KR20020003878A - Thermosetting polymer systems and electronic laminates - Google Patents

Abstract

The present invention relates to a resin system comprising at least one epoxy resin with little nitrogen and no chain extension and at least one curing agent which is a mixture of at least one phenolic resin and a copolymer of allyl functional material and maleic anhydride.

Description

Thermosetting Polymer Systems and Electronic Laminates {THERMOSETTING POLYMER SYSTEMS AND ELECTRONIC LAMINATES}

Printed wiring boards are increasingly being used as substrates in high frequency microprocessor chip packages and as high density substrates in high frequency telecommunications. These two end uses include low heat dissipation factor to avoid signal loss and maintain signal integrity; Low moisture absorption to form a stable substrate that does not require bake-out; There is a need for dielectric materials with high thermal resistance to withstand higher wiring temperatures. Board designers prefer low heat dissipation material to allow these materials to line up at tighter spacing, allowing thin stacks with closer inner layer distances. In addition, during the formation of the high density substrate, it is desirable that the water absorption is low so that the moisture absorption is low to increase the stack stability and prevent false overlap. Many printed wiring board processing steps use an aqueous bath, which can saturate the substrate causing resin swelling. Drying the substrate after aqueous exposure is an expensive and tedious process. Finally, when the substrate is used in some chips in packaging and board applications, higher thermal resistance allows the wiring bond temperature to increase through out.

Circuit board laminate resin systems are well known in the art. US Patent No. 3,686,359 discloses an electronic circuit board laminate based on curing cycloaliphatic epoxides with anhydride curing agents. This citation discloses that laminates using cycloaliphatic materials and anhydrides have excellent water absorption, low dielectric constant, and low heat dissipation factors. However, this formulation has a low Tg's.

U.S. Patent 4,623,578 discloses epoxy crosslinked polanhydride based laminates. Anhydride-based copolymers such as styrene maleic anhydride first react with amino aromatic compounds forming phenol imides. The resulting polyimide reacts with the epoxy to form a thermoset network. Laminates made with this process have good thermal properties but have high water absorption problems due to the imide portion.

U. S. Patent No. 5,620, 789 discloses cured suppressed resin compositions used in the manufacture of electronic laminates. The thermosetting occasional system uses boric acid to inhibit hardening.

Most printed wiring board laminates are made of fiberglass polymer substrates and fillers are added to increase electrical properties or improve board processing. Copper foil is typically coated on the laminate surface to impart a conductive medium for circuit formation. In a typical glass reinforced laminate, the system contains three phases and two interfaces. That is, the phase comprises a glass fiber, a resin matrix, and a copper foil, and the two interfaces are the region between the resin and the glass, the region between the copper foil and the laminate surface.

The interfacial region serves as an adhesive layer that bonds the resin to the glass or the copper foil to the laminate surface. The dominant binder coated on the glass fibers prior to immersion and coated on the copper foil prior to lamination controls the adhesion. The binder is a silane having hydrolyzable silicon end groups that react with the glass or copper surface and reactive organic end groups that bind to the resin matrix. Binders are important to control laminate cohesion integration and to maintain circuit adhesion. If these interfaces are of high quality with adequate adhesion, they have little effect on the chemical, thermal, moisture or electrical properties of the laminate.

The electrical properties of the laminate (in particular the dielectric constant Dk and the heat dissipation factor Df) basically depend on the resin matrix and the glass fibers. Glass types such as D-glass or Q-glass can reduce the Dk and Df of the substrate. However, this glass type is more difficult to drill compared to standard electrical grade, E-glass. Therefore, most of the intervening laminates are based on E-glass fabrics and the dielectric and heat dissipation properties must be controlled by the resin composition.

Heat and moisture absorption properties are mainly controlled by the resin formulation. As moisture is absorbed on the resin, it penetrates into the printed wiring board substrate and slightly penetrates the glass fibers. Resin systems typically have lower thermal properties than glass and are the weakest at elevated temperatures. Elevated laminate substrates will be created using resin systems that have high thermal properties that withstand moisture and are reflected at high glass transition temperatures. Current FR4-based laminates using dicyandiamide (DICY) as a curing agent in combination with epoxy resins exhibit high dielectric constants, very high water absorption, and do not provide adequate thermal resistance. Higher performance resins of bismaleimide triazine, epoxy novolac, or polyimide-based resins can be used to increase moisture absorption with increased thermal properties, but the degree of moisture absorption still remains an expensive drying and processing step. And electrical properties do not meet high frequency applications. Thus, there is still a need for resin systems that combine low dielectric constants and low heat dissipation factors with high heat resistance and low water absorption.

The present invention relates to thermoset polymers which exhibit excellent electrical and thermal properties upon curing, while absorbing very little moisture. The invention also relates to printed wiring board laminates made of thermoset polymers. The laminate exhibits excellent dielectric constants, dissipation factors, thermal properties and reduced water absorption.

The present invention includes resin systems having low water affinity upon curing.

The present invention also includes a resin system that provides a cured material having high performance electrical and thermal properties upon curing.

The present invention further includes electrical materials and laminates produced using the resin system of the present invention that include good electrical and thermal properties and low moisture absorption.

In one embodiment, the present invention provides a composition comprising at least one epoxy resin with little chain extension; A resin system comprising at least one phenolic resin and at least one curing agent which is a mixture of a copolymer of allyl functional material and maleic anhydride, wherein the resin system is almost free of nitrogen.

In another embodiment, the present invention is a laminate comprising a reinforcing material immersed in one or more resin systems of the present invention. In laminates, the reinforcing material may be unwoven or woven paper, cloth, glass or any useful useful in the manufacture of reinforcement prepregs and cores used in the manufacture of circuit boards and circuitized substrates. It may be another material.

Description of Embodiment

The present invention relates to high Tg, low moisture absorbing resin systems and underfills made using laminates, encapsulants and resin systems. The resin system of the present invention uses an epoxy resin cured with phenol and anhydride-based resins and may include optional components such as soft or reinforced components or fillers.

An important aspect of the present invention is the use of a resin system that does not include groups containing nitrogen. Resin comprising groups containing nitrogen generally provide products with unwanted electrical properties, low Tg, and high moisture absorption. Removing resin nitrogen and using a limited class of epoxy resins with phenol and anhydride curing agents will provide a useful resin system.

The epoxy resin used in the present invention should not be formed by chain extension or contain no nitrogen. Elongated chains are problematic for low Tg compared to high epoxy equivalents. If the epoxy contains nitrogen (such as the aniline moiety), Tg tends to be high, but the water absorption rapidly increases. In addition, epoxy containing nitrogen is generally toxic and difficult to treat.

Preferred resins are resins with little nitrogen, resins with low hydrolyzable chlorides, low epoxy equivalents, and combinations thereof. The epoxy resin used in the resin system of the present invention should be almost free of nitrogen. Epoxy resins containing groups containing nitrogen provide unwanted electrical properties, high moisture absorption properties in the cured product. By removing nitrogen groups from epoxy resins and from other resin system components, improved products can be obtained.

The resin system of the present invention should be almost free of nitrogen and preferably free of nitrogen. The term "almost free of nitrogen" is meant herein to include less than 1% by weight of nitrogen in the receiving system of the present invention. The term "nitrogen-free" means herein that the resin system of the present invention contains less than 0.1% by weight of nitrogen.

Preferred epoxy resins useful in the resin system of the present invention are selected from multifunctional types. Such epoxy resins can be various cresol novolacs or phenol novolacs. Preferably, the epoxy resin is a resin derived from trisphenol resins prepared using low hydrolyzable chloride contents, low hydroxyl moieties, and minimal chain extension. Such resins may be prepared according to US Pat. Nos. 4,468,508 and 4,876,371 and 5,008,350, each of which is incorporated herein by reference.

Preferred epoxies useful in the resin system of the present invention have the following structural formulas and mixtures thereof:

In the preceding resin formula, N is an integer from 1 to 300; X ₁ and X ₂ are each independently selected from hydrogen or halogen Cl, F and Br; R ₁ , R ₂ , R ₃ , R ₄ and R ₅ are each individually selected from hydrogen and an alkyl group, and the term “alkyl” refers to a straight or branched chain alkyl moiety having 1 to 20 carbon atoms; G is to be.

Examples of epoxy resins having the above-identified formulas include Quatrex6410 (Ciba-Geigy), Bren 304 (Nippon Kayaku), ESCN-195X (Sumitomo), TNM574 (Sumitomo Chemical), EPPN 502H (Nippon Kayaku), And NC6000 (Nippon Kayaku).

The resin system of the present invention includes one or more curing agents. One skilled in the art knows that the purpose of the curing agent is to react with the pentagonal oxirane ring in the epoxy resin to generate the polymer network. The epoxy resin and the hardener have a combined epoxy equivalent to hardener equivalent ratio of 0.7 to about 1.3. The epoxy to curing agent equivalent ratio is preferably about 0.9 to 1.1. Examples of curing agents include phenol novolac, cresol novolac, aromatic amines, cyanate esters such as polycresol cyanate, styrene maleic anhydride copolymers, 4,4 '-(2-acetoxy-1,3-glycerol) Aromatic anhydrides such as -bisanhydrotrimellitate, and vinyl alkyl maleic anhydride copolymers such as poly (maleic anhydride- alt -1-octadecane), and mixtures thereof.

Preferred curing agents are phenol resins mixed with a copolymer of allyl functional material and maleic anhydride. Particularly useful phenol resins for preferred curing agents are compounds of the formula: or mixtures thereof:

Wherein R ₁ , R ₂ , and R ₃ are each individually selected from hydrogen and an alkyl group and the term “alkyl” refers to a straight or branched chain alkyl moiety having 1 to 20 carbon atoms and n is from 1 to 300. Examples of useful phenolic resins having the foregoing structure include SDI711 (Borden Chemical), MU-12700 (Schenectady International), and MEH7500 (Meiwa Plastics).

The second component of the preferred curing agent is a copolymer of allyl functional material and maleic anhydride. Most preferred allyl functional material is styrene. Generally allyl functional material and maleic anhydride will be combined in a weight ratio of about 15: 1 to about 1: 1. Preferably, the allyl functional material is styrene and the weight ratio of styrene to maleic anhydride is about 5: 1.

Preferred copolymers useful for the curing of the present invention have the formula:

Wherein R _a is , Branched and straight chain alkyl groups having 1 to 20 carbon atoms, and combinations thereof, R ₁ is as defined above and R _b and R _c are each selected individually from a polymerization initiator or terminator, respectively. do. Suitable polymerization initiators are free radical type initiators. This initiator is a product of Du Pont and is sold under the VAZO ^R product line. Dupont initiators are substituted azonitrile compounds that pyrolyze and produce free radicals. The most common azonitrile is 2,2-azobis (butyronitrile) (AIBN). AIBN produces two 2-cyanoisopropyl radicals which constitute the terminal groups R _b and R _c . Other useful initiators include Bazo 64 and Bazo 68 made by Dupont.

For the purposes of the present invention, inappropriate epoxy curing agents are dicyandiamide (DICY) based curing agents. DICY-based systems supply cured epoxy resins with portions containing significant nitrogen and having higher moisture content, inadequate electrical properties, and lower Tg than the temperature produced by the curing agent of the present invention. In addition to the catalyst, all resin components should be almost free of nitrogen as defined above.

The resin composition of the present invention may contain components in addition to the epoxy resin and the curing agent described above. Optional ingredients include inorganic fillers such as silica powder fine silicon oxide powder, talc, and clay. Other optional ingredients include flame retardants such as antimony trioxide phosphate and aluminum trihydrate; Flow control agents such as phenol terminated polyether sulfone, polyvinyl butyrate, magnesium hydroxide and polyether imide; And dyes or pigments to control color, and surfactants to control surface appearance.

The following examples illustrate preferred embodiments of the invention as well as preferred methods of using the compositions of the invention. The examples are not intended to limit the scope of the invention described in the appended claims.

Example 1

The examples compare the properties of commercial FR-4 laminates made with the DICY curing agent system and laminates made using the resin composition of the present invention. Each laminate was prepared by coating a resin on 7628 woven glass, drying and curing with an intermittent gel point (b-stage prepreg). This prepreg was laminated in four layers between the copper foils and fed to the press under appropriate temperature and pressure to cure. Press conditions were dropped at 180 ° F, pressured at 200psi, and 10 ° F / min. The temperature was ramped to 392 ° F under pressure at speed. The temperature was maintained at 392 ° F. for 1 hour after cooling to room temperature before opening the stack stack. The outer copper foil layer was etched in a conventional etchant to remove the copper layer to form an unclad laminate. All laminates contained a resin fraction in size of about 40% by weight. The resin systems used to prepare the prepregs are described in Tables 1 and 2.

Table 1

Resin formulation

Formulation One 2 3 4 5 6 7 8 TMH574 51.48 g 34.93 g 39.74 g 15.27 g EPPN-502H 45.26 g 56.84 g 71.95 g NC6000 50.86 g Quatrex6410 56.40 g 91.69 g 54.13 g 48.64 g 41.94 g 56.17 g BA59P 29.41 g 31.30 g 35.87 g 41.83 g 30.97 g 29.60 g Bren304 61.14 g 102.81 g MEH7500 10.51 g HRJ12700 12.74 g SMA EF30 102.71 g 102.87 g 109.31 g 108.16 g 109.18 g 103.37 g SMA 2000P 98.65 g SMA 1000P 84.73 g PMA solvent 84.80 g 84.80 g 84.80 g 84.80 g 84.80 g 84.80 g 84.80 g 84.80 g MEK solvent 75.20 g 75.20 g 75.20 g 75.20 g 75.20 g 75.20 g 75.20 g 75.20 g 2-methyl imidazole 0.11 g 0.11 g 0.11 g 0.11 g 0.11 g 0.11 g 0.11 g 0.11 g Boric acid 0.9 g 0.9 g 0.9 g 0.9 g 0.9 g 0.9 g 0.9 g 0.09g all 400 g 400 g 400 g 400 g 400 g 400 g 400 g 400 g

TABLE 2

Resin formulation

Formulation 9 10 11 TMH574 51.48 g 51.48 g 51.48 g EPPN-520H NC6000 Quatrex 6410 56.40 g 56.40 g 56.40 g BA59P 29.41 g 29.41 g 29.41 g BREN 304 MEH7500 HRJ12700 SMA EF30 102.71 g 102.71 g 102.71 g SMA 2000P SMA 1000P PMA solvent 84.80 g 84.80 g 84.80 g MEK solvent 75.20 g 75.20 g 75.20 g 2-methyl imidazole 0.11 g 0.11 g Boric acid 0.09 Tetra butyl phosphonium acetate 0.48 g all 400 g 400 g 400 g

Table 3 below describes the compositions and functional groups of the components identified in Tables 1 and 2.

TABLE 3

Composition Description

ingredient Chemical formula Functional group TMH574 Multifunctional epoxy resin Epoxy EPPN502H Multifunctional epoxy resin Epoxy NC6000 Multifunctional epoxy resin Epoxy Quatrex 6410 Brominated epoxy resin Epoxy BREN 304 Brominated epoxy resin Epoxy BP59P Brominated Phenolic Resin Hardener MEH7500 Phenolic resin Hardener HRJ12700 Phenolic resin Hardener SMA EF30 Styrene Maleic Anhydride Hardener SMA2000P Styrene Maleic Anhydride Hardener SMA1000P Styrene Maleic Anhydride Hardener PMA solvent 1-methoxy-2-propanol acetate Resin system solvent MEK solvent Methyl ethyl ketone Resin system solvent 2-methyl imidazole 2-methyl imidazole catalyst Boric acid Boric acid catalyst Terabutyl phosphonium acetate Tetrabutyl phosphonium acetate catalyst

Before measuring laminate properties, all laminate samples were equilibrated at 24 ° C. and 50% relative humidity (RH). Water absorption at 85 ° C. and 85% RH was measured as saturation point. Table 4 below summarizes the results of the FR-4 DICY system compared to the laminate of the present invention.

Table 4

Formulation Conventional FR4 One 2 3 4 5 6 7 8 Tg ℃ by DMA 160 221 221 228 231 234 212 212 225 Water Absorption (%) 85 ℃, 85% RH 1.20 0.24 0.27 0.34 0.37 0.54 0.27 0.25 NA Barcol Hardness (%) 96.5 97.0 93.9 102.3 92.3 98.5 91.6 NA NA Z-axis CTE20-288 ℃ 120.0 NA 100.0 92.2 84.1 103.0 92.5 NA NA Dk 1.2 GHz 4.55 4.01 4.02 4.09 4.15 4.31 3.92 NA NA Dk600 MHz 4.55 4.01 4.01 4.08 4.17 4.31 3.93 NA NA Dk300 MHz 4.58 4.04 4.04 4.04 4.19 4.34 3.94 NA NA Dk100 MHz 4.62 4.07 4.07 4.12 4.23 4.39 3.97 NA NA Df1.2 GHz 0.0112 0.0093 0.0102 0.0098 0.0115 0.0143 0.0090 NA NA Df600 MHz 0.0118 0.0093 0.0100 0.0097 0.0117 0.0143 0.0090 NA NA Df300 MHz 0.0122 0.0089 0.0096 0.0093 0.0113 0.0139 0.0087 NA NA Df100MHz 0.0129 0.0086 0.0091 0.0093 0.0112 0.0136 0.0084 NA NA

The resin system of the present invention supplies a resin having a higher Tg value and lower water absorption compared to the FR4 resin. Dielectric constants (Dk) are typically between 0.3 and 0.6 lower than FR4 materials. The heat release factor (Df) is low and some formulations are less than 0.0090.

Example 2

This example measured whether the resin curing properties and the resulting laminate thermal properties could be elevated by deforming the resin catalyst package. Laminates using the resin system of the present invention were prepared according to Example 1. The resin system used included various catalyst combinations. Laminate properties were evaluated according to the method described in Example 1 and reported in Table 5 below.

Table 5

Catalytic effect

FR4 9 10 11 Tg ℃ by DMA 160 221 220 220 Water Absorption (%) 85 ° C, 85% RH 1.20 0.24 0.25 0.34 Barcol Hardness (%) 96.5 97.0 93.5 95.2 Z-axis CTE20-288 ℃ 120.0 NA 105.0 61.8 Dk 1.2 GHz 4.55 4.01 3.84 3.91 Dk600 MHz 4.55 4.01 3.85 3.91 Dk300 MHz 4.58 4.04 3.86 3.95 Dk100 MHz 4.62 4.07 3.89 3.96 Df1.2 GHz 0.0112 0.0093 0.0088 0.0090 Df600 MHz 0.0118 0.0093 0.0087 0.0089 Df300 MHz 0.0122 0.0089 0.0083 0.0086 Df100MHz 0.0129 0.0086 0.0081 0.0086

Boric acid-imidazole catalyst packages have been used successfully in the present invention. However, removing boric acid or using a phosphonium catalyst to provide a pure imidazole catalyzed system did not have a detrimental effect on laminate properties. In addition, providing boric acid lowered the dielectric and heat dissipation factors to increase laminate properties.

Claims (13)

One or more epoxy resins with little chain extension; And at least one curing agent that is a mixture of at least one phenolic resin and a copolymer of an allyl functional material and maleic anhydride, wherein the resin system is substantially free of nitrogen. The resin system of claim 1 wherein the epoxy resin is selected from the following formulae and mixtures thereof: Wherein n is from 1 to 300; X ₁ and X ₂ are each independently selected from hydrogen, Cl, F and Br; R ₁ , R ₂ , R ₃ , R ₄ and R ₅ are each independently selected from hydrogen and straight and branched chain alkyl moieties having 1 to 20 carbon atoms; G is to be. The resin system of claim 2 wherein the epoxy resin is of the formula: Wherein R ₁ is a t-butyl group, R ₂ , R ₃ , and X ₁ are each hydrogen and n is from 1 to 300. The resin system of claim 2 wherein the epoxy resin is of the formula: Wherein R ₁ , R ₂ , R ₃ , R ₅ and X ₂ are each hydrogen and X ₁ is bromine. The resin system of claim 1, wherein the phenolic resin is selected from compounds having the formula and mixtures thereof: Wherein R ₁ , R ₂ and R ₃ are each individually selected from hydrogen and straight or branched chain alkyl moieties having from 1 to 20 carbon atoms, n is from 1 to 300 and X ₁ and X ₂ are hydrogen, Cl , F and Br are each individually selected. The resin system of claim 1 wherein the phenol resin is of the formula: Wherein R ₁ , R ₂ , R ₃ and X ₁ are each hydrogen and n is from 1 to 300. The resin system of claim 1 wherein the copolymer of allyl functional material and maleic anhydride has the formula: Wherein R _a is , Straight and branched chain alkyl moieties having 1 to 20 carbon atoms, and combinations thereof, R ₁ is selected from hydrogen and straight and branched chain alkyl moieties having 1 to 20 carbon atoms, R _b and R _c is each selected individually from the polymer initiator or terminator. The resin system according to claim 1, wherein the copolymer of allyl functional material and maleic anhydride is styrene maleic anhydride. The resin system of claim 1 wherein the equivalent ratio of epoxy resin to curing agent is about 0.9 to about 1.1. The resin system of claim 1 wherein the allyl functional material and maleic anhydride are combined in a weight ratio of about 15: 1 to about 1: 1. A laminate comprising a woven material immersed in the resin system of claim 1. The laminate of claim 11, wherein the woven material is woven glass and the laminate is selected from prepregs, cores, or combinations thereof. Epoxy resins of the formula (I); A nearly nitrogen-free resin system comprising at least one phenolic resin of formula (II) and at least one curing agent that is a mixture of a allylic functional material of styrene maleic anhydride of formula (III) and a copolymer of maleic anhydride : (I) (II) Wherein G is R ₁ , R ₂ , R ₃ , R ₅ , and X ₂ are each hydrogen, X ₁ is bromine, n is from 1 to 300, R _a is Wherein R ₁ is selected from hydrogen and straight and branched chain alkyl moieties having from 1 to 20 carbon atoms, and R _b and R _c are each selected individually from a polymerization initiator or terminator.