Thermosetting resins and laminates

Details Thermosetting resins and laminates Thermosetting resins and laminates

2000-09-07

2001-10-23

Mullis, Jeffrey (Department: 1711)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Mixing of two or more solid polymers; mixing of solid...

C525S069000, C525S242000, C525S333700

Reexamination Certificate

active

06306963

ABSTRACT:

FEDERALLY SPONSORED RESEARCH
Not Applicable
BACKGROUND OF THE INVENTION
The invention disclosed herein describes thermosetting resin compositions useful as a matrix resin for electrical substrate applications. The thermosetting polymers are characterized by exceptional adhesion to copper foil combined with excellent thermal and electrical performance. This combination of properties is not achievable with compositions of the prior art.
The thermosetting resin compositions disclosed in U.S. Pat. No. 5,223,568 of Landi et al. comprise a polybutadiene or polyisoprene resin which is a liquid at room temperature and has a molecular weight less than 5,000 combined with a solid butadiene or isoprene containing polymer capable of cross-linking with the former polybutadiene or polyisoprene resin. Such compositions are described as generally useful for making electrical substrate materials; however, cure temperatures in excess of 250° C. are employed. These cure temperatures exceed the limitations of most commercially available and cost-effective equipment.
U.S. Pat. No. 5,571,609 of St. Lawrence et al. describes an electrical substrate material similar to Landi et al. but with incorporation of woven glass fabric and particulate filler. The electrical substrates formed from these compositions afford copper foil adhesions (peel bonds) that range from 2.1 to 5 pounds per inch width via test method IPC-TM-650 2.4.8 on one ounce per square foot copper foil. Peel bonds in this range are marginal for many electrical substrate applications. Low peel bonds can render subsequently fabricated electrical circuits with poor reliability and cause failures during high temperature soldering and reflow soldering operations.
A need continues to exist for a thermosetting resin composition useful as a matrix resin for an electrical substrate capable of being manufactured on commercially available high-speed processing equipment such as described in U.S. Pat. Nos. 4,587,161 and 4,803,022 of Barrell et. al., preferably at cure temperatures of less than about 250° C., more preferably less than about 180° C. It is especially desirable to have electrical substrates made from compositions having high glass transition temperatures, e.g., greater than about 150° C., and having high levels of adhesion (e.g., peel bonds over about 7 pounds per inch width for one ounce per square foot copper foil) to metal foil, preferable copper foil. Additionally, a need exists for compositions having Theological properties suitable for continuous lamination without the addition of solvents. Compositions that require solvents for lamination can have deficiencies associated with the incomplete removal of the solvent during the impregnation process. Additionally, the environmental emission and personal exposure of some of the most commonly used solvents can be of considerable concern.
A need continues to exist for thermosetting resin compositions with excellent electrical properties suitable for use in high frequency applications. For a polymer dielectric to be suitable for use at broadband high frequencies, it is highly desired for the dielectric constant to be stable over decades of frequency and over the environmental extremes of humidity and temperature.
SUMMARY OF THE INVENTION
The needs discussed above have been generally satisfied by the discovery of a composition comprising:
(a) about 1 to 99%, preferably at least about 50% by weight of one or more ethylenically unsaturated aromatic monomers (EUAM) having the formula:
wherein R
1
represents a hydrogen, an alkene group, or alkyl group and n=1, or wherein R
1
represents halogen atoms and n=1 to 3, and R
2
represents a hydrogen atom or an alkyl group,
(b) about 1 to 99%, preferably from about 1% to about 50% by weight of a vinyl-terminated polymer (VTP) having the formula:
wherein R
3
represents CH
3
or H, R
4
is an urethane or ester residue, Q represents a polybutadiene homopolymer or a butadiene-styrene copolymer, and k is on average less than 3, and
(c) about 1 to 99%, preferably from about 1% to about 50% by weight of a chemically modified polyphenylene ether resin (CMPPE) having aliphatic unsaturation moieties, i.e. aliphatic carbon-carbon double bonds, and having an intrinsic viscosity less than about 0.6 dl/g, preferably less than about 0.30 dl/g, more preferably between about 0.07 and 0.15 dl/g, as measured in chloroform at 30° C.; wherein all weight percentages are based on the combined weights of components (a), (b), and (c).
Such compositions optionally also may contain a polymerization catalyst and/or initiator, a flame-retardant compound, and/or one or more fillers, reinforcing agents, or fillers and reinforcing agents.
A further embodiment of this invention particularly useful for printed circuit boards is a thermoset composition comprising reaction products of the aforementioned composition that may further include other additives such as, for example, a fibrous reinforcement.
Compositions described herein may be used to impregnate fibrous reinforcement clad with copper to form an electrical circuit board offering excellent dielectric and thermal properties, and accelerated rates of polymerization in formation of the compositions. Moreover, such compositions can be made flame-retardant. The thermosets made using the compositions and electrical composite substrates as described herein can exhibit dielectric constants as low as 2.7 and the dissipation factors as low as 0.002 at 10 GHz. In a preferred embodiment, composites made the composition exhibit consistency of electrical properties over temperature and frequency. For example, dielectric constants can be obtained that vary only 15 parts-per-million per degree Celsius and by 0.05 from 1 MHz to 10 GHz. In a preferred embodiment, the electrical properties generally do not vary significantly in humid environments since the typical moisture absorption of the invented composition is less than 0.05% by weight, measured as the weight gain after 24 hours at room temperature in water.
The description that follows provides further details regarding this invention.
DESCRIPTION OF THE DRAWINGS
Not applicable.
DETAILED DESCRIPTION OF THE INVENTION
The ethylenically unsaturated aromatic monomer (EUAM) at high weight percentages (e.g., greater than about 50% by weight) affords a thermosetting resin composition with favorable electrical properties. As the level of EUAM is increased, the dielectric constant and dissipation factor is reduced. High speed digital applications for copper-clad circuit boards favor lower dielectric constant, while high frequency wireless communication applications for copper-clad circuit boards favor both lower dielectric constant and lower dissipation factor. It has been unexpectedly found that as the level of halogenated styrene monomer increases in total percentage of the EUAM component, the glass transition temperature of the cured resin increases and the composition is rendered fire resistant. For example, if the EUAM component is changed from substantially styrene to substantially dibromostyrene, the glass transition temperature of the resin will increase from about 100° C. to about 180° C. Higher glass transition temperatures are generally favored for copper-clad circuit board applications.
Thermosetting resins based upon substantially 100% of the EUAM component do not afford favorable compositions for copper-clad circuit board applications. While the electrical properties of such a composition may be acceptable, the mechanical properties, especially adhesion to copper foil, are extremely deficient. For example, a thermosetting composition comprising substantially 100% dibromostyrene will have a favorable dielectric constant of about 2.4 and dissipation factor of about 0.002. However, the adhesion to copper foil to this resin composition will be less than 2 pounds per inch width for 1 ounce per square foot copper foil and the mechanical properties will be sufficiently low to cause substantial cracking problems during fabrication presumably due to the brittleness of the re

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