Authored By:
Xiaoping Lei, Amanda J Stuart, Ashby de la Zouch
H K Wentworth Limited
Summary
The most common epoxy encapsulation compounds available on the market utilize specialised fillers, such as Alumina trihydrate (ATH), to provide a high level of flame retardancy. Such fillers decompose endothermically at 200˚C producing water which cools the substrate. This inhibits the effects of the ignition source and reduces the substrates' ability to sustain a flame. Such fillers are therefore extremely efficient and as such are utilized in many applications where high operating temperatures and viscosity are not crucial requirements for the user.
Due to the decomposition temperature being relatively low, the stability of encapsulation compounds which incorporate ATH in their formulation are limited above 150-200˚C. In addition, the use of such fillers dramatically increases the viscosity, making the resins difficult to work with when encapsulating complicated geometries or where space is limited. To overcome these limitations, a novel flame retardant system has been investigated. Although still a filler, approximately 10 times less material is required to produce a flame retardant system, therefore making it possible to formulate a flame retardant encapsulation resin with viscosities of less than 700mPa s, whilst still meeting UL94 V-0. In addition, this novel system does not decompose at temperatures around 200˚C and exhibits excellent stability at very high temperatures, including those seen in typical reflow profiles.
This paper details the advantages of this novel flame retardant system, highlighting the performance advantage over standard metal hydroxide fillers and concludes with possible applications when formulated into an encapsulation resin.
Conclusions
A novel, non-halogenated, highly effective flame retardant has been evaluated alongside conventional flame retardants commonly used in epoxy encapsulation resin formulations. The proposed resin, utilizing this novel flame retardant, was found to have a vastly improved thermal stability when compared to standard epoxy encapsulants. This unique feature makes it possible for the encapsulation resin to pass through reflow profiles without affecting its performance properties. The novel flame retardant has a much higher efficiency; when attempting to achieve UL94 V-0, it requires only one tenth of the quantity by weight in comparison to systems utilizing alumina trihydrate (ATH).
As a result, a much lower viscosity encapsulation resin can be formulated, providing a user-friendly resin for applications with complicated geometry, limited space or forspecialist application requirements, such as underfilling. The summarised results show that the proposed resin made from the novel flame retardant also has a much lower density than standard materials, providing cost and weight savings for the end user/assembly, without any compromise of the electrical properties.
An Electrolube brand epoxy encapsulation resin has been formulated using the novel flame retardant system and is currently available on the market, making it an ideal choice for applications where the resin is to be subjected to very high temperatures, including those seen in typical reflow profiles. Work is now continuing to establish the additional uses and benefits of this novel flame retardant system in a variety of applications.
Initially Published in the IPC Proceedings
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