Stock material or miscellaneous articles – All metal or with adjacent metals – Foil or filament smaller than 6 mils
Reexamination Certificate
2000-01-12
2001-03-06
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
All metal or with adjacent metals
Foil or filament smaller than 6 mils
C148S411000, C148S412000, C148S414000, C148S432000, C148S433000, C148S435000, C148S554000, C148S681000, C148S684000, C420S469000, C420S472000, C420S473000, C420S474000, C420S487000, C420S488000, C420S491000, C420S492000, C420S494000, C420S496000, C420S497000, C420S499000, C420S500000, C428S901000
Reexamination Certificate
active
06197433
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the invention
This invention relates to flexible wiring members such as flexible printed circuits (hereinafter called “FPCs”) having excellent flex performance with ease of fabrication.
Printed wiring boards based on organic substrate are roughly divided into two types; rigid type with a rigid, copper-clad laminate consisting of glass-epoxy and paper-phenol substrates and flexible type with a flexible, copper-clad laminate consisting of polyimide and polyester substrates. Copper foil is mainly employed as conductive material for the printed wiring boards. The foil products are classified into electrodeposited and rolled foils depending on the manufacturing processes used.
Of the printed wiring boards, those for flexible printed circuits (FPCs) are fabricated by laminating a copper foil to a resin substrate and joining the layers with adhesive or with the application of heat and pressure into an integral board. In recent years, multilayer boards known as built-up boards have come into extensive use as effective means for high-density packaging or mounting. The copper foil that is used to form components for FPCs is, for the most part, rolled copper foil.
FPCs are largely used in printer heads, hard disk drives, and other components where wiring or conductive connections to movable parts are required. They are subjected to more than a million times of repetitive bending in service. With the recent tendency toward miniaturization and higher performance levels of devices, the requirement for the flex performance is becoming severer than heretofore.
The material for copper foil to be used in FPCs is mostly tough-pitch copper (containing 100-500 ppm oxygen). The foil is manufactured by hot rolling an ingot of such material and then repeating cold rolling and annealing alternately until a predetermined thickness is achieved. The rolled copper foil is then plated for surface roughing for enhanced adhesion to a resin substrate. Following the roughing plating, the copper foil is cut into pieces and each piece is laminated to a resin substrate. To join the copper foil and resin together, an adhesive of thermosetting resin, e.g., epoxy, is used. The adhesive is hardened by heating at 130 to 170° C. for several hours to several days. Thereafter the copper foil is etched to form various wiring or conductive patterns.
The flex property of a copper foil is markedly improved by recrystallization annealing over that of the foil as rolled. Therefore, the foil is used in the annealed state as an FPC component. The annealing is done either by heat treatment after the roughing plating and cutting into a size or by utilizing the heating at the time of joining to the resin substrate. The reason for which the annealing is performed during the course of fabrication rather than using an annealed copper foil from the beginning is that, when the copper foil is soft after annealing, it can be deformed or wrinkled upon cutting and laminating to the resin substrate, and a foil hard as rolled is preferred because of the ease of fabrication into an FPC.
For enhanced flex performance of an FPC, improving the flex fatigue property of a rolled copper foil as the starting material is beneficial. The flex fatigue property of an annealed copper foil is improved with the development of its cube texture. In order to help develop the cube texture, it is effective in the copper foil manufacturing process to increase the final rolling reduction ratio and decrease the grain diameter with the annealing immediately before the final rolling (Japanese Patent Application No. 10-101858).
Actually, however, a copper foil manufactured by such a process shows a sharp drop of the softening temperature due to an increase in the plastic strain accumulated by rolling. In extreme cases the foil, even stored at room temperature, can soften after a long period of storage (refer, e.g., to Japanese Patent Application Kokai No. 10-230303).
As noted already, a softened copper foil, if used in the fabrication of an FPC, can cause troubles such as foil deformation and seriously affect the ease of FPC fabrication. For these reasons it is necessary, when the above manufacturing process is adopted to obtain a copper foil with improved flex property, to heighten the softening temperature of the copper foil to a proper level.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a rolled copper foil for FPCs which combines excellent flex property with adequate softening property, by appropriately elevating the softening temperature of a high-flexing rolled copper foil to eliminate the troubles that can otherwise result from its softening during storage.
The present invention settles the problems of the prior art and concerns the following:
(1) A rolled copper foil for flexible printed circuits characterized in that it contains not more than 10 parts per million by weight of oxygen, has a softening-temperature rise index T defined as T=0.60[Bi]+0.55[Pb]+0.60[Sb]+0.64[Se]+1.36[S]+0.09[Fe]+0.02[Ni]+0.76[Te]+0.48[Sn]+0.16[Ag]+1.24[P] (each symbol in the brackets representing the concentration in ppm by weight of the element) in the range of 4 to 34, the concentrations of the elements being in the ranges of [Bi]<5, [Pb]<10, [Sb]<5, [Se]<5, [S]<15, [As]<5, [Fe]<20, [Ni]<20, [Te]<5, [Sn]<20, [Ag]<50, and [P]<15 (each symbol in the brackets representing the concentration in ppm by weight of the element), and the foil has a thickness in the range of 5 to 50 &mgr;m, a half-softening temperature of 120 to 150° C., is capable of continuously retaining a tensile strength of at least 300 N/mm
2
at 30° C., and possesses excellent flex property and adequate softening property.
(2) A rolled copper foil for flexible printed circuits according to (1) above, characterized in that the total amount of one or more of the components Ti, Zr, Hf, V, Ta, B, Ca, and Nb is not more than 20 ppm by weight.
(3) A rolled copper foil for flexible printed circuits according to (1) or (2) above, characterized in that the intensity (I) of the (200) plane determined by X-ray diffraction of the rolled surface after annealing at 200° C. for 30 minutes, with respect to the X-ray diffraction intensity (I
0
) of the (200) plane of fine copper powder, is I/I
0
>20.0.
(4) A method of manufacturing the rolled copper foil for flexible printed circuits according to (1), (2), or (3) above characterized by a process which comprises hot rolling an ingot, repeating cold rolling and annealing alternately, and finally cold rolling the work to a foil, the annealing immediately preceding the final cold rolling being performed under conditions that enable the annealed recrystallized grains to have a mean grain diameter of not greater than 20 &mgr;m, the reduction ratio of the final cold rolling being beyond 90.0%, whereby excellent flex property and adequate softening property are achieved.
DETAILED DESCRIPTION OF THE INVENTION
When a copper foil is made by a process which involves a high reduction ratio or formation of fine grains to produce a developed cube texture, its flex fatigue property is improved but its softening temperature becomes too low. However, judicious control of the constituents in the material to raise the softening temperature will enable the resulting copper foil to have an adequate softening temperature.
The expression “adequate softening temperature” as used herein may be defined by two conditions:
(1) While the tensile strength of an as-rolled copper foil is in the range of 400-500 N/mm
2
, the foil should retain a tensile strength of not less than 300 N/mm
2
after standing at 30° C. for one year.
(2) The copper foil should soften upon heat treatment either after roughing plating and cutting into a s
Jones Deborah
Koehler Robert R.
Nippon Mining & Metals Co., Ltd.
Seidel Gonda Lavorgna & Monaco, PC
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