During pcb manufacturing process printing machine technics parameters adjustment and influence
During the pcb manufacturing process, there are many scraper shapes and materials. From the production materials, there are two types of rubber (polyurethane) scrapers and metal scrapers; according to the shape, they can be divided into diamond and tail.
A. Rubber (polyurethane) scraper. The rubber scraper has a certain flexibility and hardness of 75 ° ~ 85 ° Shore. During the pcb manufacturing process, rubber scrapers are mostly used for screen printing and partial thinning or partial thickening of the stencil.
B.Metal scraper. The metal scraper is wear-resistant and has a long service life (about 100,000 times, about 10 times that of a rubber scraper), and is used for metal stencil printing with good flatness. It is suitable for printing with various pitches and densities, especially for narrow pitch and high density printing. It also has a long service life and is the most widely used.
During the pcb manufacturing process, when the blade head pressure is too large or the material is soft, it is easy to be inserted into the hole of the metal stencil (especially the large window hole), and the rubber scraper is used to dig out the solder paste of the hole, causing the printing pattern to be concave and the printing effect is poor.. Even with a high-hardness rubber scraper, although the cutting property is improved, the effect of filling the solder paste is still poor. For this reason, a scraper in which a metal piece is embedded in the front edge of the rubber scraper and a metal piece protrudes on the bracket by about 40 mm is called a metal blade, and is used to replace the rubber blade. It shows the operation condition and effect of the metal scraper and the rubber scraper.
The using of metal scrapers during pcb manufacturing process has the following advantages: excellent consistency from large, deep windows to ultra-fine pitch printing; long scraper life without correction; no solder sag and high and low undulations during printing , greatly reducing or even completely eliminating solder bridging connection and leakage.
Scraper shape and structure. The shape of the rubber scraper is diamond and trailing.
The diamond scraper consists of a square polyurethane material (10mm x 10mm) and a bracket. The square polyurethane is sandwiched between the brackets and formed 45° front and rear. This type of scraper can be used for bi-directional printing with a single scraper. At the end of each stroke, the scraper can skip the edge of the solder paste, so only a general scraper can be used for two-way shaving. Typical equipment is the SP-200 printing machine produced by MPM. However, the amount of solder paste of the diamond scraper is not easy to control, and it is easy to contaminate the scraper head, which brings a workload to the cleaning. In addition, when printing with a diamond-shaped blade, the edge of the PCB should be flattened to prevent the blade from crushing the edge of the stencil.
During pcb manufacturing process, the trailing scraper is generally in the form of a double scraper. This type of scraper is most commonly used. It consists of a rectangular polyurethane and a fixed bracket. The polyurethane is fixed on the bracket. Each stroke direction requires a scraper. The entire work requires two scrapers. The scraper is controlled by a micro-cylinder so that the solder paste can be driven in sequence without skipping the solder paste, so the scraper contacts the solder paste portion relatively little.
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