Thermal and thermomechanical modelling of polymer overmoulded electronics

• Published in: Microelectronics international 2007-07, Vol.24 (3), p.66-75
• Main Authors: Sarvar, Farhad, Whalley, David C., Hutt, David A., Palmer, Paul J., Joo Teh, Nee
• Format: Article
• Language: English
• Subjects: Electronics industry; Modelling; Polymers
• ISSN: 1356-5362
• DOI: 10.1108/13565360710818439

Purpose The encapsulation of electronic assemblies within thermoplastic polymers is an attractive technology for the protection of circuitry used in harsh environments, such as those experienced in automotive applications. However, the relatively lowthermal conductivity of the encapsulating polymer will introduce a thermally insulating barrier, which will impact on the dissipation of heat from the components and may result in the buildup of stresses in the structure. This paper therefore seeks to present the results from computational models used to investigate the thermal and thermomechanical issues arising during the operation of such electronic modules. In particular, a twoshot overmoulded structure comprising an inner layer of water soluble and an outer layer of conventional engineering thermoplastics was investigated, due to this type of structure's potential to enable the easy separation of the electronics from the polymer at the endoflife for recycling. Designmethodologyapproach Representative finite element models of the overmoulded electronic structures were constructed and the effects of the polymer overmould were analysed through thermal and thermomechanical simulations. Investigations were also carried out to explore the effect of materials properties on the overmoulded structure. Findings Models have shown that some power derating of components is required to prevent temperatures exceeding those in unencapsulated circuits and have quantified the benefits of adding thermally conductive fillers to the polymer. Simulations have also clearly demonstrated the benefits of foamed polymers in reducing thermal stresses in the assemblies, despite their poorer thermal conductivity compared with solid polymers. Originalityvalue The paper illustrates the thermal issues affecting the overmoulded electronics and gives some guidelines for improving their performance.