Conductive paste

The conductive carriers in the conductive carbon paste are graphite and carbon black. Carbon black is a non-metallic conductor. It is difficult to combine with oxygen and other things in the air, thus effectively ensuring the reliability and durability of the membrane switch. Graphite has smaller frictional coefficient. It is a solid lubricant that, when applied to contacts, it facilitates rapid separation after the contacts are closed.

Graphite has high wear resistance, which ensures that membrane switch can withstand millions of contacts. The dense carbon coating can hinder the migration of other metal ions, thereby effectively ensure the stable electrical performance.

When the carbon coating is applied to the lead socket, it can facilitate the insertion and removal of the leads and connecting terminals. In addition, the low price and easy availability of raw materials are the biggest advantages of conductive carbon paste.

Resistance value

Resistance value is an important indicator for conductive ink. The value is usually expressed in two ways: volume resistivity and surface resistance. Volume resistivity is the resistance of the medium to electric current per unit volume. The unit is Ω·cm. Surface resistance is the thing produced by surface leakage current between opposite sides of a square for 1 unit area of dielectric surface. The unit is Ω.

If expressed in terms of volume resistivity, it is difficult to obtain a cured 1 cm3 sample of conductive paste for testing. It can only be a theoretical value, and lacks authenticity and realizability in reflecting the performance of conductive paste.

Then, we express it in terms of surface resistance. We know that the cross-sectional area is inversely proportional to the resistance value. The solidified film of conductive paste is affected by the density and aggregation state of conductor particles. The surface conductive properties are different from other things.

Here, the conductive film has a particularly prominent impact on the resistance value at a volume height of square centimeters. When using surface resistance to reflect the resistance value of the conductive film, we must define a feasible and practical thickness value.

What are the reasons for the high resistance of membrane switch circuits?

1. The silver paste is not fully stirred before silkscreen printing.

2. After silkscreen printing, the baking time is not enough, and the temperature is too low.

3. The mesh of the screen is too fine.

4. Too thin silver paste or too much diluent, resulting in less silver content. Or non-silver paste-specific diluent is used.

5. Raw materials, such as silver paste, are not good.

What can we do to solve these problems?

1. Make sure the silver paste is fully stirred before silkscreen printing, and stir thoroughly when adding silver paste.

2. Control the baking time and temperature.

3. Replace the screen with a coarser mesh to make it qualified.

4. Check the concentration of silver paste. Pay attention to the addition of diluent. Make sure to use the diluent matching the silver paste.

5. Replace raw materials, such as silver paste, with quality that meets the requirements.

Do buttons on membrane switch have resistance?

Generally speaking, buttons have no resistance, because membrane switches are actually open and close conductive switches. When you press the button, due to the contact between the metal foils, current can go freely between them, forming a path. When the button is released, the path is broken, and so is the current.

However, in some special applications, for example, when it is necessary to generate a continuous signal after pressing the button so that the controller can work well, the button may have a certain resistance. This is usually done by adding some resistors and capacitors to the circuit.