Photoimagable dielectric, its manufacture and use in electronics

The process of making a photoimagable dielectric comprising the steps of

• (a) preparing a mixture of a polyfunctional epoxy resin and the condensation product of a bisphenol and an epihalohydrin,
• (b) incorporating an effective amount of a cationic photoinitiator into the mixture,
• (c) exposing at least a portion of the mixture to a source of actinic radiation, and
• d) further processing the resin mixture using heat or other means to crosslink the exposed portion of resin mixture.

The process of using a photoimagable polymer comprising:

• a) preparing a resin mixture of a polyfunctional epoxy resin having more than two epoxy groups and the condensation product of a bisphenol and an epihalohydrin, wherein the polyfunctional epoxy comprises between about 30 parts and about 70 parts by weight per 100 parts of the resin mixture, and the condensation product comprises between about 70 parts and about 30 parts by weight per 100 parts of the resin mixture.
• b) incorporating an effective amount of a cationic photoinitiator into the mixture,
• c) applying the mixture to an electronic substrate to form a layer thereupon, and
• d) exposing the at least a portion of the layer to a source of actinic radiation to cure the polymer.

The process of making a photoimagable dielectric having a flex fatigue life of at least about 10,000 cycles at about a 3% strain, and a glass transition temperature of at least about 140° C., comprising the steps of

• a) based on 100 parts by weight of a resin mixture, preparing a mixture of between about 30 parts and about 70 parts of a polyfunctional epoxy resin comprising the triglycidyl ether of tris(hydroxy phenyl) and between about 70 parts and about 30 of a diglycidyl ether of bisphenol A and optionally including the addition to the resin mixture of up to 10 parts of a third epoxy resin capable of improving the flex fatigue life of the polymer without lowering the glass transition temperature below about 140° C. wherein the third epoxy resin is selected from the group consisting of an epoxidied phenolformaldehyde novolac having a weight per epoxide between about 172 and about 179 and a diglycidyl ether of bisphenol A having a weight per epoxide between about 600 and about 950;
• b) incorporating an effective amount of a cationic photoinitiator comprising a triphenyl sulfonium compound, into the mixture, and
• c) processing the resin mixture including the steps of 1) exposing at least a portion of the layer to a source of actinic radiation, 2) subjecting the exposed portion to heat to at least partially cure the exposed material, 3) removing unexposed material, 4) exposing the partially cured mixture to actinic radiation a second time, and 5) heating to fully cure the partially cured mixture to form the dielectric.