Estimated reading time: 7 minutes

ECWC 2014: The Base Materials Session

There had been many studies into the toxicology of flame retardants. Although it was obviously important to protect people from death or serious injury by fire, there was concern that the materials used to provide that protection did not present risks to human health or the environment. TBBPA, the common brominated flame retardant in PCB materials, had been studied exhaustively and there had been no evidence of risk to human health from toxic gases resulting from combustion, and no clear scientific justification for restricting the use of halogenated flame retardants. Studies in relation to REACH and RoHS legislation had not raised concerns about the continued use of halogenated flame retardants, although ultimately consumer choice would continue to be a significant factor whatever the science indicated.

Morgan concluded by quoting Neils Bohr: “Prediction is very difficult, especially if it's about the future,” but did predict that fire safety would remain a primary requirement for electronic and electrical equipment and to ensure fire safety there would always be a need to incorporate flame retardants into plastic systems in electronic and electrical equipment that would otherwise pose a significant fire safety risk.

Morgan’s presentation had been principally focused on flame retardants chemically incorporated into the epoxy polymer. Carsten Ihmels from Nabaltec described the use of metal hydrides and oxides as functional fillers, to improve the flame retardancy, thermal stability, thermal expansion, thermal conductivity, and processability of thermosetting resins.

Ihmels suggested the use of combinations of functional fillers and organic flame retardants to achieve the considerable advantages of a highly flame retardant polymer formulation with a good balance of cost, electrical, thermo-mechanical, and processing properties. He discussed the effects of combining metal hydrates and other fillers together with various halogen-free organic flame retardants on parameters like flame retardancy, thermal stability, thermal expansion, thermal conductivity, and processability.

Aluminium hydroxide had historically been popular as a halogen-free flame retardant filler for PCB laminates, decomposing at elevated temperature to release water and consume energy. But it was unstable at lead-free soldering temperatures and its use could lead to reliability problems such as delamination and CAF.

Boehmite, a crystalline form of aluminium oxide hydroxide available in a wide range of particle sizes, had a much higher decomposition temperature and could be used as a filler in thermally demanding applications to enable cost-effective manufacture of highly thermally stable aluminium hydroxide-free prepregs and laminates with excellent mechanical and thermal properties. Being a mineral filler, Boehmite could be used to dramatically reduce Z-axis thermal expansion of the laminate, and by partial or total replacement of commonly used fillers like silica or quartz, below-Tg CTE values as low as to 30ppm could be achieved. Additionally, using boehmite as a filler offered significant improvement in thermal conductivity for applications like substrates for LED lighting. The technical advantages of higher heat resistance combined with high reliability at lower cost opened new market opportunities for halogen-free materials in automotive, military and avionics. Even high quality consumer electronics could be successfully produced at competitive cost with high yield.

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