1. Angle of the scraper
In the electronic processing production process, the angle of the scraper affects the size of the scraper to the vertical direction of the force of the solder paste the smaller the angle, the greater the vertical force, by changing the angle of the scraper can change the resulting pressure scraper angle if greater than 80 °, the solder paste can only keep the original shape forward and not rolling, when the vertical force is almost no, the solder paste will not be pressed into the printing template window opening. The optimal setting of the scraper angle should be 45 ° ~ 60 °, when the solder paste has a good rolling nature.
2. The speed of the scraper
Squeegee speed is fast, the force on the solder paste also becomes larger. Considering the actual situation of solder paste pressed into the window, that is, solder paste pressed into the time instead of becoming shorter. If the squeegee speed is too fast, the solder paste cannot roll and only slides on the printing plate. Because the solder paste flow into the window takes time, which can be clearly felt when printing fine-pitch QFP graphics, when the squeegee runs along the QF side perpendicular to the squeegee pad on the solder paste graphics than the other side to full, so some printers have a squeegee rotation 45 ° function to ensure that the fine-pitch QFP yuan printing when the amount of solder paste on all sides of the uniform maximum printing speed should ensure that the FQFP pad solder paste printing The longitudinal and horizontal direction is uniform and full, usually when the scraper speed is controlled at 20~40mm/s, when the board brush effect is better.
3. Scraper pressure
When the solder paste is rolling, a positive pressure will be applied to the vertical balance of the squeegee device, which is usually called printing pressure. Solder paste printing machine pressure will cause insufficient solder paste scraping, if the printing pressure is too large and will lead to leakage behind the stencil and in the surface of the steel plate left scratches. Therefore, the general pressure of the scraper is set at 5-12N/(25mm) The ideal scraper pressure should be just to scrape the solder paste from the surface of the steel plate clean.
4. Scraper width
If the squeegee is too wide relative to the PCB, then it requires more pressure, more solder paste to participate in its work, thus causing a waste of solder paste. The general width of the scraper for the PCB length (printing direction) plus about 50 mm for the best, and to ensure that the scraper head falls on the metal template.
5. Printing gap.
Usually keep the PCB and the template zero distance (early also requires control in 0 ~ 0.5mm, but there should be zero distance when the FQFP), some printing machines also require the PCB plane slightly higher than the plane of the template, after adjusting the metal template of the template is slightly propped up, but the height of this propped up should not be too large, otherwise it will cause damage to the template, from the scraper running action, the scraper running freely on the template, both Requires the scraper where the solder paste all scraped away, not leaving excess solder paste, but also requires the scraper can not leave scratches on the template.
6. Separation speed.
Solder paste printing, the instantaneous speed of the steel plate leaving the PCB is a parameter related to the quality of printing, the ability to adjust the quality of the printing machine is also reflected in the parameters of good or bad, especially important in precision printing. Early printing machine is a constant speed separation, advanced printing machine in the steel plate leaving the solder paste graphics have a tiny dwell process to ensure access to the best printing graphics.
7. Squeegee shape and production materials.
Squeegee head production materials, shape has been a hot topic in the printing solder paste. Squeegee shape and production materials are many, from the production materials can be divided into polyurethane hard rubber and metal squeegee two categories. At present, with the common use of stainless steel plate, printing machine squeegee are used metal squeegee, which is made of high hardness alloy, fatigue resistance, wear resistance, bending resistance and other properties are very high. When the edge runs on the stencil, the solder paste can be easily pushed into the window, from the larger, deeper window to ultra-fine pitch printing are excellent consistency; in addition, the metal squeegee life is long, without correction, the stencil is not easy to damage; printing without solder depression and high and low undulation phenomenon. Metal squeegee printing quality is significantly better than the effect of rubber squeegee.
