KR970004760B1 - Method of manufacturing printed circuit boards - Google Patents

Abstract

None.

Description

Printed Circuit Board Manufacturing Method

1a to 1f schematically show a cross section of an inner layer of a multilayer printed circuit board at different processing steps during the manufacturing process according to the invention.

2a to 2l schematically show the cross section of a multilayer printed circuit board at different processing steps during the manufacture of an outer layer with a through hole according to the invention.

* Explanation of symbols for main parts of the drawings

1, 20, 22: carrier substrate 2, 23, 24: copper foil

3, 31: Photoresist 8, 9, 34: Motorized path

25, 26, 27: conductive structure 28: through hole

29: the wall

The present invention relates to a method of manufacturing a printed circuit board in which a metal conductor structure is manufactured on an insulating material, for example, an electrostrip material carrier substrate, according to a desired pattern. In particular, the invention relates to a method of using a carrier substrate on which a metal foil, for example copper foil, is laminated on the surface.

Known methods for manufacturing printed circuit boards are known. For example, 1988, Mr. McGraw-Hill. F. Printed Circhits Handbook by C. F. Coombs, Jr (Editor); 1982, EP-A2-0150733, Eugene Ji. It is disclosed in publications such as Eugen G. Leuze Veriag, Handbuch der Leiterplattent entechnik by Kunther Hermann.

Print and etch methods are used, in particular, to produce one-sided printed circuit boards in which conductive paths are applied to only one side of a substrate, for example, a low packing density printed circuit board. The printing and etching method begins with a substrate of nonconductive material in which a copper layer is laminated on one or both sides of the substrate. The conductive structure of the printed circuit board may be applied, for example, by using screen-printing or photography (to apply, expose and develop a photoresist).

In manufacturing a double-sided printed circuit board or a multilayer printed circuit board, one of a subtractive method, a fully-additive method, or a semi-additive method is used. Can be.

The subtractive method starts with a copper-clad rusted carrier plate, for example an epoxy resin plate reinforced with glass fibers with copper foil on both sides of a plate typically having a thickness of 35 micrometers.

The inner layer of the multilayer circuit is first manufactured by applying a positive resist to the substrate. The resist is then exposed to light and developed according to the pattern of conductive structures produced on the substrate. The unhidden copper is then etched, the resist removed and the surface conductive path oxidized to form a protective layer. Finally, the inner layers so produced are pressed together into a package to form a multilayer circuit.

In order to create an inner layer with through holes, the outer layer of the multilayer circuit and the double-sided circuit developed according to the subtractive method requires some additional processing steps. First, a hole in which an electrical contact is formed is drilled. The walls of the through holes are metallized by chemical deposition of copper.

Next, the metallized wall of the through hole is reinforced. The conductive path is formed using a panel or pattern plating method. Finally, the outer layer is covered with a solder barrier layer.

The subtractive method suffers from the significant loss of copper since most of the relatively thick copper foil must be etched to create a conductive path. In addition, since it is inevitable that the bottom of the conductive path is etched, the subtractive method is limited to the production of conductive structures having a certain dimension, ie, the width and / or spacing of the conductive path, which is between 80 and 100 micrometers.

The pulley-additive method for manufacturing printed circuit boards is a subtractive method in that the starting substrate of insulating material is not covered with copper foil, but the substrate is a catalytic base laminate or covered with an adhesive. Is different. After drilling the through hole and applying the resist, the sleeve and the conductive path of the through hole are formed by chemical deposition of copper.

In the semi-additive method, the starting material is the same material used in the pulley-additive method. However, after drilling through holes, the entire surface of the substrate is covered with a thin layer of chemically deposited copper. Thereafter, a negative resist is applied and the walls of the through holes and the conductive structures are electroplated. After removing the resist, the thin copper layer between the conductive structures is etched.

As compared to the pulley-additive method, the semi-additive method has the advantage that the metal sleeve of the through hole consists of electroplated copper with substantially increased ductility. The disadvantage is that there are more process steps. The disadvantage of the pulley-additive method in view of the subtractive method is the poor adhesion of the conductor structure on the substrate, which is an insulating material. The advantage of the additive method in the light of the subtractive method is that the additive method in principle produces a finer conductor structure.

British Patent No. 1,056,814 discloses a method of manufacturing a printed circuit board having conductive passages through an insulated carrier substrate. In this method, the wall of the through hole is made exclusively conductive by electroless metal deposition. The method includes a sensitizing step, in which during the deposition of the electroless metal on the wall of the through hole, the wall is treated with a photosensitive solution at least to ensure good adhesion of the metal to the wall. The metal layer is also deposited on the conductive path on the surface of the insulated carrier substrate to roughen that path.

It is an object of the present invention to produce a printed circuit board having a width and separation between the conductor structures to produce a thin conductor structure of 50 micrometers or less, while at the same time providing a good attachment of the conductor structure on the insulating carrier substrate. To provide a way.

According to the invention, this object is solved by providing an insulating carrier substrate on which metal foil is laminated on its surface, and by producing the final conductor structure by chemical metal deposition in the pattern of the conductive paths corresponding to the desired pattern. Such a conductive path is made as the base layer portion of the metal foil first laminated to the carrier substrate. The deactivation step is carried out by washing with patterned conductive pathways and prior to chemical metal deposition, for example with hydrochloric acid. In this step, any material other than the conductive path on the insulating carrier substrate is removed to prevent the deposition of metal between the paths.

The present invention is based on the discovery that metal foils are pre-laminated and that very thin conductor structures can be obtained when the foils use a carrier substrate that is substantially thinner than the foils used in conventional subtractive methods. According to the invention, the finally required cross section of the conductor structure is produced by electroless chemical deposition of metal on a thin metal foil pattern. During the chemical metal deposition step, no catalyst (activator) or resist is provided on the substrate such that the metal is deposited only on the pattern of the previously generated metal pathway. In addition, the chemical metal deposition step ensures that any defects in the pattern of conductor paths generated in the previous step are compensated for. Such defects may be due to narrowed or scratched portions in the conductor path caused during the manufacturing of the pinhole or conductor path in the thin metal foil laminated to the circuit board. As a result of chemical metal deposition, a uniform final conductor structure is obtained without scratching. Since the metal foil forming the base layer of the conductor structure has been firmly laminated to the carrier substrate, it is ensured that the final conductor structure is well attached to the carrier substrate. The use of thin metal foil enables precise etching of the desired pattern, thus enabling the fabrication of fine conductor structures of small dimensions. According to the method of the present invention, it becomes easy to achieve a conductor structure having dimensions of 50 micrometers or less so that printed circuit boards of very high mounting density can be manufactured.

According to one aspect of the invention, the required conductor cross-section is a composition of a chemical bath that immerses a printed circuit board for chemical metal deposition by adjusting the time during which chemical metal deposition takes place to form the final conductor structure. Can be generated by appropriately selecting. The required cross section may be determined by the required ohmic resistance of the final conductor structure, or the impedance requirement or the requirement regarding the heat dissipation of the current carrying conductor.

The method of the present invention can be used to make a single sided printed circuit board or to produce an inner layer of a multilayer printed circuit board without through holes or an outer layer of a multilayer printed circuit board comprising metallization of the through holes.

According to a preferred embodiment of the present invention, a pattern of conductive paths is formed on a substrate having a thin metal thin layer by photography, in which the photoresist layer is applied on the metal foil, exposed according to the desired pattern and then etched. It is developed by the process. The use of thin resist layers also contributes to the achievement of thin conductor structures.

According to another embodiment of the invention, the resist is a wet laminated dry resist. Alternatively, it would also be possible to use liquid resists.

In the manufacture of printed circuit boards with through holes, it is advantageous to provide an intermediate step of electroplating the walls of the through holes, since the DC electrically deposited metal ensures higher ductility. This is important because the through holes can be subjected to increased mechanical stress, especially during soldering.

Metals deposited during chemical metal deposition can be copper, nickel or nickel and gold. The use of nickel or nickel / gold has the advantage that the thickness of the electroplated copper layer at the walls of the through-holes can be kept smaller than if low ductile copper was used to form the final layer of the printed circuit board because of the good ductility of nickel. Has In addition, nickel / gold finishes applied on solder pads have some advantages over copper finishes when electronic components are bonded to a printed circuit board.

In one embodiment of the present invention, after a chemical metal deposition step, a solder mask is applied to a printed circuit board, and the solder mask is exposed and developed to produce a pattern of a solder barrier layer. In this embodiment, the only parts that remain free of solder barrier on the surface of the substrate are where the electronic components are soldered or glued and through holes. Subsequently, chemical metal deposition is performed in that empty portion, ie on top of the chemically deposited metal layer. Preferred metals used for this final metal deposition are nickel, or nickel / gold.

In addition, the present invention does not require any special material as an insulating carrier substrate and has the advantage that materials and materials inherently known in various process steps can be used. Moreover, no solvent is needed, including chlorinated hydrocarbons, so the whole process is ecologically beneficial. According to another advantage, the desired cross section of the final conductor can be achieved in an easy manner by correspondingly adjusting the chemical metal deposition period. This is especially important when there are stringent requirements regarding the impedance of conductor structures on printed circuit boards.

Embodiments of the present invention are described in detail as follows with reference to the drawings.

1 shows the method of the present invention for producing an inner layer of a multilayer printed circuit board without a through hole.

Referring to FIG. 1A, a circuit board made in accordance with the present invention starts with a carrier plate 1 of insulating material such as epoxy resin, polyimide or cyanate ester reinforced with glass fibers. The plate 1 covers both sides of the thin copper foil 2 which is intimately bonded to the carrier plate 1 by all known processes.

For example, it is possible to start with an insulating substrate in which a thin layer of copper foil is laminated with good adhesion. The thickness of the copper foil 2 is selected according to the desired dimensions of the conductor structure to be applied to the substrate. According to a practical embodiment, the thickness of foil 2 may be 17.5, 10 or 5 micrometers.

In the next step shown in FIG. 1B, a photoresist layer 3 is applied onto the copper foil 2 on both sides of the substrate. Any known type of photoresist may be used. In one embodiment of the present invention, an aqueous alkali dry photoresist layer is wet-loaded onto the copper layer 2 on both sides of the substrate.

The resist 3 is exposed by an intaglio mask, using all known processes, which have a pattern of conductor structures to be applied to the substrate. Thereafter, the relief image is developed according to a method which is essentially known in the manufacture of printed circuit boards. The result is shown in FIG. 1C, wherein reference numerals 4 and 5 denote portions of the pattern of the photoresist corresponding to the pattern of the desired conductive path. Then, the portion of the copper foil 2 not covered by the resists 4 and 5 is etched by any known process, so that the structure of the structure shown in FIG. It is formed into a pattern. The etching solution may be, for example, a hydrogen chloride solution of copper chloride.

After etching, it is preferable to completely clean the position on the surface of the substrate 1 not covered with the resist 5 so as to deactivate the substrate by cleaning with an appropriate solution so as not to contain any contaminants such as metallic foreign matter. Do. The reason for this deactivation step is that any residue left on the substrate from the preceding step may act as a nucleus of unwanted metal growth in the subsequent step of electroless metal deposition (described in connection with Figure 1f). The reaction (wash) solution is preferably concentrated hydrochloric acid.

By washing with hydrochloric acid, it has been found by the present invention that the copper (1) chloride obtained in the etching step (Fig. 1d) can be dissolved as a chlorine compound and removed from the substrate. Washing with hydrochloric acid also removes any residues due to contaminated chemicals such as ferric chloride. Moreover, metal (iron, nickel) wear and dust (calcium sulfate) are removed by this cleaning step. As a result of the deactivation step, no foreign matter is present on the surface of the insulating carrier substrate 1 between the patterns of the conductor structures 8 and 9 covered with the resists 4 and 5.

Thus, in the step of chemical metal deposition described next with respect to FIG. 1f, the metal will only be deposited on the conductor pathway but not between them.

The result is shown in the step of FIG. 1E, in which the resist is removed by any suitable method used in the manufacture of a printed circuit board. At this time, the insulating carrier substrate 1 is covered with a pattern of conductive paths 8, 9 having a thickness of the metal foil 2 first stacked on the substrate 1.

Finally, copper is chemically deposited on top of the conductive paths 8, 9 to form the desired final cross section of the conductor on the substrate.

The result is shown in FIG. 1f showing the chemically deposited layers 10, 11 on top of the copper layers 8, 9. For this process step, an additive bath known for chemical copper deposition can be used. Since the substrate was not provided with a catalyst or reactant, and the space between the conductors was cleaned with a deactivator such as hydrochloric acid so that there was no foreign matter that could act as a nucleus due to metal deposition on the insulated carrier substrate, copper was an initial etching step. It is deposited only on the portions 8, 9 of the first copper foil 2 which has been etched in. The rest of the substrate 1 remains free of copper. It has been found that by using the method of the present invention, a uniform conductive path of small dimensions can be created. In the foregoing description, the generation of conductors was described on only one side of the substrate, but it should be appreciated that, as can be seen from FIG. 1, the pattern of conductors can be produced on both sides of the substrate by the method.

After etching, copper residues may remain in the carrier substrate region outside the desired conductive paths 8, 9. This situation, for example, results in a relatively finely processed laminated copper foil 2 such that the surface of the foil in contact with the substrate is not at all rough so that all portions of the foil disposed between the desired conductor structures can be etched cleanly. It can be overcome by using.

It should be noted that the method described in connection with FIGS. 1A-1F can be used for the production of a single layer printed circuit board having conductor structures on one or both sides of the substrate or for the manufacture of an inner layer of a multilayer printed circuit board without through holes. .

In another embodiment of the present invention for producing the inner layer, an additional process step is applied to the steps shown in FIGS. 1a and 1b. This embodiment starts with a very thin copper foil 2 laminated on both sides of the carrier substrate 1, for example a copper foil having a thickness of about 5 micrometers. Then, for example, a copper layer having a thickness of 3 to 5 micrometers is deposited on the copper foil 2 by electroless method. In the next step a photoresist is applied over copper similar to that shown in Figure 1b. Subsequent steps are the same as those described in the above embodiment described in connection with FIGS. 1b to 1f. Other embodiments described above may be used even if the initial copper foil 2 laminated to the insulated carrier substrate is very thin to include pinholes. The electroless copper deposition over the entire copper foil has the purpose to create a uniform copper layer without any defects.

It should be noted that various modifications are possible to the process of the two described embodiments of the present invention for making the inner layer. Since it is essential that the final conductor structure be produced by chemical metal deposition of a pre-generated conductive pathway pattern, the process begins with a carrier substrate on which a thin metal foil is laminated. With regard to the materials for producing the process steps and the pattern of the desired conductive pathways, many alternatives are possible.

Next, a process according to the present invention for producing an inner layer of a multilayer printed circuit board having through holes and an outer layer is described with reference to FIG. Figure 2a shows a multilayer package of a printed circuit board in which the conductive structure 25 comprises a first substrate 20 of insulating material preferably applied according to a process as described in connection with the first drawing. Copper foil 23 similar to copper foil 2 of FIG. 1 is laminated on the other side of the substrate 20. The second substrate 22 has conductive structures 26 and 27 on one side and a copper foil 24 on the other side. The adhesion layer 21 is sandwiched between the substrates 20 and 22.

The entire configuration is compressed together to form a package.

In the first step shown in FIG. 2B, the through hole 28 is drilled in accordance with the desired pattern. The wall 29 of the through hole is then activated, for example by nucleation due to palladium, resulting in chemical copper deposition. In the next process step, a relatively thin copper layer 30 (shown in FIG. 2C) is chemically deposited on the entire surface of the substrate, including the wall 29 of the through hole.

According to FIG. 2D, the photoresist layer 31 is applied to both sides of the substrate on top of the layer 30. The photoresist layer 31 may be the same as the photoresist layer 3 of FIG. 1B. The resist is then exposed by an embossed mask according to the pattern of the desired conductor structure to develop the negative image. That is, when the final conductor is formed, a portion 33 of the substrate is formed in which the edge 32 of the through hole 28 is not covered with the resist (see also FIG. 2E).

In the step according to FIG. 2F, the electroplating operation of the walls of the through holes and the voids 32 and 33 is performed in the resist layer 31. The conductive path 34 and the metallized walls and edges 46 of the through holes formed in this manner are then electroplated with metal resist layers 35 and 36, such as tin layers (Fig. 2g). Thereafter, the photoresist 31 is removed in a known manner (FIG. 2h).

According to FIG. 2i, the uncovered copper is etched using, for example, an ammonia alkaline etching solution, and then the metal resist 46 is removed (FIG. 2j). As a result, the substrate is now covered with a pattern of conductive paths, where portions 45 of the original copper foil 23 form a base layer. Thereafter, a cleaning operation with concentrated hydrochloric acid as described in connection with FIG. 1d is performed to remove all residues remaining from the insulating carrier substrate between the conductive paths.

Now, in accordance with an important step of the method of the present invention, the conductive path 37 and the conductive wall 36 of the through hole are subjected to chemical copper deposition. That is, copper 39, 40 is chemically deposited on paths 37, 38 to produce the final cross section of the conductor (FIG. 2K). Finally, a solder barrier layer 41 is applied to cover the portion of the substrate surface on which no metal is deposited. The creation of the conductor structure on the bottom face of the multilayer substrate and the creation of the conductor structure on the top face described above are done in the same way at the same time.

According to the practical practice of the present invention, when using copper foils 2, 23 having a thickness of 17.5 micrometers and resists 3, 31 having a thickness of 15 micrometers, dimensions of 50 micrometers or less are used. Having a conductor structure can be created. When chemical copper deposition (Figures 1f and 2k) is performed for about 3 1/2 hours, the thickness of the chemically deposited layer is about 12 micrometers, resulting in a total thickness of about 30 micrometers of conductor structure. do. It should be appreciated that various chemical baths may be used for the chemical copper deposition step so that the layer of desired thickness may vary depending on the chemical bath used. Although the thickness of conductor structures of about 30 micrometers is now common for printed circuit boards, the present invention can produce conductor structures of any desired thickness.

In an embodiment of the present invention, the layer 30 of chemically deposited copper (FIG. 2C) may have a thickness of about 2 micrometers, and the copper layer 34 applied during the electroplating step (FIG. 2F). May have a thickness of about 15 micrometers and the tin layers 35, 36 (FIG. 2g) may have a thickness of about 5 micrometers.

The copper bath in which the circuit board is immersed during chemical structure deposition is preferably an additive bath which typically comprises the following components: cupric salts, complexing agents, reducing agents, dyes, and stabilizers, such additive baths are known in the art. Known. For example, Additive Joe, available under the name ULTRAGANTH from the Company Schering AG of Berlin, West Germany. The additive bath can be optimized by harmonically selecting the aforementioned components to ensure that the final conductor structure has good hardness, good adhesion to the copper base layer, high conductivity, and low porosity. Generally speaking, the copper bath used should ensure that the deposited copper has a structure similar to the crystal structure of the electroplated copper. In an embodiment of the invention, this can be accomplished by selecting a concentration of cupric salt in an additive bath of less than about 0.05 moles per liter.

According to another embodiment of the present invention, essentially known chemical nickel baths may be used as the step of chemical metal deposition may include chemical deposition of nickel (instead of copper).

The use of nickel has the advantage of having greater ductility than copper, which increases the mechanical strength of the hole walls. Due to this increased strength, the electroplated copper layer applied on the wall in the preceding step can be minimized. In a practical embodiment, a 10 micrometer thick layer of nickel is chemically deposited on the copper structure, so that the surface of the copper structure acts to allow the nickel to adhere well to the copper. Finally, a thin gold layer, typically 0.1 to 0.15 micrometers thick, can be applied on the nickel layer by electroless deposition. The gold layer prevents nickel passivity and thereby ensures good solderability.

Nickel / gold finishes on solder pads have another advantage of being a very suitable finish for bonding (instead of soldering) electronic components to a substrate. Moreover, nickel provides a diffusion barrier layer for any adhesive metal. Nickel / gold finishes are also beneficial when removable pads are used. Since nickel has a relatively low corrosiveness, using a nickel or nickel / gold layer as the outer layer enclosed below the copper path contributes to the high reliability of the printed circuit board.

Other embodiments described above for making the outer layer of the multilayer printed circuit board or for making the inner layer with through holes in relation to FIGS. 2A-21 may, of course, vary only within the scope of the present invention. Again, as in the inner layer process described above, the final conductor structure and the final metallization of the through-holes are electrolessly deposited on the pattern created in the preceding process starting with thin metal foil laminated to the outer substrate. Generated by step.

According to another embodiment, the metal foil on the top and bottom layers of the multilayer package may be thicker than the thickness described in the previous embodiments. One reason to start with thicker metal foils may be, for example, because it is more expensive to manufacture an insulated carrier substrate coated with very thin foils.

In such a situation, the thickness of the metal foil is reduced by etching to a thickness that achieves the desired thin conductor thickness. Then, as in FIG. 2B, a through hole is drilled. As an alternative to the chemical copper deposition step shown in FIG. 2C, several successive process steps may be used, including the electroless deposition of a thin metal layer on the entire surface of the substrate and the walls of the through-holes, followed by electroplating of the metal surface. have. Then, in a process corresponding to FIG. 2d, a photoresist layer is applied on both sides of the substrate and developed to expose the resist corresponding to the pattern of the desired conductive path.

For the generation of conductive pathways, an embossed or negative photomask may be used. That is, the pattern of the developed photoresist may correspond to the empty space between the conductive paths or the pattern of the conductive path itself. Thereafter, the space between the developed photoresist and the wall portion of the through hole may be electroplated with a metal resist. Then, the photoresist is removed, the uncovered copper is etched and then the metal resist is removed. The final conductor path is produced by chemical metal deposition prior to the electroless metal deposition step. Preferably, a process of cleaning with hydrochloric acid is performed to remove any unwanted material from the surface of the insulated carrier substrate.

The solder mask is then laminated and exposed to the surface of the substrate and developed according to a predetermined pattern. As a result, the conductive paths and the spaces between them are covered with a solder barrier layer. Only the locations where the electrical components are soldered or glued to the substrate and the periphery of the through holes and through holes on the substrate surface lack the solder barrier layer. In the next step, the nickel layer is deposited on the void on the substrate (ie, the space not covered by the solder barrier layer) by the electroless method, and then the gold layer is deposited on the nickel layer by the electroless method. The nickel layer contributes to hardness and corrosion protection and the gold layer ensures good surface conductivity. In a practical example of this embodiment, the nickel layer has a thickness of 6 to 8 micrometers and the final gold layer has a thickness of 0.1 micrometer.

In another embodiment of the present invention, a negative mask was used to expose the photoresist. In such a case, the uncovered copper is etched and then the resist is developed. The photoresist is then removed before the final conductor pathway is created by chemical metal deposition.

In all embodiments, prior to the step of depositing the electroless metal on the conductive pathway, it should be ensured that the surface of the substrate without any conductors is deactivated, preferably by cleaning with hydrochloric acid.

In all embodiments, a solder mask may be applied last to the upper and lower surfaces of the printed circuit board or multilayer package to cover portions of the conductive paths and circuit surfaces where no metal is deposited. Alternatively, the solder mask may be laminated to the substrate and then exposed and developed prior to the chemical metal deposition step. The solder pattern is selected such that the conductive paths without any metal and portions of the substrate are covered with a solder barrier layer, but not the solder pads and through holes. Then, in the final stage of electroless deposition, only the solder pads and through holes are covered with additional metal layers, for example copper or nickel or nickel / copper.

Although the invention has been described and illustrated with reference to specific embodiments, those skilled in the art will recognize that changes and changes may be made without departing from the principles of the invention as described herein and as set forth in the claims that follow. Will recognize.

Claims (16)

A method of producing a printed circuit board having a metal conductive structure according to a desired pattern on a carrier substrate made of an insulating material, the carrier substrate having a metal foil laminated on a surface of the carrier substrate, the method comprising: the carrier substrate Forming a conductive pathway on the substrate; Deactivating the carrier substrate to substantially remove all deposited material except for the conductive pathways on the carrier substrate; Forming a final conductive structure as a base layer portion of the metal foil stacked on the carrier substrate by electroless chemical metal deposition on the pattern of the conductive pathways. The method of claim 1 wherein said deactivating of said carrier substrate comprises cleaning said hydrochloric acid said carrier substrate. The method of claim 1, wherein an inner layer of a single sided printed circuit board or a multilayered printed circuit board without through holes is prepared, and the step of forming the conductive path comprises: a) applying a photoresist layer on the metal foil; Wow; b) exposing the photoresist layer to radiation according to a desired pattern of conductive pathways; c) developing the photoresist layer; and d) etching a portion of the metal foil that is not covered with the photoresist. The method of claim 1, wherein an outer layer of the multilayered printed circuit board or an inner layer having through holes is manufactured, wherein forming the final conductor structure further comprises covering the wall of the through hole with a chemically deposited metal layer. How to. 5. The method of claim 4, wherein forming the final conductor structure further comprises electroplating the through hole, and then depositing a layer by electroless chemical metal deposition on the conductive path and the wall of the through hole. How to include. The method of claim 4, wherein the forming of the pattern of the conductive paths comprises applying the photoresist layer, exposing the photoresist layer to radiation according to the pattern of the conductive path, and the photoresist layer. Developing the method. The method of claim 1, wherein the thickness of the metal foil is less than approximately 17 micrometers. The method of claim 1, wherein the photoresist is a dry resist. The method of claim 8, wherein the thickness of the photoresist layer is less than approximately 15 micrometers. The method of claim 1, wherein the metal deposited on the conductive pathway by the electroless chemical metal deposition is copper. The method of claim 1, wherein the metal deposited on the conductive pathway by the electroless chemical metal deposition is nickel or nickel / gold. The method of claim 1, wherein the metal foil is copper foil. The method of claim 10, wherein forming the final conductive structure further comprises immersing the carrier substrate in an additive bath, wherein the additive bath comprises cupric salt at a concentration of less than about 0.05 mole per liter. The method of claim 1, further comprising: applying a photosensitive protective layer to the surface after the final conductive structure is formed by chemical metal deposition; Exposing and developing the photosensitive protective layer according to a predetermined pattern; Depositing a metal by electroless metal deposition on portions of the carrier substrate surface that are not covered with the exposed and developed protective layer. The method of claim 14, wherein the photosensitive protective layer is a solder mask. The method of claim 14, wherein the metal that is electrolessly deposited comprises nickel, further comprising depositing a gold layer on the nickel layer by electroless metal deposition.

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