressure should be selected according to the different quality of glue and the working environment temperature of dispensing machine. High ambient temperature will reduce the viscosity and improve the activity of the glue. At this time, it is necessary to reduce the back pressure to ensure the glue supply, and vice versa.
In practice, we think that the inner diameter of the needle should be 1/2 of the diameter of the dispensing point, so the dispensing effect is ideal. Therefore, in the dispensing process, the needle should be selected according to the size of the pad on the PCB, which can not only ensure the quality of the dispensing point, but also improve the consumption efficiency. Different dispensing machines use different needles, some needles have a certain degree of motility. It is often neglected that the interval between the needle and PCB should be calibrated at the beginning of each work, i.e. Z-axis height calibration.
The amount of dispensing depends on the working experience. The diameter of the adhesive spot should be half of the distance between the pads. The diameter of the adhesive spot after the patch should be 1.5 times of the diameter of the adhesive spot. In this way, sufficient glue can be guaranteed to bind the components and prevent too much glue from impregnating the pad. The amount of dispensing is determined by the rotating time of the screw pump. In practice, the rotating time of the screw pump should be selected according to the room temperature and the stickiness of the glue.
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