JPH06212405A - Method of plating copper on polyphenylene sulfide substrate - Google Patents

Abstract

PURPOSE: To provide a method for plating the surface of a polyphenylene sulfide supporter with copper.

CONSTITUTION: A polyphenylene sulfide supporter is subjected to etching by RF argon plasma in a vacuum. Without breaking the vacuum, a titanium layer is sputtered to the etched surface, and then, a primary copper layer is sputtered to the surface sputtered by titanium. After the procedure of the sputtering, the supporter is electroplated with a secondary copper layer to a desired thickness. Peeling strength of 4.5 to 5.5 pound/inch can be obtd. The method in this invention is useful for producing products for EMI shields and for printed circuit boards.

COPYRIGHT: (C)1994,JPO

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates generally to improved adhesion between a polyphenylene sulfide support and a copper layer deposited on the surface of said support. More particularly, the present invention relates to a method of obtaining improved adhesion between a polyphenylene sulfide support and a copper layer electrodeposited on the surface of said support, and a product made according to this method.

[0002]

2. Description of the Related Art Metal coatings of engineering plastics (eg polyphenylene sulfide, etc.) are used for electrical or cosmetic purposes (eg, protected from electromagnetic interference (EMI), or electrically conductive in printed wiring board applications). Is used for the conductive pattern]. There is increasing industrial interest in the use of such conductive patterns and other functional applications in which metal plated plastic parts are used instead of metal only parts. In addition to being more economical from a manufacturing standpoint, these metal plated plastic parts are superior to metal parts in many important respects. While often retaining a metallic look and feel, it can often achieve significant weight savings.

However, in order to achieve these benefits, it is necessary to provide a high level of adhesion between the metal coating and the engineering plastic support. This adhesive strength can be measured as peel strength. If you don't get the high level of adhesion you need,
When exposed to temperature changes or slight strains, the metal coating may swell due to the difference in the coefficient of thermal expansion between metal and plastic in the former case and due to the difference in elastic modulus in the latter case. It may come off from the plastic support. For printed wiring board applications, the peel strength should be at least about 4 pounds per inch.

Polyphenylene sulfide has many properties desired for EMI shielding, electrical conduction, and other similar applications, such as high chemical resistance, flame retardancy, high mechanical strength and hardness. It is a substance. However, polyphenylene sulfide has not been considered as a suitable material for these applications. It is believed that satisfactory adhesion cannot be obtained between the conductive metal and the polyphenylene sulfide support.

A method known in the art for depositing metals on polyphenylene sulfide supports is electroless plating. According to the process, the surface of the polyphenylene sulfide support is first modified by chemical or physical means (eg chemical etching, grit blasting, or mechanical polishing). Then, the surface of the polyphenylene sulfide is treated with a catalyst (for example, a palladium-tin catalyst) before performing the electroless plating operation. The activated support is then immersed in an electroless plating bath (generally containing metal ions and a reducing agent) to plate the metal onto the support. After electrolessly depositing a layer of conductive metal, the support can be further plated with a conductive metal according to electroless plating or conventional electroplating to increase the layer thickness.

As can be seen from the above description, such a series of steps requires a lot of time and is therefore expensive. In contrast, the faster and lower cost method claimed herein provides adhesion comparable to the above process. Wet chemical process steps have their own problems and are necessarily costly, so it is preferable to avoid wet chemical processes altogether.

[0007]

Accordingly, it is an object of the present invention to provide a method of plating copper onto a polyphenylene sulfide support while eliminating the cumbersome and costly procedures often required in electroless plating processes. To do.

Another object of the present invention is to provide a method for producing a copper-plated polyphenylene sulfide support, characterized in that it has a peel strength of 4.5 to 5.5 pounds / inch. To do.

Still another object of the present invention is to provide a product (for example, a shielded connector or a circuit board) manufactured by such a method and having excellent characteristics.

[0010]

SUMMARY OF THE INVENTION The present invention is a method for plating copper onto a polyphenylene sulfide support. According to a broad aspect of the invention, a polyphenylene sulfide support is provided in a vacuum chamber at a radio frequency (R
F) Etch with argon plasma. Etched and argon enhanced surfaces without breaking vacuum
A layer of titanium is sputter deposited onto the ced surface as an adhesion promoting intermediate layer, and then a first copper layer is sputter deposited onto the titanium intermediate layer. A second copper layer is deposited on the first copper layer by electroplating (no peeling or blistering occurs at this time) to obtain the desired thickness.

The present invention further relates to a product comprising a polyphenylene sulfide support and a copper layer formed on said support according to the method of the present invention.

Other objects, features and advantages of the present invention will be apparent from the description below.

In the preferred method of the present invention, a dielectric support made of polyphenylene sulfide is etched by an RF argon plasma in a vacuum. A layer of titanium was sputter deposited onto the etched and argon enhanced surface without breaking the vacuum and then a first copper layer was sputter deposited onto the titanium layer. The substrate can then be electroplated with an additional copper layer without the attendant blistering or flaking. In the case of a polyphenylene sulfide support in the form of being etched in argon, sputter coated with titanium, sputter coated with copper, and electroplated with copper, about 4.5-
A peel strength of 5.5 lbs / inch is obtained.

The support may be provided with holes in the support by drilling holes prior to each step (these holes provide the conductive pattern provided on the substrate on the opposite side of the support). Necessary for connecting to the conductive pattern and / or the conductive member).

For the purposes intended by the present invention, the support is
Made of polyphenylene sulfide, a crystalline thermoplastic. Polyphenylene sulfide has desirable properties (eg high chemical resistance,
Flame retardant, high mechanical strength and hardness, etc.), suitable for EMI shield and circuit board. Preferred polyphenylene sulfide polymers include, but are not limited to, those described in US Pat. No. 4,654,826, which is incorporated herein by reference. According to the patent, a low to medium molecular weight polyarylene sulfide prepolymer is formed according to prepolymerization, and the temperature is raised by adding a phase separation system and heating the polymerization system under strongly alkaline conditions, thereby By separating the polymerization system into two phases, a high-viscosity phase (polymer solution) and a low-viscosity phase (solvent phase), and carrying out the reaction in such a state, without using an auxiliary agent, about tens of thousands of poise A fairly high molecular weight linear polyarylene sulfide having a melt viscosity of is easily obtained.

In this two-phase separation polymerization, an arylene sulfide prepolymer having a melt viscosity of 5 to 3,000 poise (at 310 ° C; shear rate = 200 sec ^-1 ) was diluted under strong alkaline conditions (10 times with water). Sometimes the reaction mixture is dissolved in a poor solvent at a pH range of 9.5 to 14); maintaining this state for 1 to 50 hours to convert the arylene sulfide prepolymer into a high molecular weight polymer; polymerization Separating the polymer from the system; and purifying the polymer after the neutralization treatment.

The process for producing high to ultra high molecular weight polyarylene sulfides according to US Pat. No. 4,645,826 is basically based on combining alkali metal sulfides and dihaloaromatic compounds. Forming a polyarylene sulfide molecule having the following structure; and / or converting the polyarylene sulfide molecule into a high molecular weight polymer. Polyphenylene sulfides having a melt viscosity of at least 3,000 poise, including polyphenylene sulfides having a melt viscosity of at least 7,000 poise, are obtained by the process disclosed in the patent.

The present invention is believed to provide strong adhesion to other crystalline thermoplastic substrates, but this has not yet been investigated.

The linear polyphenylene sulfides, crosslinked polyphenylene sulfides, and branched polyphenylene sulfides (whether homopolymers, copolymers, terpolymers, or blends of such polymers) described below are It can be used in the practice of the invention, but is not limited thereto. The polyphenylene sulfide used to make the support may optionally contain other materials such as fillers and processing aids. It is preferred to incorporate glass fibers for reinforcement.

Polyphenylene sulfide has proven difficult to plate by standard electroless and electrolytic plastic plating methods. In the case of the present invention, the support is etched with argon plasma under reduced pressure conditions and then a titanium layer and a copper layer are sequentially sputtered on one side of the support, or more typically on both sides, without breaking the reduced pressure. This has revealed that the adhesion between the copper layers plated on the polyphenylene sulfide support is enhanced. An RF energy source is used to etch the non-conductive polyphenylene sulfide support and a DC power source is used to sputter the metal film.

For a detailed description of the sputtering process and its application, see R.S. F. " Decomp by Bunshah et al.
position Technologies for
Film and Coatings : Develo
pments and Applications ,
Noyes Pub. , 1982 "and J. A. Tho
"" Sputtering ", En by rnton
cyclopedia of Polymer Scie
nce and Engineering , 9, p.
598, Wiley-Interscience,
1987 ". The use of plasma to modify the surface of materials and enhance adhesion between materials is described in H.S. V. " Fundamentals of Plasma C " by Boening
Chemistry and Technology ,
Technical Pub. Co. , 1988,
pp. 155-193, 283-306 ". As a manufacturing process, sputtering has very little impact on the environment. The only by-product of the process of the invention is a small amount of inert gas (Ar) and any solvent can be used for surface cleaning of the parts to be coated. The process of the present invention can be easily automated, which increases reproducibility from process to process and minimizes operator dependence on part characteristics.

After sputtering the titanium layer and the first copper layer onto the surface of the support, and also into the pores of the support if pores are present, an adhesive electrocoat of copper is deposited on the prepared surface. Formed, the peel strength of this coating is 4.5 to 5.5 pounds per inch.

In a preferred process for plating a polyphenylene sulfide support in accordance with the present invention, FORTRON ™ having 0.030 "holes.
Samples of 1/16 "substrates made of polyphenylene sulfide (65% glass / mineral filled) were first washed with soap and water to remove a significant amount of contaminants, then rinsed in acetone and then methanol. Washed. Ultrasonic cleaning was used to enhance the effectiveness of the solvent.The sample was subsequently blast dried and then placed in the sputtering chamber.
Sample 2 of dried polyphenylene sulfide
It was placed in the sputtering chamber 1 of the MRC-902 DC-magnetron sputtering system. The sputtering chamber 1 is an integral device, which can maintain a constant vacuum over the entire surface of the sample 2 from the time the polyphenylene sulfide sample 2 is etched to the time it is vacuum coated with titanium and copper.

The washed polyphenylene sulfide sample 2 was put into the chamber 1 through a load-lock chamber at one end of the chamber 1, and a 12 "× 12" pallet 4 was placed in the chamber 1.
Then, it was sent to the etching station 5, the titanium sputtering station 7, and the copper sputtering station 8 sequentially. At etching station 5, the sample was exposed to argon plasma for etching. In this case, only argon plasma was used to etch the support, but other inert gases can also be used. An RF energy source 6 was used to etch the non-conductive polyphenylene sulfide sample 2. The etching conditions are shown in Table I. The total reduced pressure is preferably 10 mTorr or less. In chamber 1, etching was performed while sample 2 was kept stationary at the etching position. However, the support may be rotated during the plasma treatment to ensure uniform and sufficient exposure. While being held in the etching position, the substrate 2 was exposed to argon plasma for about 30 seconds.

[0025] Etching the surface with a plasma prior to the coating operation is the final step in cleaning and preparing the substrate surface prior to applying the metallization. That is, an RF or DC potential (if used) is applied to the support so that the surface to be coated is the target of ion bombardment. This makes it possible to remove the most difficult to remove atomic scale contaminants that would otherwise interfere with the adhesion of the metal coating if such an operation were not performed. This plasma etching can also change the surface chemistry and morphology by selective etching of elements or modification of atom-atom bonds on the surface. The introduction of reactive species (eg oxygen) into each step can have a greater impact on the surface chemistry.

The same apparatus 1 used during the etching operation was used to transfer the etched substrate 2 under the sputtering targets 7 and 8 without breaking the vacuum. During this transfer, a titanium layer is sputtered from the activated titanium target 7 onto the substrate 2, a titanium layer is sputtered into the substrate 2 through the holes, and a titanium layer is deposited and then an activated copper target 8 is deposited. A copper layer was sputtered onto the titanium layer and into the substrate 2 through the holes. This copper layer provides an overplating layer on the titanium layer that is easily plateable and has a strong bond. A DC power supply was used for sputtering the metal layer. Coating parameters for titanium and copper layers
The parameters are shown in Table II. The titanium and copper layers were deposited to a thickness of 1000Å to ensure complete coverage. A thickness of at least about 200-300Å is required. The preferred thickness is 500 to 1000Å.
Larger thicknesses can be used, but at the expense of manufacturing cost and benefit.

[0027] Argon gas and oxygen (if used) are measured by an accurate electronic flow meter (electronic flow control meter).
A control meter), a valve 10 for argon gas, and a valve 11 for oxygen were used to introduce into chamber 1. The main throttle valve 13 was used and the operating temperature was maintained by the vacuum pump 12. The pressure of argon is preferably below 10 mtorr.

After applying a copper layer on the titanium coating at the copper sputtering station 8, the vacuum was released. The copper coated polyphenylene sulfide support was then exposed to ambient atmosphere and electroplated with 0.002 ″ copper.
Any conventional electroplating method can be used.

For comparative testing, the effect of plasma treatment on the adhesion of the coatings was investigated using three different etching environments (no etching; etching with argon; and etching with (argon + O ₂ )). . After exposure to one of these etching environments, a sample of polyphenylene sulfide substrate was sputtered with the titanium layer only, the copper layer only, or the titanium layer and the copper layer. The sputter coated sample was then electroplated with an additional copper layer. As described in detail below, the Sebastian adhesion test (Sebastian)
n adhesion test) and tensile test (pul)
l test) was used to evaluate all of the copper-plated samples.

The Sebastian adhesion test involves attaching epoxy coated nail studs to plated polyphenylene sulfide samples. The pin (stud) head has a diameter of 3.0 mm and the epoxy has 15
Cured at 0 ° C. Firmly support the sample, pull the stud perpendicular to the surface and record the force at break. This test has the advantage that it can be performed on fairly small test pieces.

A standard stripping test was performed on the 2.5 ″ × 2.5 ″ plaques of the electroplated polyphenylene sulfide samples as follows: A simple acid was applied to each sample after the sputtering procedure. Copper bath (a
Copper was electroplated from a cid copper bath to a metal thickness of about 0.002 ". Cut parallel to the plaque through the metal, 1.0" apart. A metal tab was pulled from the plastic at one end. A copper strip 1.0 "wide x 0.003" thick x 5.0 "long is glued to the tabs to give it sufficient length to attach to one jaw of an Instron tensile tester. Was clamped to a fixture that could be held by the other jaw of the Instron tester so that the strip being pulled remained perpendicular to the surface of the plaque during tensile testing. Designed to move. A 50 lb load cell was used and the pull rate was set at 1 inch / min. The results were recorded on a strip chart recorder using appropriate damping to obtain the desired full scale reading. The value was obtained and the chart speed was 2 inches / minute.

The results of the Sebastian and peel tests are shown in Table I.
Illustrated in II. The "Coating" section in Table III refers to the metal that is sputtered onto the surface of the polyphenylene sulfide support. The term "plasma etching" refers to the type of gas used in the plasma etching process. "Fracture mode Sebastian (FAI
LURE MODE SEBASTIAN) "shows where the metal coating broke in the Sebastian tensile test. Figure 2 shows the first titanium intermediate layer and copper without etching the vacuum and etching with argon plasma.
A reproduction of an Instron chart from a peel test obtained by sputtering coating a layer and then performing a second layer of copper on a polyphenylene sulfide support in electroplated form.

[0033] As can be seen in FIG. 2, the peel load for a polyphenylene sulfide support that has been etched, sputter coated with titanium and copper layers under reduced pressure conditions and copper plated begins at about 4.5 and is about the same during the pulling operation. It is maintained at 5.0 to 5.5. This indicates that a relatively uniform bond was obtained over the entire surface. The same test was repeated with similar results. Break Test-Loads ranged from 4 to 5 pounds. further,
A 1000 Å titanium intermediate layer and a first copper layer are sufficient for subsequent electroplating and, if coated from both sides during the sputtering operation, completely cover the sample pores (0.030 ″ diameter). Higher bond strengths may be obtained by applying different depths of etching, different interlayer compositions (eg, chromium and nickel), or thermal post-treatments.

These results further indicate that the adhesive strength of the coating can exceed the strength of the support material for certain process conditions. Titanium coatings on plasma-etched surfaces always showed adhesion strengths in excess of the cohesive strength of polyphenylene sulfide supports. The copper coating did not adhere like titanium, except in the case of (argon + O ₂ ) etching (measured by Sebastian test). Broadly speaking, a yield strength of 3 Ksi or less correlated with the metal film separated from the surface of the polyphenylene sulfide support. Value is about 5 Ksi
In the above cases, fracture generally occurred in the support material. The strength of the support material is determined by the small area contact pins of the Sebastian tester.
It was found to be variable in the range of 3.5 to 8.2 Ksi when using (pin).

It is important to note that this test method can affect the information obtained. For example, the Sebastian test uses a sample at 150 ° C.
Heating to cure the epoxy bond with the metal coating. This heating cycle will affect the bond between the metal and the polyphenylene sulfide in either the positive or negative direction.

A positive result from the Sebastian test is that the sputtered polyphenylene sulfide substrate can be exposed to at least 150 ° C. without significant loss of coating adhesion. On the other hand, a negative result is that when the curing temperature exceeds 150 ° C. by about 50 ° C., discoloration of the support and a clear decrease in adhesive strength occur. Therefore, the processing of the substrate after the plating operation may be temperature limited if the bond strength of the coating must be maintained at a satisfactory level.

In the case of the peel test, the plating process is metal /
It is believed that it affects the bonding of the polyphenylene sulfide interface and that the thickness of the sputtered film plays a role in such effects. In addition to the effect of the thickness of the sputtered coating,
Observed peel-test load
It can be seen that ad) strongly depends on the thickness of the plating layer. This point was held constant in the set tests by keeping the deposition conditions and deposition time constant.

As can be seen from the above, the present invention is
Provided are methods of plating copper on a polyphenylene sulfide support, and products made by such methods.

Although the present invention has been described in terms of a preferred embodiment, it will be appreciated by those skilled in the art that various modifications and improvements can be made without departing from the spirit, scope and disclosure of the invention. .

[Brief description of drawings]

FIG. 1 is a schematic diagram of a sputtering system used in the method of the present invention.

FIG. 2 is a copy of an Instron chart showing the load-distance relationship obtained in a peel test on a polyphenylene sulfide support plated with copper according to the method of the present invention.

Claims (14)

[Claims] 1. A method for plating copper on a polyphenylene sulfide support, comprising: (a) etching the surface of the support with RF argon plasma in a vacuum; (b) without breaking the vacuum. Sputtering a layer of titanium on the surface of the etched support as an adhesion promoting intermediate layer, and sputtering a first copper layer on the titanium intermediate layer; and (c) the first copper layer. Electroplating a second copper layer thereon to a desired thickness. 2. The method of claim 1, wherein the vacuum is adjusted to a pressure of about 8-10 mtorr. 3. The method of claim 2, wherein the polyphenylene sulfide support is etched for about 30 seconds. 4. A DC power supply is used to sputter the titanium intermediate layer and the first copper layer.
The method described. 5. The titanium intermediate layer is about 200-1000.
The method of claim 1, having a thickness of Å. 6. The first copper layer is about 200-1000Å
The method of claim 1, having a thickness of. 7. The method of claim 1, wherein the steps are performed on both sides of the support simultaneously. 8. A polyphenylene sulfide support and a copper layer formed thereon, (a) etching the surface of the support with RF argon plasma in a vacuum; (b) breaking the vacuum. Sputtering a layer of titanium on the surface of the etched support as an adhesion promoting intermediate layer and then sputtering a first copper layer on the titanium intermediate layer; and (c) the first copper. Electroplating a second copper layer on the layer to a desired thickness; 9. A product as set forth in claim 8 wherein said vacuum is adjusted to a pressure of about 8-10 mtorr. 10. The article of claim 9, wherein the polyphenylene sulfide support is etched for about 30 seconds. 11. The article of claim 8, wherein a DC power supply is used to sputter the titanium interlayer and the first copper layer. 12. The titanium intermediate layer is about 200-100.
The product of claim 8 having a thickness of 0Å. 13. The first copper layer is about 200-1000.
The product of claim 8 having a thickness of Å. 14. A product as set forth in claim 8 wherein said steps are performed simultaneously on both sides of said support.