Process for treating plastic surfaces and swelling solution

Details Process for treating plastic surfaces and swelling solution Process for treating plastic surfaces and swelling solution

1995-05-25

1997-01-07

Lusignan, Michael

Coating processes

With pretreatment of the base

Etching, swelling, or dissolving out part of the base

252 795, 427 98, 427322, B05D 304, B05D 310

Patent

active

055914888

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of the Invention
The invention is directed to a process for treating polymer-containing workpiece surfaces and to an aqueous non-aging solution.
2. Description of the Prior Art
Plastics can be coated with metals by wet-chemical processes according to various methods. Conventionally, the polymer surfaces are hydrophilized and roughened and then rendered conductive so that metal can be electrodeposited. Until a few years ago, it was conventional to seed the prepared surface with a catalytically active metal for this purpose and then to deposit a metal, usually copper, by chemical reduction from a suitable bath. In the meantime, processes have been applied which allow metal plating directly without electroless baths. An electrically conducting layer is produced instead of the catalytically active activator. This layer may comprise metal, e.g., palladium, but generally comprises a metal chalcogenide, a carbon layer produced from a carbon suspension, or an electrically conducting polymer, e.g., polypyrrole.
The following polymers are used as plastics: epoxy resin, polycarbonate, poly(phenylene oxide), polyester, polyamide, polyimide, poly(ether imide), polystyrene, poly(vinyl chloride) or acrylonitrile-butadiene-styrene copolymers (ABS).
In the fabrication of printed circuit boards in electronics, double-sided printed circuit boards or multilayer circuits require that the walls of the drilled through-holes be coated with metal so as to make contact between the metallic layers and to join wired components by soldering. For this purpose the applied metal layer should adhere securely to the printed circuit board dielectric and to already existing metal, e.g., the metal lining, and the inner layers of multilayer circuits, and should withstand the soldering process in particular.
A strong bonding between the plastic substrate and the metallic cover layer is also necessary in decorative metallization of plastic articles. This is equally true for functional metallization of articles, e.g., for shielding against electromagnetic radiation.
The strong bonding between the deposited metal and the polymer substrate and accordingly the functional quality of the workpiece to be produced is determined chiefly by the type of preconditioning process and the materials employed in this process. Usually, the first process step consists in swelling the polymer matrix. The second process step consists of an oxidative etching step which degrades and accordingly roughens the polymer matrix. Acceptable etching media are alkaline permanganate solution or chromic acid. However, other processes are known in which pretreatment consists only of swelling the substrate and not treating it in an oxidative etching solution.
Micro-roughening of the polymer substrate is required particularly for the preconditioning of through-holes in printed circuit board material so that deposited metal can adhere well. In order to clean through-holes smeared with polymers when drilled, an etching medium such as alkaline permanganate solution can remove drilling dust and smeared polymer material; however, micro-roughening is only achieved when the printed circuit board polymer has been swollen with an appropriate swelling solution prior to the etching step.
Swelling solutions generally contain water, an organic swelling agent and, usually, a substance reacting alkaline in water. As a rule, the organic swelling agents employed have high boiling points and only limited miscibility with water. Aqueous solutions of ethylene glycol derivatives are usually used for swelling polymers.
U.S. Pat. No. 3,898,136 describes the surface treatment of articles of epoxy resin and poly(phenylene oxide) resin with solvents having the general formula RO(AO).sub.n R', where R or R' represent an alkyl group or acyl group with not more than four carbon atoms and the other group represents a hydrogen atom, an alkyl group or acyl group with not more than four carbon atoms, A represents a branched or unbranched C.sub.2 - to C.sub.4 -alkene group, and

REFERENCES:
patent: 3898136 (1975-08-01), Yonemitsu et al.
patent: 4775557 (1988-10-01), Bastenbeck et al.
patent: 5049230 (1991-09-01), Patel et al.
Documents 86/052916/08; 86/007337, Jan., 1986.

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