How to control the dispensing volume?

1. The size of SMT patch dispensing volume

　　According to work experience, the size of the glue dot diameter should be half of the product spacing. In this way, it is possible to ensure that there is sufficient glue to bond the components and avoid excessive glue. The amount of glue to be dispensed is determined by the length of time. In practice, the dispensing time should be selected according to the production situation (room temperature, viscosity of the glue, etc.).

2. SMT patch dispensing pressure

The dispensing equipment provides a certain pressure to the needle tube (glue gun) to ensure the supply of glue. The pressure determines the amount of glue supplied and the speed of glue outflow. Too much pressure can easily cause glue overflow and excessive amount of glue; too little pressure will cause intermittent glue dispensing and leaks, which will lead to product defects. The pressure should be selected according to the nature of the glue and the temperature of the working environment. High ambient temperature will reduce the viscosity of the glue and improve its fluidity. At this time, the pressure value needs to be lowered, and vice versa.

3. SMT patch dispensing needle size

　　In actual work, the inner diameter of the needle should be about 1/2 of the diameter of the glue dot. During the dispensing process, the dispensing needle should be selected according to the size of the product. Different needles should be selected for products with very different sizes, which can not only ensure the quality of glue dots, but also improve production efficiency.

4. The distance between the needle and the working surface

　　Different dispensers use different needles, and some needles have a certain degree of stop. The distance between the needle and the working surface should be calibrated before the start of each work, that is, the height of the Z axis should be calibrated.

5. The viscosity of glue

　　The viscosity of the glue directly affects the quality of the glue. If the viscosity is large, the glue point will become smaller, or even drawing; if the viscosity is small, the glue point will become larger, and the product may bleed. During the dispensing process, choose a reasonable pressure and dispensing speed for glues of different viscosities.

6. Glue temperature

　　General epoxy resin glue should be stored in a refrigerator at 0～5℃, and taken out half an hour before use, so that the glue temperature is consistent with the working environment. The use temperature of the glue should be 23℃～25℃; the ambient temperature has a great influence on the viscosity of the glue, the viscosity increases when the temperature decreases, the glue flow rate decreases correspondingly, and the wire drawing phenomenon is more likely to occur. When other conditions are the same, the environmental temperature difference is 5℃, which will cause a 50% change in the amount of glue, so the environmental temperature should be controlled. At the same time, the temperature of the environment should also be ensured. If the temperature is too high, the glue dots are easy to dry and affect the adhesion.

7. Curing temperature curve

　　For the curing of glue, the general manufacturer has given a temperature curve. In practice, it should be possible to use a higher temperature to cure, so that the glue has sufficient strength after curing.

8. Bubbles

The glue must not have bubbles. A small air bubble will cause many products to have no glue; every time the hose is replaced in the middle, the air at the connection should be evacuated to prevent the phenomenon of runaway.