Excellent solder paste printing shape is horizontal and horizontal direction uniform, smooth, full, clean around, solder paste covers the pad. With such printed graphics attached to the components, after reflow welding will get a good welding effect. But if the printing process is wrong, it will produce bad printing effect.
1. Solder paste pattern dislocation:
Causes: improper alignment of steel plate and offset of welding pad; The printing machine is not accurate enough.
Hazard: easy to cause bridge connection.
Countermeasures: adjust the position of steel plate; Adjust the printing press.
2. Solder paste drawing points and depressions:
Causes: scraper pressure is too large; Rubber scraper hardness is not enough; Window to heavy
Harm: insufficient solder, easy to appear virtual welding, solder joint strength is not enough.
Countermeasures: adjust the printing pressure; Change metal scraper; Improve the template window design.
3. Too much solder paste:
Cause: template window size is too large; The clearance between plate and PCB is too large.
Harm: easy to cause bridge connection.
Countermeasures: check the size of the template window; Adjust printing parameters, especially clearance of PCB template
4. The solder paste quantity is not uniform and has a break point:
Causes: the template window wall is smooth and bad; Printing times are too many, fail to erase the residual solder paste in time; The thixotropy of solder paste is not good.
Hazard: easy to cause insufficient solder, such as welding defects.
Solution: Clean the template.
5. Figure stain:
Causes: template printing times, failed to clean the solder paste quality is poor; The steel plate quivered as it left.
Hazard: easy bridge connection.
Countermeasures: Scrub the steel plate; In solder paste. Adjust the machine.
In summary, it should be noted that solder paste parameters, such as particle size, shape, thixotropy, flux properties, and printing press parameters, such as printing pressure, speed, ambient temperature, can change at any time. The solder paste printing quality has a great influence on the welding quality, so every parameter in the printing process should be carefully treated, and the correlation coefficient should be observed and recorded frequently.