Patent GB-1384114-A (GB)
Title: Treating the surface of epoxy materials
IPC: H05K3/38
Filed: 1972-02-01
Abstract: 1384114 Treating epoxy coatings WESTERN ELECTRIC CO INC 1 Feb 1972 [11 Aug 1971] 4708/72 Heading B2E [Also in Divisions C3 and C7] A surface comprising a cured bis-phenol A- epichlorohydrin epoxy resin containing 0-2% epoxy novolac resin is treated to improve the adherence of materials by (I) exposing the surface to a swellant so as to swell the surface the swellant being selected from (a) a mixture of 1-methyl-2-pyrrolidinone with at least one compound selected from ethylene glycol, 4- hydroxy-4-methyl-2-pentanone, formic acid, b) a mixture of dimethylformamide with at least one of ethyleneglycol, 4-hydroxy-4-methyl-2- pentanone, formic acid, 1, 1, 1-trichloroethane, a mixture of methylethyl ketone and 1, 1, 2- trichloro-1, 2, 2-trifluoroethane, or a mixture of acetone and 1, 1, 2-trichloro-1, 1, 2-trifluoroethane, or (c) a mixture of (a) and (b); and (2) exposing the swelled surface to a suitable etchant containing Cr VI ions so as to etch the surface. The bis phenol A-epioholrohydrin epoxy may be brominated. The curing agent may be dicyandiamide. After the swelling treatment the epoxy surface may be either washed in a solvent or air-dried so as to move the excess swellant from the surface thereof prior to etching. A preferred etchant comprises an aqueous solution of sulphuric acid, and CrO 3 . The etchant may also comprise a surfactant, e.g. a perfluorinated sulphonate. All traces of a deposit on the etched surface may be removed by rinsing with water and treating with a reducing agent for Cr ions such as Na 2 SO 3  or alternatively with a basic agent, e.g. NaOH. Materials for deposition on the etched surface may comprise aqueous or organic based paints, lacquers, inks and adhesives, aqueous. or non-aqueous solutions of inorganic salts, aqueous or non-aqueous electroless metal deposition solutions, metals applied, e.g. by dipping, brushing, spray-coating, spin-coating, vapour deposition, electroless deposition with or without electrodeposition, sputtering. The product may then be baked, preferably at 110-160‹C for 10-60 minutes. Where an electroless technique is employed, the etched surface is sensitised by depositing or absorbing on the etched surface a sensitiser comprising Sn<SP>+2</SP> ions, then activated by depositing a catalytic metal Pd over the etched surface and then immersed in a standard electroless plating bath, e.g. containing Cu<SP>++</SP> ions. In a preferred embodiment, the etched surface is coated with a photo promoter solution which may be either a positive or a negative type, the photo promoter coated surface selectively exposed to a suitable mass to a source of radiation so that selective regions are formed which are capable of reducing a metal salt, e.g. PdCl, these regions are exposed to the metal salt and the precious metal positive region then exposed to a suitable electroless metal plating bath. In a typical Example a woven glass fibre fabric coated with a cured epoxy latex comprising the cured product resulting from curing an epoxy composition comprising 80 weight per cent uncured bis phenol A-epichlorohydrin epoxy resin having an epoxide equivalent of 400-2000 and 20 weight percent of epoxylated novolac resin having a weight per epoxide of 176-181 with 4 weight per cent dicyandiamide as curing agent is immersed in. dimethyl formamide swelling agent at 25‹C for 5 minutes, rinsed twice with solvent for a swelling agent comprising an azeotropic mixture of 1, 1, 2-trichloro-1, 2, 2, trifluoroethane and acetone, and then immersed in an aqueous etchant solution comprising 5.4 moles H 2 SO 4 , and 100 grams CrO 3 / litre of solution heated to 70‹-80‹C for 20 minutes. The etching solution was maintained at 40‹C and the epoxy-coated substrate was immersed therein for three minutes. After rinsing in water and immersing in a reducing solution comprising Na 2 SO 3  at 25‹C for 30 seconds, further rinsing in deionised water, the etched substrate was immersed in a sensitising solution comprising 1 weight per cent SnCl 4  and 0.5 weight per cent SnCl 2  . 2H 2 O at 25‹C for one minute, then rinsed with deionised water and immersed in a 0.01 molar aqueous PdCl 2  solution for 30 seconds, whereafter the substrate was immersed in an electroless copper plating bath and subjected to electroplating.