For the through holes of double-sided printed circuit boards, there is no need to use copper plating to connect the two circuits. Instead, the method of filling silver paste into the through holes can also reduce the cost of double-sided printed circuit boards. The specific process diagram is shown in Figure 4 88. This method is generally used for ordinary phenolic resin paperboard with double-sided copper coating. This method first cleans the surface of ordinary phenolic resin paperboard coated with copper on both sides, and then prints corrosion-resistant patterns on both sides using screen printing method. After corrosion, a conductive pattern is formed. After removing the corrosion-resistant layer, through holes are drilled, and silver paste is filled into the holes. In order to ensure good contact between the silver paste and the conductive patterns on both sides, the silver paste should protrude through holes, and the diameter of the protruding silver paste pattern should be greater than the aperture of the through holes. In order to block the migration of silver ions, a covering layer is added to the surface of the protruding part of the silver paste through screen printing. Subsequently, solder mask patterns and isolation patterns are printed on both sides of the screen, and screw holes for fixing the printed circuit board are stamped or drilled to process the shape. Finally, through inspection, the double-sided printed circuit board filled with silver paste through holes has been completed.