Technology to increase the life of printed circuit squeegees

The squeegee is a tool for scratching the ink on the screen to make it leak on the bearing surface. The squeegee is composed of a squeegee bar and a doctor blade. The screen printing squeegees of the single-sided printed circuit board are commonly used polyurethane squeegee. Its high strength, wear resistance and solvent resistance are very good. The shape of the squeegee is right angle.

Usually the hardness of the squeegee is indicated by color, and the color is gradually deepened with the increase of hardness. At present, most of the materials are imported materials. Generally, the red represents the hardness of 60~65o. It is a soft squeegee and is suitable for PCB solder resist patterns and character patterns. Printing; 70 ~ 75o for the hardness of the plastic scratch, some with green, and some with white, used for printing resist patterns and conductive printing materials. Targeted selection of a suitable hardness scraper will help to improve the quality of screen printing. If it is not properly selected, it will cause poor printing failures. For example, a scraper with a hardness of 75o or more is used in the PCB solder mask printing process. When the circuit pattern is denser in wire spacing, it is more difficult to print all the printing materials on the screen onto the wire. Sometimes, in order to completely print the printing material on the screen, it will increase. The printing pressure causes the screen to be damaged or a small gap is formed in the blade rubber. In the subsequent printing, there will be stripe marks along the direction of movement of the blade.

When installing the squeegee, it is necessary to select a straight, non-defective squeegee bar, and the squeegee blade shows a height of 10 to 25 mm. The softer the hardness is, the less exposed it is. Usually, hard squeegees are selected and it is not easy to bend. If you use pneumatic mesh to print PCB patterns, some glue strips are inserted into a part of the height of the scraper, and the height of the strip is more than 25mm. You can use only 1mm or 25mm according to the thickness of the strip. In the printing, due to the pressure applied to the softer scraper, the printing surface is brought into contact with the printing surface, resulting in blurred printing images, especially in the printing PCB resistance pad set is easily eroded, the ink layer thickens, affecting Curing effect of solder resist, while reducing the service life of the squeegee to a large extent.

The length of the squeegee should be selected as short as possible according to the principle of application. It is 40-50mm longer than the entire image on the screen. If it is too long, deformation will occur on both sides of the blade of the squeegee. Naturally, during the process of screen printing Bending is uneven, causing the entire ink coating to be uneven; if the squeegee is too short, when the resist pattern is printed, shadows are likely to occur on both sides of the pattern. When printing the solder resist pattern and the insulating layer and protective layer of carbon paste, both ends will Printed material sometimes cannot be printed or the ink layer on the edge is thick. In addition, after the proper length of the squeegee is cut, the sharp edges of the squeegee are cut off with a tool and sanded to make it blunt so as not to scratch the surface of the photosensitive film or the capillary photosensitive film coated on the screen. The printing process leaks ink.

To get a good printing effect, check whether the edge of the squeegee is straight before printing. Wash the squeegee immediately after use, especially when screen printing PCB solder resist patterns and character mark patterns, etc. Strong, long time dipped will make the scraper strips become soft and accelerate the wear and tear. When printing, the film layer is very thick, and the position of the resistance pad is eroded, which affects the quality of the product.

A reasonable choice is that the currently popular scraper "wheel rest system" (ie rotation system) can better improve the service life of the scraper.