Dispensing is widely used, ranging from aircraft and ships to clothes and toys. It can be said that as long as the glue reaches the place, dispensing process services are needed. It is necessary to understand the common defects and solutions in dispensing process, as follows:

1. Drawing/trailing

1.1 Wire drawing/trailing is a common defect in dispensing. The common causes are that the inner diameter of the nozzle is too small, the dispensing pressure is too high, the distance between the nozzle and the PCB is too large, the patch adhesive is expired or of poor quality, the viscosity of the patch adhesive is too good, it cannot be recovered to room temperature after being taken out of the refrigerator, and the dispensing amount is too large

1.2 Solution: replace the rubber nozzle with larger inner diameter; Reduce dispensing pressure; Adjust the "stop" height; Change the glue and select the glue with proper viscosity; After the patch adhesive is taken out of the refrigerator, it should be restored to room temperature (about 2-3h) before being put into production; Adjust the dispensing amount

2. Air strike

3.1. The phenomenon is that there is only dispensing action, but no glue output. The reason is that the patch adhesive mixes with bubbles; The rubber nozzle is blocked

3.2 Solution: The glue in the injection barrel should be de bubbled (especially the glue packed by ourselves); Replace the rubber nozzle

3. The rubber nozzle is blocked

2.1. The fault phenomenon is that the rubber nozzle has little or no glue spots The cause is generally that the pinhole is not completely cleaned; Impurities are mixed in the patch adhesive, and the hole is blocked; Miscible glue is mixed

2.2 Solution: change the clean needle; Replace the patch adhesive with good quality; The brand of patch adhesive shall not be mistaken

4. Component displacement

4.1 The phenomenon is that the components shift after the adhesive is cured, and the component pin is not on the bonding pad in serious cases The reason is that the amount of adhesive on the chip is uneven, for example, one of the two points of the chip element is more than the other; When mounting, the components shift or the initial adhesion of the mounting adhesive is low; The PCB was placed for too long after dispensing, and the glue was semi cured

4.2 Solution: check whether the rubber nozzle is blocked, and eliminate the uneven rubber discharge; Adjust the working state of the mounter; Change glue; The PCB should not be placed for too long after dispensing (less than 4h)

5. Pieces will fall off after wave soldering

5.1 The phenomenon is that the bonding strength of components after curing is not enough, which is lower than the specified value. Sometimes, chips will fall out when touching with hands The reason is that the curing process parameters are not in place, especially the temperature is not enough, the component size is too large, and the heat absorption is large; Aging of UV curing lamp; Insufficient glue; The component/PCB is contaminated

5.2 Solution: Adjust the curing curve, especially increase the curing temperature. Generally, the peak curing temperature of the thermal curing adhesive is about 150 ℃. If the peak curing temperature is not reached, flakes will fall off For the light curing adhesive, observe whether the light curing lamp is aged and whether the lamp tube is blackened; The quantity of glue and whether components/PCB are polluted should be considered

6. Floating/shifting of component pin after curing

6.1 The phenomenon of this fault is that the component pin floats or moves after curing, and the tin material will enter under the bonding pad after wave soldering. In serious cases, short circuit and open circuit will occur. The main causes are uneven patch adhesive, excessive amount of patch adhesive, or component offset during patch

6.2 Solution: Adjust dispensing process parameters; Control the dispensing amount; Adjust the process parameters of the patch