Coating processes – Direct application of electrical – magnetic – wave – or... – Pretreatment of substrate or post-treatment of coated substrate
Reexamination Certificate
1999-08-18
2001-09-04
Padgett, Marianne (Department: 1762)
Coating processes
Direct application of electrical, magnetic, wave, or...
Pretreatment of substrate or post-treatment of coated substrate
C427S539000, C427S528000, C427S531000, C427S250000, C204S192170
Reexamination Certificate
active
06284329
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to an improved method of forming adherent metal components on a polyimide substrate. More particularly, this invention relates to a method of attaching an adherent copper layer to the surface of a polyimide substrate without using a polymeric adhesive layer or a tie coat to enhance adhesion between the polyimide and the copper.
BACKGROUND OF THE INVENTION
Polyimide substrates having copper components in the form of films, coatings, lines, and pads attached to a least one surface thereof are widely used in the microelectronics industry. For example, such polyimide substrates are used in polyimide flexible circuits, printed circuit boards, and chip carriers. In another application, polyimide substrates having a copper film attached to at least one surface thereof are used to form photocells. In many of these applications, the resulting products are subjected to adverse environmental conditions that promote detachment of the copper component from the surface of the polyimide substrate. For example, the products may be subjected to environmental testing at high heat and humidity or used in outdoor service. Thus, a number of procedures have been developed to improve the adhesion of copper components to polyimide substrates.
For example, in forming circuitized polyimide substrates, a layer of chromium or titanium is first deposited onto the polyimide substrate to form a tie coat. Then a copper layer is deposited onto the tie coat, typically by a vapor deposition process such as sputtering or evaporation. The thickness of the copper layer can be increased by electroplating of copper onto the vapor-deposited layer. Thereafter, portions of the copper layer are removed by etching to form the desired circuit pattern. Unfortunately, it is also necessary to remove the tie coat by a second etch step. This second etch step is time-consuming and adds to the cost of forming the circuitized product. In addition, the waste that results from this second etch step is environmentally undesirable. Thus, additional care and cost is required to handle the waste.
Attempts have also been made to improve adhesion between copper components and polymer substrates, such as polyimide substrates, by mechanically or chemically roughening the surface of the substrate prior to deposition of a copper thereon. It is believed that the roughening improves adhesion of the copper to the polymer by mechanical interlocking. Unfortunately, such adhesion is not very durable especially when the copper-coated polymeric product is subjected to the high humidity and temperature of stress testing.
Finally, attempts have also been made to enhance adhesion by employing a polymeric adhesive layer between the copper component and the polyimide substrate. However, removal of the adhesive in selected areas of the resulting product can pose problems.
Accordingly, it is desirable to have a new method for forming adherent metal components, particularly copper components, on a polyimide substrate.
SUMMARY OF THE INVENTION
In accordance with the present invention, a method for attaching adherent metal components, particularly a copper film, on at least one surface of a polyimide substrate is provided. The method comprises the steps of: exposing at least one surface of the polyimide substrate to a reactive gas plasma that provides a level of ion bombardment of the polyimide surface sufficient to disrupt at least a portion of the imide groups on the surface and to form reactive carboxylate groups, carbonyl groups and other carbon-oxygen functional groups on the surface; and then depositing a metal film onto the chemically-modified surface without intervening exposure to air. The level of ion bombardment used to chemically modify the surface results from plasma conditions such that the expression (q)×(n
+
)×(&phgr;
f
)/p has a value of at least about 5×10
17
eV/ liter-atm; where
q=the unit electronic charge (equal to 1 for units of eV/liter-atm);
n
+
=the number density of positive ions in the plasma (liter
−1
);
(&phgr;
f
)=the potential difference between the plasma and the polyimide surface (volts); and
p=pressure in atmospheres.
The present invention also provides a copper-coated polyimide product comprising a polyimide substrate having a substantially smooth and chemically-modified surface and a copper film directly attached to the surface, i.e., the product is free of a polymeric adhesive layer or tie coat between the surface of the polyimide substrate and the copper film.
REFERENCES:
patent: 3686018 (1972-08-01), Lindblom et al.
patent: 4382101 (1983-05-01), Polak
patent: 4544571 (1985-10-01), Miller
patent: 4886681 (1989-12-01), Clabes et al.
patent: 6171714 (2001-01-01), Bergkessel et al.
patent: 13-21687 (1989-12-01), None
patent: 32-17823 (1991-09-01), None
Japan Application No. 62-089478, to Matsushita Electric Ind. Co., published on Oct. 21, 1988 JP 63255362.
Japan Application No. 3-298023, to Shin ETSU Chem. Co. LTD, published on Apr. 30, 1993.
Japan Application 4-076753, to Dainippon Printing Co. LTD, published on Oct. 29, 1993.
Japan Application 06-331282, to Murata MFG. Co. LTD, published Jun. 21, 1996.
Blackwell Kim J.
Egitto Frank D.
Knoll Allan R.
Matienzo Luis J.
Hogg William N.
International Business Machines - Corporation
Padgett Marianne
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