Chemistry: electrical and wave energy – Processes and products
Patent
1982-09-23
1984-06-26
Tufariello, T. M.
Chemistry: electrical and wave energy
Processes and products
204 40, 204 43Z, 204 55R, 204140, C25D 322, C25D 356, C25D 510, C25D 706
Patent
active
044565089
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a method of treating copper foil, which may be rolled or, preferably, electroplated, for use in the production of printed circuit boards to improve the foil's adhesion to a base material, and to laminates formed as a result of said treatment.
BACKGROUND ART
Copper foil used in the manufacture of printed circuit boards is usually bonded to a dielectric base material and various proposals have been made for improving the strength of the bond between the copper foil and the base material.
For example it is now well-established practice to apply copper dendrites to the matt surface of the foil, said dendrites often being reinforced or partially encapsulated with a continuous, coherent layer of copper. Several subsequent electrodeposited layers may then follow to achieve a bond of desired strength and one which will be largely unaffected by soldering. Metallic layers of, for example, zinc, brass or nickel may be present to separate the copper dendrites from the reactive resins in the dielectric base material. It is often difficult to control the size and distribution of the dendrites in the primary copper layer and it has therefore been proposed to add various agents to the copper of said layer in an attempt to effect such control, a preferred additive being arsenic. In such a case, a nodular or dendritic layer of metal comprising an alloy of oxidised copper with arsenic is electrodeposited onto a matt surface of the copper foil from a bath containing copper sulphate and arsenic values.
However reliable control in the growth of the dendrites, particularly the larger dendrites, is still not completely satisfactory.
DISCLOSURE OF THE INVENTION
According to the present invention there is provided a method of treating copper foil including the step of depositing onto the foil at least one nodular or dendritic layer containing zinc whereby the bond strength of the foil with an associated base material is improved.
The or each nodular or dendritic layer may be of zinc or, alternatively, brass.
The method may include the steps of depositing a nodular or dendritic layer of zinc or brass directly onto a matt surface of the foil, and encapsulating said layer with one or more layers of metal such as copper, arsenic, bismuth, brass, bronze, nickel, cobalt or zinc, or alloys/co-deposits of said metals. The presence of such encapsulating layers, which are of continuous, coherent metal as opposed to a powdery or microcrystalline dendritic deposit, can result in an increased peel strength when bonded to glass-epoxy boards compared with foil without such encapsulation of the dendrites, and furthermore ensures that, under conditions of strong resin flow during lamination--such as high pressure and temperature conditions which can cause certain epoxy resins to flow prior to setting hard--no zinc or brass dendrites are detached from the primary layer to become embedded in the resin mass.
The method may further include the step of applying over the primary layer, or the outermost encapsulating layer, a further layer containing zinc. Said further layer is preferably nodular or dendritic and is preferably an alloy of zinc and nickel, although an alloy of zinc and cobalt could be used. The amount of nickel in the alloy is conveniently within the range 3 to 15% and is preferably of the order of 10%. The provision of such a further layer increases the bond strength of the foil with a dielectric base material compared with a foil without said outer layer. Such layers are normally thinner than those applied as the innermost layer next to the basic copper foil matt.
In one method according to the invention, the treatment comprises the steps of depositing onto a matt surface of the foil a first nodular or dendritic layer of zinc, depositing a protective layer of cyanide copper over said first nodular or dendritic layer, depositing an encapsulating layer of pyrophosphate copper over said protective layer of cyanide copper, and depositing a further nodular or dendritic layer of zinc nick
REFERENCES:
patent: 3585010 (1971-06-01), Luce et al.
patent: 4049481 (1977-09-01), Morisaki
patent: 4268364 (1981-05-01), Hall
Calusaru, "Electrodeposition of Metal Powders", Materials Science Monographs, No. 3, pp. 356-360, (1979).
Bush Michael E.
Torday John
Torday & Carlisle PLC
Tufariello T. M.
LandOfFree
Treatment of copper foil does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Treatment of copper foil, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Treatment of copper foil will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2231335