GB1588998A - Process and article for printed circuit board manufacture - Google Patents

Description

(54) PROCESS AND ARTICLE FOR PRINTEL) CIRCUIT BOARD MANUFACTURE (71) We, KOLLMORGEN TECH NOLOGIES CORPORATION of Republic National Bank Building, Dallas, Texas 75201, a corporation duly organized and existing under the laws of the State of Texas, United States of America do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to the formation of articles which are useful in the production of printed circuit boards in accordance with the so-called "build-up" method. More particulary, this invention provides an insulating article having a layer of copper, the surface of which has been micro-roughened to improve the adhesion of masking materials, and which optionally comprise an oxide layer which protects the micro-roughened surface during storage and shipment.

The production of printed circuit boards by the so-called "build-up" method is known in the art. In this method, an insulating carrier or base material, e.g., a molded laminate, is provided with a thin layer of copper having a thickness of, for example, from 0.5 to 8 microns, preferably from 1 to 3 microns. After the application of a layer of masking material on selected areas of the copper surface, the desired pattern of conductor lines is built up on the unmasked areas by the galvanic or electrolytic deposition of copper and, if desired, other metals; the thin layer of copper acts as the current supply. After electrolytic deposition, the layer of masking material is removed and the thin layer of copper in the previously masked areas, which are now exposed, is treated to decompose it.

The initial layer of copper may be applied to the surface of the carrier material by known methods, such as by pressing a preformed copper foil thereon, preferably during the production of the carrier material itself. Alternatively, the copper may be applied by means of electroless metal deposition, vapor deposition or other known methods. In order to avoid deep etching of the conductor lines, which is especially undesirable in the case of narrow conductor lines, the layer of copper on the other areas must have a very small thickness. Such minute thicknesses also have a favorable effect upon the etching step with respect to lowering manufacturing costs.

In order to satisfactorily achieve better adhesion, the copper surface and masking material, e.g., a masking ink applied by screen printing, a photographic printing varnish or liquid-sensitive dry film, and moreover to avoid the formation of blisters in the masking layer during electrolytic deposition and the like, it has been proposed to chemically etch the copper surface and thus macroroughen it. Such prior art methods have a number of disadvantages, however, ranging from their great complexity and poor economy to insufficient reliability. In addition, these methods are not practical in the case of thin copper layers.

The present invention provides a method of manufacture wherein the reliability of adhesion of the masking layer to the copper surface is assured, and the formation of blisters in said masking layer is avoided; at the same time, the surface of the copper layer is protected. Unlike prior art method all of this is accomplished without decomposing the copper layer.

In its broadest aspects, this invention provides a method for manufacturing a base material covered with a thin copper layer useful in the production of printed circuit boards which is provided with a masking material to protect those areas from copper deposition which do not correspond to the conductor pattern, the method for manufacturing such base material comprising that said base material is contacted with a. finely divided abrasive material by feeding said base material through one or more pairs of rollers under pressure together with said finely divided abrasive material in suspension in water.

This invention also provides articles comprising an insulating base and a layer of copper thereon having a micro-roughened surface, the microroughening having been achieved chemically or mechanically, or both, as described above.

In accordance with this invention, the oxidizing and mechanical treatments may be used individually, or they may be used in combination in successive steps or simultaneously. When both treatments are used in succession, it is preferred that the oxidizing treatment follows the mechanical abrasion treatment, but this is not critical and the reverse sequence may also be employed.

The oxidizing treatment also results in the formation of a protective film of oxide on the surface of the copper layer, which protects said surface against mechanical damage, fingerprints, and the like, during further processing. The article protected by this oxidizing layer may thus be stored as such without danger for prolonged periods of time, or it may be used immediately by applying a layer of masking material. The masking material adheres reliably to the copper surface pretreated in accordance with this invention and shows no tendency toward the formation of blisters.

The oxide layer is removed later on during processing, e.g., by immersion in dilute sulfuric acid, or by the use of conventional oxide-cleaning techniques.

For the mechanical treatment, the carrier material having a thin layer of copper thereon is fed between a pair, preferably a plurality of pairs of rollers, the rollers having been provided with a coating of rubber or other suitable resilient material. At the same time, an aqueous suspension of finely divided material, such as quartz flour or glass dust, is fed to the rollers or to the copper surface. The micro-roughening is achieved by the pressing of the finely divided material against the copper surface.

After microroughening, the finely divided abrasive material is cleaned from the copper surface, e.g., by flushing with water at high pressure.

For the chemical treatment, an aqueous solution comprising sodium chlorite, trisodium phosphate and sodium hydroxide is preferred. Such solutions may also contain conventional additives, such as wetting agents and the like. A specific example of a suitable oxidizing solution consists of, per liter, 160 grams of sodium chlorite, 10 grams of trisodium phosphate and 10 grams of sodium hydroxide, the balance being water, and preferably distilled water.

A suitable commercially available product for the oxidizing treatment is "Ebanol" (RTM).

It is especially preferred to combine the chemical and mechanical treatments, and to add the solution of oxidizing agent to an aqueous suspension of the finely divided abrasive material.

Other modifications and variations are possible in the light of the above disclosure.

It is to be understood, therefore, that changes may be made in the particular embodiments described herein which are within the full intended scope of the invention as defined in the appended claims.

WHAT WE CLAIM IS: 1. A method for manufacturing a base material covered with a thin copper layer useful in the production of printed circuit boards which is provided with a masking material to protect those areas from copper deposition which do not correspond to the conductor pattern, characterized in that said base material is contacted with a finely divided abrasive material by feeding said base material through one or more pairs of rollers under pressure together with said finely divided abrasive material in suspension in water.

2. A method as claimed in claim 1 characterized in that the copper surface is protected by an oxide layer which protects the copper surface during storage until the masking material is applied.

3. A method as claimed in claims 1 or 2 characterized in that the surface of the copper layer is treated with an oxidizing agent which contains an abrasive material.

4. Method as claimed in claim 3 characterized in that the oxidizing agent contains a mixture of sodium chlorite, trisodium phosphate and sodium hydroxide in a watery solution.

5. Method as claimed in claims 3 and 4 characterized in that the oxidizing solution contains 160 girl sodium chlorite 10 g/l trisodium phosphate 10 g/l sodium hydroxide in water 6. Method as claimed in claim 1 characterized in that the finely divided abrasive material is suspended in water.

7. Method as claimed in claim 1 characterized in that the abrasive material is selected from among quartz flour, glass dust or a mixture thereof.

8. Method as claimed in claim 1 characterized in that the rollers comprise a resilient material.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (8)

**WARNING** start of CLMS field may overlap end of DESC **. surface, the microroughening having been achieved chemically or mechanically, or both, as described above. In accordance with this invention, the oxidizing and mechanical treatments may be used individually, or they may be used in combination in successive steps or simultaneously. When both treatments are used in succession, it is preferred that the oxidizing treatment follows the mechanical abrasion treatment, but this is not critical and the reverse sequence may also be employed. The oxidizing treatment also results in the formation of a protective film of oxide on the surface of the copper layer, which protects said surface against mechanical damage, fingerprints, and the like, during further processing. The article protected by this oxidizing layer may thus be stored as such without danger for prolonged periods of time, or it may be used immediately by applying a layer of masking material. The masking material adheres reliably to the copper surface pretreated in accordance with this invention and shows no tendency toward the formation of blisters. The oxide layer is removed later on during processing, e.g., by immersion in dilute sulfuric acid, or by the use of conventional oxide-cleaning techniques. For the mechanical treatment, the carrier material having a thin layer of copper thereon is fed between a pair, preferably a plurality of pairs of rollers, the rollers having been provided with a coating of rubber or other suitable resilient material. At the same time, an aqueous suspension of finely divided material, such as quartz flour or glass dust, is fed to the rollers or to the copper surface. The micro-roughening is achieved by the pressing of the finely divided material against the copper surface. After microroughening, the finely divided abrasive material is cleaned from the copper surface, e.g., by flushing with water at high pressure. For the chemical treatment, an aqueous solution comprising sodium chlorite, trisodium phosphate and sodium hydroxide is preferred. Such solutions may also contain conventional additives, such as wetting agents and the like. A specific example of a suitable oxidizing solution consists of, per liter, 160 grams of sodium chlorite, 10 grams of trisodium phosphate and 10 grams of sodium hydroxide, the balance being water, and preferably distilled water. A suitable commercially available product for the oxidizing treatment is "Ebanol" (RTM). It is especially preferred to combine the chemical and mechanical treatments, and to add the solution of oxidizing agent to an aqueous suspension of the finely divided abrasive material. Other modifications and variations are possible in the light of the above disclosure. It is to be understood, therefore, that changes may be made in the particular embodiments described herein which are within the full intended scope of the invention as defined in the appended claims. WHAT WE CLAIM IS:

1. A method for manufacturing a base material covered with a thin copper layer useful in the production of printed circuit boards which is provided with a masking material to protect those areas from copper deposition which do not correspond to the conductor pattern, characterized in that said base material is contacted with a finely divided abrasive material by feeding said base material through one or more pairs of rollers under pressure together with said finely divided abrasive material in suspension in water.

2. A method as claimed in claim 1 characterized in that the copper surface is protected by an oxide layer which protects the copper surface during storage until the masking material is applied.

3. A method as claimed in claims 1 or 2 characterized in that the surface of the copper layer is treated with an oxidizing agent which contains an abrasive material.

4. Method as claimed in claim 3 characterized in that the oxidizing agent contains a mixture of sodium chlorite, trisodium phosphate and sodium hydroxide in a watery solution.

5. Method as claimed in claims 3 and 4 characterized in that the oxidizing solution contains 160 girl sodium chlorite 10 g/l trisodium phosphate 10 g/l sodium hydroxide in water

6. Method as claimed in claim 1 characterized in that the finely divided abrasive material is suspended in water.

7. Method as claimed in claim 1 characterized in that the abrasive material is selected from among quartz flour, glass dust or a mixture thereof.

8. Method as claimed in claim 1 characterized in that the rollers comprise a resilient material.