Catalyst epoxy molding compounds

Catalysts for Epoxy Molding Compounds in Microelectronic Encapsulation... 

The key to the development of the proper epoxy molding compounds for microelectronic encapsulation is the catalyst in the formulation. In spite of serious limitations in epoxy molding compound performance in sensitive microelectronic devices about ten years ago, the many new developments in catalysts during the last few years have enabled tremendous improvements. However, the exact curing mechanisms of various catalysts in epoxy molding compounds are still not fully understood today. 

From the up-to-date literature and patent review of catalysts used In anhydride and phenolic cured epoxy molding compounds, It Is evident that Imidazoles and their derivatives predominate (Table I). Metal complex, trialkyl or triaryl phosphines and their complexes, Lewis acids such as zinc or stannous octoate are used to a much lesser extent (Table II). There are a few examples of tertiary amines and urea derivatives used. 

The mechanism for organometallics and Lewis acids in phenolic or anhydride cured epoxy molding compounds are still not fully understood. Lewis bases such as imidazoles can be reacted with organic acids to form salts in order to improve latency. Imidazoles are, so far, the most widely accepted as a compatible catalyst family for encapsulating microelectronics. 

In practice, epoxy-amine reactions in carbon fiber prepregs, and epoxyphenol reactions in molding compounds, are often accelerated by the addition of a Lewis acid (typically a BF3 - amine complex) or a Lewis base (often a tertiary amine), as catalysts. ... 

Generally these compositions contain an epoxy-novolac, a hardener, a catalyst, silica fillers, and an internal lubricant/mold release compound. Brom-inated epoxies and antimony trioxide are included to provide the required flame retardant characteristics. Other, unspecified additives are used to promote adhesion or to reduce corrosion rates. Because of their superior thermal capabilities and electrical properties, epoxidized novolacs are preferred over epoxy homopolymers. Near stoichiometric amounts of hardeners such as novolacs (Equation 1), anhydrides, and primary amines can be used to cure the resins in the presence of a catalyst. The linkages which are formed include ethers, esters, or secondary amines, respectively. 

---