2020 EIPC Winter Conference, Day 1

Estimated reading time: 21 minutes

Dr. Anna Graf, OEM marketing and application engineering specialist with Isola in Germany, discussed high-temperature stable base materials for e-mobility applications. She commented that there were still several challenges to be addressed, specifically driving range, charging time, and high battery cost. How could the challenges be approached? Dr. Graf explored the basic electrical architecture of electric and hybrid-electric vehicles and concluded that improvements were needed in system efficiency, power density, and miniaturisation.

New materials were required for power electronics. Silicon carbide was a more effective material than silicon but operated at higher temperatures. Ceramic-based direct bonded copper substrates had excellent thermal properties but were expensive and required specialist fabrication techniques. A high-temperature-stable FR4-like laminate could provide a cost-effective alternative.

Dr. Graf described a German government BMBF-funded project named HELP, with 15collaborating companies working to develop reliable and cost-effective high-temperature electronics for e-mobility based on PCBs made from high-temperature-resistant resin systems. The objective was an organic-based printed circuit material capable of operating at 175°C with a peak temperature of 200°C and increased temperature cycling resistance. In collaboration with the consortium, Isola had developed a halogen-free, next-generation automotive high-reliability laminate solution for high power and voltage applications that required extreme thermal stability. It was a glass-reinforced material with very low thermal expansion. Dr. Graf did not disclose the resin chemistry but made it clear that it was not epoxy. The material had processing characteristics similar to FR-4 and properties similar to polyimide.

Additional information and further discussion of base materials with high-temperature reliability came from Volker Klafki of Technolam in Germany. He began with a review of laminate developments and reliability expectations since the 1990s, up to recently-emerging requirements in connection with e-mobility when extreme anti-CAF performance and resistance to thermal ageing were demanded. The ongoing theme appeared to be, “What is sufficient now will very likely be insufficient in the future.”

Klafki summarised the criteria currently used to classify reliability: withstanding the thermal stresses of assembly, reliability during thermal cycling, and no degradation under high-temperature storage, defining end-of-life as the point at which electrical and mechanical properties had declined by 50% from their initial values. He discussed the significance of relative thermal index with reference to UL standards, and CAF resistance at high temperatures. He also described qualification procedures, properties, and process guidelines for two high-reliability proprietary laminates developed for high-temperature applications, with very low thermal expansion and superior CAF resistance.

“Quo vadis flame retardants? How can we meet ever more stringent performance and sustainability demands?” were questions posed by Dr. Adrian Beard from Clariant in Switzerland. In his presentation, he gave an overview of the many challenges facing the flame retardants industry and some solutions that were in the pipeline.

Dr. Beard explained that the regulatory and environmental pressure on halogenated flame retardants continued to grow, and flame retardants continued to be added to the candidate list for “substances of high concern.” The RoHS directive was once again under revision, and more substance restrictions might happen. The European Ecodesign Directive would restrict the use of halogenated flame retardants in electronic displays as of 2021. In Sweden, a tax on household appliances and electronics, clearly not based on science, penalised not only halogenated flame retardants but also additive phosphorus flame retardants that had good environmental and health profiles. It was clear that not only stricter chemical legislation but also the trend to non-chemical legislation could drive the transition to halogen-free flame retardants in many areas.

Dr. Beard explained that Clariant were members of the Phosphorus, Inorganic, and Nitrogen Flame Retardants Association (PINFA)—a global group of flame retardant manufacturers and users committed to fire safety and improving the health and environmental profiles of their products. Clariant themselves produced a range of flame retardants based on aluminium diethylphosphinate for advanced electronic materials, and these had achieved the highest sustainability standards. “Be prepared. Flame retardants under scrutiny usually do not come as surprises,” he stated.

The subject of brominated flame retardants continues to be a matter of regulatory controversy. Tetra-bromo-bisphenol-A (TBBPA) has traditionally been used as a reactive component in the manufacture of brominated epoxy resins. Product designers have long presumed that TBBPA is fully reacted in laminates although, there has been little public data documenting this or defining potential “free TBBPA” within the epoxy polymer.

Sergei Levchik, new product development manager at ICL-IP America—a member of North America Flame Retardant Alliance—reported a study analysing commercial laminates to determine the concentration unreacted TBBPA flame retardant in printed wiring boards.

Laminate samples selected to cover a wide Tg range—from 140–200°C—were obtained from major suppliers to the electronics supply chain. In addition, halogen-free laminates were tested as controls. Samples were prepared according to EPA Method 3545A (pressurized fluid extraction), and EPA Method 8321B (high-performance liquid chromatography, coupled with thermospray mass spectrometry and ultraviolet detector). The test method was independently validated with respect to TBBPA detection and quantification, and two control samples of TBBPA-free laminates were used.Page 4 of 5

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