Pressure Sensitive Adhesives and Elastomer EMI Gaskets: What You Need To Know
Pressure sensitive adhesive, more commonly known as PSA, is adhesive which forms a bond when pressure is applied, to join the adhesive with an EMI gasket. As the name "pressure-sensitive" indicates, the degree of bond is influenced by the amount of pressure which is used to apply the adhesive to the surface.
When it comes time to focus in on gasket electrical conductivity, it is generally not recommended to use PSA with an EMI shielding gasket. This is because the strip of adhesive inhibits true contact of the EMI shielding gasket with the mating surface, thereby decreasing the performance of the gasket. However, if a PSA system is deemed necessary, then the following guidance should be considered.
Advantages of PSA
- Eliminates fasteners or other adhesives.
- Can function as a “third hand” to facilitate difficult installations.
- Available with silicones or fluorosilicones as a permanent attachment method.
- Quick stick – readily adheres to clean surfaces.
- Conformable adhesion to curved surfaces.
- Resists humidity, moisture, natural elements.
- Eliminates alternative RTV solvent emissions and long set-up times.
Disadvantages of PSA
- Not available for round cross-sections, as there is little surface area to stick to.
- Not recommended for applications where solvent resistance is essential.
- Not recommended for applications where resistance to excessive abuse due to moving parts or traffic is required.
- Adds a shelf life to the sheet stock elastomer.
- Not available with EPDM binders.
Depending on how they are used, a PSA system may reduce the gasket through flange conductivity and/or shielding effectiveness to varying degrees. Applications such as an EMI connector gasket which requires the lowest electrical resistance ground connection should not incorporate a PSA system.
Overall, the use of PSA as an attachment method for elastomer materials is meant to aid in initial assembly operations vs. a long term means of permanent attachment. Generally, you can expect the minimum deflection of the gasket may need to be increased to obtain desired shielding results.
