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Achieving a long flex life for integrated switches

29 July 2011

Film insert moulding (FIM) applications range from small electronic devices such as mobile phones, to larger components used by car manufacturers. Common to all applications is the ability to integrate complex parts into as few production passes as possible, offering outstanding aesthetic features and high durability.

A crucial factor to the success of every FIM process is the film used for the part in question; the material has to withstand printing, UV curing, cutting, forming and injection moulding resins at high temperatures, yet retain its cosmetic appeal, as well as strength.

One of the key requirements of some FIM applications is the integration of switches. An example of this is in domestic appliances where waterproof switching may be a regulatory requirement. FIM offers a way to completely seal the switch by using the film as a membrane, bridging an aperture or shut-out in the moulding, as well as providing enough flexibility to allow actuation of an electrical switch contact mounted behind the film.

The film switch can be subject to high stresses in use, especially near the edges. For this type of applications it is important to select the appropriate film material. For example, if deep formability is required, without an excessive number of switch actuations, a polycarbonate film base should be used.

MacDermid Autotype’s FIM range consists of several different films, from polycarbonate to polyester and PMMA, the choice of which depends upon the application at hand. For the film switch example, this can be the company’s Autoflex Autoform, HiForm or Extraform product (which one depending on the required draw). Some of these films feature a novel ‘self heal’ outer surface, to make them more resistant to abrasion.

If the part has to endure a very high number of switch actuations, say up to five million, then it is better to use a polyester film base such Autoflex Autoform PE. This is also a necessity where domed switches are concerned, as this configuration concentrates even more stress on the film. Where optical clarity is specified, such as in the case of lenses, than a PMMA base like Autoflex Autoform PM may be used, though these premium films are only suitable for shallow forming. MacDermid Autotype technical director, Tim Wright summarises:

“Selecting the appropriate FIM film is closely related to the geometry of the part in question. We work closely with designers and developers in order to identify the most appropriate product, ensuring that the film we offer meets the precise usage requirements of the part in question. There is never a one-size-fits-all solution.”

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