Leverkusen, Germany - Polyurethanes may soon start to replace a range of other resins in potting compounds for electrical components, if machinery and systems developed recently take off.
Machinery supplier Isotherm AG of Uetendorf, Switzerland, and BaySystems' polyurethane systems house in Otterup, Denmark, say they have jointly developed a cost-effective way to mould housings and protect sensitive electronic components, using polyurethane systems processed in a single step by reaction injection moulding (RIM).
The developers say polyurethanes "outperform other materials and material combinations for this application, because they can be formulated precisely to meet individual requirements." They can make soft, solid elastomers or semi-rigid, impact-resistant integral skin foams and all types in between, so that a single material "can be customised to suit virtually any application."
The RIM process allows finished parts to be removed from the mould in less than two minutes - giving a cost-effective combination of making a housing and electronic encapsulation in a single production line. The PU properties can be varied by selecting different starting materials. With their low viscosity, PU reaction mixtures flow to ensure that even areas that are difficult to reach are enclosed effectively, while low internal pressure in the mould means that RIM technology can be used with inexpensive synthetic resin and aluminium moulds, the companies stress.
The "RIM process facilitates the production of moulded parts with wide variations in wall thickness," explains Gerd Viertel, an expert in PU encapsulation at BaySystems, in a 13 Jan announcement. This allows users to make thin housing shells that are "rigid and lightweight - with fully integrated reinforcing ribs, ventilation slits, spring locks and metallic design elements," Viertel added.
For electronic components, the polyurethane reaction is appropriate, as it is rapid, gentle and gives little shrinkage. Curing is at 120°C at the most. The thermal conductivity of the PU - essential to dissipate heat in electronic assemblies -- can be raised by adding fillers, the companies note.
Such encapsulation is becoming ever more vital in cars, for example, where delicate pin contacts have to be protected against oxidation caused by weathering: "Using polyurethane materials and modifying the RIM technology makes it possible to fill even the smallest spaces via, in some cases, very narrow flow paths. To this end, we have developed machines with low discharge rates of less than 15 g/s (or 10 ccm/s)," notes Daniel Lüthi, managing director of Isotherm.
Another benefit of polyurethane is that shots of as little as 2 g are possible with specially developed metering equipment. Also, increasing flame retardancy requirements, such as the UL 94 V-0 (an Underwriters' Laboratory specification), demand higher filler levels, where Isotherm can offer filler-resistant piston metering machines for cable and connector encapsulation.