Halogen free triazines, bismaleimide/epoxy polymers,...

Stock material or miscellaneous articles – Composite – Of epoxy ether

Reexamination Certificate

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C428S378000, C428S418000, C528S408000, C528S409000, C525S523000, C525S528000, C523S452000, C156S330000, C156S330900

Reexamination Certificate




This invention relates to dielectric materials, their composition, manufacture and use. More particularly, the invention relates to these materials and their use for microvias and other printed circuit applications.
Composites based on epoxy or cyanate esters and mixtures of such resins and organic or inorganic reinforcing materials have become extremely important in many technological areas and, in the PCB industry, they are considered as basic building blocks. Some of the major reasons for this include, first, the relatively simple and reliable processing of such resins and, second, the excellent mechanical and chemical properties of cured cyanate, bismaleimide and epoxy resin and their relative ease of adaptation to different applications.
Cyanate esters and blends with bismaleimides as well as epoxies in general are processed into composites and laminates primarily through the production of prepregs. For such production, organic or inorganic reinforcing materials or embedding components in the form of fibers, non-woven and woven fabrics are impregnated with the particular choice of resin. In most cases, this process is carried out using a solution of the resin in a single solvent or mixture of solvents that is relatively easy to evaporate during the prepregging operation. The resulting prepregs are tack-free and are bake processed to a level of advancement that will result in adequate flow in the subsequent lamination and consolidation stage to make the composite. The prepregs must have sufficient storage stability. For example, at least 180 days stability in storage is required for the production of circuit boards. In subsequent processing to produce circuit boards and laminates, the prepreg resin must also liquefy at elevated temperatures in the range of 100° to 160° C. and must be able to form a strong and durable bond under pressure with the reinforcing materials used for the laminate or circuit board In other words, the cross-linked resin matrix must have a high interfacial adhesion with the reinforcing materials as well as the materials to be bonded, such as treated or non treated surface of the metal conductors, cured laminates, inorganic fillers and other additives that constitute the laminate or circuit board. In other words, the cross-linked resin matrix must have a high interfacial adhesion with the reinforcing materials as well as the materials to be bonded, such as treated or non treated surface of the metal conductors, cured laminates, inorganic fillers and other additives that constitute the laminate or circuit board.
In electronic applications, the laminates are generally required to possess a wide range of favorable properties including high mechanical strength, good thermal stability, good chemical resistance, low heat distortion, a high resistance to aging, good electric insulation properties, consistent dimensional stability over a wide temperature range, good adhesion to glass and copper, a high surface resistivity, a low dielectric constant and loss factor, ease of drillability, low water absorption and a high corrosion resistance.
In addition, a key requirement that is governed by Underwriters' Laboratory (UL) is the ability to meet the flammability standard of UL 94-V0. In this test, a specimen is exposed to a defined flame positioned vertically at its lower edge. For a VO rating, the total burning time in ten tests must not exceed 50 seconds and none of the samples can exceed 10 seconds of burn time. This requirement is difficult to meet especially when the material is thin, which is the case in electronics.
Epoxy resins alone or in combinations with cyanate esters or other additives, which are widely used in the electronic industry for PCB laminate applications, meet these requirements only because they contain approximately 30-40% brominated aromatic epoxy components, based on the resin or approximately 17% to 32% bromine (based on the total resin weight). In order for an electronic device to be marketed commercially, it is desirable for the device to equal or exceed certain flammability standards specified by UL. Antimony and halogen compounds have been added to resins in order to impart flame retardance, such as the 19%-23% by weight of bromine to make brominated polyglycidyl ether of bisphenol A in epoxy resin, which is described in U.S. Pat. No.3,523,037, issued Aug. 4, 1970, to Chellis et al. High concentrations of halogenated compounds are used for other applications, often combined with antimony trioxide as a synergistic additive.
The problem with these brominated compounds is that, although they have excellent flame-retardant properties, they also have some undesirable properties. The chemical decomposition of aromatic bromine compounds release free bromine radicals and hydrogen bromide, which are highly corrosive. Additionally, when highly brominated aromatics decompose in the presence of oxygen, they may form the highly toxic brominated di-benzofurans as some past studies have shown. For this reason, interest in displacing the use of brominated aromatic epoxies has emerged in the electronic industry, primarily in Europe and Japan, where products including circuit boards having halogen-free epoxy resins are being designed and built. No attempts are currently being made by others to produce bromine- free or halogen-free cyanate esters/bismaleimide alone or in combination with epoxies for circuit board uses in the form of prepreg or resin coated copper formats for microvia technology.
Fillers with an extinguishing flame effect, such as antimony oxide, aluminum oxide hydrates, aluminum carbonates, magnesium hydroxides, borates and phosphates, have been proposed for the replacement of brominated aromatics. However, all these fillers have the disadvantage that they often seriously impair the mechanical, chemical and electrical properties of the laminates. In the case of antimony trioxide, it is listed as a carcinogen.
The flame-retardant effect of red phosphorus has also been investigated in some cases combined with finely divided silicon dioxide or aluminum oxide hydrate. Such compositions when used in electronic applications may produce corrosion problems due to the formation of phosphoric acid in the presence of moisture.
In addition, organic phosphorus compounds, such as phosphoric acid esters, phosphonic acid esters and phosphines, have been proposed as flame-retardant additives but these alternatives have not been very promising due to the plasticization effects that they may impart to the base resin.
The invention discloses a resin mixture comprising cyanate esters or triazines, with a bismaleimide, in combination with a derivative product from the reaction of a polyepoxy compound and a phosphorus-containing reactive organic compound for producing halogen free prepregs, laminates and composites, and also the halogen free prepregs and composites produced from these resin mixtures for uses such as microvia applications. The resin mixture is prepared by reacting in the presence of a polymerization catalyst such as an organometallic catalyst, a mixture of a cyanate ester monomer or prepolymer and a bismaleimide with the flame inhibiting compound. The resin mixture can also include an epoxy or a polyimide or both, added to the prepolymerized reaction mixture.
The invention also relates to a dielectric material and its method of preparation. The dielectric is free of halogen, and is composed of a resin mixture that comprises a) a cyanate ester monomer or prepolymer and a bismaleimide, and b) a derivative product from the reaction of a polyepoxy compound with at least one epoxy group per molecule, and a phosphorus-containing reactive organic compound. The compound is present in an amount wherein the elemental phosphorus content is between about 2% and about 20% based on the weight of the resin mixture. The resin mixture is polymerized using a catalyst, and optionally includes an epoxy, a polyimide and possible mixtures thereof. The catalyst typically is an organ


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