Scraping means that before welding, the surface of the welded metal should be cleaned as shown in Figure 3. A small knife, scrap steel saw blade, etc. can be used to scrape off (or use fine sandpaper or coarse rubber to wipe off) the oxide layer, oil stains, or insulation paint on the welding surface until a new metal surface is exposed. Before welding self-made printed circuit boards, it is also necessary to carefully polish one side of the copper foil with fine sandpaper or water sandpaper. Scraping is a key step to ensure welding quality, but it is often overlooked by beginners. If the scraping is not done properly, it will result in poor tin plating and welding. It should be noted that some component leads have already been silver plated, gold plated, or tinned. As long as there is no oxidation or peeling, there is no need to scratch them again. If there is dirt on the surface, use a thick rubber to erase it. The choice of thick rubber is best when using a large rubber for drawing. Some gold plated crystal transistor pins and leads may find it difficult to tin after scraping off the coating. No matter what form of "scraping" is used, it is important to continuously rotate the component pins and ensure that the entire circumference of the pins is clean.