Coating processes – Direct application of electrical – magnetic – wave – or... – Polymerization of coating utilizing direct application of...
Utility Patent
1998-10-30
2001-01-02
Pianalto, Bernard (Department: 1762)
Coating processes
Direct application of electrical, magnetic, wave, or...
Polymerization of coating utilizing direct application of...
C427S098300, C427S383100, C427S385500, C427S404000, C427S407100, C427S430100
Utility Patent
active
06168836
ABSTRACT:
FIELD OF INVENTION
The present invention relates to a process for plating metallic deposits on polymeric surfaces wherein the plated deposits have good adhesion to the polymeric surfaces. The present invention is especially suited to the manufacture of printed circuits of various types. Compositions are proposed which are platable with acceptable adhesion and reliability. The process is useful in forming permanent dielectrics or permanent resists.
BACKGROUND OF THE INVENTION
In general, many processes have been developed to plate upon dielectric or plastic substrates with good adhesion and reliability. Most of these processes have focused on developments in the plating cycle itself to achieve superior plating results. For example, see U.S. Pat. Nos. 5,332,465; 5,132,038; and 4,976,990 the teachings each of which are incorporated herein by reference in their entirety.
The process disclosed herein is useful in plating upon various substrates including, without limitation, plastic (dielectric) parts which are to be plated such as printed circuit boards, faucets, decorative parts, plastic encasements which are to be plated for resistance to electro magnetic radiation, and other functional substrates. As such, the instant invention will be further explained in the context of printed circuit manufacture, but will be seen by those skilled in the art as readily applicable to other similar applications such as the foregoing.
Printed circuit boards utilize a variety of resists in their manufacture. Typically the resists used are of a temporary or non-permanent type, meaning that the resist is used to create an image and then is later stripped from the surface. Various resists of this type are known and used in the art.
Printed circuit board designs using “permanent resists” are also known. A permanent resist is one which is used to create an image on a surface of the printed circuit board and then remains as an integral part of that surface (ie. is not stripped away) and is usually subsequently plated upon. Permanent resists used in the manufacture of printed circuit boards are described in U.S. Pat. No. 3,982,045 issued Sept. 21, 1976 to Kukanskis, the teachings of which arc incorporated herein by reference in their entirety. In addition see U.S. Pat. No. 4,882,245 issued to Gelonme et al, the teachings of which are incorporated herein by reference in their entirety. Also see U.S. Pat. Nos. 5,246,817 and 5,322,976, the teachings of which are incorporated herein by reference in their entirety. Shanefield et al., in U.S. Pat. No. 4,444,848, the teachings of which are incorporated herein by reference in their entirety, describes a modified epoxy material which plates with improved adhesion.
Attempts to manufacture useful permanent resists and printed circuit boards and packages using such resists have uncovered a number of difficulties. For a discussion of soldermasks, one type of permanent resist, and their compositions please refer to U.S. Pat. No. 5,296,334, the teaching of which are incorporated herein by reference in their entirety. Among the problems experienced are poor adhesion of the resist to the surface, particularly when temperature cycling is taken into consideration, an ability to obtain suitable photo definability of the resist, poor adhesion of subsequent metal platings to the surface of the resist, inability of the resist to withstand processing in the various subsequent processing chemicals, and/or inability of the resist to provide the appropriate dielectric properties necessary.
A process for plating upon permanent resists with good adhesion would prove very beneficial in the fabrication of printed circuit boards, surface laminar circuitry packages and other important devices. Surface Laminar Circuitry (“SLC”) is a technique whereby glass/epoxy laminate, or other substrates such as copper laminates, polyimides and polyetherimides, and a permanent resists are used to produce a structure resembling that of a semiconductor integrated circuit. This technology represents a change in the design concept of multilayer boards, and was developed to meet the requirements caused by the increasing rise of surface mounted devices for high resolution boards with high terminal pitch and enhanced wiring capability. It is an object of the current invention to provide such a process.
SUMMARY OF INVENTION
The invention herein relates to a process for plating upon a polymeric surface comprising:
1. creating a polymeric surface comprising at least one pre-polymer and at least one crosslinking agent;
2. partially, but not fully, polymerizing the surface;
3. plating a metallic deposit upon the partially polymerized surface; and
4. further polymerizing the surface.
The inventors have found that by plating upon a partially polymerized surface and thereafter further polymerizing the surface, excellent adhesion of the plated metallic deposit to the surface is achieved. The inventors have discovered that the best results are achieved if the surface is partially polymerized to a point where from 90-98% of the potential polymerization has occurred, then plated, and subsequently further polymerized.
Detailed Description of the Invention
The inventors herein have surprisingly discovered that excellent adhesion of a plated metal deposit to a polymeric surface can be achieved by first plating upon a partially polymerized surface and then subsequently further polymerizing the surface. Thus the following process is proposed:
1. plating a metallic deposit upon a polymeric surface which surface has not been completely polymerized; and
2. further curing (polymerizing) the plated upon surface. More specifically the following process is proposed:
1. creating a polymeric surface comprising at least one pre-polymer and at least one crosslinking agent;
2. partially, but not fully, polymerizing the surface;
3. plating a metallic deposit upon the partially polymerized surface; and
4. further polymerizing the surface.
The polymeric surfaces to be plated upon can be a wide variety of surfaces with the main requirement being that the surface be only partially polymerized when plated upon and then subsequently further polymerized. The inventors have had particular success with epoxy, epoxy-novolac and polyimide surfaces.
It has been found to be particularly advantageous to formulate the material comprising the polymeric surface such that it partially polymerizes in response to exposure to a certain level of temperature (heat) and/or a particular wave length of radiation and further polymerized in response to exposure to some higher level of temperature (heat). The foregoing is most reasonably accomplished by using two (or more) different pre-polymers and/or crosslinking agents in formulating the composition which comprises the polymeric surface. For example, the surface composition may comprise one pre-polymer and crosslinking agent which polymerize in response to exposure to temperatures of at least 100° C. (or a particular wavelength of radiation of 254 nm ) and another pre-polymer and crosslinking agent which polymerize in response to exposure to temperatures of at least 150° C. Thus the polymeric surface would be subjected to temperatures of 130° C. for a sufficient time to fully polymerize the first pre-polymer and crosslinking agent and thereafter plated upon. Subsequent to plating the polymeric surface would be exposed to temperatures of 1 60° C. for a time to sufficiently polymerize the second pre-polymer and crosslinking agent. It pre-polymer but two crosslinking agents each of which responds to different temperature or wavelengths of radiation.
Alternatively the composition which comprises the polymeric surface may comprise only one pre-polymer or type of pre-polymer and one crosslinking agent or type of crosslinking agent. In this case the composition would merely be subjected to heat and/or radiation, as applicable, to an extent such that the composition is only partially cured. Care must be taken to insure consistency in the amount of cure or polymerization prior to plating. The composition is then plated
Castaldi Steven
Krol Andrew
Kukanskis Peter
Carmody & Torrance LLP
MacDermid Incorporated
Pianalto Bernard
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