Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From phenol – phenol ether – or inorganic phenolate
Reexamination Certificate
1998-11-10
2001-03-27
Dawson, Robert (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From phenol, phenol ether, or inorganic phenolate
C528S403000
Reexamination Certificate
active
06207786
ABSTRACT:
FIELD OF INVENTION
Ternary systems of benzoxazine, epoxy, and phenolic resins are useful in electronic equipment where they can function as underfilling between a circuit and a substrate. The epoxy acts as a viscosity reducing reactive diluent and crosslink enhancer. The phenolic resin can function as a polymerization catalyst for the benzoxazine and/or a hardener for the epoxy resin. Benzoxazine increases the Tg and decreases water up-take as well as all the usual advantages of benzoxazine over epoxies and phenolics.
BACKGROUND
Epoxy resins with various hardeners have been used extensively in the electronics industry both as adhesives and as a matrix in various substrates. Mixtures of epoxy resins and benzoxazines have been taught as potentially useful in the electronics industry as the epoxy resins can reduce the melt viscosity of benzoxazines allowing for the use of higher filler loading while maintaining a processable viscosity. However the epoxy resin undesirably increase the temperature at which the benzoxazine polymerizes.
SUMMARY OF INVENTION
Ternary blends of benzoxazine, epoxy and phenolic resin or phenolic molecule were found to have a wide range of desirable properties not generally achievable with simple blends of any two components. The benzoxazine resin imparts mechanical strength, low water uptake, and thermal curability to the blend. The epoxy resin imparts increased crosslink density and lower viscosity to the blend. The phenolic resin provides a lower polymerization temperature for the benzoxazine and improved thermal stability when substituted for the epoxy component. The benzoxazine increases the thermal stability of the ternary blend thus opening the possibility of lower filler loading (typically added for higher modulus and flame retardency) with equivalent physical properties and low flammability. The epoxy can also raise the Tg of the blend due to higher crosslink density.
The benzoxazine and the phenolic resin impart exceptional thermal stability to the blend as these two components generally have good thermal stability to weight loss up to about 370° C. The tendency for benzoxazines and phenolic resins not to support flame propagation makes the ternary blend a desirable material in applications where flammability is to be avoided.
DETAILED DESCRIPTION
Desirable blends of benzoxazine, epoxy and phenolic resins include from about 10 to about 80 weight percent of benzoxazine monomer, from about 10 to about 80 weight percent of an epoxy reactant, and from about 1 or 10 to about 80 weight percent of a phenolic resin or a phenolic molecule. The ternary system can be used in conjunction with known catalysts for benzoxazine, phenolic, and/or epoxy, while phenolic component also acts as an initiator and catalyst for both benzoxazine and epoxy resins. The phenolic resin or phenolic molecule can be used in a lower amount than the other components due to its ability to act as a catalyst for the benzoxazine polymerization and as a hardener for the epoxy reactant. When the phenolic resin is used in a larger amount, e.g. above 10 weight percent of the blend, it can function both as a part of the matrix and as catalyst and/or hardener. The weight percents are based on the blend of the benzoxazine monomer, the epoxy reactant and the phenolic resin or molecule.
A more preferred range for the benzoxazine monomer would be from about 10, 15 or 20 to about 60, 65 or 70 weight percent of the blend of the three components. The benzoxazine imparts to the blend good thermal curability, high mechanical properties such as strength, and low water uptake on exposure to moisture or water.
A more preferred range for the epoxy reactant would be from about 10 or 20 to about 60, 65 or 70 weight percent of the blend. The epoxy reactant provides improved crosslink density, low melt viscosity, flexibility, and possibly enhanced adhesion to polar substrates. Desirably the epoxy resin is used in an amount sufficient to lower the melt viscosity of the benzoxazine to below 1 Pa.s or below the melt viscosity of the benzoxazine component alone at 100° C. Rheometrics RMS-800 with 50 mm diameter parallel plate fixture, 200 gom torque force rebalance transducer, 100° C., and a shear rate of 6.3 reciprocal seconds. Epoxy resins may detract from water resistance as they pick up water.
A more preferred range for the phenolic resin or molecule would be from about 1, 2, 3, 5, or 20 to about 50 or 60 weight percent of the blend. The phenolic resin or molecule functions as a catalyst lowering the polymerization temperature of the benzoxazine monomer, functions as a hardener for the epoxy resin, and can serve as an additional matrix resin.
The blend of the three above components can be formulated with a variety of other components to achieve utility for specific applications. The blend is desirable due to its high Tg, good thermal stability, low melt viscosity, ability to be filled with fillers, good adhesion etc. It is particularly applicable in electronics as an underfilling. Underfilling is a plastic molding compound that goes into a gap between an integrated circuit or die and the substrate. It mechanically couples the circuit or die to the substrate. It decreases residual stress and thermal fatigue in solder joints between the circuit or die and the substrate.
Underfilling needs to have low void formation, good wetting characteristics, significant adhesion, low stress buildup, and high thermal conductivity. Voids act as hot spots and weak points in thermal fatigue tests. Thus they reduce the lifetime of the product. Lower viscosity reduces voids as trapped gas bubbles can migrate to the surface more quickly in low viscosity blends. Depending upon the application underfilling may need a high glass transition temperature so that it maintains high modulus at higher temperatures that may be generated in some electronic applications. In these higher temperature applications good thermal stability is also required so that the physical properties essential to the bond and support functions do not decrease significantly enough to cause a failure in one or more electrical connections.
Benzoxazines is used herein to refer to any chemical compound that has the characteristic benzoxazine ring. Benzoxazines are prepared by reacting a phenolic compound with an aldehyde and an amine, desirably an aromatic amine. U.S. Pat. No. 5,543,516, hereby incorporated by reference, sets forth a generally solventless method of forming benzoxazines. Optionally, solvents can be used to prepare benzoxazines as is well known to the art. The reaction time can vary widely with reactant concentration, reactivity and temperature. Times desirably vary from a few minutes for solventless to a few hours, e.g. 6 or 10 for diluted reactants. If a water based solution of formaldehyde is used as one reactant then a water miscible organic solvent is sometimes desirable. If one or more reactant is a liquid it may be used to dissolve the other components. If all of the components are solids they may be premixed as solids and then melted or first melted and then mixed. The temperature of reaction can be determined by routine experimentation noting the formation of benzoxazine and less desired products and optimizing temperature and time for a desirable product. Desirable temperatures are from about 0° C. to about 250° C., and preferably from about 0 or 50° C. to about 150° C.
The benzoxazine synthesis reaction may be conducted at atmospheric pressure or at a pressure up to about 100 psi. In some instances, a reaction carried out under pressure constitutes a preferred mode since fewer byproducts are produced. When a polyfunctional benzoxazine is being prepared, higher pressures generally results in relatively higher amounts of difunctional benzoxazine monomers.
The relative amounts of reactants required will depend upon their chemical nature, e.g., the number of reactive groups taking part in the reaction. The stoichiometry is well within the skills of those conversant with the art, and the required relative amounts of reactants are readily selec
Ishida Hatsuo
Rimdusit Sarawut
Aylward D.
Dawson Robert
Edison Polymer Innovation Corporation
Hudak & Shunk Co. L.P.A.
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