Reasons and analysis of the drop :

1. The amount of glue is not enough. Under the same conditions, the IC has more glue than the element. The solution is: firstly, it can increase the glue point of a single IC. This requires changing the stencil opening or adjusting the dispensing procedure. Secondly, increase the amount of glue in a single glue point, which also requires adjustment of the sizing process;

2. The curing is incomplete. Under the same conditions, the adhesive IC has more glue than the adhesive component, so it may not be completely cured under the same curing conditions. The solution is to extend the time of the reflow furnace or increase the temperature accordingly. If necessary, the reflow oven can be passed twice;

3. The problem of IC itself, in addition to the gap between IC and pcb, there is also a material problem of IC itself. Generally, IC is molded by EMC. In theory, the bonding performance with glue should be very good, but if the IC uses a special release agent during the molding process, it may also cause a significant decrease in the adhesion to the glue, which may require corresponding treatment of the surface of the IC.

4. The defect of the screen design causes the amount of printed red glue to be insufficient. After curing, the components are not completely stuck and easily fall off. This problem is easier to improve. First, check if the mesh is made to fit the design. Secondly, if the opening of the original screen is a square opening, the arc can be expanded outward when the length is constant, and the area of ​​the opening is increased by changing the opening to an elliptical shape. In addition, the prior art generally adopts contact printing, and the scraper will cut off the glue of the large glue point. Therefore, the thickness of the screen is basically the same as the height of the glue point, and whether the thickness of the screen is suitable or not, the printing effect is also affected.

5. Improper control of the scraper when printing SMT red glue will result in poor printing. In the case of manual printing, the pressure of the scraper should ensure that the printed glue dot is clear, the surface is flat and the thickness is suitable; the blade speed should be controlled to ensure that the colloid is rolling rather than sliding relative to the scraper, in general, 20 -40mm / s is suitable; the angle of the scraper is preferably 45 – 60 degrees. In addition, the operator’s proficiency in control of speed, pressure, and repeated printing during printing also has a great influence on the printing effect.

6. The curing temperature of SMT red glue is too high, lead to the red glue becomes brittle after curing, and it is easy to fall off due to vibration during the production process. The curing temperature of red glue should be determined according to the actual situation. At present, the maximum curing temperature of imported red glue commonly used in the production process of electronic controllers for household appliances should be controlled below 160 °C. The curing effect can be evaluated by the thrust test after curing. The thrust tester tests the component with the force parallel to the substrate. The maximum thrust that the component can withstand varies according to the size of the component. Commonly for 0603, 0805, 1206 package , the thrust is typically between 1kg and 2kg.

7. The use of SMT red glue and the storage of red rubber sheets are not strictly controlled during the production process. In general, many factories have strict requirements for the low temperature storage and access of red glue, but the temperature control during the production process, the placement of red rubber sheets, the opening of the red glue and the processing of the remaining materials after printing are not strict control. First, dispensing and printing operations should be performed at 23 ± 3 °C to achieve optimum coating quality. Secondly, the opened and stirred red glue should be used within 24 hours. The printed red glue board should be cured within 12 hours. The daily used materials can not be mixed with the newly opened red glue, and can not use a colloid that will shrink.

Any other problem about red glue component drop ,welcome contact us .Thanks .