Photoresist composition and printed circuit boards made therewith

Claim 2

A photocurable composition comprising: (a) an epoxyfunctional resin which is capable of being cured by the action of a cation-­producing photoinitiator; (b) a reactive diluent for (a) which is soluble in developing solvents for photoresists; (c) a cationic photoinitiator; (d) optionally, an indicator which changes color in response to radiation and which can crosslink with (a) during curing; (e) optionally, a coating aid; and (f) optionally, a photosensitizer;

Claim 3

wherein (a) comprises at least about 65 wt. % of the resin solids, preferrably from about 78 to about 83 wt. % resin solids, and is dissolved in a suitable solvent, (b) comprises from about 10 to about 35 wt. % of the resin solids, preferrably from about 12 to about 17 wt. % resin solids, (c) is present in an amount of from about 2 to about 6 parts per 100 parts by wt. of resin, preferrably of about 4 parts per 100 parts resin, and is dissolved in a suitable solvent, (d) is present in an amount of from 0 to about 5 wt. % resin solids, (e) is present in an amount of from 0 to about 0.5 parts per 100 parts resin and (f) is present in an amount of from 0 to about 1 wt. % based on the weight of the resin solids.

Claim 4

wherein (a) comprises at least about 65 wt. % of the resin solids, preferrably from about 78 to about 83 wt. % resin solids, and is dissolved in a suitable solvent, (b) comprises from about 10 to about 35 wt. % of the resin solids, preferrably from about 12 to about 17 wt. % resin solids, (c) is present in an amount of from about 2 to about 6 parts per 100 parts by wt. of resin, preferrably of about 4 parts per 100 parts resin, and is dissolved in a suitable solvent, (d) is present in an amount of from 0 to about 5 wt. % resin solids, (e) is present in an amount of from 0 to about 0.5 parts per 100 parts resin and (f) is present in an amount of from 0 to about 1 wt. % based on the weight of the resin solids.

Claim 5

The composition of Claim 1 wherein (a) is an epoxy-­functional novalac having an average of at least two epoxy groups per molecule, preferrably with at least eight epoxy groups.

Claim 6

The composition of Claim 1 or 2 wherein (b) is a cycloalaphatic epoxide, e.g. - epoxycyclohexylmethyl-3,4 epoxycyclohexyl carboxylate, or - 7-oxabicyclo(4.1.0)heptane-3-carboxylic acid, 7-oxabicyclo(4.1.0)hept-3-ylmethyl ester.

Claim 7

The composition of one of the Claims 1 - 3 wherein (c) is a triarylsulphonium salt or mixtures thereof, e.g. - a mixture of triarylsulphonium hexafluoro antimonate and thio phenoxy triaryl sulphonium hexafluoro antimonate.

Claim 8

The composition of one of the Claims 1 - 4 wherein (d) is an epoxidized tris-hydroxyphenyl methane.

Claim 9

The composition of one of the Claims 1 - 5 wherein (e) is a non-ionic surfactant, e.g. fluorinated hydrocarbon.

Claim 10

The composition of one of the Claims 1 - 6 wherein (f) is selected from the group consisting of perylene, anthracene and mixtures thereof.

Claim 11

A printed circuit board which comprises at least one epoxy resin-containing substrate on which is disposed an imagewise pattern of the cured composition of one of the Claims 1 - 7.

Claim 12

The method of making the composition of Claim 1 which comprises the steps of: (1) dissolving (a) in a solvent which will dissolve substantially all of (a) which is not partially crosslinked in an amount which will comprise at least about 65 wt. % of the resin solids in the composition, preferrably 78 - 83 wt. %; (2) filtering the solute from step (1) to remove any partially crosslinked (a); (3) adding from about 10 to about 35 wt. % resin solids of (b), preferrably 12 - 17 wt. % and from about 2 to about 6 parts per 100 parts resin of (c) with stirring; and, optionally, (4) adding a suitable solvent to adjust the viscosity of the composition to from about 600 to about 2,000 centipoise.

Claim 13

The method of Claim 9 wherein the solvent of steps (1) and (4) is methyl ethyl ketone, methyl isobutyl ketone or a mixture thereof.

Claim 14

The method of Claim 9 wherein, in step (3), sufficient (d) is added to constitute up to about 5 wt. % resin solids.

Claim 15

The method of Claim 9 wherein, in step (3), sufficient (e) is added to constitute up to about 0.5 parts per 100 parts resin.

Claim 16

Method of making a printed circuit board which comprises the steps of: (A) coating a photocurable resin composition onto a substrate; (B) exposing the coating on the substrate to an imagewise pattern of radiation to which the composition is responsive in an amount sufficient to at least partially cure the composition, preferrably by exposure to ultra­violett light which imagewise pattern is the negative image of a desired printed circuit pattern; (C) developing the exposed composition with a solvent which will dissolve the non-exposed areas of the coating; D) advancing the cure of the developed imagewise coating, preferrably by exposure to heat or ultraviolett light; and (E) depositing a conductive material on the portions of the substrate which are not covered by the developed imagewise coating in order to form a partially cured printed circuit board construction; characterized in that there are comprised: in step (A), the coating of the composition of Claim 1 onto an epoxy-containing substrate to a thickness of at least about 38,1 µm; and the additional step of further curing, preferrably by exposure to heat, the construction of step (E) to a point at which the coefficient of thermal expansion in the z axis of the fully cured imagewise coating and the epoxy resin-­containing substrate are substantially the same.

Claim 17

The method of Claim 13 wherein, in step (C), the solvent is a chlorinated solvent, e.g. 1,1,1-trichloroethane.

Claim 18

The method of Claim 13 wherein, in step (A), coating is accomplished by placing the composition of Claim 1 on a carrier film, removing the solvents in the composition until a coating thickness of not less than about 38,1 µm has been achieved and a glass transition temperature of from about 25 to about 35° C has been achieved and thereafter transferring the composition to an epoxy resin-containing substrate.