WO1997049549A1

WO1997049549A1 - A process for producing polytetrafluoroethylene (ptfe) dielectric boards on metal plates

Info

Publication number: WO1997049549A1
Application number: PCT/US1997/012761
Authority: WO
Inventors: James C. Youngblood; Jean Louis Castel
Original assignee: Park Electrochemical Corporation
Priority date: 1996-06-26
Filing date: 1997-06-26
Publication date: 1997-12-31
Also published as: AU3735797A

Abstract

The present invention is directed to a process for making a dielectric circuit board using polytetrafluoroethylene (PTFE) as the dielectric material by bonding a thick metal plate bearing a plurality of copper layers to a polytetrafluoroethylene (PTFE) substrate. In particular, the present invention relates to a process for bonding a thick copper or brass plate to a PTFE dielectric material to produce dielectric circuit boards. This invention further provides PTFE clad thick metal dielectric circuit boards which are suitable for use in high frequency microwave applications.

Description

A PROCESS FOR PRODUCING POLYTETRAFLUOROETHYLENE (PTFE) DIELECTRIC BOARDS ON METAL PLATES

FIELD OF THE INVENTION This invention relates to a process for making a dielectric circuit board using polytetrafluoroethylene (PTFE) as the dielectric material by bonding a metal plate bearing a plurality of copper layers to a polytetrafluoroethylene (PTFE) substrate. In particular, the present invention involves a process for bonding a copper or brass plate to a PTFE dielectric material to produce dielectric circuit boards. This invention further relates to PTFE clad thick metal dielectric circuit boards which are suitable for use in high frequency microwave applications.

BACKGROUND OF THE INVENTION Dielectric boards are commonly used in the electronics field. These boards generally consist of a conductive layer, such as a sheet of conductive metal and a dielectric material layer, such as a dielectric resin impregnated base material. Typical resins that can be used to impregnate the base material include, for example, phenolic resins, epoxy resins, polyimides, polyesters and the like. Base materials suitable for producing dielectric boards include, for example, woven and non-woven glass fibers.

Dielectric boards are presently manufactured using a variety of techniques. One technique involves placing copper foil on top of a partially cured resin impregnated base material and bonding the materials together using a laminating press. The heat and pressure of the laminating press causes the partially cured resin to adhere to the copper foil to produce a copper clad laminate.

This process has several drawbacks. The copper foil sheets, which range in thickness from 9-1 10 μm in thickness, are difficult to handle. Furthermore, great care must be taken to exclude all dust particles from between the surface of the copper foil and the press plates to preserve the surface quality of the laminate.

U.S. Patent No. 3,984,598 describes a process of producing copper-clad dielectric boards in which a stainless steel press plate is coated with silane prior to and subsequent to being electroplated with copper. The copper- clad press plate is then laminated to a resin-impregnated base material using a laminating press. The press plate is separated from the copper-clad dielectric board upon cooling. The copper coating on the dielectric board ranges in thickness from 5 to 12 μm. The disadvantage of this process is that the silane layer on the stainless steel plate makes it very difficult to uniformly electroplate the surface of the steel plate.

U.S. Patent Nos. 4,71 5, 1 1 6 and 4,781 ,991 describe a process for producing copper-clad dielectric boards by sequentially depositing two layers of copper, a thin copper layer followed by a coarse dendritic layer, onto the polished surface of a flat metallic press plate. The total thickness of the plated copper layer ranges from 3 to 12 μm. The metallic press plate may be stainless steel, titanium or chromium-plated steel. The copper plated press plate is subsequently joined to a dielectric material using a laminating press. Upon cooling the laminating press, a force sufficient to disturb the adhesion between the copper and the press plate is created. The copper clad dielectric material completely detaches from the press plate, forming a dielectric material plated with a layer of copper ranging in thickness from 3 to 1 2 μm.

This process has several disadvantages. For certain electrical applications, such as high frequency microwave applications, a much thicker layer of metal is required for the dielectric board. The process described in U.S. Patent Nos. 4,71 5, 1 1 6 and 4,781 ,991 , does not join a thick metal plate to the dielectric material which is required to produce the PTFE clad thick metal dielectric boards of this invention. Polytetrafluoroethylene (a fully fluorinated copolymer of hexafluoropropylene and tetrafluoroethylene) is desirable for use in dielectric boards because it resists chemical attack and has good electrical insulating properties. However, the desirable chemical properties of PTFE make it difficult to create a strong bond between this material and the surface of a finished copper or brass plate.

The present invention provides a reliable and cost-effective process for bonding PTFE to a metal plate. In particular, the present invention involves a process for producing PTFE clad thick metal dielectric boards. Despite the efforts described in the prior art, a simple, cost-effective process which promotes strong adhesion between PTFE and a metal plate to produce clad thick metal PTFE dielectric materials has not been available until the advent of the present invention. It has now been unexpectedly discovered that by plating a thin layer of copper onto the surface of a copper or brass plate, the plated copper will not release from the plate and forms a strong bond between the plate and the overlying copper.

OBJECT OF THE INVENTION It is an object of the invention to provide a process for bonding PTFE to a metal plate.

A further object of the present invention is to provide a process for producing a PTFE clad thick metal dielectric circuit board.

A further object of the invention is to provide a metal plate bound to PTFE. A still further object of the invention is to provide a process for bonding PTFE to a thick metal plate which comprises depositing a first thin layer of copper onto one surface of a thick metal plate, depositing a layer of copper having a microcrystalline dendritic structure onto a surface of said first copper layer, encapsulating the microcrystalline layer with a thin layer of copper and a thin layer of zinc and bonding PTFE to the thin zinc layer.

Another object of the invention is to provide clad thick metal PTFE dielectric boards useful in high frequency microwave applications. SUMMARY OF THE INVENTION

The present invention involves a process for bonding PTFE and copper to a metal plate to create a dielectric circuit board. According to the invention, the metal plate (made of copper and/or brass) is first made the cathode in a copper plating bath and a thin layer of fine copper is plated on the surface of the plate. The copper plated metal plate is then made the cathode in a concentrated copper sulphate bath and a coarse layer of copper is deposited on the fine copper layer that is already present. A layer of copper having microcrystalline dendritic structure is deposited on the coarse copper layer by placing the copper plated metal plate in a concentrated copper sulphate bath.

A thin layer of copper is then plated onto the dendritic structure. The plated copper layer is then covered with a thin layer of zinc. The zinc surface is placed in contact with a suitable PTFE substrate (such as a coated fabric or film) and the entire multi-layer assembly placed in a laminating press and heated. The high temperature in the press causes the PTFE (Teflon) to melt. The pressure of the laminating press causes the melted PTFE to be forced into the microcrystalline dendritic structure plated on the surface of the copper and/or brass plate. After the press is opened, the resulting product is a PTFE (Teflon) dielectric circuit board that is securely and uniformly bound to a metal plate.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a cross-sectional view of a PTFE clad dielectric circuit board in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention comprises a process for producing dielectric circuit boards comprising polytetrafluoroethylene (PTFE) bound to a metal plate. According to the invention, a plate (1 ) made of copper and/or brass is mechanically abraded to provide a uniform surface roughness. The plate (1 ) is then made the cathode in a copper plating solution and an initial layer of fine copper (2) is plated onto the surface of the metal plate (1 ). The copper coated plate is then made the cathode in a concentrated copper sulphate bath to deposit a coarse layer of copper sulphate (3) on the initial copper layer (2). A layer of microcrystalline dendritic copper (4) is then deposited on the coarse copper sulphate layer (3). The dendritic copper layer (4) is encapsulated with a layer of copper pyrophosphate (5). A layer of zinc (6) is plated over the copper pyrophosphate (5). A PTFE substrate (7) is placed adjacent to the zinc layer (6) and the entire assembly placed in a laminating press which is heated. Pressure and heat applied by the laminating press causes the molten PTFE into the interstices in the micro-crystalline dendritic copper. The resulting product is a PTFE (Teflon) microwave laminate that is uniformly and securely bonded to the metal plate. The thick metal plate { 1 ) of the present invention is made of copper or bras and has at least one surface. The surface of the thick metal plate (1 ) is initially smooth. The metal plate (1 ) has a thickness of 0.5 mm to 6.0 mm.

The surface of the metal plate (1 ) may be etched or roughened using conventional techniques prior to being plated with copper. For example, conventional mechanical abrasion techniques such as brushing with an abrasive brush, sanding, etc. may be used to roughen the surface. Alternatively, conventional chemical methods may also be used to etch the surface of the plate. These methods include, for example, contacting the surface of the plate with an aqueous solution containing one or more of the following constituents: nitric acid, hydrochloric acid, phosphoric acid, sulfonic acid, acetic acid, copper compounds such as copper chloride, copper sulphate, iron compounds such as ferric chloride, ferric sulphate and potassium chloride. In one preferred embodiment, a thick copper plate (1 ) that is 1 .56 mm thick is mechanically roughened to produce a uniform surface roughness with a center line average of 0.2 microns. The metal plate (1 ) may be washed with an aqueous solution such as distilled water following the abrasion step.

Following the abrasion of the metal plate surface, an initial layer of copper phosphate (2) is deposited on the metal plate surface using well known plating techniques. The copper pyrophosphate layer (2) is generally between about 2.1 and 2.3 microns thick. The initial layer of copper (2) deposited onto the heavy metal plate (1 ) becomes part of the heavy metal plate. Without being bound to a single theory, it is believed that the copper is bound to the metal plate by the following process. At the surface of a crystal lattice making up a grain of the metal plate, there is a force field which is an extension of the lattice forces. Metal atoms that arrive at the surface during deposition are constrained to occupy positions continuing the grain structure of the metal plate, even though this may differ from the normal lattice structure of the metal atoms being deposited. The adhesion between the initial copper layer and the metal plate occurs when the first layer of deposited atoms engage the lattice forces of the metal plate. This causes the plated metal to be atomically bound to the base metal, such that the plated metal cannot release from the metal plate provided the surface of the plate is not contaminated. The initial layer of copper (2) may be deposited on the heavy metal plate (1 ) by making the plate the cathode in a concentrated copper pyrophosphate bath containing an anode.

Examples of anodes which may be used in the process of the present invention, include, for example, oxygen free high conductivity (OFHC) copper anodes and iridium anodes. In a preferred embodiment, an OFHC copper anode (Erico, Andrezieux Boutheon, France) is used when the copper plating solution is copper pyrophosphate and an iridium anode (Permelec, Milan, Italy) and is used when the copper plating solution is copper sulphate.

In one embodiment of the invention, a copper plate (1 ) is made the cathode by placing the copper plate and an oxygen-free high conductivity (OFHC) copper anode in a concentrated copper pyrophosphate bath having a copper concentration ranging from between about 20 to about 24 g/l, an ammonia concentration ranging from between about 0.2 to about 0.4 g/l and a pH ranging from 8.0 to 8.5. After the initial thin layer of copper (2) has been uniformly deposited on the surface of the thick metal plate (1 ), a coarse layer of copper sulphate (3) is deposited on the initial copper layer (2). The copper sulphate layer (3) is deposited on the initial copper layer (2) by placing the heavy metal plate, which serves as the cathode, into a tank containing a copper sulphate solution and an anode. The copper sulphate layer (3) is generally between about 4.7 to 5.0 microns thick.

In one embodiment of the invention, the copper sulphate solution has a copper concentration ranging from about 100 to about 105 g/l, a sulfuric acid concentration ranging from about 80 to about 100 g/l and a pH below 1 .0. The anode in this embodiment is an iridium anode.

A microcrystalline dendritic layer of copper (4) is subsequently deposited on the coarse layer (3) by making the copper plated plate the cathode in a copper sulphate bath containing an anode. A microcrystalline dendritic layer has a branched crystalline structure that is porous, providing this layer with a high surface area. The high surface area is useful in forming a strong bond between the metal plate and the dielectric material. The dendritic layer (4) is generally between about 1 .15 to 1 .3 microns thick. In one embodiment of the invention, the copper plated plate is made the cathode and placed with an iridium anode in a copper sulphate solution with a copper concentration ranging from between about 18 to about 20 g/l, a sulfuric acid concentration ranging from between about 50 to about 70 g/l and a pH approximately less than 1 . After the microcrystalline dendritic layer of copper (4) has been deposited on the coarse copper layer (3), a thin layer of copper pyrophosphate

(5) is plated on the dendritic copper layer (4) by placing the heavy metal plate bearing a plurality of copper layers into a tank containing a copper pyrophosphate solution and an anode. The copper plated thick metal plate serves as the cathode. A thin layer of copper (5) is deposited on the dendritic copper layer (4) during the electrolytic reaction. The thin layer (5) is generally between about 0.38 to 0.5 microns thick.

In a preferred embodiment of the invention, the copper pyrophosphate solution has a copper concentration ranging from between about 20 to about 24 g/l, an ammonia concentration ranging from between about 0.2 to about 0.4 g/l and a pH ranging from between about 8 to about 8.5 and the anode is an OFHC copper anode.

Next, a thin layer of zinc (6) is uniformly deposited on the thin copper pyrophosphate layer (5) that was deposited on the dendritic copper layer (4) of the thick metal plate. A thin zinc layer (6) is deposited on the thin copper pyrophosphate layer (5) by making the plate the cathode by placing the plate into a tank containing a zinc oxide solution and an anode. The thin layer of zinc

(6) is generally between about 0.21 to 0.25 microns thick. In one embodiment, the zinc oxide plating solution has a zinc concentration ranging from between about 7 to about 10 g/l, a sodium hydroxide concentration ranging from between about 100 to about 140 g/l and a pH greater than 12 and the anode is an iridium anode. After each of the plating steps, water, preferably purified by conventional means, e.g. distillation or deionization, may be used as a rinse to remove any remaining solvents, solutions or other debris which may be present on the plate surface. Purified water is also preferred for use in the solutions employed in practicing the present invention in order to avoid problems in the plating process caused by contaminates such as hard water components, metal ions, organic impurities or other contaminates commonly found in water.

After these sequential plating steps are complete, the zinc layer (6) of the thick metal plate is bound to polytetrafluoroethylene (PTFE) (7) in a laminating (or caul) press. PTFE is a fully fluorinated copolymer of hexafluoropropyleneand tetrafluoroethylene which has good electrical insulating properties. This material is highly resistant to oxidation and chemical attack. PTFE has a high softening point (approximately 320°C), a low coefficient of friction and does not stick well to other materials. There a several types of PTFE materials that may be bound to the zinc layer (6) of the thick metal plate according to the process of the present invention. Examples of PTFE materials, include, for example, a PTFE coated fabric or film.

According to the process of the present invention, a polytetrafluoroethylene (PTFE) material (7) is bound to the zinc layer (6) on the thick metal plate by placing the PTFE material on top of the zinc layer of the thick metal plate and placing the entire multi-layer assembly in a laminating press. Any commercially available laminating press which is capable of holding the metal plate multi-layer assembly and simultaneously heating to a temperature sufficient to melt the PTFE material and exerting pressure sufficient to force the PTFE material into the pores of the dendritic copper layer on the thick metal plate may be used in the present invention. Examples of suitable PTFE materials contemplated by the present invention include, for example, pure PTFE and PFA films ranging in thickness from approximately 25 to 200 microns, a 1080 style woven E-Glass coated with a silane finish having a resin content ranging from approximately 30% to 80%, a 106 style woven E-glass having a resin content ranging from approximately 40% to 80%, and a 7628 style woven E-glass having a resin content ranging from approximately 40% to 65%. In the process described herein, the PTFE material is melted by heating a laminating press to a temperature between about 392° to 396 °C and is forced into the pores on the zinc layer of the heavy metal plate by exerting a pressure between about 250 and 275 psi for a time period ranging from approximately 5 hours and 45 minutes to approximately 6 hours. Examples of suitable laminating presses contemplated by the present invention include, for example, high laminating presses produced by Siemplekamp, French Oil Machine Company and Adamson United. The pressure exerted by the laminating press forces the PTFE that is melted by the heat of the laminating press into the microcrystalline dendritic structure formed on the heavy metal plate during the plating process.

Following the heating process, the laminating press and the thick metal plate bound to a PTFE material are allowed to cool to room temperature. This usually takes between about 1 hour and 45 minutes and 2 hours. The laminating press continues to exert pressure ranging from approximately 250 to 275 psi on the metal plate during the cooling process.

When the assembly has reached approximately room temperature ( 18°C) the laminating press is opened and the PTFE dielectric board is removed from the laminating press. The initial copper layer (2) that was first deposited on the copper or brass plate (1 ) remains adhered to the plate (1 ).

The plating and metal deposition procedures of the present invention are carried out in conventional plating tanks. Any container suitable for holding the plating solutions and plates of the present invention may be employed. Commercially available containers may be made of various types of materials, including for example, glass and synthetic materials such as polyethylene or polystyrene plastic material.

The PTFE dielectric board assembly is especially desirable for use as an electrical circuit board in high frequency microwave applications.

The present invention will be further illustrated by reference to the following working examples. It should be understood that the invention is not limited to the specific examples or the details described therein. EXAMPLE I A copper plate 12" X 36" and 1.56 mm thick (1 ) was brushed with a "scoth brite" nylon bristle abrasive wheel (55' x 12") impregnated with aluminum oxide particles to provide a uniform surface roughness with a center line average of 0.2 microns on both sides of the plate. Following the abrasion step, the copper plate (1 ) was washed with a pressurized water rinse to remove all traces of abrasive from the plate.

The copper plate (1 ) was then placed vertically into a polyethylene tank containing a copper plating solution consisting of copper pyrophosphate with a copper concentration between 20 and 24 g/l, an ammonia concentration of 0.2 to 0.4 g/l and a pH ranging from 8 to 8.5. (See Table I).

TABLE I CONCENTRATIONS OF THE CHEMICAL PLATING PROCESS SOLUTIONS

The copper pyrophosphate solution was purchased from M&T Chemicals. A copper Oxygen-Free, High Conductivity (OFHC) copper anode (Erico, Andrezieux Boutheon, France) was placed into a tank containing the copper plate and pyrophosphate solution. The copper plate was made the cathode in one electrical circuit connected to a DC power supply. The copper pyrophosphate plating solution was pumped through the tank for 540 seconds at a flow rate of 2500 liters per hour, a temperature of 52 °C. A current of 7.37 AMPS (See Table II) was passed through the solution by the power supply causing a thin layer of copper (2) approximately 2.2 to 2.3 μm to be deposited onto the copper plate (1 1 ). Following the initial copper plating process, the copper plate was removed from the tank and washed twice with distilled water at ambient temperature for 60 seconds at a flow rate of 300 liters per hour.

Next the plate was placed vertically into a tank containing a copper sulphate plating solution having a copper concentration ranging from

100-105 g/l, a sulfuric acid concentration of 80 to 100 g/l and a pH below 1 .0. The copper sulphate solution was purchased from M&T Chemicals. An iridium anode (Permalec) was placed in one end of the tank. The copper plate plated with an initial copper layer (2) was located at the other end of the tank and the tank filled with the copper sulphate solution. The copper plate served as the cathode. The iridium anode was parallel to the copper plate. The first copper plating solution was pumped through the tank for 130 seconds at a flow rate of 3000 liters per hour, a temperature of 61 °C and a current of 134.08 AMPS (See Table 2). A coarse layer of copper sulphate (3) ranging in thickness from 4.8 to 5.0 μm was deposited onto the initial copper layer

(2).

Following the deposit of the coarse copper sulphate layer (3), the copper plate was removed from the tank and rinsed with distilled water for 60 seconds at a flow rate of 500 liters per hour at ambient temperature. After being rinsed, the copper plate was placed vertically into a tank containing a second copper sulphate plating solution having a copper concentration ranging from 1 8 to 20 g/l, a sulfuric acid concentration ranging from 50 to 70 g/l and a pH below 1 .0. The second copper sulphate solution was purchased from M&T Chemicals. An iridium anode similar to the one employed in the preceding step was also placed at the other end of the tank, causing the copper plate to become cathodic. The second copper sulphate plating solution was pumped through the tank for 6.6 seconds at a flow rate of 2000 liters per hour, at ambient temperature and at a current of 268.17 AMPS (See Table 2). A layer of copper 1.2 to 1 .3 μm thick having a microcrystalline dendritic structure (4) was deposited onto the coarse cooper sulphate cooper layer (3). The copper plate was again removed from the tank containing the copper pyrophosphate solution and rinsed with distilled water for 60 seconds at a flow rate of 500 liters per hour at an ambient temperature.

Next, the copper plate was placed vertically into a plastic tank containing a copper pyrophosphate plating solution having a copper concentration ranging from 20 to 24 g/l, an ammonia concentration of 0.2 to 0.4 g/l and a pH ranging from 8.0 to 8.5. The copper pyrophosphate solution was purchased from M&T Chemicals. An OFHC copper anode (Erico, Andrezieux Boutheon, France) was placed into the tank containing the copper plate and pyrophosphate solution, causing the copper plate to become cathodic. The OFHC copper anode was located and spaced apart from the copper plate in the tank. The copper pyrophosphate plating solution was pumped through the tank for 185 seconds at a flow rate of 2000 liters per hour, a temperature of 52°C and at a current of 19.44 AMPS. During this plating step, a thin layer of copper (5) approximately 0.4 to 0.5 μm thick was deposited on the dendritic copper layer (4).

The copper plate was removed from the tank containing the copper pyrophosphate solution and rinsed with distilled water rinse for 60 seconds at a flow rate of 500 liters per hour at ambient temperature. A thin layer of zinc (6), approximately 0.2 to 0.25 μm thick was then plated on the thin copper pyrophosphate layer (5) to encapsulate this layer. To accomplish this step, the copper plated plate was placed into a tank containing a zinc oxide solution having a zinc concentration ranging from 7 to 10 g/l, a sodium hydroxide concentration ranging from 100 to 140 g/l and a pH greater than 12. The zinc oxide solution was purchased from M&T

Chemicals. The copper plate was bathed in the zinc oxide solution for 20 seconds at ambient temperature (See Table 2). A thin layer of zinc (6) (approximately 0.25 μm thick) was formed over the copper plate during this process. Following this final plating process, the copper plate was removed from the zinc oxide solution and rinsed with distilled water for 60 seconds at a flow rate of 500 liters per hour at ambient temperature.

The thin zinc layer (6) on thick copper plate with a plurality of copper layers was bound to a polytetrafluoroethylene (PTFE) dielectric material (7). A PTFE coated fabric, 1080 style woven E-Glass coated with silane finish was placed in contact with the zinc layer of the copper plate and the entire assembly placed in a laminating press (Siemplekamp) and heated for 6 hours to a temperature of 340 °C at a pressure of 250 psi, causing the PTFE in the fabric to melt on top of the zinc layer of the copper plate.

The press was held closed during the heating step and the PTFE/plate assembly maintained under a pressure of 250 psi and a temperature of 340°C for approximately 6 hours. The assembly was then allowed to cool to room temperature. After cooling, the PTFE dielectric board bound to the heavy metal plate was removed from the laminating press. The initial copper layer

(2) that had been plated onto the copper plate did not release from the plate (1 ).

TABLE II THE SEQUENTIAL STEPS OF THE CHEMICAL PLATING PROCESS

Claims

What is claimed is:

1 . A process for making a dielectric circuit board by bonding polytetrafluoroethylene (PTFE) to a metal plate which comprises: (a) depositing a first copper layer onto a metal plate; (b) depositing a coarse layer of copper onto the first copper layer; (c) depositing a layer of copper having a microcrystalline dendritic structure onto the coarse copper layer; (d) depositing a second copper layer onto the microcrystalline dendritic copper layer; (e) depositing a zinc layer onto the second copper layer; and (f ) bonding PTFE to the zinc layer.

2. The process according to claim 1 wherein the metal plate comprises copper or brass.

3. The process according to claim 1 wherein the metal plate is between 0.5 mm and 6.0 mm thick.

4. The process according to claim 1 which comprises providing the metal plate with a uniform surface roughness having a center line average of 0.2 μm.

5. The process according to claim 1 wherein the first copper layer of step (a) is deposited onto the metal plate by making the metal plate the cathode of an electrical circuit, placing said plate into a tank containing a copper plating solution and an anode, holding said plate in said tank for a time period sufficient to plate the copper or brass plate with said first copper layer.

6. The process according to claim 5 wherein the first copper layer is approximately 2.2 μm thick.

7. The process according to claim 5 wherein the copper plating solution comprises copper pyrophosphate having a copper concentration ranging from 20 to 24 g/l, an ammonia concentration ranging from 0.2 to 0.4 g/l and a pH ranging from 8.0 to 8.5 and the anode is an Oxygen Free High Conductivity (OFHC) copper anode.

8. The process according to claim 1 which comprises depositing the coarse copper layer of step (b) onto the first copper layer by placing the metal plate into a tank containing a copper sulphate solution and an anode, and holding said plate in said tank for a time sufficient to deposit a coarse layer of copper particles onto the metal plate.

9. The process according to claim 8 which comprises depositing a coarse copper layer having an approximate thickness of 4.8 μm.

10. The process according to claim 8 wherein the copper sulphate solution has a copper concentration ranging from 100 to 105 g/l, a sulfuric acid concentration ranging from 80 to 100 g/l and a pH less than 1.0 and the anode is an iridium anode.

1 1. The process according to claim 1 which comprises depositing the layer of microcrystalline dendritic copper of step (c) onto the coarse copper layer by placing the metal plate into a tank containing a copper sulphate solution and an anode, and holding said plate in said tank for a time sufficient to deposit a microcrystalline layer of copper onto the metal plate.

12. The process according to claim 11 wherein the microcrystalline dendritic layer of copper layer is approximately 1.2 μm thick.

13. The process according to claim 1 1 wherein the copper concentration of said copper sulphate solution is between 18 and 20 g/l, the sulfuric acid concentration is between 50 and 70 g/l the pH is less than 1 .0 and the anode comrpises iridium.

14. The process according to claim 1 which comprises depositing the second copper layer of step (d) onto the microcrystalline dendritic copper layer by placing the metal plate into a tank containing a copper pyrophosphate solution and an anode for a time sufficient to deposit a thin layer of copper onto the microcrystalline dendritic copper layer.

15. The process according to claim 14 wherein the second copper layer is approximately 0.4 μm thick.

16. The process according to claim 14 wherein the copper pyrophosphate has a copper concentration ranging from 20 to 24 g/l, an ammonia concentration ranging from 0.2 to 0.4 g/l and a pH ranging from 8.0 to 8.5 and the anode is an OFHC copper anode.

17. The process according to claim 1 which comprises depositing the zinc layer of step (e) onto the second copper layer by placing the metal plate into a tank containing a copper pyrophosphate solution and an anode for a time sufficient to deposit a thin layer of zinc onto the second copper layer.

18. The process according to claim 1 7 wherein the thin zinc layer is approximately 0.2 μm thick.

19. The process according to claim 17 wherein the zinc oxide solution has a zinc concentration ranging from 7 to 10 g/l, a sodium hydroxide concentration ranging from 100 to 140 g/l and a pH greater than 12 and the anode is an iridium anode.

20. The process according to claim 1 which comprises binding the PTFE to the zinc layer in step (d) by placing the PTFE in contact with the zinc layer on the metal plate, placing the metal plate into a laminating press and heating the laminating press for a time and at a temperature and pressure sufficient to cause the PTFE to melt and to be forced into the microcrystalline dendritic structure plated on the surface of the metal plate and cooling the laminating press to room temperature.

21. The process according to claim 20 wherein the PTFE dielectric material comprises a PTFE coated fabric or film that is a member selected from the group consisting of pure PTFE films ranging in thickness from approximately 25 to 200 microns, a 1080 style woven E-Glass coated with a silane finish having a resin content ranging from approximately 30% to 80%, a 106 style woven E-glass having a resin content ranging from approximately 40% to 80%, and a 7628 style woven E-glass having a resin content ranging from approximately 40% to 65%

22. A PTFE dielectric board on a metal plate comprising: (a) a metal plate; (b) a first copper layer on said plate; (c) a layer of course copper on said first copper layer; (d) at least one layer of copper having a microcrystalline dendritic structure on said course copper layer; (e) a layer of zinc on said microcrystalline dendritic copper layer; and (c) a PTFE dielectric material joined to the zinc layer.

23. A PTFE dielectric board produced according to the process of claim 1 .