The dispensing system must transfer uniform and precise adhesive height and dot shape at different volumes onto the surface of PCB solder mask. The adhesive should possess adequate attachment capability, also called “green strength”, to hold the components in place until cured. This cured adhesive must then hold the SMD components in the right position until reflow or wave soldered
When dispensing adhesive onto the PCBs, a number of parameters are essential to obtain a good result. The parameters for each type of system are described below.
Time and Pressure
With regards to a time / pressure system, a fairly high air pressure is applied to the top of adhesive cartridge for a controlled period of time (ms) so as to transfer the required adhesive volume to the PCB. It is important that the air pressure is accurately adjusted and periodically checked to sustain uniform dot sizes.
Nozzle Size
There are some dispensing units that feature two to four dispensing heads on the gantry. Each is equipped with a different nozzle diameter and standoff foot, allowing the machines to dispense adhesive dots in a wide range of sizes.
Stand Off
A twisted or bent PCB can lead to a large variation in the adhesive dot size and thus a variation in the strength of the component attachment. The use of a standoff foot will not only guarantee a more uniform dot height but would also, to some extent, dictate the dot height.
Temperature Control
The viscosity of the adhesive is of utmost importance. In order to lower adhesive dot volume and shape deviation, an adhesive temperature control system should be used.
Other Products in this Category
PD 955PY
SMT Adhesive Dispensing (Jar) PD 955M