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What is conductive foam?

Views: 10618 Update date: Nov 23,2017

Conductive foam is similar to standard packaging foams but with one crucial difference – the addition of carbon to the polymer mix during the manufacturing process to provide a high level of conductivity. This allows any electric current to pass through the cell structure of the foam and away from the component. Generally, the foam will have permanent conductive performance, meaning it is ideal for multi-trip packaging and in-plant handling applications. Its performance isn’t affected by atmospheric conditions.

 

This ESD safe material will typically have a surface resistivity of fewer than 104 ohms/sq. and a volume resistivity of fewer than 104 ohms/cms, which offers a quicker transfer of any static charge to a grounding source or adjacent conductive material.

 

Conductive Foam: Conductive foam is a polyethylene foam filled with carbon (as are all black ESD foams), giving it its conductive properties and color. Conductive foam is designed for repeat use, and will act like a Faraday cage when an item is fully enclosed within it. Because of this a silver conductive bag is not needed as an outer container when using conductive foam. Conductive foam will drain batteries if their contacts have a path the foam, so care must be taken to prevent this (by insulating the contacts or using a static dissipative foam layer between the conductive foam and the item being packed). There are two grades of conductive foam: lead-insertion grade and component grade. Lead-insertion grade conductive foam is designed to have components directly mounted into the foam via their leads, and will drain charge off of attached components. Cushion grade conductive foam is designed to package something like a circuit board or hard disk drive. Conductive foam should be used when it's properties as a faraday cage and conductor are needed (e.g. shunting a component to ground). It has a surface resistance of 10^4 Ohms or less. It is the most expensive type of ESD foam.


Anti-Static Foam: Anti-Static foam is a polyurethane foam that is chemically doped with an anti-static agent (surfactant) and colored with a pink dye for identification. Anti-static foam will not generate static charge when it rubs against itself, but will happily pass a charge through itself to anything contained within. Because anti-static foam does not provide shielding it must be placed within a shielding bag. Another key property of anti-static foam is that it has a shelf life when exposed to the environment. Thus it is usually used as a one-time foam for shipping components. It is the least expensive type of ESD foam. It has a surface resistance of 10^9 to 10^10 Ohms or less (the higher this number the more slowly a charge is dissipated).


Static Dissipative Foam: Static Dissipative foam is a polyethylene foam that is either black carbon-impregnated, or pink colored and doped with surfactants. The black carbon version is permanent, and has a lower carbon content than conductive foam. The pink version has a limited lifetime, but lasts much longer than pink anti-static foam. Static Dissipative foam is the general goto foam for reusable applications, unless you require the specific properties of Conductive foam. Like anti-static foam, static-dissipative foam must be contained within a faraday cage.


Conductive foam

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