Source: http://www.google.com/patents/US6210862?dq=7,346,545
Timestamp: 2014-03-09 16:10:06
Document Index: 715492201

Matched Legal Cases: ['application No. 07', 'application No. 08', 'application No. 08', 'application No. 08', 'application No. 09', 'application No. 09', 'application No. 09']

Patent US6210862 - Composition for photoimaging - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Sign inAdvanced Patent SearchPatentsAccording to the present invention, an improved photoimagable cationically polymerizable epoxy based solder mask is provided that contains a non-brominated epoxy resin system and from about 0.1 to about 15 parts, by weight per 100 parts of resin system, of a cationic photoinitiator. The non-brominated...http://www.google.com/patents/US6210862?utm_source=gb-gplus-sharePatent US6210862 - Composition for photoimagingAdvanced Patent SearchPublication numberUS6210862 B1Publication typeGrantApplication numberUS 09/150,824Publication dateApr 3, 2001Filing dateSep 10, 1998Priority dateMar 3, 1989Fee statusPaidAlso published asUS6576382, US20020177072Publication number09150824, 150824, US 6210862 B1, US 6210862B1, US-B1-6210862, US6210862 B1, US6210862B1InventorsRichard Allen Day, David John Russell, Donald Herman GlatzelOriginal AssigneeInternational Business Machines CorporationExport CitationBiBTeX, EndNote, RefManPatent Citations (47), Non-Patent Citations (10), Referenced by (12), Classifications (18), Legal Events (5) External Links: USPTO, USPTO Assignment, EspacenetComposition for photoimagingUS 6210862 B1Abstract According to the present invention, an improved photoimagable cationically polymerizable epoxy based solder mask is provided that contains a non-brominated epoxy resin system and from about 0.1 to about 15 parts, by weight per 100 parts of resin system, of a cationic photoinitiator. The non-brominated epoxy-resin system has solids that are comprised of from about 10% to about 80% by weight, of a polyol resin having epoxy functionality; from about 0% to about 90% by weight of a polyepoxy resin; and from about 25% to about 85% by weight of an difunctional epoxy resin. Since the photosensitive cationically polymerizable epoxy based solder mask does not contain bromine, it is particularly advantageous halogens in waste processing chemicals or in incinerated scrap circuit boards are regulated by environmental concerns. The photosensitive cationically polymerizable non-brominated epoxy based solder mask has a glass transition temperature greater than about 100� C., preferably greater than about 110� C. The solder mask dries to a tack-free film; thus, artwork used in the photoimaging process will not stick to the dried soldermask film. The polyol resin which is a condensation product of epichlorohydrin and bisphenol A, has a weight average molecular weight of between about 40,000 and 130,000. The polyepoxy resin is an epoxidized multi-functional bisphenol A formaldehyde novolak resin having a weight average molecular weight of 4,000 to 10,000. The epoxidized diglycidyl ether of bisphenol A has two epoxide groups per molecule, a melting point of between about 80� C. and about 110� C. and a weight average molecular weight of between about 600 and 2,500. The invention also relates to a cationically polymerized solder mask.
FIELD OF THE INVENTION This invention relates generally to photoimagable compositions, and more particularly to a solder mask having cationically polymerizable non-brominated epoxy resin system.
BACKGROUND OF THE INVENTION There are many different instances where photoimagable solder masks are used in various industrial processes. In one particular process the solder mask is applied to printed circuit board, then photolithographic techniques are employed to reveal various underlying structures on the board while masking others so that solder may be applied to the exposed structures. During the solder applying process the solder will adhere to the exposed underlying components and be prevented from adhering where the remaining material operates as a solder mask.
SUMMARY OF THE INVENTION According to the present invention, an improved photoimagable cationically polymerizable epoxy based solder mask is provided that contains a non-brominated epoxy resin system and from about 0.1 to about 15 parts, by weight per 100 parts of resin system, of a cationic photoinitiator. The non-brominated epoxy resin system has solids that are comprised of from about 10% to about 80% by weight, of a polyol resin having epoxy functionality; from about 0% to about 90% by weight of a polyepoxy resin; and from about 25% to about 85% by weight of an difunctional epoxy resin. Since the photosensitive cationically polymerizable epoxy based solder mask does not contain bromine, it is particularly advantageous halogens in waste processing chemicals or in incinerated scrap circuit boards are regulated by environmental concerns. The photosensitive cationically polymerizable non-brominated epoxy based solder mask has a glass transition temperature greater than about 100� C., preferably greater than-about 110� C. The solder mask dries to a tack-free film; thus, artwork used in the photoimaging process will not stick to the dried soldermask film.
DETAILED DESCRIPTION OF THE INVENTION The present invention provides a photoimagable solder mask which comprises a cationically polymerizable epoxy resin system and a photoinitiator. The solder mask is stable at 320� C. for 30 minutes and has a glass transition temperature greater than about 100� C., preferably greater than about 110� C., more preferably about 120� C. The photoimageable solder mask is applied to a substrate by conventional coating techniques such as roller coating, wound wire rod coating and curtain coating, for use as a solder mask. However, the photo solder mask can be used for other applications, such as an etch mask, permanent plating resist or protective coating. In this particular solder mask application, the photoimagable solder mask is typically coated by conventional coating techniques onto substrate to a thickness of about 0.5 to about 4.0 mils or more, dried, photoimaged and developed. The developed areas reveal the desired underlying metallized portions of the substrate wherein solder is to be applied, and the remaining solder mask material is cured and remains on the board as a solder mask during the application of solder by any conventional technique. Thus, the system of this invention must have satisfactory rheological properties for application techniques, it must be sensitive to exposure to radiation, which conventionally is in the 330 to 700 nm region, without any significant absorption to thereby allow penetration of the exposure radiation completely through the film; and it must also have the necessary physical and chemical properties to resist degradation during the soldering process.
In general, the non-brominated epoxy resin system contains a phenoxy polyol resin which is a condensation product of epichlorohydrin and bisphenol A, herein also referred to as the �polyol resin�. The weight average molecular weight of the polyol resin is between about 40,000 and about 130,000 preferably from about 60,000 to about 90,000 and a weight per epoxide of from about 20,000 to about 65,000, preferably about 30,000 to about 45,000. Preferably the polyol resin is a difunctional epoxy resin. A suitable resin of this type was formerly sold by Union Carbide Corporation under the trademark PKHC and is currently sold by Phenoxy Resins Incorporated, also under the trademark PKHC. This resin has an epoxide value of about 0.03 equivalents per kg, a weight per epoxide of about 37,000, and a Tg, that is, glass transition temperature, of about 98� C.
The second resin in the system, although optional, is preferred. The second resin is an epoxidized multi-functional bisphenol A formaldehyde novolak resin with a medium range molecular weight and at least about 3 epoxy groups per molecule, also referred to herein as the �polyepoxy resin�. The weight average molecular weight of the polyepoxy resin is between about 4,000 and about 10,000 preferably from about 5000 to about 7000 and the weight per epoxide is from about 180 to about 500, preferably from about 190 to about 250. A suitable resin of this type formerly sold by Hi-Tek Polymers under the Trade Mark EpiRez� SU-8, is now sold by Shell Chemical Company, Houstan Tex., under the trademark Epon� SU-8. This resin is an octa-functional resin and has an epoxide value of about 4.7 equivalents per kg, a weight per epoxide of about 215, a melting point of about 82� C. and a Tg of about 210� C., in its fully cured state.
EXAMPLE 1 A solder mask composition was prepared by combining 28.5 parts of the phenoxy resin PKHC, 24 parts of the multifunctional epoxy resin Epi-Rex� SU-8, 43 parts of the difunctional, diglycidal ether of Bisphenol A, Epi-Rez� 522-C, and 5 parts of the cationic photoinitiator UVE 1014. The solids content was adjusted to 40% with PGMEA solvents, and the mixture was stirred for about 5 hours to provide a photoimageable coatable solder mask. The mixture was coated by wound wire rod draw down onto substrates, specifically copper clad NIPS, and dried to obtain a tack free film.
EXAMPLE 2 A solder mask composition was prepared as in Example 1, except that 28 parts of the phenoxy resin PKHC, 67 parts of the difunctional, diglycidal ether of Bisphenol A, Epi-Rez� 522-C, and no Epirez� SU-8 were used.
EXAMPLE 3 A solder mask composition was prepared as in Example 1, except that 28.8 parts of the phenoxy resin PKHC, 24 parts of the multifunctional epoxy resin Epi-Rex� SU-8, and 43 parts of the difunctional, diglycidal ether of Bisphenol A, Epi-Rez� 530-C were used.
EXAMPLE 4 A solder mask composition was prepared as in Example 1, except that 28.8 parts of the phenoxy resin PKHC, 24 parts of the multifunctional epoxy resin Epi-Rex� SU-8, and 43 parts of the difunctional, diglycidal ether of Bisphenol A, D.E.R. 664 were used.
COMPARATIVE EXAMPLE A A solder mask composition was prepared for 30 parts of the polyol PKHC resin, 45 parts of Epirez 5183 from High-Tek Polymers now sold by Shell Chemical Company, under the trademark Epon� 1183, 25 parts Epirez� SU-8, 5 parts photoinitiator, 0.05 pph ethyl violet dye and 0.03 pph of the surfactant Fluorad FC 430 were mixed and applied as above in Example 1.
Examples 1-5 and Comparative Example A were tested for solderability in a conventional manner using the following �solder shocking� test which is a common method of testing solder mask performance under typical soldering stresses seen in industrial processes. The coated substrate is photoimaged, developed, and fully cured. The part is submerged in molten solder, maintained at 500� F.�25�, for 10-20 seconds. After the submersion into the solder, the part is allowed to cool to room temperature and inspected. Visual inspection for cracking, flaking, blistering, or noticeable degradation of the material is performed. If the solder shock does not physically degrade the material, as confirmed by visual inspection, then the solder mask passes the solder shock test criteria. The results are shown below in Table I.
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