20.12.2001 :: Johanna Merenheimo :: <johanna.merenheimo premix.fi>
Great cost savings with PRESEAL thermoplastic EMI gaskets
EMI gaskets are predominantly used in cellular phones and their base stations. Silicone based materials dominate the market today. While providing good material properties the silicone based gaskets have certain limitations and drawbacks especially in regard to mass production friendliness. The PRESEAL thermoplastic gaskets offer huge possibilities in simplifying gasket manufacturing and assembling.
Silicone gaskets used today between two PCB:s often consist of an LCP plastic frame, which supports the silicone gasket. This slow manufacturing process includes several steps as well as expensive raw materials. When producing the same construction with PRESEAL thermoplastic gasket material, a simple two-component injection moulding procedure can be used. Instead of the highly expensive LCP plastic needed in the silicone construction due to silicone curing temperature requirements, a cheap supporting plastic like PP, modified PS, ABS or PC/ABS can be used. The manufacturing process is greatly simplified, the throughput is dramatically increased and the raw material cost is significantly reduced.
The simple two-component injection moulding process opens up totally new construction design options to the mechanical designers for future models. As an example, the gaskets can be moulded directly together with the shell or other structural plastic part of the cellular phone. In addition to reducing EMI, the material can also be used for grounding, shock absorption and also as a heat sink due to its relatively good heat conductivity.
Silicone based gaskets on metal plates require priming for good adhesion. The priming process requires the use of “nasty” chemicals. Priming is not required with PRESEAL. The adhesion to the metal can also be improved through simple changes in construction.
Extruding PRESEAL based gaskets even into complicated profiles is simple. Several materials can be combined in the profile through co-extrusion. This results in improved mechanical properties and multifunctional gaskets. In addition to reducing EMI, the same gasket profile can function as a dust and as a weather seal. Also metal cores can easily be incorporated.
Producing gaskets through sheet extrusion and subsequent stamping can also be done economically since the leftover material can be reused.
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