Envalior’s new PPS compound cuts EV busbar stress cracking risk by over 70%

CTE compatibility between copper and thermoplastic insulation determines whether overmolded busbars survive thermal cycling in service

(Image courtesy of Envalior)

As EV powertrains migrate to higher voltages and more compact packaging, the thermal cycling loads placed on overmolded busbars are intensifying. Envalior’s new Xytron M5080ET addresses the specific failure mode that matters most in this context: stress cracking at the copper-plastic interface driven by coefficient of thermal expansion mismatch. The compound has already cleared approval with several customers, and series production development projects have been completed, placing it in the procurement window rather than the development pipeline.

CTE mismatch is the central engineering problem for overmolded busbars

Copper busbars in EV powertrains carry high-voltage current between the battery, control unit, drive system, and charging unit. Overmolding with an engineering thermoplastic provides electrical insulation from the surrounding environment, but the thermal expansion coefficients of copper and most plastics differ significantly. Under rapid and repeated temperature changes, that mismatch generates cyclic stress at the interface, leading to stress cracking in the plastic insulation layer. A crack that creates a short circuit in a power control unit or electric drive axle does not degrade performance gradually; it can cause failure of the entire assembly.

PPS compounds offer the best stress crack resistance among the thermoplastics used for busbar overmolding. The engineering challenge with conventional filled PPS is that thermal expansion remains poorly matched to copper, particularly in the direction perpendicular to melt flow. Envalior developed M5080ET specifically to close that gap, including at temperatures above 150°C.

M5080ET reduces CTE mismatch perpendicular to melt flow

Xytron M5080ET is a 50% glass-fibre-and-mineral-filled, impact-modified PPS compound whose thermal expansion is closer to copper than comparable materials, even perpendicular to the melt flow direction and glass fibre orientation in the part. That stability is maintained at elevated temperatures, reducing the risk of stress cracks across the service life of the component.

Envalior’s internal testing compared M5080ET against similar PPS compounds in thermal shock cycles between -50°C and 180°C. The compound achieved more than 70% higher stress crack resistance under those conditions. The weldlines in the component, formed where converging melt fronts meet, were approximately 17% stronger than in comparable materials. Both figures are from Envalior’s own testing rather than independent certification, but customer approvals and completed series production development projects provide external validation of the performance data.

The material achieves V-0 classification in the UL 94 test at a specimen thickness of two millimetres, meeting the flame resistance requirements for plastic components in batteries and electric drive trains to protect vehicle occupants in the event of a fire. Volume resistivity and dielectric strength remain high before and after ageing, including at elevated temperatures. High creep resistance and low water absorption produce dimensionally stable components, and Envalior states that the dimensional stability of the compound enables the design of very compact assemblies.

Series-qualified for power control units and electric drive axles

The broader commercial driver for M5080ET is the industry shift toward higher operating voltages, stronger currents, and more compact assembly designs in EV powertrains – a combination that raises thermal shock requirements for busbar insulation across the powertrain stack. Xytron M5080ET is positioned for the higher-temperature end of that range, targeting power control units and electric drive axles where operating temperatures exceed 150°C.

Envalior places M5080ET within a broader thermoplastic portfolio for EV busbar applications that spans Durethan PA6, Akulon PA66, Pocan PBT, and ForTii PPA grades, each targeting different temperature windows, voltage classes, and geometries. M5080ET sits at the higher-temperature end of that range, and the powertrain trends driving its development – higher voltages, stronger currents, denser packaging – show no sign of easing. How far operating temperatures in overmolded busbar applications continue to rise will determine whether 150°C remains an adequate design threshold or becomes a staging post..

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