14 - Benzocyclobutene Resins

Abstract

Benzocyclobutene (BCB) or bicyclo(4.2.0)octa-1,3,5-triene is also called cardene, cyclobutabenzene, and cyclobutarene. The four-membered ring in benzocyclobutene imparts a ring strain. Therefore, this class of molecules is especially reactive. Benzocyclobutene derivatives serve as important building blocks for natural product syntheses and for polymers and advanced materials. Benzocyclobutene polymers are known as thermosetting polymers having high thermal stability, but they are flammable. Both the flammability and brittleness of BCB resins can be reduced by adding a brominated acrylate, such as pentabromobenzyl acrylate (PBA) monomer to the BCB resins, causing them to react to form a resulting flame retardant thermoset material. Polymer films from BCB formulations exhibit many desirable properties for microelectronic applications. In particular, they have a low dielectric constant and dissipation factor, low moisture absorption, rapid curing and low temperature cure without generating byproducts, minimum shrinkage in curing process, and no Cu migration issues. Because of these properties, applications are found in bumping/wafer level packaging, optical wave guides, and flat panel display. Diffractive gratings made from benzocyclobutene can withstand temperatures up to 300°C with only small optical and topographical changes after 45 min., whereas conventional photoresist gratings change drastically within a few minutes under these conditions.