Knowledge Points of Automatic Dispenser

In accordance with work experience, the diameter of the glue spot should be half the spacing of the pad, and the diameter of the glue spot should be 1.5 times the diameter of the glue spot after placement. This will ensure that there is sufficient glue to bond the parts and avoid excessive glue to stain the pad. The amount of dosing is determined by the rotation time of the screw pump. In practice, the pump rotation time should be selected according to the production conditions (room temperature, glue viscosity, etc.).

Dispensing pressure (back pressure)

At present, the dispenser adopts a screw pump to supply the dispensing needle hose, the pressure to ensure that there is sufficient glue to supply the screw pump. If the back pressure is too large, it is easy to cause glue overflow and too much glue; if the back pressure is too small, it will cause intermittent glue and leakage, thus causing defects. Pressure should be in accordance with the same quality of glue and the temperature of the working situation to choose. If the temperature is high, the viscosity of the glue will be lowered, the fluidity will be better. At this time, it is necessary to reduce the back pressure to ensure the supply of glue, and vice versa.

Needle size
In fact, the inner diameter of the needle should be dispensing point diameter of 1/2. automatic dispensing machine in the dispensing process, dispensing needles should be in accordance with the pad size on the printed circuit board to choose: for example, 0805 and 1206 pad size is no difference, you can choose the same kind of needle, but for the different pads, you should choose different needles, not only to ensure the quality of the glue point, but also to improve production efficiency.

Distance between automatic dispenser needles and PCB boards

Different automatic dispensers use different needles, some of which have a certain stop. At the beginning of each job, the distance between the needle and the PCB should be calibrated, i.e. z-axis height calibration.

Glue temperature: general epoxy resin glue should be stored in 0-5 ℃ refrigerator, use should be taken out 1/2 hour in advance, so that the glue temperature fully consistent with the working temperature. The use of glue temperature should be 23 ℃ -25 ℃; the situation temperature of the viscosity of the glue has a great impact, if the temperature is too low, the glue point will become smaller, resulting in drawing. Situation temperature difference of 5 ℃, will cause 50% of the dispensing amount of change. Therefore, the situation temperature should be controlled. At the same time, the situation temperature should also be ensured that the glue spot with small humidity is easy to dry, affecting the adhesion.