Solder paste printing machine is an important equipment in the front section of SMT line, mainly using the stencil to print the solder paste on the specified pad, the good or bad solder paste printing, directly affect the final solder quality. The following to explain the technical knowledge of the printing machine process parameters settings.
1. Squeegee pressure.
The squeegee pressure should be based on the actual production product requirements. Pressure is too small, there may be two situations: squeegee in the process of advancing downward force is also small, will cause the leakage of the amount of insufficient printing; second, the squeegee is not close to the surface of the stencil, printing due to the existence of a tiny gap between the squeegee and PCB, increasing the printing thickness. In addition, the squeegee pressure is too small will make the stencil surface to leave a layer of solder paste, easy to cause graphics sticking and other printing defects. On the contrary, the squeegee pressure is too large will easily lead to solder paste printing is too thin, and even damage the stencil.
2. Scraper angle.
Scraper angle is generally 45° ~ 60°, solder paste with good rolling. The size of the angle of the scraper affects the size of the vertical force of the scraper on the solder paste, the smaller the angle, the greater the vertical force. By changing the scraper angle can change the pressure generated by the scraper.
3. Squeegee hardness
The hardness of the squeegee will also affect the thickness of the printed solder paste. Too soft squeegee will lead to sink solder paste, so should use a harder squeegee or metal squeegee, generally using stainless steel squeegee.
4. Printing speed
Printing speed is generally set to 15 ~ 100 mm / s. If the speed is too slow, the solder paste viscosity is large, it is not easy to miss the print, and affect the printing efficiency. Speed is too fast, the squeegee through the template opening time is too short, the solder paste can not be fully penetrated into the opening, easy to cause solder paste is not full or leakage of defects.
5. Printing gap
Printing gap refers to the distance between the bottom surface of the stencil and the PCB surface, stencil printing can be divided into contact and non-contact printing two types. Stencil printing with a gap between the PCB is called non-contact printing, the general gap of 0 ~ 1.27mm, no printing gap printing method is called contact printing. Contact printing stencil vertical separation can make the printing quality affected by Z small, especially for fine pitch solder paste printing. If the stencil thickness is appropriate, contact printing is generally used.
6. Release speed
When the squeegee completes a printing stroke, the instantaneous speed of the stencil leaving the PCB is called the demoulding speed. Proper adjustment of the release speed, so that the stencil leaves the PCB when there is a short stay process, so that the solder paste from the stencil openings are completely released (demolded), in order to obtain the Z best solder paste graphics. The separation speed of PCB and stencil will have a greater impact on the printing effect. The demoulding time is too long, easy to the bottom of the stencil residual solder paste; demoulding time is too short, not conducive to the upright solder paste, affecting its clarity.
7. Stencil cleaning frequency
Cleaning stencil is a factor to ensure the quality of printing, cleaning the bottom of the stencil in the printing process to eliminate the dirt at the bottom, which helps prevent PCB contamination. Cleaning is usually done with anhydrous ethanol as the cleaning solution. If there is residual solder paste in the opening of the stencil before production, it must be cleaned before use, and to ensure that no cleaning solution remains, otherwise it will affect the soldering of the solder paste. It is generally stipulated that the stencil must be cleaned manually with stencil wipe paper every 30 minutes, and the stencil must be cleaned with ultrasonic and alcohol after production to ensure that there is no residual solder paste in the stencil opening.
Post time: Dec-09-2021