Method for manufacturing printed circuit boards
The use of a capping metal and mask layer with laser ablation in printed circuit board manufacturing addresses environmental and efficiency issues of photoresist-based processes, achieving precise conductor tracks with reduced waste and lower costs.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- GEBR SCHMID GMBH & CO
- Filing Date
- 2021-07-15
- Publication Date
- 2026-05-19
AI Technical Summary
The existing manufacturing processes for printed circuit boards involve environmentally harmful photoresist materials that are not reusable, leading to complex and expensive waste treatment, and require additional steps for resist removal, which can cause deviations in conductor tracks due to temperature and pressure during pressing.
A method using a capping metal layer and a mask layer formed from metals and/or polymers with high chemical resistance, structured by laser ablation, allowing for the replacement of photoresist processes and enabling an environmentally friendly, cyclical manufacturing system.
This method reduces waste and manufacturing costs while achieving precise conductor track formation with reduced need for monitoring and correction, ensuring high resolution and compliance with impedance and signal speed requirements.
Smart Images
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Abstract
Description
Technical Field
[0001] The present invention described below relates to a method for manufacturing a printed circuit board and also to a printed circuit board manufactured by such method.
Background Art
[0002] A printed circuit board (hereinafter abbreviated as PCB) serves as a carrier for electronic components and ensures their electrical contact. Almost all electronic devices include one or more printed circuit boards.
[0003] A printed circuit board always includes a base substrate which is in a non-conductive form and at least one substrate surface thereof has a structure composed of conductor tracks (hereinafter abbreviated as conductor structures) for electrical contact of electronic components. Generally, the base substrate of a printed circuit board is made of fiber-reinforced plastic, polymer film or laminated paper. The conductor tracks are usually made of a metal such as copper.
[0004] In the simplest case, only one side of the base substrate has a conductor structure. However, more complex circuits often require multiple conductor track planes, in which case a multilayer printed circuit board (hereinafter abbreviated as multilayer substrate (MLB)) is required. In these cases, for example, conductor structures are provided on both sides of a carrier layer, or an MLB is formed by combining a number of base substrates each having one conductor track plane. Specifically, a base substrate provided with conductor structures on both sides can also form the basis of a multilayer structure. The conductor tracks of the various conductor track planes can be electrically connected to each other by vias. For this purpose, for example, holes can be drilled in the base substrate and the walls of the drill holes can be metallized.
[0005] Conductive structures are typically formed subtractively on a base substrate using photoresist (or simply resist) in a multi-stage photolithography process, and the solubility of the photoresist in the developer can be affected by radiation (more specifically, UV radiation). In one common procedure, a metal layer (usually a copper layer) is formed on the base substrate and covered with a photoresist layer. The photoresist layer can be laminated onto the metal layer, for example. Subsequently, in an exposure step, the photoresist layer is exposed to the aforementioned radiation, and subregions of the layer are protected from radiation exposure by an exposure mask. Depending on the photoresist and developer used, the exposed or unexposed subregions of the photoresist layer are readily soluble in the developer and can be removed in a downstream step (resist removal). In this downstream step (development step), subregions of the metal layer on the base substrate are not covered and can be removed wet chemically in a further downstream step (etching step). The remainder of the metal layer after the subsequent complete removal of the resist forms the desired conductive structure. This structure can be optionally reinforced during the deposition step, for example, by electrodeposition of a suitable metal.
[0006] Therefore, this manufacturing process dictates that the conductor tracks are located on the surface of the base substrate. In the case of MLB manufacturing, this can be disadvantageous. If the surface of the base substrate on which the conductor tracks are provided is pressed against another base substrate, monitoring and correction are often required thereafter due to deviations caused by temperature and pressure during pressing. Conductor tracks on the surface of the base substrate are particularly subjected to such stresses. Generally speaking, the smaller the distance and dimensions of the conductor tracks on the substrate, the greater the need for corresponding monitoring and correction, for example, with respect to existing impedance and signal speed requirements. [Overview of the project] [Problems that the invention aims to solve]
[0007] For environmental reasons, as explained, there are problems with the subtractive etching of metal layers formed on a base substrate. Commercially available photoresists are not reusable. The resulting waste liquid contains small amounts of organic compounds, and consequently, treating them in an environmentally friendly manner is complex and expensive. Moreover, many processes require the removal of the resist formed after subtractive etching in a separate process step. [Means for solving the problem]
[0008] The present invention was based on the objective of developing a procedure for manufacturing printed circuit boards that can avoid or at least reduce the problems described. To achieve this objective, the present invention proposes a method described below, and more specifically, a preferred embodiment of a process having the features of claim 1 described below. The development of the present invention is subject to the dependent claims. All claim expressions are incorporated into this description by reference.
[0009] The present invention's method for manufacturing a printed circuit board having a metal conductor structure always involves steps a. to e. described immediately after this, i.e., a. To provide a base substrate embodied as a film or plate, having a first substrate surface and a second substrate surface, and consisting at least partially of a non-conductive organic polymer material, wherein the first substrate surface is covered with a capping metal layer. b. Locally removing the capping metal layer and This includes locally removing the capping metal layer, c. Adhering the mask layer to the capping metal layer, d. Locally removing the mask layer with a laser, wherein the first substrate surface is divided into at least one first sub-region where the first substrate surface is covered only by the capping metal layer, and at least one second sub-region where the first substrate surface is covered by both the capping metal layer and the mask layer. e. Removing the capping metal layer of at least one first sub-region with an etching solution. This is achieved by [method]. The method is characterized in particular by the following steps: f. The mask layer is formed from a metal and / or metal compound and / or polymer material that has greater chemical resistance to the etching solution than the metal of the capping metal layer.
[0010] The present invention enables the replacement of conventional photoresist processes in PCB manufacturing. Instead of photoresist used in conventional methods, a mask layer is formed using metals and / or metallic compounds and / or polymer materials, which have the advantage of being structured by laser ablation techniques. The metal or metallic compound ablated in step d above can be removed, for example under suction, collected, and reused to form, for example, a further mask layer. Thus, the method of the present invention enables the environmentally friendly fabrication of printed circuit boards in a cyclical system.
[0011] In a preferred development of the present invention, the method is characterized by features a. to c. described immediately thereafter, namely, a. The capping metal layer is formed from copper, b. The etching solution is a solution for etching copper, c. The metal and / or metal compound and / or polymer material on which the mask layer is formed has greater chemical resistance to the etching solution than copper. It additionally includes at least one of the following. More preferably, steps a. to c. described immediately before this are implemented in combination with each other.
[0012] Those skilled in the art understand that the copper in question does not necessarily have to be ultra-high purity copper. Preferably in small amounts, the capping metal layer may optionally contain one or more other metals. Thus, the capping metal layer may also consist of copper alloys.
[0013] A suitable alternative to copper or copper alloys as a capping metal is, in principle, nickel-chromium alloys. In this case, the etching solution is a solution for etching the nickel-chromium alloy. In this case, the metal and / or metallic compound and / or polymer material on which the mask layer is formed must have greater chemical resistance to the etching solution than the nickel-chromium alloy.
[0014] In general terms, chemical resistance as used in this invention is understood to mean that a metal or alloy in contact with an etching solution has a low tendency to dissolve in the solution. Therefore, when in contact with an etching solution, one metal will be more chemically resistant than another, and will dissolve more slowly under the same conditions (specifically, the same etching solution and the same temperature).
[0015] The capping layer should be uninterrupted, regardless of the material it is composed of. Preferably, the capping layer has a thickness in the range of 10 nm to 10 μm, more preferably in the range of 20 nm to 6 μm. The etching solution is more preferably an etching solution based on copper chloride or ammonium persulfate. This is especially true when the capping metal layer is formed from copper or a copper alloy.
[0016] In principle, to form a capping metal layer, more specifically, it is possible to attach a thin metal foil, more specifically a thin copper foil, as a capping metal layer to the first substrate surface by lamination. However, the preferred method is steps a. to c. described immediately after this, i.e., a. In order to provide a base substrate, a capping metal layer is formed on the first substrate surface by physical vapor deposition (PVD) or chemical vapor deposition (CVD), b. The capping metal layer is formed on the first substrate surface by sputtering, c. The capping metal layer is formed by a wet chemical coating process. includes at least one of.
[0017] Metallization by physical and chemical vapor deposition, and the formation of metal layers by wet chemical coating processes or sputter deposition are state-of-the-art and do not require further explanation. As a specific preference, a copper layer is attached to the base substrate as a capping metal layer by sputtering. It may be preferable to attach an adhesion-promoting adhesive layer to the first substrate surface before forming the capping metal layer or while attaching the capping metal layer.
[0018] In a preferred development of the present invention, the method is the feature a. described immediately thereafter, namely, a. The metal and / or metal compound on which the mask layer is formed absorbs the radiation of the laser more strongly than the metal of the capping metal layer absorbs. additionally includes.
[0019] The laser used for removing the mask layer is preferably a laser having a wavelength in the range of 266 nm to 12 μm. Accordingly, it is particularly preferable that the mask layer is remarkable in that its light absorbency at a predetermined wavelength of the laser within this range is higher than the light absorbency of the underlying capping metal layer. This can be achieved specifically through the selection of an appropriate metal or an appropriate metal compound. Since the polymer material on the metal layer has relatively low heat resistance, it can be easily removed by laser exposure. The laser can be used in pulsed or continuous mode.
[0020] In a preferred development of the present invention, the method is the additional feature a. or b. described immediately thereafter, namely, a. The mask layer is formed from titanium or zinc, or b. The mask layer is formed from a metal oxide, a metal nitride or a metal carbide, more specifically, from titanium dioxide, titanium nitride or zinc oxide additionally includes.
[0021] Titanium and zinc have proven particularly suitable for capping metal layers of copper or copper alloys, not only in terms of chemical resistance but also in terms of light absorption. Titanium and zinc can be deposited onto substrates by, for example, sputtering or CVD, and are also reusable.
[0022] Certain compounds of titanium and zinc possess similar beneficial properties. Specifically, these include the titanium dioxide, titanium nitride, and zinc oxide materials already mentioned above. These materials have also proven particularly suitable for use in the context of the present invention, especially when using a copper mask layer.
[0023] In some preferred embodiments, the titanium and zinc used in the context of the present invention may contain impurities, such as doping elements. However, typically, the titanium and zinc have a purity of >95%, preferably >98%.
[0024] In some embodiments, within the context of the present invention, it may be preferable to form the mask layer from the aforementioned polymer materials, more specifically from non-photosensitive polymers. Particularly suitable in this context are mask layers made of polyamide or epoxy resin. However, in principle, any polymer material that can be removed from a metal surface by a laser is suitable.
[0025] In a preferred development of the present invention, the method incorporates additional features a. to e. described immediately thereafter, namely, a. The mask layer is formed with a thickness thinner than the capping metal layer, b. The mask layer has a thickness in the range of 5 nm to 10 μm or 10 nm to 10 μm, c. The mask layer is formed by physical or chemical vapor deposition, d. The mask layer is formed by sputtering, e. The mask layer is formed by a wet chemical coating process. It additionally includes at least one of the following. More preferably, steps a. and b. described immediately before this are implemented together with and in combination with one of features c., d., and e.
[0026] More preferably, the mask layer is formed with a thickness in the range of 5 nm to 1000 nm, more preferably 5 nm to 500 nm, and especially particularly 5 nm to 250 nm. This is especially true for embodiments in which the mask layer is formed from titanium, zinc, titanium dioxide, titanium nitride, and zinc oxide. When polymer materials are used, the layer may also have a thickness in the μm range (e.g., in the range of 2 to 10 μm).
[0027] In a particularly preferred first variant of the method, the method has feature a. described immediately after this, namely, a. After the capping metal layer is removed, the mask layer of at least one second sub-region is removed, and the capping metal layer remains in the second sub-region as a conductive structure or as part of a conductive structure. It is further characterized by...
[0028] The localized removal of the capping metal layer using the masking step is then completed. The capping metal layer remaining in the second sub-region forms a metal conductor structure or part of a metal conductor structure. Subsequently, the manufacturing of the printed circuit board can be continued in the conventional manner. For example, the conductor structure can be protected by coating with solder resist. Free contacts can be coated with precious metals such as gold, silver, or platinum. In principle, it is also possible to attach an insulating layer to the conductor structure to construct an MLB, and further conductor structures are introduced or applied to the free surfaces of the insulating layer, and optionally, these further conductor structures are connected to the previously formed conductor structure by vias.
[0029] In a particularly preferred second variant of the alternative method, the method has features a. to d. described immediately thereafter, namely, a. After removing the capping metal layer of at least one first sub-region, the first substrate surface is exposed to plasma, thereby ablating the polymer material of at least one first sub-region and forming at least one recess. b. At least one recess is filled with filler metal, c. The capping metal layer and mask layer of at least one second sub-region are completely removed. d. The first substrate surface is arbitrarily flattened together with the at least one filled recess. It is further characterized by at least one of the following.
[0030] More preferably, steps a, b, and c described immediately before this are implemented in combination with each other. Step d is any subsequent step. However, in some embodiments, the complete removal of the capping metal layer and the mask layer can also be performed during the planarization by step d. Thus, steps c and d may be identical in some embodiments.
[0031] In one preferred embodiment of this modified form, step c is performed before step b, i.e., after the first substrate surface has been exposed to the plasma, and firstly, the capping metal layer and mask layer of at least one second sub-region are completely removed. As a result, a first substrate surface with recesses is obtained, free from the capping metal layer and mask layer. In that example, in a downstream step, ideally following the planarization in step d, the recesses are filled with filler material.
[0032] According to this second modification of the method, the conductive structure or a portion of the conductive structure is formed in at least one recess, rather than in a second sub-region. As a result, a conductive structure embedded in the base substrate is obtained.
[0033] In a particularly preferred embodiment, the mask layer is not removed as part of a separate removal step. Instead, the mask layer is preferably removed during plasma treatment according to feature a of a particularly preferred second variant of the method described. Surprisingly, this has proven to be efficiently possible when the mask layer is formed from one of the materials mentioned above (titanium, zinc, titanium dioxide, titanium nitride, zinc oxide, or polymer materials), more specifically when the mask layer is formed with the aforementioned thickness, i.e., 5 nm to 1000 nm, more preferably 5 nm to 500 nm, and particularly preferably 5 nm to 250 nm. This thickness is generally sufficient to protect the capping metal layer in all other areas while the etching solution is used in at least one first sub-region. However, even in the case of metallic titanium and zinc, they are not thick enough to withstand plasma treatment. Also, in the case where the mask layer is made from a polymer material, the mask layer can be several micrometers thick. Therefore, with a sufficiently long processing time, the mask layer can be removed by plasma without leaving any residue. This method allows the process to be shortened into a single complete step, significantly increasing its efficiency. Regardless of the method by which the mask layer is removed, a common characteristic of the materials described (titanium, zinc, titanium dioxide, titanium nitride, zinc oxide, or polymer materials) is that they are environmentally and physiologically unproblematic in the process underway. After their mask layers are removed, titanium, zinc, titanium dioxide, titanium nitride, and zinc oxide can be reused. The mask layer can optionally be removed simultaneously with the capping metal layer, for example, as part of the etching process described below. During the removal process, polymer materials are decomposed by plasma and converted into a state that can be disposed of by wastewater. This is especially true when the polymer material includes the polyamide or epoxy resins mentioned above.
[0034] In the development of particularly preferred first and second modifications of the method, a method for constructing a multilayer printed circuit board is employed. In this multilayer circuit board, according to the second modification, a conductor structure embedded in a base substrate and obtained, or according to the first modification of the method, a capping metal layer remaining in a second sub-region and functioning as a conductor structure, forms a first conductor structure, which can optionally be connected to further conductor structures of the printed circuit board.
[0035] In this development, the method incorporates the additional features a.~f. described immediately below, namely, a. Covering the first conductor structure with an insulating layer, wherein the composite assembly with the base substrate has a bottom surface that is in direct contact with the first conductor structure and an upper surface that is at least partially made of a non-conductive organic polymer material and faces away from the first conductor structure. b. If not already present, a capping metal layer is formed on the upper surface of the insulating layer. c. Locally removing the capping metal layer in order to divide the upper surface into at least one first sub-region where the capping metal layer is not present on the upper surface and at least one second sub-region where the upper surface is covered with the capping metal layer. d. Applying plasma to the upper surface, thereby ablating the polymer material of at least one first sub-region to form at least one recess, e. Filling at least one recess with filler metal, f. Completely remove the capping metal layer of at least one second sub-region in order to form a second conductor structure or a part of a second conductor structure. It additionally includes at least one of the following. As a preference, at least features a. to c. described immediately before this are realized in combination with each other. Subsequently, in a preferred embodiment, the three steps of features d. to f. are carried out in combination.
[0036] However, similar to the particularly preferred first modification of the method described above, it is also possible that the capping metal layer remaining in the second sub-region of the upper surface already forms the second metal conductor structure or part of the metal conductor structure. In this case, steps d. to f. described immediately before this are unnecessary.
[0037] The localized removal of the capping metal layer, involving the splitting of the upper surface of the insulating layer, as described in step c. immediately preceding this, can, in a preferred embodiment, be carried out in the same manner as the localized removal of the capping metal layer on the first substrate surface of the base substrate.
[0038] The insulating layer is preferably embodied as the base substrate provided in step a of claim 1. Therefore, preferably, the insulating layer is embodied as a film or plate and consists at least partially of a non-conductive organic polymer material. In particularly preferred embodiments, the insulating layer and the base substrate are identical in those embodiments.
[0039] Through multiple repetitions of steps a. to c. (especially steps a. to f.) described immediately before this, it is possible in principle to sequentially construct an MLB with as many layers as desired.
[0040] In a preferred development of the present invention, the method is characterized by features a. to c. described immediately thereafter, namely, a. The base substrate and / or insulating layer have a thickness in the range of 10 μm to 3 mm, preferably in the range of 10 μm to 2 mm. b. The organic polymer material of the base substrate and / or insulating layer is a thermoplastic polymer material, preferably selected from the group including polyimide, polyamide, Teflon, polyester, polyphenylene sulfide, polyoxymethylene, and polyetherketone. It includes at least one of the following. As for preferences, features a. and b. described immediately before this are realized in combination with each other.
[0041] More preferably, each of the base substrate and the insulating layer comprises a film of a polymer material, more specifically, a film of one of the polymer materials described. This is particularly true when the manufactured printed circuit board is multilayer in its embodiment. In the case of a single-layer printed circuit board, in one preferred embodiment, a relatively thick base substrate is selected, which is embodied as a board.
[0042] More preferably, the method of the present invention, more specifically, a particularly preferred second variant of the method, is the additional features a.~c. described immediately thereafter, namely, a. The base substrate and / or insulating layer include a filler, more specifically, a dielectric filler. b. The base substrate and / or insulating layer is a polymer film having a filler, c. The filler has an average particle size (d50) < 1 μm. Characterized by at least one of the following: The preferences are those described immediately before, features a. and b., and in particular, features a. to c., which are realized in combination with each other.
[0043] The base substrate and / or insulating layer may optionally include fillers, more specifically dielectric fillers. For example, each of the base substrate and / or insulating layer is a film of one of the polymer materials described, in which silicon dioxide particles are embedded.
[0044] Suitable dielectric fillers specifically include metal oxides or metalloid oxides (specifically, aluminum oxide, zirconium oxide, or titanium oxide, in addition to silicon dioxide) and other ceramic fillers (particularly silicon carbide, boron nitride, or boron carbide). Silicon may also be used at an optional choice. The filler is preferably in the form of particles, and more specifically, has an average particle size (d50) in the nanometer range (<1 μm). To facilitate handling, the base substrate can be attached to a carrier or auxiliary substrate, for example, made of glass or aluminum, for processing purposes.
[0045] Another preferred development of the present invention, specifically a particularly preferred second variant of the method, is that the method proceeds as described immediately after, i.e., steps a. and b. a. The plasma is provided using a processing gas from the group including O2, H2, N2, argon, helium, CF4, C3F8, CHF3, and mixtures of the aforementioned gases (such as O2 / CF4). b. Applying plasma at a temperature in the range of 15°C to 200°C, preferably in the range of -15°C to 80°C. It includes at least one of the following. As for preferences, features a. and b. described immediately before this are realized in combination with each other. More preferably, the processing gas used to provide plasma as part of the present invention comprises at least one reactive gas from the group including CF4, C3F8, and CHF3.
[0046] Plasma etching is also a cutting-edge technology. In plasma etching, a processing gas is used that can transfer the etching material into the gas phase. The gas containing the material removed by etching is discharged, and a new processing gas is introduced. Thus, the removal is continuous. Particularly preferred for use in the context of the present invention is, for example, an inductively coupled plasma (ICP plasma) generated by an ICP generator with a DC bias. The processing gas described immediately before this is particularly well suited for etching the preferred polymer materials specified above.
[0047] In this context, it is important that in at least one first sub-region of the first substrate surface and / or at least one first sub-region of the top surface, the base substrate and / or insulating layer made of polymer material are in direct contact with the plasma, while at least one second sub-region of the first substrate surface and / or at least one second sub-region of the top surface are covered by their respective capping metal layers. Generally speaking, metals are plasma-etched more slowly than polymer materials, especially when using the described processing gas. Consequently, when the plasma is applied, a recess is formed only in the area of at least one first sub-region of the first substrate surface, and the capping metal layer and mask layer (the latter at least temporarily) form a barrier protecting each of the at least one second sub-region from the plasma. In this method, the surface of the base substrate and the surface of the insulating layer can be structured to have recesses in a targeted manner and with high precision.
[0048] In a particularly preferred embodiment, plasma is used as part of an anisotropic etching process. In this example, ideally, plasma ions are accelerated perpendicular to the surface of the substrate being etched. The accelerated ions provide physical sputtering ablation. Particularly suitable are anisotropic etching processes, including embodiments of reactive ion etching (RIE) and reactive ion beam etching (RIBE).
[0049] Accordingly, in a preferred embodiment, the method of the present invention, more specifically, a particularly preferred second variant of the method, is the steps and / or features a.~c. described immediately thereafter, namely, a. Plasma is used as part of an anisotropic etching process, b. In an anisotropic etching process, plasma ions are accelerated perpendicularly to the first substrate surface and / or top surface, c. The processing gas used to provide the plasma includes at least one reactive gas from the group including CF4, C3F8, and CHF3. Characterized by at least one of the following: In terms of preferences, features a. and b. described immediately before this, or more specifically, features a. to c. described immediately before this, are realized in combination with each other. Surprisingly, the presence of the aforementioned microparticle filler has been found to be advantageous in the results of plasma ablation of materials.
[0050] In another preferred development of the present invention, the method is described immediately thereafter in steps a. to c., namely, a. To fill at least one recess in the first substrate surface and / or upper surface of the insulating layer of the base substrate, at least one recess is metallized in one step, and the metallized at least one recess is filled with a filler metal in a downstream step. b. At least one recess is metallized by physical or chemical vapor deposition, more specifically by sputtering of the first substrate surface or by a wet chemical method. c. The first substrate surface and / or top surface is metallized over the entire area. It includes one of the following. In terms of preferences, features a. and b. described immediately before this, more specifically a. to c., are realized in combination with each other. Preferably, a thin layer of copper or a copper alloy is formed as part of the metallization process.
[0051] In the case of wet chemical metallization, the metallization process is achieved, for example, by depositing copper from a solution.
[0052] The filling of the filler metal is preferably carried out by electrochemical deposition. More preferably, the filling is achieved by a so-called via filling method, which can primarily perform deposition in at least one recess, while simultaneously reinforcing at least one second sub-region capping metal layer and optionally a mask layer, and while minimizing unwanted deposition on the first substrate surface and / or top surface, and optionally performing deposition in drilled holes or blind holes.
[0053] The metallized layer applied to the entire area ensures that the entire substrate surface can be coated, for example, by enabling electrical contact with the first substrate surface and / or top surface, allowing for the positioning of cathode contacts therefor for subsequent electrochemical deposition.
[0054] Suitable filler metals include, in principle, all metals and alloys that can be used to fabricate a conductor track structure on a printed circuit board. However, certain preferences may exist. a. The filling metal used to fill at least one of the recesses is copper or a copper alloy. In another preferred development of a particularly preferred second variant of the method, the method proceeds to step a. or b. described immediately thereafter, namely, a. Removal of the capping metal layer and / or mask layer of at least one second sub-region of the substrate surface and / or upper surface is performed by an etching step, or b. Removal of the capping metal layer and / or mask layer of at least one second sub-region is performed by mechanical work on the first substrate surface and / or top surface. Includes. The etching step is a conventional etching step that uses a strong acid, such as hydrochloric acid.
[0055] If the capping metal layer is to be removed mechanically, it can be removed, for example, by polishing and / or grinding. The objective is to completely remove the respective capping metal layer of at least one second sub-region. Only in this manner is the formation of the conductive structure or a part of the conductive structure completed.
[0056] Furthermore, complete removal of the capping metal layer of at least one second sub-region preferably includes removal of the filler metal of at least one first sub-region, and optionally, removal of the filler metal of at least one recess region, to the extent that at least the filler metal protrudes beyond one or more ends of at least one recess.
[0057] A specific advantage is that, with respect to the mechanical work on the first substrate surface, it is possible not only to remove the capping metal layer but also to planarize the first substrate surface at the same time. The preferred purpose of planarization is to flatten the first substrate surface so that the conductor tracks do not protrude from the surface. Instead, the conductor structure is preferably completely embedded in at least one recess.
[0058] In a preferred embodiment, the external conductive structure formed according to the method is protected by coating with solder resist. The free contacts can be coated with a precious metal such as gold, silver, or platinum.
[0059] According to the described method, printed circuit boards can be manufactured with extremely high resolution in the μm range at a lower cost and complexity and with lower manufacturing costs (and with a higher yield) than those permitted by prior art. In the case of MLB manufacturing, more specifically, a beneficial feature of using the sequential construction described is that the conductive structure is embedded in the base substrate. The pressure acting on the conductive structure when the base substrate and insulating layer are pressed together is relatively low, resulting in beneficial outcomes related to existing impedance and signal speed requirements. In this regard, the fact that extremely precise channels can be formed by plasma etching also has a positive effect.
[0060] In principle, it would also be possible to form such channels using a laser. In comparison, plasma etching offers the advantage of forming all channels and other recesses simultaneously and in a single step during the plasma etching process, which is generally several times more cost-effective and faster. Moreover, plasma etching can achieve higher resolution.
[0061] Further features, details, and selections of the present invention will become apparent from the claims and abstract, both of which are incorporated by reference into this description, as well as from the following description of preferred embodiments of the present invention, and by reference to the drawings. [Brief explanation of the drawing]
[0062] [Figure 1] The process of the method of the present invention, according to a particularly preferred second variant described above, is shown below. [Figure 2] The process of another embodiment of the method of the present invention is shown. [Figure 3] The process of another embodiment of the method of the present invention is shown. [Modes for carrying out the invention]
[0063] In the method shown in Figure 1, step A provides a base substrate 101. In step B, the first substrate surface 101a of this substrate is covered with a capping metal layer 102. In step C, a mask layer 103 of titanium or zinc is attached to the capping metal layer 102 by sputtering for partial ablation of the capping metal layer 102. Alternatively, the mask layer may be formed from one of titanium dioxide, titanium nitride, zinc oxide, or the polymer materials described above. In step D, the mask layer 103 of the first sub-region 104 is removed by laser ablation. In step E, the capping metal layer 102 of the first sub-region 104 that is no longer covered by the mask layer 103 is removed by an etching solution. Here, the substrate surface 101a, which was originally completely covered by the capping metal layer 102, is divided into a first sub-region 104 without the capping metal layer 102 and a second sub-region 105 that remains covered by the capping metal layer 102 and the mask layer 103. In step F, plasma is applied to the substrate surface 101a. Sub-region 105 is protected from the plasma by the capping metal layer 102 and the mask layer 103, but the effect of the plasma on sub-region 104 is that the material is ablated, resulting in the formation of a recess 106. However, if the plasma effect is sufficient, the mask layer may also be removed in this step. In step G, the recess 106 is metallized by sputtering, and then in step H, the recess 106 is filled with filler metal 108 by electrochemical deposition. Next, in step I, excess filler metal 108 is mechanically removed along with the capping metal layer 102 and mask layer 103 of the sub-region 105 (if such removal has not yet been performed). In this step, the conductor structure 109 embedded in the recess 106 is formed.
[0064] In step J, an insulating layer 110 is directly laminated onto a substrate surface 101a having a conductive structure 109 for the formation of an MLB. In step K, the upper surface 110a of the insulating layer is covered with a capping metal layer 111. In steps L, M, and N, similar to steps C, D, and E, the capping metal layer 111 is again locally removed, along with the attachment and local removal of a mask layer 112 of titanium (or titanium dioxide, titanium nitride, zinc oxide, or one of the polymer materials described above) by laser ablation. Here, the upper surface 110a of the insulating layer 110, which was originally completely covered with the capping metal layer 111, is divided into a first sub-region 113 without the capping metal layer 111 and a second sub-region 114 that remains covered with the capping metal layer 111 and the mask layer 112. In step O, plasma is applied to the upper surface 110a of the insulating layer 110. Sub-region 114 is protected from the plasma by the capping metal layer 111 and the mask layer 112, but the effect of this plasma on sub-region 113 is that the material is ablated, resulting in the formation of recesses 115. Here again, if the plasma action is sufficient, it may be possible to remove the mask layer at the same time. In step P, in contrast to the case where the base substrate 101 is worked on, the capping metal layer 111 and the mask layer 112 are removed by etching. Furthermore, one of the formed recesses 115 is connected by a drill hole 116 to a recess 106 of the first conductive structure 109, which is already filled with filler metal 108. In step Q, the recess 115 including the drill hole 116 is metallized by sputtering, and then in step R, the recess 115 is filled with filler metal 118 by electrochemical deposition. Subsequently, in step S, the excess filler metal 118 is mechanically removed along with the capping metal layer 111 and the mask layer 112 of sub-region 114. In this step, the conductor structure 119 embedded in the recess 115 is formed. In step T, the solder resist 120 is applied, and then the individual contacts of the conductor structure 119 are partially gold-plated 121.
[0065] In the method shown in Figure 2, a base substrate 101 is provided, its first substrate surface 101a is covered with a capping metal layer 102 made of copper, and its second substrate surface 101b is covered with a capping metal layer 107 made of copper. In step A, a titanium mask layer 103 is attached to the capping metal layer 102 by sputtering. In step B, the mask layer 103 is locally ablated by laser ablation, dividing the first substrate surface 101a into at least one first sub-region 104 where the first substrate surface 101a is covered only by the capping metal layer 102, and at least one second sub-region 105 where the first substrate surface 101a is covered by both the capping metal layer 102 and the mask layer. In step C, the capping metal layer 102 in at least one region 104 is removed by an etching solution. Finally, in step D, the mask layer 103 is removed. The capping metal layer 102 remaining in the second sub-region 105 forms a metal conductor structure or a part of a metal conductor structure.
[0066] In the method shown in Figure 3, the same base substrate 101 as in the method shown in Figure 2 is provided. Similar to Figure 2, in step A, a titanium mask layer 103 is attached by sputtering, and in step B, it is locally ablated by laser ablation, so that the first substrate surface 101a includes a first sub-region 104 where the first substrate surface 101a is covered only by the capping metal layer 102. Next, in step C, the capping metal layer 102 of at least one region 104 is removed by etching solution. In step D, the substrate surface 101a is exposed to plasma, and the material is ablated in at least one sub-region 104, resulting in the formation of a recess 106. Subsequently, the capping metal layer 102 and the mask layer 103 are removed without leaving any residue, and at this stage, optionally, the mask layer may also be ablated by plasma. In step E, the recess 106 is metallized (not drawn) by sputtering, and then the recess 106 is filled with filler metal 108 by electrochemical deposition. In step F, the substrate surface 101a is planarized. In this procedure, excess filler metal 108 is mechanically removed. Here, the conductor structure 109 embedded in the recess 106 is formed.
Claims
1. A method for manufacturing a printed circuit board having a metal conductor structure, a. A step of providing a base substrate (101) which is embodied as a film or plate and has a first substrate surface (101a) and a second substrate surface, and which is at least partially made of a non-conductive organic polymer material, wherein the first substrate surface (101a) is covered with a capping metal layer (102), b. A step of locally removing the capping metal layer (102) Having the ability to locally remove the capping metal layer (102), c. Attaching the mask layer to the capping metal layer, d. Locally removing the mask layer with a laser, such that the first substrate surface (101a) is divided into at least one first sub-region (104) where the first substrate surface (101a) is covered only by the capping metal layer (102), and at least one second sub-region (105) where the first substrate surface (101a) is covered by the capping metal layer (102) and the mask layer. e. Removing the capping metal layer (102) of at least one first sub-region (104) with an etching solution. Achieved by, f. A method wherein the mask layer is formed from titanium, zinc, titanium dioxide, titanium nitride and / or zinc oxide.
2. The following additional features, namely, a. The capping metal layer is formed from copper, b. The etching solution is a solution for etching copper, c. The metal and / or metal compound on which the mask layer (103) is formed has greater chemical resistance to the etching solution than copper. The method according to claim 1, comprising at least one of the following.
3. The following additional features, namely, a. The metal and / or metal compound on which the mask layer (103) is formed absorbs the laser radiation more strongly than the metal in the capping metal layer (102) absorbs it. The method according to claim 1 or 2, comprising:
4. The following additional features, namely, a. The mask layer (103) is formed from titanium or zinc. The method according to any one of claims 1 to 3, comprising:
5. The following additional features, namely, a. The mask layer (103) is formed to be thinner than the thickness of the capping metal layer (102), b. The mask layer (103) has a thickness in the range of 5 nm to 10 μm, The method according to any one of claims 1 to 4, comprising at least one of the following.
6. The following additional features, namely, c. The mask layer (103) is formed by physical or chemical vapor deposition, d. The mask layer (103) is formed by sputtering, e. The mask layer (103) is formed by a wet chemical coating process. The method according to any one of claims 1 to 5, comprising at least one of the above.
7. The following additional features, namely, a. After the capping metal layer (102) is removed, the mask layer (103) of at least one second sub-region (105) is removed, and the capping metal layer remains in the second sub-region as a conductor structure or as part of a conductor structure. The method according to any one of claims 1 to 6, comprising:
8. The following additional features, namely, a. After removing the capping metal layer (102) of the at least one first sub-region (104), the first substrate surface (101a) is exposed to plasma, thereby ablating the polymer material of the at least one first sub-region (104) and forming at least one recess (106). The method according to any one of claims 1 to 6, comprising:
9. The following additional features, namely, b. The at least one recess (106) is filled with the filling metal (108), The method according to claim 8, wherein the method is characterized by having the following:
10. The following additional features, namely, c. The capping metal layer (102) and the mask layer (103) of at least one second sub-region (105) are completely removed in order to form a conductor structure (109) or a part of a conductor structure. The method according to claim 8 or 9, having the following characteristics.
11. The following additional features, namely, d. The first substrate surface (101a) is flattened together with the at least one filled recess (106), The method according to claim 9, having the following characteristics.
12. The following additional features, namely, a. Covering the first conductor structure (109) obtained according to any one of claims 7 to 11 with an insulating layer (110), It has, The method according to any one of claims 7 to 11, wherein the insulating layer (110) is located within a composite assembly of the base substrate (101) and the insulating layer (110) and has a bottom surface that is in direct contact with the first conductor structure (109) and an upper surface (110a) that is at least partially made of a non-conductive organic polymer material and faces away from the first conductor structure (109).
13. The following additional features, namely, b. Forming a capping metal layer (111) on the upper surface (110a) of the insulating layer (110), The method according to claim 12, having the following characteristics.
14. The following additional features, namely, c. Locally removing the capping metal layer (111) in order to divide the upper surface (110a) into at least one first sub-region (113) on the upper surface (110a) where the capping metal layer (111) is not present, and at least one second sub-region (114) on the upper surface (110a) where the capping metal layer (111) is covered. The method according to claim 12 or 13, having the following characteristics.
15. The following additional features, namely, d. Applying plasma to the upper surface (110a) thereby ablation processing of the polymer material in the at least one first sub-region (113) to form at least one recess (115), The method according to any one of claims 12 to 14, comprising:
16. The following additional features, namely, e. Filling the at least one recess (115) with filler metal (118), The method according to claim 15, having the following characteristics.
17. The following additional features, namely, f. Completely remove the capping metal layer (111) of at least one second sub-region (114) in order to form a second conductor structure (119) or a part of a second conductor structure (119). The method according to any one of claims 12 to 16, comprising:
18. The following additional features, namely, a. The base substrate (101) and / or the insulating layer (110) have a thickness in the range of 10 μm to 3 mm. The method according to any one of claims 12 to 17, comprising:
19. The following additional features, namely, b. The nonconductive organic polymer material of the insulating layer (110) is selected from the group including polyimide, polyamide, Teflon, polyester, polyphenylene sulfide, polyoxymethylene, and polyether ketone. The method according to any one of claims 12 to 18, comprising:
20. The following additional features, namely, a. The base substrate (101) and / or the insulating layer (110) contain a filler, The method according to any one of claims 12 to 19, comprising:
21. The following additional features, namely, b. The base substrate (101) and / or the insulating layer (110) is a polymer film of a non-conductive organic polymer material. The method according to claim 20, comprising:
22. The following additional features, namely, c. The filler has an average particle size (d50) < 1 μm. The method according to claim 20 or 21, having the following characteristics.
23. The following additional features, namely, a. O ２ , H ２ , N ２ Argon, helium, CF ４ , C ３ F ８ CHF ３ The plasma is provided using a processing gas from the group including the aforementioned mixture of gases. The method according to any one of claims 8 to 11 and 15, comprising:
24. The following additional features, namely, b. Applying the plasma at a temperature in the range of -15°C to 200°C, The method according to any one of claims 8 to 11, 15 and 23, comprising:
25. The following additional features, namely, a. The plasma is used as part of an anisotropic etching process. The method according to any one of claims 8 to 11, 15, 23 and 24, comprising:
26. The following additional features, namely, b. The plasma is used as part of an anisotropic etching process, and in the anisotropic etching process, the ions of the plasma are accelerated perpendicular to the first substrate surface (101a) and / or the upper surface (110a). The method according to claim 15, having the following characteristics.
27. The following additional features, namely, c. The plasma is provided using a processing gas containing at least one reactive gas from the group including CF ４ , C ３ F ８ and CHF ３ . The method according to claim 24 or 25, having the following characteristics.