Silver Paste in Membrane Switch: Parameters, Issue and Precautions

Label:Silver Paste, Membrane Switch

Oct 19, 20235200

Silver Paste in Membrane Switch: Parameters, Issue and Precautions

For membrane switches, layers composed of different materials play different roles and jointly complete the function of this component in electrical products. The circuit layer is the main functional one of the membrane switch. It is designed according to something required by the product. The conductive silver paste is printed on PVC, PC or PET materials, and then combined with the panel layer and spacer.


 

Silver paste is important material to make sure membrane switch works well. Understanding the performance of conductive silver paste is the main condition for high quality and reducing costs. We can select appropriate raw materials through certain parameters.

 

1. Silver content

 

Silver content is one of the important parameter. In some point, the amount of silver contained in the membrane switch determines the basic condition of the conductive ability. Membrane switches from various manufacturers have different silver content. The general silver content is about 65% (weight ratio).

 

2. Non-volatile content

 

This thing in membrane switch is irrelevant to customers. What's more, the non-volatile content is the sum of various solid substances. It does not mean the silver content alone. The labeling of the solid content has no practical significance.

 

3. Resistance value

 

It is an important parameter indicating the performance of conductive ink. The value is usually showed in two ways: volume resistance and surface resistance. Volume resistance is the resistance of 1 cubic centimeter of dielectric to leakage current. The unit is Ω·cm. Surface resistance is also called surface specific resistance or surface resistivity, which is defined as the surface leakage current generated by each square of the dielectric surface between the opposite sides of the square. The unit is Ω.

 

When producing circuit layer of membrane switch, pay attention to the precaution of silver migration.

 

Silver migration is an issue. In the humid environment with a DC voltage gradient, water molecules penetrate into the surface of the silver-containing conductor, and electrolyze to form H+ and O2-. Under the action of electric field and OH?, silver dissociates to produce Ag+. Under the action of electric field, Ag+ migrates from high potential to low potential, and form floc or dendrite-like expansion, forming black oxidized silver on the boundary where high and low potentials are connected.

 

Precaution

 

1. Widen the gap outside the wire as much as possible, and keep the voltage (potential) low.

 

2. Apply a layer of carbon paste or blue transparent insulating ink with a thickness >30μm on the circuit.

 

3. To prevent silver from accelerating migration in humid environment, add vents around the membrane switch during design.

 

4. Pay attention to the hygienic conditions of the printing environment. Dust and pinholes should be avoided when silkscreen printing the insulating coating. If dust and debris fall into the wire circuit, they cause a decrease in electrical performance under certain conditions.

 

5. If the silver paste insulation protective layer is insufficiently cured, or the solvent is excessive, the insulation of the spacer will be reduced, thereby reducing the anti-migration of silver in humid air.


 

The following three-stage curing method should be used for drying after silkscreen printing.

 

a. 2/3 time (specified temperature);

b. Leave at room temperature for 1 to 2 hours;

c. Infrared drying takes 1/3 of the time (specified temperature).

 

This brings the resistance to its optimal value.

 

Use protective insulating coating, transparent green ink, and UV light curing should be thorough, that is, wavelength 180~420nm, power 80~120W/cm. The UV speed is accurately adjusted, and the screen used is 160-300 mesh/inch (64~120T/cm, depending on the situation).


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