Thermal Conductive plastic vs anodised aluminum cell phone housing ?

[Maverick123456]

Hi All,

What are the pros and cons of using a thermal conductive plastic cell phone housing compared to that of an anodised alumumium one?

The former is lighter in terms of weight and virtually scratch proof. In terms of aesthetic, anodized aluminum offers better finishing, but unless hard anodizing is used, scratches can occur as evidently seen in the new Iphone 5.

What about EMI shielding? Don't think thermal conductive plastic is capable of providing EMI shielding ?

What about manufacturing cost ? Is injection molding of thermal plastic more or less cost effective than metal stamping process of aluminum?

Thank you for the time

regards,

 

[patprimmer]

Well there are a truckload of pros and cons.

Firstly, thermally and electrically conductive are two quite different things and just because material rank pretty much the same in both that is not necessarily true. Take carbon vs copper for instance. Copper is great at both, but carbon is only really good for electricity.

Although there are some plastics that are inherently reasonably electrically conductive, most conductive plastics use some pretty fancy fillers.

For EMI shielding you need electrically conductivity. We will presume permanent as that also makes a difference.

This can be done by adding high surface area carbon black or stainless steel fibres for instance. Neither helps thermal conductivity much. For thermal, typically aluminium flake is added. It has a moderate affect on electrical also.

All three have some influence on mouldability, appearance and physical properties.

Certainly aluminium flakes combined with SS fibre or carbon black should give both types of conductivity but these things can be unpredictable.

All the above fillers range from quite expensive to extraordinarily expensive.

Obviously high loadings of carbon black severly limits colour choice to basic black with maybe a metalic glitter through it from aluminium flake or SS fibre.

Aluminium flake gives a distinctive glitter and renders even clear plastics pretty well opaque. SS fibre makes clear plastic slightly cloudy or pearlescent.

Anodised aluminium offers both thermal and electrical insulation. The anodising puts a non conductive layer on the surface but it is a trivial task to break through that.

Hard anodising severly limits the colours you can use and how evenly they apply and which grades of aluminium you can use. All anodised colours have a transparent look to them.

As to cost, aluminium is typically more expensive than cheap plastics but still cheaper than expensive plastics. Conductive plastics tend to be very expensive.

For simple parts, metal pressing is generally cheaper, but once the part gets a bit complex, the moulding process is mostly cheaper.

Aluminium is usually stronger re breakage, but plastic is usually better able to rebound from a deflection leaving no dent.
Re scratch resistance, aluminium is better than most plastics, but if it's colour coated a scratch shows up as it's not through colour whereas a plastic part can be through coloured. Plastic parts, especially with fillers in the plastic can show visable flow lines.

Regards
Pat
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