There are two main processes commonly used in the red glue dispensing processing of SMT patch processing. One is to use a needle tube for dispensing, and the amount of red glue used in the SMT patch varies with the components. There are generally two ways to change, manual and automatic dispensing machines, and the other is to use SMT-processed steel mesh to perform red glue printing by brushing glue.Either way may cause some machining problems, so how do these machining defects arise?
First lost parts after wave soldering.
The reasons are complicated:
1. The adhesive force of the patch glue is not enough.
2. It has been hit before wave soldering.
3. There are many residues on some components.
4. The colloid is not resistant to high-temperature impact
Second, the patch glue mix.
The chemical composition of the patch glue used by different SMT patch processing manufacturers may be very different, and mixed-use is prone to many defects, such as:
1. Difficulty curing;
2. The adhesive force is not enough;
3. Seriously dropped parts after wave soldering.
The solution is to clean the stencils, scrapers, dispensing heads, and other parts that are prone to mixing and avoid mixing different brands of patch glue.
3. Component offset
Component offset is a bad phenomenon that is prone to occur in high-speed placement machines in SMT placement processing. The main reasons are:
1. It is the offset in the X-Y direction when the printed board moves at a high speed. This phenomenon is easy to occur on components with a small coating area of the patch adhesive. The reason is that the adhesion is not good.
2. The amount of glue applied to the components is inconsistent, the strength of the glue is unbalanced when it is heated and cured, and the end with a small amount of glue is easy to shift.
Four, collapse
Too much fluidity of the patch glue will cause a slump. The common problem of a slump is that it will cause a slump after being dispensed for too long. If the patch glue extends to the pads of the printed circuit board, it will cause poor soldering.
5. Drawing
Wire drawing is the phenomenon that the patch glue cannot be broken when the SMT patch is processed and dispensed, and the patch glue is connected in a filamentous manner in the moving direction of the dispensing head. There are many wires, and the patch glue covers the printed pads, which will cause poor soldering.
Third insufficient amount of glue or leakage.
Causes and solutions:
1. The stencil used for printing is not cleaned regularly and should be cleaned with ethanol every 8 hours.
2. The colloid has impurities.
3. The opening of the stencil is unreasonably too small or the dispensing pressure is too small, and the designed amount of glue is insufficient.
4. There are bubbles in the colloid.
5. If the dispensing head is blocked, the dispensing nozzle should be cleaned immediately.
6. The preheating temperature of the dispensing head is not enough, and the temperature of the dispensing head should be set at 38°C.
