Curing epoxy molding compounds

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. 

Increasing the quantity of fillers may contribute to lowering thermal expansion coefficients and increasing thermal conductivity of cured epoxy molding compounds, but too large an increase causes an increase in viscosity and decrease in fluidity of resin compounds before curing These are serious problems in the actual molding process. 

These resins (Resole or Novolac) are used as curing agents or hardeners for epoxy molding compounds for electronics applications such as computer components. 0-cresol-formaldehyde resins have heen also used to modify phenol-formaldehyde resins, and in laminates. 

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. 

Diaminodiphenyl sulfone curing agent, epoxies molding compounds 2-Phenyl imidazole... 

To provide flame retardancy to epoxy molding compounds, methods 1) and 2) are used, where a reactive type agent is employed in the former, and an additive type serves in the latter Generally, cured resin compounds combined with flame retardant agents... 

Phenohc resins (qv), once a popular matrix material for composite materials, have in recent years been superseded by polyesters and epoxies. Nevertheless, phenohc resins stiU find considerable use in appHcations where high temperature stabiHty and fire resistance are of paramount importance. Typical examples of the use of phenoHc resins in the marine industry include internal bulkheads, decks, and certain finishings. The curing process involves significant production of water, often resulting in the formation of voids within the volume of the material. Further, the fact that phenoHcs are prone to absorb water in humid or aqueous conditions somewhat limits their widespread appHcation. PhenoHc resins are also used as the adhesive in plywood, and phenohc molding compounds have wide use in household appliances and in the automotive, aerospace, and electrical industries (12). 

Aromatic amines are widely used as curing agents for epoxy resins. However, they are not used as widely in adhesive formulations as they are in composites, molding compounds, and castings. They offer cured epoxy structures with good heat and acid resistance. 

After the primary amines, acid anhydrides are the next most important class of epoxy curing agents, although these are not used as often in adhesive systems as they are in casting compounds, encapsulants, molding compounds, etc. The most common types of anhydrides are hexahydrophthalic anhydride (HHPA), phthalic anhydride (PA), nadic methyl anhydride (NMA), and pyromellitic dianhydride (PMDA), although there are several others. Chemical structures of several anhydrides are illustrated in Fig. 5.6. 

We have investigated the recovered glassfiber-resin powder for its properties as a filler for epoxy resin compounds which are used as paints or adhesives, and compared it to conventional fillers, such as talc and calcium carbonate. The epoxy resin compound, composed of bisphenol A type epoxy resin (50.0wt%), aliphatic polyamine type hardener (18.0wt%) and filler (32.0%), was prepared. Strength and thermal expansion properties were measured for the molded epoxy resin compound cured 23°C for 7 days. Viscosity was measured for the epoxy resin compound before adding the hardener. Adhesive strength was measured by tearing two ferric boards bonded with the epoxy resin compound which was composed of bisphenol A type epoxy resin (49.2wt%), polyaminoamide type hardener (18.0wt %), and filler (32.8wt%), and was cured at 23°C for 7 days. 

All samples were prepared from a commercially available epoxy cresol novolac-phenol formaldehyde novolac-tertia-ry amine based molding compound. Pelletized preforms were heated to 85°C in a RF preheater prior to being transfer molded at 180°C/68 atm. for 90 sec. Molded samples were cooled in air to room temperature and stored in a desiccated environment until testing or subsequent thermal treatment. Post mold curing, PMC, was accomplished in a gravity oven at 175°C for a period of 4 hours. Samples without post mold curing are designated by NPMC. 

AI3-50034 EINECS 211-581-7 Imidazole, 2-phenyl- IH-lmidazole, 2-phenyl- NSC 255226 Phenylimidazole 2-Phenylimidazole 2-Phenyl-IH-imidazole. Epoxy curing agent for printed circuit boards, molding compounds, potting accelerator for dicyandiamide and anhydrides. Leaflets mp = 1469.3° bp = 340° insoluble in H2O, very soluble in EtOH. BASF Cap. Janssen Chimica Lancaster Synthesis Co. 

These ready to use molding compounds combine resin, reinforcement, mineral fillers, and various additives as required, controlling cure, shrinkage and other properties. The main resin used is, predominantly, TS polyester (unsaturated polyester) resin, with others being used such as epoxies and vinyl esters. Similarly, the main reinforcement is, predominantly, glass fiber, but fibers offering higher performance are added where specific properties are needed. 

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