GTS Flexible Materials manufactures metal foil laminates for use in RFID tags.  Constructed of Copper or Aluminium foils laminated to plastic films, these materials come in a wide range of thickness.. RFID tags

GTS are continuing to emphasise the advantages of using flexible circuits as a replacement for car wiring systems.  The use of a suitable adhesive system and choice of films makes flexible circuits able to be used even in areas of high humidity such as the doors.  Products such as GTS5670, PEN based laminates have been tested and approved to 3000 hours at 85C and 95% RH.
The advantages for the OEM's lie in the weight and space savings of flexible circuitry compared to round wire bundles, and is a good example of future Environmental Benefits.

A recent addition to the wide range of speciality products has been the introduction of a range of thin, coated films for use in capacitor wrapping. A number of different films are available including polyester, PPS and PEN.

GTS has traditionally used brominated flame-retardants in its products because of their high efficiency in the prime function of reducing risk associated with fire. The main drawback is the evolution of large quantities of smoke during a fire.

Risk assessment of fire generally comes down in favour of the use of such flame-retardants, as the risk associated with smoke is less than the benefits associated with reduction in fire spread. This is a complex issue and further reading is suggested – see the reference below 1.

In the last few years there have been several high profile cases where smoke toxicity has been associated with deaths and injury, and where the benefits of using flame retardants is less clear.

Some organisations also ban brominated flame-retardants, among other chemicals, because of the damage that could be caused to equipment by toxic products of combustion 2.

GTS produces products which contain Non-Halogenated Flame Retardants (NHFR), whose emission of toxic by products is much reduced. The efficiency of these chemicals as flame-retardants is less than the halogenated ones; however increasing their proportion in the final product can compensate this for.

One example is GTS3480NHFR, and epoxy based tape, which incorporates NHFR components. This has achieved an ULVTM-0 rating 3.

3.  UL file: E172854

European legislation such as the Waste from Electronic Equipment regulations means that companies involved with soldering of components are looking at removal of lead from the process.

This will in general lead to higher process temperatures as the alternative alloys have a higher melting point. A Tin-Silver-Copper alloy, for example, has a melting point of 216 C, compared to the standard 60/40 Tin-Lead, which is 183 C.

While the increased temperature has to be considered carefully for components, generally materials such as rigid boards will not be affected. For flexible substrates the increased temperatures may be critical.

The most obvious example is the use of solder on Copper-Polyester laminates. Polyester film has a melting point of 260C and a glass transition temperature of 82C, therefore soldering is done carefully, with heat being directed to the copper and away from the film. Typically this is done with a fast solder application applying the solder directly to the copper areas and not generally heating the substrate.

Low melt point solders containing Bismuth are also used. A typical melting point for a Bismuth alloy is 163 C, which makes the processing much easier. Infrared reflow can be done with these alloys for example.

An increase in solder temperature due to the use of Lead-Free alloys will need careful handling to avoid distortion or even destruction of the film.

Alternative flexible materials are available, such as PEN or Polyimide laminates, which are less affected by increased processing temperatures, and these should also be considered when removing lead from the process.

(See information on products: GTS 5670, GTS 7800).

Lead free / lower melt point alloys are also available, such as a Tin-Silver-Copper-Bismuth alloy and can be used with Polyester laminates because the melting point, at 188 C, is similar to that of Tin-Lead. The use of these alloys in the application should be confirmed with the solder manufacturers, as high temperature ageing properties can be worse.

In conclusion should manufacturers of flexible circuits want to change to Lead-Free alloys, consideration should be given to the effect of higher processing temperatures on the choice of plastic film.

GTS manufacturers a wide range of materials and can advise on those, which are most suitable for the process conditions.