How to solve the problem of stencil printing red plastic drawing?
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First, the basic knowledge of steel mesh SMT patch red plastic: red rubber scraping rubber is divided into hand manual scraping rubber and mechanical scraping rubber (machine scraping is divided into semi-automatic scraping rubber, automatic scraping rubber). The same red plastic is on the same thickness steel mesh. Because of the different slit widths, the height of the red rubber glue points is not the same.
Second, the steel mesh SMT patch red plastic mesh material is mainly steel plate, in addition to plastic mesh plate, copper mesh plate. The thickness of the steel mesh plate is generally between 0.15 and 0.20 mm, the width of the 0603 component is 0.25 to 0.28 mm, the 0805 component is 0.30 to 0.33 mm, and the seam length is about 10% of the pad length.
Third, the speed of the steel mesh SMT patch red glue is set according to the viscosity of the red glue. The higher the viscosity, the slower the speed, the lower the viscosity, the faster the speed, the speed is 0.5cm~8cm/Sec are normal. As long as it can guarantee the effect of red rubber scraping construction. At the same time, the speed of the squeegee is also closely related to the condition of the board. The red rubber scraping pressure will also be adjusted according to the viscosity of the red rubber. The actual operation can scrape the red rubber on the steel mesh after the scraper is scraped.
Fourth, the analysis of common problems of steel mesh SMT patch red plastic:
Copper mesh SMT patch red glue is usually stirred before printing to reduce its viscosity and facilitate red printing. In the red plastic printing process, the steel mesh should be cleaned frequently.
1. Overfill: Due to the low viscosity of the red glue or the too large width of the steel mesh.
2, the machine does not scrape the scraper: it may be because the surface of the scraper is too rough or the proportion of red rubber is too low; or the ambient temperature is too low; the red rubber touch index is too high.
3, the amount of glue is too small: usually the steel mesh slit width is too small or the steel mesh is not clean, has blocked holes.
4, red plastic collapse: it is due to poor reddensile thixotropy; or the moisture absorption rate is too fast.
First, the introduction of steel mesh SMT patch red plastic:
In the red glue process, many factories have used glue dispenser dispensing or 0.2-0.3mm stencil printing red plastic. However, for products that need to be self-inserted and then patched and have more placement points. The dispensing efficiency of the dispenser is too low and the stencil printing cannot be completed. Of course, some factories choose to install the chip first and then insert the component, so that the chip component has the danger of stress damage and falling parts when the component is inserted.
Second, the steel mesh SMT patch red plastic process requirements and use precautions
The process of patch red glue-wave soldering is: coating glue, one patch, one curing, one wave soldering and one cleaning. The following describes the patch red glue process in detail.
Steel mesh SMT patch red plastic storage before curing
The patch red glue is stored in a single component form, and requires stable performance, long life, consistent quality, non-toxic and tasteless, and is suitable for quick and convenient use in production. Since the mounted components are very small, the patch red glue is often applied to the center of the two pads. It is usually coated on the PCB by silk screen printing, pressure dispensing, etc. Therefore, it is required that the red glue is not coated. Brushed, no tailing, the shape and size of the glue dot are consistent, smooth, full and not collapsed.