/How do printing process parameters affect the offset printing process?
In the pcb assembly factory, most customers who use offset technology are often very experienced in solder paste printing technology. The process parameters related to the offset printing technology can be determined by reference to the process parameters of the solder paste printing technology. Below, Jingbang Electronics talks about how the printing process parameters affect the offset printing process.
(1) Template. Relative to solder paste printing, the metal template used for offset printing technology is a little thicker, generally 0.2 to 1 mm. Considering that the glue does not have the characteristics of automatic shrinkage of the solder paste to the PCB pad during reflow soldering, the size of the module leakage hole should be smaller, and the size is too large, so that the glue is printed on the pad of the printed board, affecting the element. Soldering of the device. This is especially true when the printed board has poor wiring accuracy and poor print alignment accuracy. This should be especially noticeable for PCB offset printing with small size chips.
(2) Printing gap. The gap between the stencil and the PCB during offset printing is called the print gap and is usually set to a small value (rather than zero) so that the stencil can be peeled off after the squeegee has been scraped. If zero gap (contact) printing is used, a smaller separation speed (0.1 to 0.5 mms) should be used.
If a thin template is used, the glue point can reach a certain height only when there is a certain printing gap between the template and the PCB. During printing, the glue is pressed between the mesh of the stencil and the gap between the stencil and the PCB. When the template is slowly separated from the PCB (e.g., 0.5 mms), the glue is pulled out and dropped to obtain a more or less conical shape.
When using contact printing, the height of the stencil is limited because the thickness of the stencil is relatively small. For large dots (such as 1.8mm), the height is similar to the thickness of the template; for medium-sized dots (such as 0.8mm), irregular dot shapes may occur. Because the adhesion of the glue to the template and the PCB is almost equal, when the template is separated from the PCB, the template will lengthen the glue, so the height of the glue point should be greater than the thickness of the template. For small glue points of 0.3~0.6mm, due to the surface tension of the glue and the adhesion to the template, some of the glue will remain in the template. The height of these glue points is low, but the consistency is very good.
(3) Scraper. Scraper hardness is a relatively sensitive process parameter. Generally, a high-hardness scraper or metal scraper is used, because a low-hardness scraper, such as a rubber scraper, “hollows” the glue in the template leak. The blade pressure should be just as good as scraping the surface of the template.
I will share these points with you. If you need more information, please pay attention to us. Shenzhen FASTPCBA Co., Ltd. is a professional SMT chip processing, pcba processing one-stop manufacturer, with more than 15 years of PCBA circuit board chip processing experience, can provide PCBA OEM, PCB circuit board production, SMT chip processing , component procurement, patch plug-in soldering, assembly testing and other one-stop services.
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