Stock material or miscellaneous articles – All metal or with adjacent metals – Composite; i.e. – plural – adjacent – spatially distinct metal...
Reexamination Certificate
1997-03-20
2001-11-27
Nakarani, D. S. (Department: 1773)
Stock material or miscellaneous articles
All metal or with adjacent metals
Composite; i.e., plural, adjacent, spatially distinct metal...
C428S632000, C428S658000, C428S674000, C428S341000, C428S901000, C427S419200, C427S419500
Reexamination Certificate
active
06322904
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to the thin copper foils which are used in manufacturing printed circuit boards (PCB). More particularly, the invention relates to copper foils having improved ability to resist the abrasion which leads to the formation of deep scratches and tears during handling.
It has been found, particularly in more demanding applications where relatively thin copper foils are used (e.g. one-half ounce/ft
2
or 18 &mgr;m thick), that when copper foil surfaces are exposed, that they can be damaged by abrasion, especially those which are relatively soft, such as copper foils which exhibit high percentage elongation at elevated temperatures. When scratches become severe, they can lead to tears in the foil and thus can cause rejection of the laminate or the partially completed PCB. In some cases, laminates may be rejected for their appearance even though severe damage has not occurred. Consequently, it is desirable to avoid abrasion damage insofar as possible.
Another common problem in the manufacture of PCBs is “resin spots”. These are particles of resins, such as epoxy resins, adhering to the surface of the foil. Such particles interfere with the etching process used to make circuit lines and can lead to defects which cause rejection or reworking of a circuit board. Coating copper foils with thin layers of benzotriazole (BTA) has been found to reduce the number of “resin spots”, but further improvement is needed in the industry, particularly when fine circuit lines are being made and very small resin particles are present.
It has been the practice in the industry to treat copper foils to protect them from corrosion during the period between their manufacture and their use in making printed circuit boards. One such treatment has been to apply benzotriazole and/or related compounds. For example, in U.S. patent application Ser. No. 08/496,502 now abandon both benzotriazole and aminotriazole or their derivatives were applied to rust-proof copper foil. Under the rust-proofing layer in the typical case would be a layer of electrodeposited zinc or a zinc alloy, followed by a chromate layer. It also was found that powdered epoxy resin did not adhere to the foil. The use of benzotriazole or aminotriazole alone was not as satisfactory
U.S. patent application Ser. No. 08/686,574 now abandoned discloses the use of aminotriazole and/or its isomers to resist adherence of epoxy resin particles and to resist discoloration when soldering.
In Japanese patent application 1994-85417 the use of benzotriazole or its derivatives was shown to improve solderability and adhesion of resists on the shiny side of the foil.
In Japanese patent application 1994-85455 the use of benzotriazole or its derivatives was shown to improve resistance to moisture and thus the storage life of a treated copper foil. As with the 85417 application, the treatment was placed on the shiny side of the foil. The foil was first plated with zinc or a zinc alloy, then a chromate treatment was added, followed by coating with the benzotriazole.
The present inventors have been concerned with preventing damage to copper foils during handling and have found a method which substantially improves their abrasion resistance. The copper foils made according to the invention have the added advantage of further reducing the number of resin particles adhering to the exposed copper foil.
SUMMARY OF THE INVENTION
In one aspect, the invention is an improved copper foil for use in making printed circuit boards which has increased resistance to abrasion damage and thus minimizes scratching and tearing. A first layer of zinc or zinc alloy is applied to the foil followed by a second layer of benzotriazole (BTA) or a derivative thereof, hereinafter generally referred to as “BTA” (with the exception of the examples below) sufficient to provide the desired increased abrasion resistance. Preferably, the second layer of BTA is a uniform deposit of at least 5 mg/m
2
of foil, most preferably a uniform deposit of about 5 to 8 mg/m
2
is applied.
In another embodiment, a layer of chromate is deposited between the first zinc or zinc alloy layer and the second BTA layer. The intermediate chromate layer should be sufficiently thin to avoid interfering with the bonding of BTA to zinc and preferably it will be a uniform deposit of no more than about 1.5 mg/m
2
.
In another aspect, the invention is a method of applying a BTA layer of the desired thickness by contacting the foil surface with an aqueous solution of BTA at a temperature of at least 20° C., preferably 40-70° C., for a period of time sufficient to attain the desired thickness. Optionally, after the contacting with BTA solution, the treated foil surface is washed with water to remove excess BTA not bound to the zinc or zinc alloy layer.
In still another embodiment, the invention comprises a laminate for use in making printed circuit boards consisting of an insulating substrate layer and at least one layer of the copper foil of the invention in which the surface of the foil containing the first and second layers described above is exposed.
The invention also includes in another aspect a printed circuit board comprising a laminate made with the copper foil of the invention.
REFERENCES:
patent: 4093768 (1978-06-01), Cordts et al.
patent: 4731128 (1988-03-01), Casullo
patent: 5028513 (1991-07-01), Murakami et al.
patent: 5567534 (1996-10-01), Yano et al.
patent: 195 12 196 A1 (1995-10-01), None
patent: 0 700 238 A1 (1996-03-01), None
patent: 80007717 B (1980-02-01), None
patent: 1240683 A (1989-09-01), None
patent: 3066496 A (1991-03-01), None
patent: 4202780 A (1992-07-01), None
patent: 5025407 A (1993-02-01), None
patent: A 6-85455 (1994-03-01), None
patent: A 6-85417 (1994-03-01), None
Abstract for RD 302013 A, dated Jun. 10, 1989.
Dobashi Makoto
Hata Hiroshi
Kurihara Hiroaki
Sudo Tatsuya
Takahashi Naotomi
Jenkens & Gilchrist
Mitsui Mining & Smelting Co. Ltd.
Nakarani D. S.
Rickman Holly C.
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