NL8700833A - Prodn. of printed circuit panel on insulating substrate - by forming pattern of material contg. metal nuclei, using spray head, followed by electroless metallising - Google Patents

Abstract

In prodn. of a printed circuit panel, by appln. to an electrically insulating substrate of a material contg. metal nuclei, in a pattern, where the metal nuclei have a catalytic effect on the formation of a metal in an electroless metallising bath. A conducting metal layer is deposited in the desired pattern in an electroless metallising bath. The material contg. metal nuclei is a nucleating liq. which is applied as droplets by means of a spray-head which is displaced in the desired pattern w.r.t. the substrate.

Description

r k% .. v «i PHN 12,081 1 N.V. Philips' Incandescent lamp factories.

"Method of Manufacturing a Printed Wiring Panel".

The invention relates to a method for manufacturing a printed wiring panel, in which a metal seed containing material is patterned on an electrically insulating substrate, which metal seeds act catalytically on the formation of a metal in an electroless metallization bath, after which an electroless metallization bath a conductive metal layer is deposited in the desired pattern.

United States Patent US 4504529 discloses a method in which a dielectric powder is patterned xerographically on a substrate and sensitized with a metal compound to allow electroless metallization in the desired pattern. Such a xerographic method is especially suitable for applying conductive patterns to flat substrates.

The object of the invention is to provide a method with which wiring patterns can also be produced in a simple manner printed on non-flat substrates. The object of the invention is to provide a method with which very narrow conductive tracks can be manufactured, for instance with a width of less than 100 µm. Another object of the invention is to provide an entirely additive metallization process that satisfies the stated conditions.

This task is fulfilled according to the invention by a method as described in the preamble, which method is further characterized in that the metal-germ-containing material is a dripping liquid which is applied in the form of drops by means of a spray head which is placed in the desired pattern is moved relative to the substrate.

The term metal germs here refers to both metallic germs and also germs which contain a metallic compound. Such germs can be sensitized in known manner for electroless metallization. The metal pattern will generally serve to provide electrical connections, but it can also be used for identification purposes, for example in the form of alphanumeric characters.

In a preferred embodiment of the method according to the invention, the drops are formed by pulses from a piezoelectric element. The viscosity of the sprouting liquid is preferably 0.5 to 100 mPa.s.

For example, a device with a movable piezoelectric nozzle is known for applications in inkjet printing units. US-A-4560584 discloses a type of similar device which is used for applying solder shielding lacquer to a printed circuit board.

In order to obtain a strong adhesion between the substrate and the patterned metal layer, it is expedient for the germination liquid to comprise a binder, for instance by applying an adhesive known per se. In addition, it may be necessary to etch the surface of the adhesive layer to make the metal seeds accessible to the electroless metallization bath.

In a suitable embodiment of the method according to the invention, the metal seeds consist of an organic metal compound, preferably an organic metal complex compound. It is known per se to use such compounds for this purpose, see for example published European patent application EP 166327, which describes a method according to which a substrate is completely covered with a metal layer in an electroless metallization bath, after which in a subtractive process a conductor pattern is manufactured. The said European patent application also describes means for sensitizing such compounds.

In a special embodiment of the method according to the invention, the germination liquid applied to the substrate is irradiated by means of a light guide, for instance an optical glass fiber. The light guide is preferably placed in a fixed position relative to the nozzle, for example attached to it. Adhesion to the substrate can be improved by the application of heat, and in some cases the germs can be activated by the application of light.

For applications in non-planar substrates, where a soldering process can be replaced by laser welding, for example, and where £V c. f · - :: -ξ r 5 PHN 12.081 3 when the substrate can be subjected to various shaping processes before or after the application of the conductor pattern, it is expedient that a thermoplastic plastic which is resistant to a temperature of at least at least a temperature is chosen as the substrate material. 180 ° c. Suitable substrate materials for the indicated purposes are, for example, polyiaide, polyetheriaide, polyether sulfone, polysulfone and polyvinylidene sulfide, with or without reinforcing materials such as glass fibers.

According to a preferred embodiment of the method according to the invention, wherein a good adhesion between the substrate 10 and the conductive metal layer is obtained, the substrate is chemically roughened before applying the germination liquid, for example by swelling the surface layer in a solvent. .

In an alternative embodiment of the method according to the invention, the substrate for applying the germination liquid is subjected to an irradiation treatment to render the surface hydrophilic, thereby improving the adhesion between substrate and metal layer. Suitable per se known irradiation treatments are an ultraviolet light treatment in ozone, a plasma treatment and a corona treatment.

If desired, the metal layer deposited in the electroless metallization bath can be galvanically reinforced. The measures of the various preferred embodiments of the method according to the invention can also be used in combination with one another.

In US patent US 4230788 a method of manufacturing printed wiring panels is disclosed in which a photosensitive material is applied to the substrate, after which germs are formed by exposure through a mask in the desired pattern, which catalytically act on the formation of a metal in an electroless metallization bath. The use of a mask has made this method unsuitable for manufacturing very narrow metal tracks, for example with a width of about 100 µm.

German patent DE 2319998 describes a method for manufacturing printed wiring panels, in which liquid metal drops are applied at high temperature from a movable spray head to a substrate. The track gauge ii · ··, f- - · t / PHN 12.081 4 has not been reported, and due to the high temperature of the molten metal, this method is less suitable for application on thermoplastic substrates.

Exemplary embodiments of the method according to the invention are explained with reference to a drawing, in which Figure 1 is a schematic longitudinal section through a nozzle with piezoelectric element, suitable for use in the method according to the invention,

Figure 2 is a schematic cross section through an alternative nozzle with piezoelectric element suitable for use in the method according to the invention,

Figure 3 is the structural formula of the repeat unit of a polyether sulfone, and wherein

Figure 4 is the structural formula of the repeat unit 15 of a polyetherimide.

In Fig. 1 a tubular nozzle is shown in cross-section, comprising a thin-walled glass tube 10 and a piezo-ceramic tube 13 arranged around it. The outside and inside of the piezoceramic tube 13 are respectively connected to electrical connecting wires 14 and 15. One end of the glass tube 10 is connected by means of a hose 16 to a storage vessel not shown in the figure, in which the germination liquid is located . At the other end of the glass tube 10 there is a glass nozzle 18 (diameter of the opening, for example 0.08 mm), from which pulses of liquid droplets 19 generated by electrical voltage in the piezo-ceramic tube 13 spurt out at a speed of about 2 m / s and a frequency which can be values up to 10 kHz. The tubular nozzle is especially suitable for use with liquids that have a viscosity greater than 5 mPa.s, preferably between 20 and 30 mPa.s.

Figure 2 shows in cross-section a planar nozzle, which comprises a basic body 20, for example of steel, which is provided with a pressure chamber 21 which is covered with a membrane 22, for example also of steel. On the diaphragm 22 is mounted a piezoelectric disk 23, which is electrically connected to connecting wires 24 and 25. The pressure chamber 21 is connected by means of a hose 26 to a storage vessel not shown in the figure, in which the view is located. n: f: ~ \ * \ * * 'PHN 12.081 5 t liquid. The spray head is provided with a cover plate 27, therein an opening 28 (diameter, for example 0.05 mm) from which, under the influence of pulses generated by electrical voltage in the piezo-ceramic disc 23, liquid droplets 29 spray out at a speed of approximately 2 m / s and a frequency which can be values up to 10 kHz. Between the base body 20 and the cover plate 27 there is a base body 30 of plastic, which is provided with a pressure channel 31, which connects the pressure chamber 21 and the opening 28 to each other. The planar nozzle is suitable for use with liquids having a viscosity greater than 0.1 mPa.s.

Pit feed incs example 1.

According to this example, polyether sulfone is used as substrate material for the printed wiring panel to be manufactured.

Other suitable substrate materials are polyetherimide, polyimide, poly sulfone and polyvinylene sulfide. The substrate material can be used in the form of a flexible foil or a rigid plate, and if desired be reinforced with fillers such as glass fibers. The substrate can also have a non-planar, three-dimensional shape.

The polyether sulfone film, see Figure 3, for example

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Victrex 300P type, commercially available from ICI, is subjected to an ultraviolet irradiation treatment in an ozone atmosphere to render the surface hydrophilic. A plasma or corona treatment can also be used with good results for this purpose.

The surface of the film is then roughened by immersing it in a mixture of 80% by weight dimethylforamide and 20% by weight isopropanol for 5 seconds and then rinsing with water and dilute hydrochloric acid (10% by volume).

With the aid of a tubular nozzle, see figure 1, germination liquid is applied to the foil in the desired pattern, for which purpose the nozzle is displaced relative to the surface of the foil in an automated process, for instance computer-controlled. To produce a printed wiring pattern on a non-planar substrate, the nozzle must be movable in three independent directions, and the nozzle may need to be rotatable to also change the spray direction.

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The germination liquid used according to this example contains 4.5 grams of palladium (II) chloride, 100 grams of tin (II) chloride and 500 ml of hydrochloric acid (36%) per liter of water. 50 volume% ethylene glycol has been added to this liquid to slightly increase the viscosity. Another suitable sprouting liquid containing the same components is MetexR activator 9070M, commercially available from MacDermid.

The foil is treated with a 10% by weight solution of formaldehyde in lye (1 N NaOH), whereby the germs are activated. Then, in 30 minutes, a layer of 2-gauge copper is deposited in an electroless seller bath of the following composition: 0.3 M copper (II) nitrate, 0.05 M of the tetrasodium salt of ethylenediamine tetraacetic acid, 0.05 M sodium hydroxide, and 0.06 M formaldehyde.

For example, the copper bath Metex1 * 9027, commercially available from MacDermid, can also be used for this purpose.

To obtain good adhesion, the foil is dried at a temperature of 100 ° C for 2 hours. The conductor tracks are then amplified in a galvanic process, for example with copper to a layer thickness of 30 µm. Instead of copper, or in addition to it, nickel can also be applied, if desired, both galvanically and electrolessly. A nickel top layer is particularly suitable when electrical components are to be attached by laser welding, which may be the case with a non-flat substrate, for example. Because polyether sulfone is transparent, it is possible to irradiate the weld 25 through the substrate.

Pit lining example 2.

A polyetherimide foil with 20% by weight glass

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fibers, see Figure 4, for example, type 2200, commercially available from the General Electric Company, are corona treated to render the surface hydrophilic. Instead of a corona treatment, a treatment with an oxidizing acid, for example a mixture of nitric acid and hydrofluoric acid, may also be used for that purpose.

The surface of the foil is then roughened by immersing it in dichloromethane for 10 seconds and then rinsing with water and dilute hydrochloric acid (10 volume%).

1. PHN 12,081 7

Using a plenary nozzle, see Figure 2, germination liquid is applied to the foil in the desired pattern, see example 1. The germination liquid used according to this example is an acid-free, colloidal copper solution containing 1 to 2 grams of copper per liter. A suitable germination fluid of this type is RonacatR Catalyst M, commercially available from Leo Ronal.

The foil is treated with a 10% by weight solution of formaldehyde in lye, which activates the germs. Then, a layer of copper with a thickness of 30 µm is deposited in a flowless seller bath, for example in RonadepR 100, commercially available from Deo Ronal.

The foil is then dried, as indicated in example 1. If desired, a nickel or tin layer can be deposited on the copper layer in a known manner for protection. Other metals, such as gold, can also be used.

Output example 3.

A film of unfilled polysulfone, for example of the type UdelR 1700, commercially available from Union Carbide, 20 is subjected to a corona treatment to render the surface hydrophilic.

Using a tubular nozzle, see example 1, germination liquid is applied to the foil in the desired pattern. According to this example, the seed liquid consists of a colloidal mixture of tin and palladium, to which 5% by weight of an acrylic resin has been added as binder. Other suitable binders include, for example, acetate butyrate resins, cellulose acetate, polyester and materials of the same composition as the thermoplastic substrate.

After being dried, the adhesive layer (binder with 30 metal seeds) is opened to make the metal seeds accessible, for example by testing with a basic solution of MnO 2. The metal seeds are then activated, for example with a basic solution of formaldehyde.

Then, a 30 µm thick copper layer is deposited at 50 ° C in 10 hours, after which the printed wiring panel is dried and, if desired, provided with additional metal layers.

After mechanical operations such as drilling and milling, r '- "r'

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.0 12.081 8 τ connection wireless electrical components mounted on the printed wiring board. The components are soldered using a solder paste at a temperature of 215 ° C, after which it can be determined that the adhesion of the copper layer to the substrate is still sufficiently strong.

Output example 4.

This example is followed as in example 3, with the difference that instead of metallic tin and palladium germs 10 an organic palladium compound is used, for example 4-cyclohexene-1,2-dicarboxylic acid imide-palladium (II) chloride. Such compounds are described, for example, in published European patent application EP 166327. After opening the adhesive layer, the organic palladium compound is decomposed to form metallic palladium. Such a reduction can be performed with a liquid or vapor reducing agent, for example formaldehyde, or under the influence of ultraviolet light irradiation.

With the method according to the invention it is possible to produce printed wiring panels in a clean and simple process with a high degree of reliability. Very narrow metal tracks, for example up to 70 µm, can be produced. Since non-flat substrates can also be used, it is possible to obtain a very high packing density, wherein the substrate combines electrical and mechanical functions, and can for instance form part of the casing of a device.

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Claims (10)

1. A method for manufacturing a printed wiring panel, in which a metal germ-containing material is patterned on an electrically insulating substrate, which metal germs act catalytically on the formation of a metal in an electroless metallization bath, after which a gel is deposited in an electroless metallization bath. The metal layer is deposited in the desired pattern, characterized in that the metal seed-containing material is a sprouting liquid which is applied in the form of drops by means of a spray head which is displaced in the desired pattern relative to the substrate. Method according to claim 1, characterized in that the drops are formed by pulses from a piezoelectric element. A method according to claim 2, characterized in that the viscosity of the germination liquid is 0.5 to 100 mPa.s. Method according to claim 1, characterized in that the germination liquid comprises a binder. Method according to claim 4, characterized in that the metal seeds consist of an organic metal compound, preferably an organic metal complex compound. Method according to claim 1, characterized in that the germination liquid applied to the substrate is irradiated by means of a light guide. 7. A method according to claim 1, characterized in that a thermoplastic plastic which is resistant to a temperature of at least 180 ° C is chosen as substrate material. A method according to claim 7, characterized in that the substrate is roughened up chemically before applying the germination liquid. 9. A method according to claim 7, characterized in that the substrate for applying the germination liquid is subjected to an irradiation treatment to render the surface hydrophilic. 10. A method according to claim 1, characterized in that the metal layer deposited in the electroless metallization bath is galvanically reinforced. P f:;