Metal Backer Membrane Keypad

Selection of screen for membrane switch screen production in membrane switch factory

Membrane switch conductive silver paste is a mixture of metal silver particles with good conductivity, conductive resin and solvent, and metal silver particles are the main factor determining the resistance of the switch. Since the size, composition and shape of the metal silver particles of the membrane switch silver pastes of different manufacturers are different, when printing the circuit, try to make the conductive silver particles pass through the screen smoothly, which requires the membrane switch circuit to be printed. The selected screen should not be too high or too dense. The mesh is high and the gap is relatively small, which will hinder the passage of silver paste during printing.

The circuit printed in this way has a large resistance value, which cannot reach the small resistance value required by the customer. Although the fine screen can print straight lines and make the printed circuit graphics beautiful, in the microscopic state, it is only a loose structure, and the solid content of metallic silver particles is very small. Most of them fail to pass through the wire mesh. This kind of pattern not only has a large resistance value, but also the current of the line is not smooth, which will also affect the service life of the line, so it cannot meet the practical application.

According to the experience of the membrane switch factory, it is generally appropriate to use a 200-mesh~250-mesh wire mesh. In addition, due to the different thickness of the material made of the same mesh, the size of the voids is also different. For the membrane switch circuit, monofilament, plain woven thin wire mesh should be used. This kind of wire mesh has fine wire diameter, small gap and smooth surface, and the silver paste will not be embedded in the wire mesh, which is beneficial to the smoothness of the silver paste during printing. Low resistance value and long service life.

In short, in order to allow the conductive printing material, especially the flake silver particles in the silver paste, to pass smoothly, it is necessary to choose a screen with a slightly lower mesh number, and the wire diameter is required to be smaller and the hole width is relatively large. The smoothness of the circuit pattern refers to the sharpness of the edge, which is not only for the sake of appearance, but also for the impact on electrical parameters. Unclean wires may reduce the edge resistance of adjacent wires. Especially in high temperature and high humidity situations, it is easy to cause silver ions to extend along the edge of the wire zigzag and cause silver ion migration, resulting in short circuit between wires and other faults.

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