Low Volume Assembly for Electrolysis Water Cup
SMT dispensing process requirements and characteristics, dispensing process in SMT assemlby is mainly used for lead element through hole insertion (THT) and surface mount (SMT) co-existence of paste insertion mixed process.
In the whole low volume assembly production process, we can see that one side of printed circuit board (PCB) components from the beginning of the glue curing, to the final wave soldering welding, the interval is a long time, and need many other processes, the component curing appears especially important. PCB point B surface--mount B side-- reflow soldering solidified--silk screen printing A side--mount A-side--reflow soldering welding--automatic instrumentation --Manual flow interpolation--wave soldering B side--process control in dispensing process.
The following process defects in low volume assembly are easy to occur in the production: unqualified size of glue point, wire drawing, glue dip and dye welding pad, bad curing strength not easy to drop pieces and so on.Therefore, the control for technical parameters is the way to solve the problem.
According to work experience,the glue point diameter size should be half of the distance between the welding pad, the glue point diameter after mounting should be 1.5 times the diameter of glue point.This ensures that there is sufficient glue to hold the elements together and prevents excessive glue from soaking the pad.The dispensing amount depends on the length of dispensing time, the actual production should be based on the situation (room temperature, glue viscosity, etc.) to choose the glue parameters.
Dispensing pressure. The dispensing machine currently uses a pressure applied to the dispensing needle cylinder to ensure that enough glue is extruded from the dispensing nozzle.Too much pressure is easy to cause excessive amount of glue;If the pressure is too small, there will be a phenomenon of broken glue and leakage points, resulting in defects. Choose pressure should accord to same quality glue and working environment temperature. High environment temperature can make glue viscosity decrescent, fluidity becomes good, then need to reduce pressure to assure glue supply at this moment, vice versa.
In practice, the inner diameter of the dispensing nozzle should be 1/2 of the diameter of the dispensing nozzle. In the dispensing process, the dispensing nozzle should be selected according to the size of the welding pad on the PCB: for example, the size of 0805 and 1206 welding pad does not differ much, the same needle can be selected, but for the welding plate with great difference,it is necessary to select different dispensing nozzle, so as to ensure the quality of dispensing nozzle and improve production efficiency.
Dispensing nozzle and PCB board distance. Different dispensing machine with different needles, dispensing nozzle has a certain degree of immobility. At the beginning of each work, the stop rod of the dispenser should be guaranteed to contact the PCB.
Temperature of glue general epoxy resin glue should be kept in the refrigerator of 0-50C, when using should take out 1/2 hour in advance to make glue and working temperature are consistent adequately.The service temperature of glue should be 230C-250C;Environmental temperature has a great influence on the viscosity of glue. If the temperature is too low, the glue point will become smaller and will occur wire drawing phenomenon. A difference of 50C in ambient temperature will result in a change of 50% of the dispensing amount. Therefore, the ambient temperature should be controlled. At the same time, the temperature of the environment should also be guaranteed, small humidity can make glue point easy to dry, affect the adhesive force. Viscosity of glue directly affects the quality of point glue. Viscosity is large, the glue point will become smaller, or even make wire drawing; Viscosity is small, glue point will become larger, and then may be seepage dyeing pad. In SMT dispensing process, should choose a reasonable pressure and dispensing speed for different viscosity of glue. In practice low volume assembly, a higher temperature should be used to solidify the glue so that it has enough strength after solidification .Bubble glue must not have bubbles. A small bubble can cause many pads to be glue-free. Each time the glue should always empty the air in the bottle, to prevent empty beating.
For the adjustment of the above parameters, any change in parameters shall affect other aspects, should accord to the way of point and surface. At the same time, defects may be caused by multiple aspects. Possible factors shall be checked item by item and then excluded.In a word, we should adjust the parameters according to the actual situation in production to ensure the production quality and improve the production efficiency.