Membrane Switch Circuit Production Requirements

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Circuit layer printing is the most important factor reflecting the inherent quality of membrane switches. Circuit should be restricted by parameters such as current, resistance, withstand voltage, insulation, and life span. This is also a concrete manifestation of the penetration of screen-printed products into functional and high-tech fields. To ensure the function of the circuit, the screen of the printed circuit should be guaranteed first. Combining the requirements of the circuit parameters and the requirements of the structural elements in the circuit for screen printing are described below.

 

(1) The resistance of a wire made of the same thick conductor is inversely proportional to the cross-sectional area of the wire; the current passed is proportional to the cross-sectional area; its contact abrasion resistance is proportional to the thickness of the contact. It can be seen that the thickness of the circuit pattern printed by the membrane switch is the basic condition to ensure the performance of the switch. Under general conditions, the thickness of the conductor pattern should not be less than 30 microns. For this reason, the thickness of the plate-making film should first be guaranteed.

 

(2) The thickness of the dense conductive pattern, although it is the basis for laying the conductive parameters, but because the printed circuit pattern of the membrane switch is aggregated by particles of conductive metal (usually silver), in the printed material, the barrier between the resin binder and the metal particles, the barrier of impurities to the conductor particles, and the barrier caused by the mesh of the screen during the screen printing process to the circuit pattern, etc., will affect the density of the conductor pattern, thereby affecting the performance of the electrical parameters.  For the compactness of the circuit printing layer, in addition to the thickness of the printing plate, on the other hand, it is necessary to consider how the printing plate screen allows the printing material, especially the flake silver particles in the silver paste, to pass smoothly. This requires a slightly thicker mesh and larger aperture ratio.

 

(3) The smoothness of the circuit pattern is not due to the need for appearance. Considering the impact on electrical parameters, the unclean wires may reduce the insulation resistance of the adjacent two wires, especially at high temperature and high humidity. In this case, the migration of silver ions will extend along the saw tooth, causing short circuits between lines and failure of switches. In summary, the principle requirements for making circuit printing plates can be summarized as: film thickness, coarse mesh, large aperture, and edge light. To meet the requirements of these aspects, we can use the direct method of film film, or the combination of direct method and direct method, to maximize the strengths and avoid weaknesses to meet the requirements.