Kemtron manufacture a range of conductive Elastomers as gaskets, O-Rings and Extrusions for shielding of electronic devices.
The base Elastomer for normal environments is Silicone, and for environments where oil and fuel are present, Kemtron offers Fluorosilicone. Both have a wide temperature range of -40°C to +160°c and up to +200°C for some grades.
The base elastomer is then combined with a conductive filler. The balance between the conductive filler and the elastomer is exact to ensure a good conductive path, whilst still maintaining the elastomeric properties of the silicone.
The three main fillers that Kemtron offer are as follows:
- Nickel plated Graphite
- Silver plated Aluminium
- Silver plated Copper
Commonly, the conductive Elastomer will have a shore A hardness of between 60 and 75 depending on its grade and still maintain good tensile strength, this will ensure the gasket will deflect sufficiently when under compression giving a good emi and environmental seal. The electrical properties of the conductive Elastomer are measured in volume resistivity – ohms-cm and shielding effectiveness stated in db however the two do not directly correlate with each other. The volume resistivity of silver plated aluminium in silicone will be max 0.008Ωcm giving a shielding effectiveness at 2Ghz of 102db whereas nickel coated graphite will have a volume resistivity more than 10 times greater but exhibits a similar shielding effectiveness.
Nickel coated graphite in silicone is the most cost effective conductive Elastomer and gives excellent shielding characteristics even though the material is much more resistive than precious metal plated particle Elastomers. This excellent performance can be accredited to the fact that the nickel graphite particles are very irregular in shape and have sharp edges, when the gasket is put under pressure being compressed between two surfaces the particles dig into the surface giving very low contact resistance, graphite is also a good microwave absorber thereby enhancing the shielding performance.
Kemtron is always working to improve its product range, offering a flame-retardant version of nickel graphite in silicone, tested and approved to the international standard UL94V-0. Also compounded an unfilled fluorosilicone to meet MIL-C-25988.
With onsite tooling engineers, Kemtron offers a range of profiling, and sizing to suit a variety of applications to shield your materials, click here for more information.