Stock material or miscellaneous articles – All metal or with adjacent metals – Composite; i.e. – plural – adjacent – spatially distinct metal...
Reexamination Certificate
2000-01-21
2001-12-11
Koehler, Robert R. (Department: 1775)
Stock material or miscellaneous articles
All metal or with adjacent metals
Composite; i.e., plural, adjacent, spatially distinct metal...
C148S530000, C249S078000, C249S114100, C249S187100, C427S123000, C428S679000, C428S680000, C428S577000, C428S686000, C428S687000, C428S564000, C428S545000, C428S457000, C428S926000, C428S940000, C156S580000
Reexamination Certificate
active
06329077
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
The present application claims priority under 35 U.S.C. § 119 of Austrian Patent Application No. 82/99, filed on Jan. 21, 1999.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a plate-shaped compression mold for producing sheet laminates made of synthetic resins and having a metal coating on at least one surface thereof. In addition, the invention relates to a process for producing a pressing plate of a plate-shaped compression mold, and a process for producing sheet laminates, in particular printed circuit boards with copper coatings, wherein a corresponding compression mold is employed.
2. Discussion of Background Information
Technical laminates are flat elements, produced by stacking and thermal compression molding of substrates, which are impregnated with synthetic resin, for example, phenolic resin. Paper, fiber mats, such as glass fiber mats, and the like can be used as substrates. The curing process of the synthetic resin at high temperature can take place in several steps. Particularly, partially cured or pre-cured plates are prepared, provided with coatings or the like and/or stacked, and are completely cured in plate-shaped compression molds, for example between pressing plates, under the action of compressive forces and heat, whereby so-called multilayer boards can be produced.
Printed circuit boards, which are used for producing electronic devices and similar assemblies, are synthetic resin laminated elements, which have, at least on one side, a metal coating, in particular a copper coating. These circuit boards are produced by placing copper foil, usually having a thickness of from about from 5 &mgr;m to about 35 &mgr;m, on the flat surface(s) of the pre-cured laminate, clamping the resulting structure between pressing plates with extremely high surface quality, and heating same under pressure to a temperature of between 150° C. and 450° C. such that complete curing of the synthetic resin takes place.
Pressing plates for making technical laminates generally have a surface area of as much as 3.0 m
2
or more and a thickness of about 0.8 mm to about 3.0 mm with the least possible variation in thickness and extremely high surface quality. Because of the chemical stress and the atmospheric attack, these pressing plates must have high corrosion resistance and a high degree of hardness as well a high wear resistance. To meet these requirements, martensitic chromium steels are usually used for pressing plates, with the plates being tempered according to special hardening processes. Precipitation hardenable iron-base alloys are also used as pressing plate materials.
A great disadvantage of these pressing plate materials is their comparatively low thermal coefficient of linear expansion of about 10.0×10
−6
/K to 13.0×10
−6
/K at room temperature. If, during the circuit board production process, the working surface of the pressing plate is pressed against the copper foil of the laminate and the system is brought to a curing temperature of, for example, 230° C., the copper with a thermal coefficient of linear expansion of 16.8×10
−6
/K expands more than the compression surface of the mold. This difference in expansion behavior of the mold and the coating of the laminate upon heating to the curing temperature of the resin can result in warping and wrinkling of the copper foil and make such printed circuit boards unusable.
To avoid this disadvantage, it has already been attempted to make the pressing plates from a material which has a thermal coefficient of linear expansion which is at least close to that of the coating metal copper. Besides hard bronzes, austenitic steels and similar alloys, whose thermal coefficient of linear expansion is from 16×10
−6
/K to 17×10
−6
/K, have been used. While wrinkles and warping of the coating foil during curing of the laminate resin due to a temperature increase during molding can be avoided with these mold materials, the service life of such pressing plates is short. This disadvantage is caused by the fact that, due to the low hardness as well as the flow characteristics under local pressure stress of these materials and because of their low wear resistance, dents caused, for example, by foreign bodies, such as grains of dust and the like and/or borders or edges of the laminate, may be formed in the working surface. During compression of the next circuit board, these dents create a bump on the metal coating which is disadvantageous since upon etching of the conductors the Ohmic resistance in the corresponding layer area will differ from that in the rest of the layer.
SUMMARY OF THE INVENTION
The present invention eliminates the disadvantages of the known pressing plate materials and provides a compression mold of the type mentioned above with which, along with improved quality of the laminates, in particular of printed circuit boards, a long service life can be obtained. The present invention also provides a process with which an improved compression mold for the processing of technical laminates, in particular of circuit boards, can be produced. Additionally, the invention provides a process for the production of sheet laminates wherein an improved compression mold is utilized, as well as sheet laminates produced by such a process.
The present invention relates to a plate-shaped compression mold for producing sheet laminates which include synthetic resin and a metal coating on at least one side or surface thereof. The surface of the compression mold that is adapted to contact the metal coating of the sheet laminate has a Rockwell C hardness (HRC) of higher than about 44, preferably higher than 45, and most preferred higher than 46, and a thermal coefficient of linear expansion which differs from that of the metal coating by not more than about 2.5×10
−6
/K, preferably not more than about 2.0×10
−6
/K, and most preferred not more than about 1.4×10
−6
/K.
One of the advantages of the compression mold of the present invention is that in this system the shearing stress caused by a temperature change and the stress in the direction of the active compression surface can be kept low so that no disadvantageous warping or wrinkling of the metal coating occurs. The stipulated hardness of the mold surface that comes into contact with the metal coating prevents the formation of dents caused by foreign bodies, such as grains of dust, burrs, and the like and/or by borders or edges of the laminate, in the mold surface.
The plate-shaped compression mold according to the present invention will usually have a (preferably heatable) pressing plate as the surface adapted to contact the metal coating of the sheet laminate.
Both for an improvement of corrosion resistance and for reduction of wear and an adhesive tendency of the working surface of the mold, it is particularly advantageous for it to have a hard coating.
With a view to improved mold service life and to high product quality it is highly advantageous if a pressing plate that is to come into contact with the metal coating of the laminate includes corrosion resistant metal or alloy with face-centered cubic atomic structure, especially if technical laminates with copper coatings or copper layers, for example, printed circuit boards, are to be produced. Copper has a face-centered cubic atomic structure which may be the reason for an advantageously similar thermal coefficient of linear expansion.
If, as has been found, the compression mold or the pressing plate, respectively includes corrosion-resistant austenitic steel and has on its working surface a (well known) microcracked hot chromium/hard chromium layer with a Vickers hardness, determined with a load of 0.1 kg (HV
0.1
), of greater than 900, very high mold service lives and better product quality can be achieved, even if thin copper foils in the range of about 5 &mgr;m thickness are used as metal coatings of the laminates. Preferably, the HV
0.1
is greater than 1000 and mo
Jerlich Werner Josef
Kugler Alfred
Bohler Bleche GmbH
Greenblum & Bernstein P.L.C.
Koehler Robert R.
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