KR100899588B1 - Use of metallic treatment on copper foil to produce fine lines and replace oxide process in printed circuit board production - Google Patents

Abstract

The present invention relates to the manufacture of printed circuit boards with improved etching uniformity and resolution. This process eliminates the need for black oxide treatment to improve adhesion and improve the ability to optically inspect printed circuit boards. The process includes (a) depositing a first surface of an electrically conductive layer on a substrate having a first surface and a rough second surface opposite thereto; (b) depositing a thin metal layer of a material having a different etching resistance from the electrically conductive layer on the rough second surface of the electrically conductive layer, wherein steps (a) and (b) are performed by (a) )-> (b) or (b)-> (a). A photoresist is then deposited on the metal layer; The photoresist is exposed to an image shape and developed to reveal portions of the underlying metal layer. By removing the exposed portion of the underlying metal layer, thereby revealing the portion of the conductive layer located below it; The exposed portion of the underlying conductive layer is removed to produce a printed circuit layer.

Description

USE OF METALLIC TREATMENT ON COPPER FOIL TO PRODUCE FINE LINES AND REPLACE OXIDE PROCESS IN PRINTED CIRCUIT BOARD PRODUCTION}

The present invention relates to the manufacture of a printed circuit board with improved etching uniformity and resolution. The method according to the present invention eliminates the need for black oxide treatment to improve adhesion and improve the ability to optically inspect printed circuit boards.

Printed circuit boards are widely used in the field of electronics. These printed circuit boards are useful for large scale applications such as missiles and industrial control equipment as well as small scale applications such as telephones, radios and personal computers. In particular, when using a printed circuit, it is important to ensure the good performance of the circuit by increasing the precision and resolution for very small lines and space widths (about 100 μm or less).

In the manufacture of small and large scale equipment, the ability to produce precise features with very small dimensions on the order of 100 μm or less is very important. As circuit patterns become smaller, the accuracy of the etching process becomes more important. It is well known in the art to use known photolithography techniques to manufacture printed circuit boards with small features with high precision. Generally, an electrically conductive foil is deposited on a substrate and then a photoresist is deposited on this foil. The photoresist is then exposed to an image shape and developed to form small lines and spaces of a predetermined pattern. These small lines and spaces are then etched up to the conductive foil.

Typically the matte side of the foil is laminated onto the substrate because the matte side of the foil is rougher than the glossy side of the foil and has better adhesion to the substrate. However, it has been found that laminating the foil to the substrate with the glossy side down allows for more precise etching, since the copper crystals are oriented vertically near the matte surface and are long, resulting in less side etching or horizontal etching. Because. In addition, the need for excessive etching to remove the tooth structure and the treatment agent from the substrate is further eliminated, resulting in better uniformity of etching.

When laminating the glossy surface of the foil on the substrate, it is necessary to roughen the surface to provide sufficient adhesion. One way to do this is to plate a nodule on the glossy surface of the copper foil. One example of this type of copper product is the name MLS available from Oak-Mitsui Inc, based in Dessert Falls, NY. Another method is used to deposit a roughened layer, such as a nodule, on each side of the foil to form a "double treated" foil. Using this process results in better resist adhesion and also excludes oxide processes. This is undesirable in industry as the roughening layer of the exposed side of the foil may be damaged during handling.                 

If the matte surface is in contact with the laminate, another known method of roughening the polished surface is chemical microetching (sodium persulfate, available from MacDermid, Waterbury, Connecticut, or Shipley Ronel, Marborough, Mass.). Or copper foil in advance by using sulfuric acid / hydrogen peroxide) or pumis scrubbing (a machine sold by IS in Italy and Isioki in Japan). The surface is then chemically treated to deposit a layer of black copper oxide (also available from MacDermid and Shipley Ronel), allowing other insulating substrates to be deposited on the circuit. This chemical treatment sequence is undesirable because it is cumbersome and results in waste disposal issues associated with the chemicals used. Therefore, there is no problem related to the dual processing of the conductive foil in the art, there is no need for black oxide processing during the processing of the multilayer circuit board, and there is a need for a method of etching lines and spaces of the circuit with high resolution and precision. .

There is a continuing effort in the art to improve the technology of manufacturing circuit boards to improve the precision of their features. For example, US Pat. No. 5,240,807 teaches a photoresist article having a built-in etching mask that is portable and comfortable for enhancing image contrast and reproducing very small dimensions. A portion of the conductive foil located below the photoresist is selectively etched to form circuit lines of a predetermined pattern. U. S. Patent No. 6,042, 711 discloses another technique for providing a metal foil having a metal layer composed of a powdery dendritic deposit and a metal flash layer and having improved peel strength. International application publication WO 00/03568 also discloses a method of forming circuit lines on a substrate by coating a rough conductive metal layer with a copper foil carrier.

U. S. Patent No. 5,679, 230 discloses another technique for providing a copper foil for use in the manufacture of a printed circuit board. This copper foil can be used to make multilayer circuit boards without requiring conventional black oxide treatment to improve adhesion.

The present invention provides a technique for depositing a thin metal layer (metal thin film layer) on a conductive layer on a substrate to solve the problems of the prior art. This metal layer acts as an etching mask during the etching of the conductive layer and improves the precision and resolution of the etching. After etching, the thin metal layer remains on the conductive layer, eliminating the need for an oxide layer.

In addition, the metal layer used in this method has high uniformity and reflectivity, so that the printed circuit formed by this method is more compatible with automatic optical inspection equipment than the prior art printed circuit. In addition, the metal layer used herein has high mechanical strength and high resistance to mechanical damage such as surface scratches and drag marks.

The present invention relates to a method for manufacturing a printed circuit layer, the method

(a) depositing on the substrate a first surface of an electrically conductive layer having a first surface and a rough second surface opposite thereto;

(b) depositing a thin metal layer of a material having a different etching resistance from the electrically conductive layer on the rough second surface of the electrically conductive layer,                 

(c) depositing a photoresist on the metal layer;

(d) exposing and developing the photoresist in the form of an image to reveal portions of the underlying metal layer;

(e) removing the exposed portions of the underlying metal layer to reveal portions of the conductive layer located thereunder;

(f) fabricating the printed circuit layer by removing the exposed portions of the underlying conductive layer.

It includes, and the steps (a) and (b) may be performed in the order of (a)-> (b) or (b)-> (a).

In addition, the present invention,

(a) depositing on the substrate a first surface of an electrically conductive layer having a first surface and a rough second surface opposite thereto;

(b) depositing a thin metal layer of a material having a different etching resistance from the electrically conductive layer on the rough second surface of the electrically conductive layer,

(c) depositing a photoresist on the metal layer;

(d) exposing and developing the photoresist in the form of an image to reveal portions of the underlying metal layer;

(e) removing the exposed portions of the underlying metal layer to reveal portions of the conductive layer located thereunder;

(f) removing the exposed portions of the underlying conductive layer

Wherein the steps (a) and (b) are performed on the printed circuit layer manufactured by the method, which may be performed in the order of (a)-> (b) or (b)-> (a). It is about.

The present invention generally provides a method for manufacturing a printed circuit layer and a printed circuit board.

In carrying out the method according to the invention, the first step is to deposit a layer of electrically conductive material on a suitable substrate. Typical substrates are those suitable for processing into printed circuits or other microelectronic devices. Suitable substrates for the present invention include, but are not limited to, polymers reinforced with materials such as glass fibers, Kevlar, aramid paper, polybenzoxoleate paper, or mixtures thereof. Of these, epoxy reinforced with glass fibers is the most preferred substrate. Also suitable are semiconductor materials, for example gallium arsenide (GaAs), silicon, and silicon-containing compositions such as crystalline silicon, polycrystalline silicon, amorphous silicon, epitaxial silicon, silicon dioxide (SiO ₂ ), and mixtures thereof. Etc. The thickness of the substrate is preferably from about 10 μm to about 200 μm, more preferably from about 10 μm to about 50 μm.

The conductive layer preferably comprises a material such as copper, zinc, brass, chromium, nickel, aluminum, stainless steel, iron, gold, silver, titanium or mixtures or alloys thereof. Most preferably, the conductive layer is a copper foil.

The copper foil is preferably produced by electrodepositing copper on a rotating metal drum from solution. The side of the foil facing the drum is generally a smooth or glossy side, while the other side has a relatively rough surface and is also known as a matt surface. Drums, usually made of stainless steel or titanium, act as a cathode and receive copper when it is deposited from solution. In general, the anode consists of a lead alloy. A cell voltage of about 5-10 volts is applied between the anode and the cathode to deposit copper, during which oxygen is released from the anode. The copper foil is then separated from the drum, cut to the required size and laminated onto the substrate. It is desirable to perform lamination for about 30 minutes in a press of at least about 175 ° C. The press is under a vacuum atmosphere of at least 28 inHg and is preferably maintained at a pressure of about 150 psi.

It is desirable, but not necessarily, to deposit the micronodule of a metal or alloy by electrolytically treating the glossy side of the copper foil to form a rough copper deposit and electrolytically treating the matte side. Not necessarily. These nodules are preferably copper or copper alloys and do not increase the surface roughness but increase the adhesion to the substrate. The microstructure of the foil surface is measured by a profilometer, such as Perthometer model M4P or S5P, available from Mahr Feinpruef Corporation, Cincinnati, Ohio. The surface morphology of the peak and valley surface structures is outlined in Section 2.2.17 of the industry standard IPC-TM-650, Institute for Interconnecting and Packaging Circuits, 2115 Northbrook Sanders Road, 60062, Illinois, USA. Is measured accordingly. In this measurement procedure, the measurement length Im is chosen with respect to the sample surface. Rz is defined as the average of the maximum mountain height versus bone height of five consecutive sample lengths (Io = Im / 5) within the range of the measurement length Im. Rt is the maximum roughness depth and is the maximum vertical distance between the highest peak and the lowest valley within the measurement length Im range. Rp is the maximum leveling depth and the height of the highest mountain in the measurement length (Im) range. Ra (average roughness) is defined as the arithmetic mean value of all absolute distances from the centerline of the roughness profile within the measurement length Im range.

Important parameters in the present invention are Rz and Ra. Surface treatment results in a surface structure with acid and valleys and a roughness parameter Ra of about 1 μm to about 10 μm and Rz of about 2 μm to about 10 μm.

When surface treatment is carried out, the surface structure has acid and valleys on the polished surface and the roughness parameter Ra is about 1 μm to about 4 μm, preferably about 2 μm to about 4 μm, more preferably about 3 μm to about 4 μm. Is formed. The Rz value is about 2 μm to about 4.5 μm, preferably about 2.5 μm to about 4.5 μm, more preferably about 3 μm to about 4.5 μm.

When surface treatment is carried out, the surface structure has acid and valleys on the matte surface and the roughness parameter Ra is about 4 μm to about 10 μm, preferably about 4.5 μm to about 8 μm, more preferably about 5 μm to about 7.5 μm. Is formed. The Rz value is about 4 μm to about 10 μm, preferably about 4 μm to about 9 μm, more preferably about 4 μm to about 7.5 μm.                 

The glossy surface has a copper deposit of about 2 μm to 4.5 μm thick, and preferably has an average roughness Rz of 2 μm or more. The matte surface preferably has a roughness Rz consisting of about 4 μm to 7.5 μm. The micronodule of the metal or alloy is about 0.5 μm in size. If desired, other metals such as zinc, indium, tin, cobalt, brass, bronze, etc. may be deposited as the micro nodules. Such methods are described in more detail in US Pat. No. 5,679,230, which is incorporated herein by reference. The peel strength of the glossy surface is from about 0.7 kg / linear cm to about 1.6 kg / linear cm, preferably from about 0.9 kg / linear cm to about 1.6 kg / linear cm. The peel strength of the matte surface is from about 0.9 kg / linear cm to about 2 kg / linear cm, preferably from about 1.1 kg / linear cm to about 2 kg / linear cm. Peel strength is measured according to Industry Standard IPC-TM-650 Section 2.4.8 Revision C.

The thickness of the conductive layer is preferably about 0.5 μm to about 200 μm, more preferably about 9 μm to about 70 μm. The conductive layer may also be coated on the substrate using other well known metal deposition methods such as electroless deposition, coating, sputtering, deposition or lamination.

It is also desirable to electrolytically treat both sides of the foil with a thin metal layer, although this is not necessarily the case, and this treatment is preferred prior to lamination, but it is not necessary. Preferably, the metal layer is electrolytically deposited on the conductive layer. In addition, the metal layer may be deposited on the conductive layer (after lamination to the substrate) by coating, sputtering, vapor deposition or lamination. The metal layer is a thin film and preferably includes a material selected from nickel, tin, palladium, platinum, chromium, titanium, molybdenum, alloys thereof, and the like. Most preferably, the metal layer comprises nickel or tin. The thickness of the metal layer is preferably about 0.01 μm to about 10 μm, more preferably about 0.2 μm to about 3 μm. This metal layer acts as an etching mask to form a predetermined pattern of circuit lines and spaces that are etched into the conductive layer.

Once the metal layer is deposited on the conductive layer, the next step is to selectively etch away a portion of the metal layer and form an etch pattern on the metal layer. This etching pattern is formed by well known photolithography techniques using photoresist compositions. First, the photoresist is deposited directly on the thin metal layer. Photoresist compositions are either positive or negatively functional and are generally commercially available. The main function of the resist is to form only a thin metal layer and do not have to withstand harsh etching conditions, so the resist can be very thin (5-20 μm). This enables better resolution. Suitable positive functional photoresists are well known in the art and may include o-quinone diazide radiation sensitizers. o-quinone diazide radiation sensitizers are described in US Pat. No. 2,797,213; 3,106,465; 3,106,465; 3,148,983; 3,130,047; 3,201,329; 3,785,825; And o-quinone-4 (or 5) -sulfonyl-diazide as disclosed in US Pat. No. 3,802,885. When o-quinone diazide is used, preferred binder resins include water-insoluble binder resins, aqueous alkali-soluble binder resins, swellable binder resins, and the like. Novolak is preferable. Suitable positive photodielectric resins include, for example, those sold under the trade name AZ-P4620 by Clariant Corporation, Sommerville, NJ, and Shipley's I-line photoresist. Negative photoresist is also widely available.

The photoresist is then exposed to active radiation, such as visible light in the spectrum, light in the ultraviolet or infrared region, in the form of an image through a mask, or image shape by electron beam, ion beam, neutron beam or X-ray radiation. Is scanned. The actinic radiation can be in the form of non-interfering light or interfering light, such as, for example, light from a laser. Thereafter, the photoresist is developed in the form of an image using a suitable solvent such as an aqueous alkaline solution, so that the portion of the metal layer located below is exposed.

As a result, the exposed portions of the underlying metal layer are removed through well known etching techniques, but the portions located below the residual photoresist are not removed. Suitable etchant includes, but is not limited to, an acidic solution such as cupric chloride (preferably for etching nickel) or nitric acid (preferably for etching tin). Ferric chloride or sulfuric acid peroxide (hydrogen peroxide including sulfuric acid) is also preferred. During this step, the portion of the conductive layer underlying the metal layer to be etched away is exposed. The patterned metal layer thus forms a high quality etching mask for etching the conductive layer with high precision and accuracy.

Next, the exposed lower portion of the conductive layer is removed by etching, but the portion of the conductive layer located below the remaining portion of the metal layer is not removed. Suitable etchant includes, but is not limited to, alkaline solutions such as ammonium chloride / ammonium hydroxide. Thereafter, the circuit board is cleaned and dried. As a result, the printed circuit board has excellent uniformity, resolution and performance.

In another preferred embodiment in which the metal layer comprises nickel, a one pass etching process may be performed. In this embodiment, after the image is formed and developed in the photoresist, the exposed portion of the metal layer and the electrically conductive layer located below it can be etched in a second copper etchant respectively. In the case of etching another metal layer comprising tin, the suitable etchant cannot adequately etch the conductive foil located below, so a second etching step is still necessary. The single etching step is suitable for etching lines or spaces of about 3 mils or more. In addition, when using a single etching step, it may be necessary to increase the time to stay in the etchant, possibly 10% to 25%, depending on the etching system. Higher spray pressures and temperatures can achieve the same results. After etching the circuit lines and spaces through the metal and conductive layers, the residual photoresist can be selectively removed from the surface of the metal layer by stripping off the remaining photoresist with an appropriate solvent or by ashing by well-known ashing techniques. In addition, after etching the metal layer, but before etching the conductive foil, the photoresist may be removed.

In a preferred ashing process, the plasma is generated in a microwave plasma generator disposed upstream of the stripping chamber, and the stripping gas passes through the generator and enters the reactive paper stripping chamber formed from the gas in the plasma. Plasma ions are separated from the plasma group by filtration or the like. As used herein, the term "radical" is intended to define neutral particles, such as molecular fragments or atoms, generated by the upstream plasma generator. The plasma generator may include any plasma generator known in the art. Plasma generators capable of supplying groups substantially free of ions or electrons are disclosed, for example, in US Pat. Nos. 5,174,856 and 5,200,031, the contents of which are incorporated herein by reference. Generally, any type of commonly generated plasma may be used in the practice of the present invention, but using a plasma generated by a microwave plasma generator, such as a model AURA plasma generator commercially available from GaSonics, San Jose, CA, may be used. desirable. Another upstream plasma generator capable of supplying a substantially electron- and / or ion-free group is commercially available from Applied Materials under the name Advanced Strip Passivation (ASP) Chamber. Plasma ahser is also commercially available from Mattson Technology, Fremont, California. In addition, by using in-situ ashing in an etching chamber such as that sold by Tokyo Electron Ltd. under the name TEL DRM 85, the ashing can be performed by an anisotropic method.

In this regard, other insulating substrates can be deposited on the circuit without further roughening steps and without the black oxide treatment of the matte side of the foil. The thin metal layer does not need to be removed after etching, serves as an oxide substitute and provides sufficient adhesion to form a multilayer structure. In addition, the metal layer is more uniform and reflective than the conductive foil alone, and is easily inspected using well-known automated optical inspection (AOI) equipment.

The following non-limiting examples illustrate the invention well.

Example 1

The glossy side of the copper foil is treated with a copper nodule and the Zn-Cr boundary layer is covered. The matt surface is also treated with nodule, but later with nickel. The foil is laminated on the glass fiber impregnated with epoxy (with a glossy surface in contact with the material) to form a substrate. The substrate is coated with a liquid photoresist with a thickness of 12 μm and exposed to ultraviolet light through a mask to form an image. Potassium carbonate is used to develop the photoresist and expose the nickel surface. Nickel is removed using cupric chloride etching to expose the copper below. The copper is etched using a system based on ammonia to form traces. The photoresist is removed using a sodium hydroxide solution. Holes are punched around the substrate based on the image pattern. These holes are used for matching. The trace is inspected using an automatic optical inspection machine and repaired if necessary (if possible). The finished substrate with etched traces (cores) is laminated between the epoxy glass fibers with another core (if necessary) and the copper foil (outer). These printed circuit board "blanks" are drilled, external circuits are formed, and solder masks and solders are completed. The completed board is then inspected and assembled.

Example 2

Example 1 is repeated except that the matte side of the laminate abuts the substrate and is treated with Zn-Cr. The polished surface is plated with nodules as in Example 1, but is treated with nickel.

Example 3

Example 2 is repeated except that the polished surface is microetched and roughened prior to treatment with nickel.

Example 4

Example 2 is repeated except that the polished surface is roughened by fumig scrubbing prior to treatment with nickel.

Example 5

Example 1 is repeated except that the photoresist is of permanent nature and is not removed after etching.

Example 6

Example 1 is repeated except etching in one step with cupric chloride.

Example 7

Example 1 is repeated except that the photoresist is exposed using a direct laser imaging system.

Example 8

Example 1 is repeated except that tin is plated instead of nickel and etching is performed with nitric acid.                 

Example 9

Copper foil is prepared by electrodepositing copper from solution onto a rotating metal drum according to example 1 of US Pat. No. 3,293,109. The copper is dissolved in sulfuric acid and then electrodeposited at a temperature of 40-60 ° C. in a solution consisting of copper in the form of 70-105 g / L copper sulfate and 80-160 g / L free sulfuric acid. The solution comes in contact with a rotating metal drum, usually made of titanium, which acts as a cathode and receives copper when copper is deposited from the solution. The anode consists of alloy lead. A cell voltage of about 5-10 volts is applied between the anode and the cathode to deposit copper, during which oxygen is released from the anode. The copper forms on the drum a continuous copper film with a thickness of about 18 μm to 70 μm, which is removed by dividing into the required width and finally wound on a roll. The side of the foil facing the drum is smooth ("glossy surface"), while the other side has a relatively rough surface ("matte surface").

The glossy or matte side of the copper foil sample is treated according to US Pat. No. 5,679,230 to form a surface nodule. The glossy or matte side of another copper foil sample is micro etched with cupric chloride. The surface roughness and peel strength of the copper sample are measured. Surface roughness is measured according to IPC-TM-650 Section 2.2.17, and peel strength is measured according to IPC-TM-650 Section 2.4.8 Revision C. Note the following results.

Copper foil side process Surface Roughness (Ra) (μm) Peel Strength * (kg / linear cm) Polished cotton none 0.25 <0.18 " Micro etching 1.20 0.39 " Nodule 3.56 1.52 Matte surface none 5.08 0.63 " Micro etching 5.72 0.93 " Nodule 7.60 1.91

* Peel strength was measured by laminating copper on an epoxy prepreg.

This simulates the peel strength inside the finished circuit board.

While the invention has been described and described in detail with reference to preferred embodiments, those skilled in the art will readily appreciate that various modifications and changes can be made without departing from the spirit and scope of the invention. The claims will be construed to protect the disclosed embodiments, the foregoing modifications, and all equivalents thereto.

Claims (43)

As a method of manufacturing a printed circuit layer, (a) depositing on the substrate a first surface of an electrically conductive layer having a first surface and a rough second surface opposite thereto; (b) depositing a thin metal layer made of a material having a different etching resistance from the electrically conductive layer on the rough second surface of the electrically conductive layer; (c) depositing a photoresist on the metal thin film layer; (d) exposing and developing the photoresist in an image shape to reveal a portion of the metal thin film layer located below; (e) removing the exposed portions of the underlying metal thin film layer, thereby revealing portions of the conductive layer located thereunder; (f) fabricating the printed circuit layer by removing the exposed portions of the underlying conductive layer. Wherein the steps (a) and (b) are performed in the order of (a)-> (b) or in the order of (b)-> (a). The method of claim 1, wherein after performing step (a), step (b) is performed. The method of claim 1, wherein after performing step (b), step (a) is performed. The method of claim 1, wherein the step (a) is performed by first roughening the second surface of the electrically conductive layer, followed by treatment with a second metal, and then depositing the first surface of the electrically conductive layer on the substrate. Printed circuit layer manufacturing method. The method of claim 1, wherein step (a) is performed by first roughening the second surface of the electrically conductive layer and then depositing the first surface of the electrically conductive layer on the substrate. The method of claim 1, wherein step (a) is performed by first depositing the first surface of the electrically conductive layer onto the substrate and then roughening the second surface of the electrically conductive layer first. The method of claim 1, wherein the average roughness Ra of the second rough surface of the electrically conductive layer is 1 μm to 10 μm. The method of claim 1, wherein a micro nodule of metal or metal alloy is provided on or in the rough second surface of the electrically conductive layer. The method of claim 1, wherein the rough second surface of the electrically conductive layer is micro etched. After the steps (a) to (f) are repeated one or more times to produce a plurality of printed circuit layers, the plurality of printed circuit layers are attached to each other by one or more intermediate layers to form a printed circuit board. Composite manufacturing method containing. The method of claim 1, further comprising removing any residual photoresist after step (e). The method of claim 1, further comprising removing any residual photoresist after step (f). The method of claim 1, wherein the electrically conductive layer comprises an electrically conductive foil. The method of claim 1, wherein the metal thin film layer comprises a metal foil. The method of claim 1, wherein the conductive layer comprises a material selected from the group consisting of copper, brass, stainless steel, aluminum, nickel, and alloys and mixtures thereof. The method of claim 1, wherein the conductive layer is a copper foil. The method of claim 1, wherein the conductive layer is laminated on a substrate. The method of claim 1, wherein the conductive layer is deposited on the substrate by electrolytic deposition or electroless deposition. The method of claim 1, wherein the conductive layer is deposited on the substrate by coating, sputtering, or vapor deposition. The method of claim 1, wherein the metal thin film layer comprises a material selected from the group consisting of nickel, tin, palladium, platinum, chromium, molybdenum, titanium, and alloys and mixtures thereof. The method of claim 1, wherein the metal thin film layer comprises nickel. The method of claim 1, wherein the metal thin film layer comprises tin. delete The method of claim 1, wherein the metal thin film layer is deposited on the conductive layer by an electrolytic deposition technique or an electroless deposition technique. The method of claim 1, wherein the metal thin film layer is deposited on the conductive layer by coating, sputtering, or vapor deposition. delete delete delete delete delete delete delete delete (a) depositing on the substrate a first surface of an electrically conductive layer having a first surface and a rough second surface opposite thereto; (b) depositing a thin metal layer made of a material having a different etching resistance from the electrically conductive layer on the rough second surface of the electrically conductive layer; (c) depositing a photoresist on the metal thin film layer; (d) exposing and developing the photoresist in an image shape to reveal a portion of the metal thin film layer located below; (e) removing the exposed portions of the underlying metal thin film layer, thereby revealing portions of the conductive layer located thereunder; (f) removing the exposed portions of the underlying conductive layer Wherein the steps (a) and (b) are performed in the order of (a)-> (b) or in the order of (b)-> (a) Circuit layer. 35. The printed circuit layer of claim 34, wherein the electrically conductive layer comprises an electrically conductive foil. 35. The printed circuit layer of claim 34, wherein the metal thin film layer comprises a metal foil. 35. The printed circuit layer of claim 34, wherein the conductive layer comprises a material selected from the group consisting of copper, brass, stainless steel, aluminum, nickel, and alloys and mixtures thereof. The printed circuit layer of claim 34, wherein the conductive layer comprises a copper foil. 35. The printed circuit layer of claim 34, wherein the metal thin film layer comprises a material selected from the group consisting of nickel, tin, palladium, platinum, chromium, molybdenum, titanium, and alloys and mixtures thereof. 35. The printed circuit layer of claim 34, wherein the metal thin film layer comprises nickel. The printed circuit layer of claim 34, wherein the printed circuit layer is prepared by a process of performing step (a) and then performing step (b). The printed circuit layer of claim 34, wherein the printed circuit layer is prepared by a process of performing step (a) after performing step (b). delete