Stock material or miscellaneous articles – Composite – Of metal
Reexamination Certificate
1999-05-27
2004-05-04
Jackson, Monique R. (Department: 1773)
Stock material or miscellaneous articles
Composite
Of metal
C428S458000, C428S461000
Reexamination Certificate
active
06730409
ABSTRACT:
TECHNICAL FIELD
The present invention relates to improving the adhesion of a polymer to an underlying substrate and especially to an underlying metallic substrate such as copper.
BACKGROUND OF INVENTION
In the manufacture of printed circuit cards and boards, a dielectric sheet material is employed as the substrate. A conductive circuit pattern is provided on one or both of the major surfaces of the substrate.
A conductive pattern can be formed on the surface of the substrate using a variety of known techniques. These known techniques include the subtractive technique and the additive technique. In the subtractive technique, a blanket layer of copper on the substrate is selectively etched to form the desired circuit pattern. It is well known to etch a pattern in the metallic surface such as copper by applying to the surface a photoresist, exposing the photoresist through a pattern of actinic radiation, removing the exposed or unexposed portion of the resist depending upon the type of resist to expose the underlying metal, and then etching the exposed metal with a suitable etchant. In the additive process, typically the photoresist is applied to the surface of the substrate, followed by being exposed through a pattern to actinic radiation and removing the exposed or unexposed portions of the resist depending upon the type of resist employed to expose the underlying substrate and the desired circuitry to be subsequently provided. Next, the exposed substrate is typically coated with a metallic layer such as copper from an electroless plating bath followed by electroplating to achieve the desired line thickness.
However, the bond of the photoresist or photoactive layer to the metal surface has not always been adequate, especially for exposure to various plating baths and/or etching compositions. However, as can be appreciated, the adhesion of photoresists to the underlying metallic surface is critical not only in fine-line subtractive circuitization, but also in other photoresist-based manufacturing processes such as pattern electroplating and solder mask applications. In solder mask applications, a photoactive polymeric solder mask is applied and defined by photolithographic techniques to uncover those underlying portions whereby solder is to be deposited while protecting other areas from having the solder deposit.
In view of the adhesion problems between these polymers and underlying metallic surfaces, a number of surface texturing/screening processes have been suggested for enhancing such adhesion. Some examples include providing pumice on foil copper to roughen its surface in the case of subtractive circuitization, sulfuric acid pretreatment of additive copper surfaces in the case of Sn/Pb electroplating, copper oxide treatment of copper in the case of certain solder mask applications, and vapor blast treatment of gold in the case of certain solder mask applications to chip carriers.
However, despite the attempts to enhance adhesion, failures which in turn result in the scrapping of product still occur periodically. The adhesion existing between photoactive polymers and underlying metallic substrates remains borderline, at most, in many cases. For instance, it has been observed that the interface between additive copper and various photoresists is susceptible to separation during immersion tin and subsequent Sn/Pb electroplating due to increased immersion times, photoresist mis-registration, and rinse impurities that might be present in the sulfuric acid pre-clean prior to applying the resist.
Accordingly, the need remains for providing enhanced adhesion between photoactive polymers and metallic surfaces in order to yield more robust as well as potentially more cost-effective, photoactive-based processes.
SUMMARY OF INVENTION
The present invention provides for improved bonding of polymers to metallic surfaces. It has been found according to the present invention that polymers can be firmly and adherently bound to the desired metallic surface by employing a water soluble polymeric material, which prevents “curling” or lifting of the other polymer from the metallic surface and, consequently, prevents undercutting during etching in the case of photoactive polymers.
In particular, the adhesion between the polymer and metallic surface is enhanced by providing a layer of a water soluble polymeric material between the polymer and the metal surface. Specifically, the present invention is directed to a structure which comprises a metallic surface, a layer of a first polymeric material and a water soluble polymeric material located between the metallic surface and the layer of the first polymeric material.
The present invention is also directed to a process for fabricating the above structure which comprises the steps of providing a metallic surface, providing a water soluble polymeric material on the metallic surface and providing a layer of a polymeric material on the water soluble polymeric material.
In addition, the present invention relates to an electronic package that comprises a substrate, a metallic conductive layer on the substrate, a water soluble polymeric material on the metallic conductive layer and a polymeric layer located on the water soluble polymeric material wherein the polymeric layer has been developed to provide a pattern corresponding to desired circuitry.
The present invention also relates to a process for fabricating the above-defined electronic package which comprises providing a substrate and a metallic conductive layer on the substrate, providing a water soluble polymeric material located on the conductive layer, providing a photoactive polymeric film on the water soluble polymeric material, imagewise exposing the photoactive polymeric material to actinic light, and developing by removing photoactive film.
Still other objects and advantages of the present invention will become readily apparent by those skilled in the art from the following detailed description, wherein it is shown and described only the preferred embodiments of the invention, simply by way of illustration of the best mode contemplated of carrying out the invention. As will be realized the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, without departing from the invention. Accordingly, the description is to be regarded as illustrative in nature and not as restrictive.
BEST AND VARIOUS MODES FOR CARRYING OUT INVENTION
The present invention relates to improving the adhesion of polymeric materials and especially photoactive polymeric materials to a variety of metallic conductive surfaces. Examples of suitable metals include copper, gold, aluminum, silver, alloys of these metals and conductive metallic compounds such as metallic silicides and titanates. Other suitable metals include titanium, niobium, tantalum and tungsten. The preferred metal is copper and copper alloys such as copper aluminum alloys.
In a typical structure, the metallic conductive layer is present on an underlying substrate such as a dielectric substrate. Typical dielectric substrates employed in fabricating printed circuit cards and boards include thermoplastic and thermosetting resins. Typical thermosetting polymeric materials include epoxy, phenolic base materials and polyamides. The dielectric material may be molded articles of the polymers containing fillers and/or reinforcing agents such as glass filled epoxy or phenolic based materials. Examples of some suitable thermoplastic polymeric materials include polyolefins such as polypropylene, polysulfones, polycarbonates, nitrile rubbers and ABS polymers.
In accordance with the present invention, the metallic surface is treated or coated with a water soluble polymeric material. The water soluble polymers employed according to the present invention typically have weight average molecular weights of at least about 100,000 and more typically about 500,000 to about 1,000,000. The water soluble polymeric materials include both ionic polymeric materials and non-ionic polymeric materials. Exa
Angelopoulos Anastasios P.
Cangelosi Joan
Fuerniss Stephen Joseph
Kotylo Joseph Alphonse
Matienzo Luis Jesus
Cangelosi Joan
Connolly Bove & Lodge & Hutz LLP
Jackson Monique R.
Samodovitz Arthur J.
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