Membrane Switch Inspection Methods

Label:Conductive Silver, Insulation Printing, Bubbling Quality, Loop Resistance, Salt Spray Test

Oct 19, 202024308

Membrane Switch Inspection Methods

1. Shape: shape, conductor line, insulation treatment, liner combination, etc. should meet the requirements of the drawing or provide physical samples.


2. Material: panel, substrate, silver paste, carbon ink, spacer, adhesive, adhesive, reinforcing plate, insulation printing should meet the requirements of the drawing.


3. Check appearance quality: The scope of this inspection is wide.


Panel: There must be no obvious defects (such as lack of strokes in characters that affect readability; stains, light transmission points; deinking, stains, scratches; transparent window overflow, residual glue, etc.); no offset phenomenon (printing sleeve Plate deviation ≤ 0.2mm; upper and lower line key combination deviation ≤ 0.5mm; circuit and key sheet, panel and face key combination deviation ≤ 0.3mm; panel and circuit combination after the surrounding blank area deviation ≤ 0.2mm; panel The offset between the button bump and the substrate is less than or equal to 0.5mm).

 

Circuit: There must be no residual material scraps, foreign matter, stains, bumps, grease attached to the surface and inside, fingerprints on the circuit, and burrs on the edge of the finished product; all circuits and contacts must not have cuts through the surface and the inside (that is, the cuts are caused by the circuit Cut up to the substrate), minor scratches are also based on the principle that it does not affect its impedance. The carbon ink surface scratches are based on the principle that they do not affect the line conduction, and the line must not have any foreign matter attached to it.


Conductive silver: Generally, the thickness of silver paste is controlled at 7-12μm, and it should be uniform and smooth, without obvious defects and pinholes. No disconnection or short circuit is allowed. Carbon ink: The carbon ink covering the silver paste circuit should ensure that the silver paste is completely covered, with a thickness of 8-10μm, and there must be no obvious protrusion of the silver paste.


Insulation printing: no insulating ink is allowed to adhere to all the contact points of the membrane switch. The insulating ink surface should be flat to avoid any defects such as bubbles or pinholes that affect the insulating effect.


Jumpers: All jumper parts are in accordance with the requirements of line conductors, and all jumper products must pass 100% open, short circuit and insulation resistance tests. Ensure that there is no open, short circuit and insulation resistance should be greater than 500MΩ (500VDC for 1 minute). Punching flash and die extrusion size: The punching flash and extrusion size should not be greater than 0.2mm, and the position should be toward the side without conductors.


4. Check the color: use the visual method to compare with the sealed sample to see if there is any color difference. The color requirement is particularly strict with the color difference meter.


5. Ink adhesion inspection: the ink is attached to the transparent tape and pressed by hand to ensure that there are no bubbles and then peel off quickly after 10 seconds, and there should be no ink falling. After the insulating ink is dried, press the ink surfaces against each other and press for 24 hours to ensure that the insulation does not stick to each other. After 1 minute of sticking with pressure sensitive tape and pressing by hand without bubbles, it peeled off quickly and no ink came off.


6. Bubbling quality: equal height and balanced strength. Flat type: 57~284g force, touch: 170~397g force.


7. Peel strength: the peel strength of the glue should not be less than 8N/25mm.


8. Folding strength: After drying the silver paste, carbon ink circuit or silver circuit covered with carbon ink, the circuit resistance should be measured first, and then the circuit should be folded 180 degrees, and the fingers should be pressed for 2kg/2 seconds. Then make it return to the plane, repeat it for 5 times, and then measure its resistance. The resistance increased after being folded 5 times does not exceed 300% of the original resistance.


9. Hardness: Use H-grade drawing pen tip, apply 1kg thrust to the circuit at 45 degrees, and the circuit must not peel off the conductive ink or produce light transmission.


10. Dimensions: The allowable tolerances without tolerances on the drawings are shown in Table 1, and the rest comply with the drawings.


11. Loop resistance: The resistance of the loop should not be greater than 100Ω. For the total length of the loop greater than 150cm and special requirements, the loop resistance is separately specified on the drawing.


12. Insulation resistance: In a normal temperature and humidity environment, the insulation resistance of the conductor line is greater than 500MΩ (500VDC for 1 minute). After high temperature and constant humidity test, salt spray test, it should be no less than 20MΩ.


13. Life: The number of times of contact and conduction of each key without reed should be 1 million times. The number of reeds and tactile conduction should be 500,000.


14. High temperature: After the membrane switch is subjected to a high temperature of 55±2°C for 72 hours, the appearance quality of the membrane switch should meet the requirements of the drawing. After recovering for 2 hours under normal atmospheric conditions, the measured insulation resistance value should meet the requirements.


15. Low temperature: After the film is subjected to a low temperature of -10±3°C for 16 hours, it is restored under normal atmospheric conditions for 2 hours, and the water droplets on the surface are wiped off. The measured loop resistance value should meet the requirements.


16. Constant heat and humidity: The membrane switch is subjected to 40±2℃, relative humidity is 93 (+2% -3%), after 96 hours of constant heat and humidity test, it is restored under normal atmospheric conditions for 2 hours, and the insulation resistance and loop resistance are measured. , The button force should meet the requirements.

17. Salt spray test: The membrane switch is subjected to 5% sodium chloride salt solution, the temperature in the test space is 35±2℃, (connector is sealed) after 72 hours of salt spray test, it will be restored under normal atmospheric conditions for 2 hours, The insulation resistance should meet the regulations.




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