Stock material or miscellaneous articles – Composite – Of metal
Reexamination Certificate
2001-08-17
2004-07-27
Jackson, Monique R. (Department: 1773)
Stock material or miscellaneous articles
Composite
Of metal
C428S469000, C428S471000, C428S472000
Reexamination Certificate
active
06767643
ABSTRACT:
BACKGROUND OF INVENTION
1. Field of Invention
The present invention relates to a copper-alloy foil to be used for a laminate sheet of a printed circuit board.
2. Description of Related Art
The printed circuit board, which is frequently used for the electronic circuit of electronic machines, is roughly classified, depending upon the kind of base resin, as a rigid board comprising glass-epoxy material or paper-phenol, and a flexible board comprising polyimide or polyester. Copper foil is mainly used as the conducting material of the printed circuit board. The copper foil is classified, depending upon the production process, as electro-deposited copper foil and wrought copper foil. The electro-deposited copper foil is produced by means of electrolytically precipitating copper from a copper sulfate bath on a titanium or stainless-steel drum. The wrought copper foil is produced by means of plastically forming copper by rolling rolls. A characteristic of the wrought copper foil resides in that the surface profile of the rolling rolls is printed on the surface of a foil, so that the foil has a smooth surface. Incidentally, a sheet having 100 &mgr;m or less of thickness is generally referred to as the foil.
Resin substrates and copper foils are laminated by using a binder, followed by heating and exerting pressure to the binder to cure it. A printed circuit board is thus manufactured. Polyimide resin film and polyester resin film have heretofore been mainly used as the resin substrate of a flexible board. Wrought copper foil is mainly used as the foil of a flexible board, because it has good flexibility.
A binder consisting of a thermosetting resin such as epoxy resin and the like is used for laminating a copper foil and the resin. The laminated copper foil and resin is heated and subjected to pressure at 130 to 170° C. for 1 to 2 hours. The binder is thus cured. The copper foil is then etched to form it into various circuit patterns. The electronic parts are connected and mounted on the conductor patterns by solder. Since the materials of the printed circuit board are repeatedly exposed to such high temperature, they are required to be heat-resistant. Lead-free solder is used in recent years in the light of anti-environmental pollution concerns. The melting point of the lead-free solder becomes accordingly high with the result that higher heat-resistance is required for the printed circuit board. Polyimide, which exhibits higher heat resistance than polyester, is therefore broadly used.
The flexible substrate is characterized by its flexibility. The flexible substrate is, therefore, used for the conductors of movable parts and can, thus, be mounted in the electronic machines in a bent state. The flexible board is, therefore space-saving material. In addition, since the flexible substrate is thin, it is used for the interposer of a semiconductor package or an IC tape carrier of a liquid-crystal display. The width of the conductors and the inter-conductor spacing of an electronic circuit are narrowed, since high-density mounting is required in these applications. However, since the polyimide resin used broadly in the flexible substrate is hygroscopic, it may detrimentally absorb moisture of the atmosphere and deform, unless it is handled under a dry state subsequent to laminating the copper foil to the polyimide by heating and pressure application. When the printed circuit board, for which the polyimide is used, is delineated to such fine pitch as required in recent years, a problem in dimensional stability arises. The frequency of electric signals is increased in personal computers and communication from a traveling body. The resin substrate having a small relative dielectric constant is required to cope with the frequency increase mentioned above.
Employment of liquid crystal polymer is considered to meet the requirements of a resin substrate used in the printed circuit board described above. The liquid crystal polymer is a super-engineering plastic and is classified as thermotropic type and lyotropic type. The thermotropic liquid crystal is used for the printed circuit board. The thermotropic liquid crystal is characterized by high strength, chemical resistance, lower hygroscopicity and superior dimension as stability compared to the polyimide. The relative dielectric constant of the liquid crystal is approximately 3.0 and is thus lower than the approximately 3.5 of polyimide. The liquid crystal is, therefore, suitable for the resin substrate used under high frequency. Although the liquid crystal belongs to the aromatic polyester-based thermoplastic resin, the liquid crystal exhibits excellent heat resistance and can be used for such an application to be solder-bonded. Meanwhile, since the liquid crystal softens upon heating to the melting point or higher, when the copper foil as the conductor material and the liquid-crystal polymer are heated and subjected to pressure, they can be laminated under thermal fusion-bonding without a binder.
Regarding the polyimide resin broadly used at present for the printed circuit board, its coefficient of thermal expansion is 2.7×10
−5
/° C. and is different from that of copper, i.e., 1.6×10
−5
/° C. The printed circuit board is, therefore, liable to deflect during heating. On the other hand, the molecules of the liquid crystal are in the form of thin rods, and hence the coefficient of thermal expansion is different in the directions of longitudinal axis and the short axis of molecules. It is, therefore, possible to control the orientation of the molecular arrangement of the liquid crystal and to utilize these properties thus to adjust the coefficient of thermal expansion. The thermal coefficient of the liquid crystal can be made to agree with that of the copper, i.e., the conductor material. As a result, the printed circuit board becomes difficult to deflect. Although the liquid crystal and the copper foil can be laminated with a binder, when the binder having a different coefficient of thermal expansion from that of the liquid crystal and copper is sandwiched between them, the dimensional stability is impaired. Desirably, the liquid crystal and the copper foil are directly laminated to retain high dimensional stability of the printed circuit board.
Pure copper or a copper alloy with small additive elements is used as the copper foil-conductors. Since the fine pitch of copper conductors, narrowing and thinning of electronic circuits are concurrently realized, the copper foil is required to have small loss of direct-current resistance and high electrical conductivity. Copper is a material having excellent electrical conductivity. In the application, where importance is attached to the electrical conductivity, pure copper having 99.9% or more of purity is generally used. However, the heat resistance of copper is drastically lowered with the increase in purity. When copper having higher purity is laminated on a resin substrate such as polyimide substrate or is heated during the solder bonding, the copper foil more detrimentally deforms or fractures, thereby lowering its reliability Therefore, both electrical conductivity and heat resistance are required.
It has been attempted to thermally fusion-bond the liquid crystal resin-substrate and copper foil without a binder as follows. A film of the liquid crystal polymer and a wrought copper foil are heated to the melting point of the liquid crystal polymer or higher and are subjected to pressure by means of a heating press machine or heating rollers. The adherence of the liquid crystal and the wrought copper foil turned out, however, to be poor, and they were likely to peel. Specifically, when the liquid crystal having the structural formula given below and copper foil are thermally fusion-bonded at 345° C., the 180° peeling strength (according to the stipulation of JIS C 5016) of the resultant laminate is only approximately 4N/cm.
The copper foil conductor is likely to peel from the liquid crystal of the printed circuit board. Such problems as fracture of the conductor are likel
Miyake Junji
Nagai Hifumi
Tomioka Yasuo
Birch & Stewart Kolasch & Birch, LLP
Jackson Monique R.
Nippon Mining and Metals Co., Ltd.
LandOfFree
Copper-alloy foil to be used for laminate sheet does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Copper-alloy foil to be used for laminate sheet, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Copper-alloy foil to be used for laminate sheet will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3204038