Method for producing an etch-resistant pattern on a metal surface

Abstract

A method of forming a metal pattern on a substrate is provided. The method includes applying a chemical surface activation solution having an activator that chemically activates a metal surface to the metal surface; non-impact printing an etch-resistant ink on the activated surface to produce an etch-resistant mask according to a predetermined pattern, wherein at least one ink component within the etch-resistant ink undergoes a chemical reaction with the activated metal surface to immobilize a droplet of the etch-resistant ink when it strikes the activated surface; performing an etching process to remove unmasked metal portions not covered by the etch-resistant mask; and removing the etch-resistant mask.

Description

[0001] Invention Field

[0002] Embodiments of the present invention relate to manufacturing printed circuit boards by applying an etch-resistant mask using non-impact orienting, such as inkjet printing.

[0003] background

[0004] Printed circuit boards (PCBs) are widely used in most electronic products. PCB manufacturing is considered cheaper, faster, and more accurate than using other wiring methods such as point-to-point construction. However, there is an ongoing search for simpler and more cost-effective manufacturing processes that will maintain high quality and be able to produce PCBs to specific needs, including smaller, more cost-effective batches, larger batches with high production volumes, on-demand boards, denser circuit boards, thinner traces, and others.

[0005] In PCB manufacturing, copper trace patterning is typically achieved by applying an etch-resistant photomask to a copper layer laminated to an insulating material board and then removing the exposed copper portions through an etching process, leaving only the desired copper traces (also known as image patterning) as conductive paths. The etch-resistant pattern can be applied on top of the copper layer using an additive method, such as through non-impact printing (e.g., inkjet printing). Conventional inkjet materials have relatively low viscosity, and therefore, when ink droplets strike a non-absorbent surface such as copper, uncontrolled diffusion of the droplets and other phenomena such as aggregation, coalescence, and extensive dot gain often occur. Consequently, printed patterns formed by inkjet printing techniques may exhibit poor quality or copper traces, including, for example, detail defects, inconsistent line widths, poor line edge smoothness, short circuits between adjacent lines, and broken pattern lines. Brief description of the attached diagram

[0007] The subject matter considered to be the present invention is specifically pointed out and expressly claimed in the concluding section of the specification. However, when combined with the appendix... Figure 1 When reading this invention, both in terms of its organization and operation methods, its objects, features, and advantages, can be best understood by referring to the following detailed description, in conjunction with the accompanying drawings:

[0008] Figure 1 This is a flowchart of a method for producing an etch-resistant mask according to some embodiments of the present invention; and

[0009] Figure 2A A photograph of an exemplary etch-resistant mask printed on unactivated copper is shown; and

[0010] Figure 2BA photograph of an exemplary etch-resistant mask printed on an activated copper surface according to an embodiment of the present invention is shown.

[0011] It will be understood that, for simplicity and clarity, the elements shown in the accompanying drawings are not necessarily drawn to scale. For example, for clarity, the dimensions of some elements may be enlarged relative to others. Furthermore, reference numerals may be repeated in the drawings where deemed appropriate to indicate corresponding or similar elements.

[0012] Overview

[0013] Embodiments of the present invention include a method for forming a metal pattern on a substrate. The method may include applying a chemical surface activation solution having an activator that chemically activates the metal surface to a metal surface coupled to the substrate; non-impact printing resist ink onto the activated surface to generate a resist mask according to a predetermined pattern, wherein at least one ink component in the resist ink undergoes a chemical reaction with the activated metal surface to fix droplets of the resist ink when the activated surface is struck; performing an etching process to remove unmasked metal portions not covered by the resist mask; and removing the resist mask.

[0014] In some embodiments, the metal pattern formed according to embodiments of the present invention comprises pattern lines with a width of less than 50 micrometers. In some embodiments, the etch resist mask produced according to embodiments of the present invention comprises lines with a width of less than 50 micrometers. In some embodiments, the metal pattern formed according to embodiments of the present invention comprises pattern lines with a width of less than 30 micrometers. In some embodiments, the etch resist mask produced according to embodiments of the present invention comprises lines with a width of less than 30 micrometers.

[0015] In some embodiments, the method may include removing the chemical surface-activating solution from the surface using a solvent prior to printing. In some embodiments, the ink component undergoing the chemical reaction is an anionic component. In some embodiments, the ink component undergoing the chemical reaction with the activated surface is a polymeric component selected from acrylates, phosphates, sulfonates, or mixtures thereof. In some embodiments, the activator may include at least one of the following: copper salts, iron salts, chromium-sulfuric acid, persulfates, sodium chlorite, and hydrogen peroxide, or mixtures thereof.

[0016] In some embodiments, applying the chemical surface-activating solution includes immersing the metal surface in a bath containing the chemical surface-activating solution for approximately 10-60 seconds. In some embodiments, applying the chemical surface-activating solution includes spraying the chemical surface-activating solution onto the metal. In some embodiments, non-impact printing of etch-resistant inks on the activated surface includes inkjet printing.

[0017] Detailed description

[0018] In the following detailed description, numerous specific details are set forth in order to provide a complete understanding of the invention. However, those skilled in the art will understand that the invention can be practiced without these specific details. In other instances, well-known methods, procedures, and components have not been described in detail so as not to obscure the invention.

[0019] Embodiments of the present invention relate to methods for forming or applying an etch-resistant mask on a metal layer by non-impact printing, for example, during the manufacture of a printed circuit board (PCB). A method for applying an etch-resistant mask to a metal surface according to embodiments of the present invention may include applying a chemical surface-activating solution on top of the metal surface to chemically activate the metal surface, then removing / washing off the chemical surface-activating solution and printing (e.g., inkjet printing) an etch-resistant ink on top of the activated surface. According to embodiments of the present invention, the reactive components of the etch-resistant ink undergo a chemical reaction with the activated surface to fix droplets of the liquid composition upon impact with the surface. The chemical reaction may instantaneously cause a significant increase in the viscosity of the ink droplets (e.g., an increase of one or two orders of magnitude) upon impact with the activated surface.

[0020] In some embodiments, the reactive component in the etch-resistant ink (ink component) may be an etch-resistant component, and in other embodiments, the reactive component may be different from the etch-resistant component. According to some embodiments, more than one reactive component of the etch-resistant ink may undergo a chemical reaction with components on the activated surface.

[0021] The metal layer may be a copper layer laminated onto an insulating, non-conductive substrate. For ease of explanation, the following description refers to a copper surface. It should be recognized that other metal surfaces, such as aluminum, stainless steel, gold, and others, are equally suitable for embodiments of the invention.

[0022] Reference Figure 1 , Figure 1This is a flowchart of a method for producing an etch-resistant mask according to some embodiments of the present invention. According to embodiments of the present invention, as shown in block 110, the method may include applying a chemical surface-activating solution to a metal surface on which an etch-resistant pattern will be printed. In some embodiments, the chemical surface-activating solution may be, or may include, any etch solution capable of chemically activating the surface. A chemically activated surface may be defined as a surface that does not react with the etch-resistant ink material prior to surface activation, but reacts after surface activation to cause the fixation of etch-resistant ink droplets. Surface-activating solutions may include, for example, copper salts, iron salts, chromium-sulfuric acid, persulfate, sodium chlorite, and hydrogen peroxide. In some embodiments, applying the chemically activated solution may include immersing the surface in a bath containing the chemically activated solution, spraying the chemically activated solution onto the surface, and any other suitable method. In some embodiments, the method may include subjecting the metal surface to the chemically activated solution (e.g., by immersion, spraying, or the like) for a predetermined amount of time, such as 10 seconds, 20 seconds, 30 seconds, 60 seconds, or more.

[0023] As shown in box 115, in some embodiments, the method may optionally include removing the chemically activated solution using, for example, an alcohol solution. For example, the method may include using ethanol to remove residues of the chemically activated solution from the surface. In some embodiments, a liquid other than an alcohol solution may be used to remove the chemically activated solution from the surface, such as propanol, isopropanol, or acetone.

[0024] As shown in box 120, in some embodiments, the method may include non-impact printing (e.g., by inkjet printing) of an etch-resistant ink onto an activated surface according to a predetermined pattern to create an etch-resistant mask. The etch-resistant ink may contain an etch-resistant polymer component that chemically reacts with the activated surface to immobilize droplets of the etch-resistant ink upon impact with the activated surface. In some embodiments, a separate ink component, distinct from the etch-resistant component, chemically reacts with the activated surface to immobilize droplets of the etch-resistant ink upon impact with the activated surface.

[0025] Non-limiting examples of etch-resistant polymer reactive components may be acrylate, styrene acrylate, phosphate ester and sulfonate polymers, yielding molecular weights (Mw) from 1,000 to 17,000.

[0026] In some embodiments, the etch-resistant reactive polymer component may be water-soluble and may include a reactive anionic component. Non-limiting examples of anionic etch-resistant reactive components may include at least one anionic polymer (in alkaline form) with a pH above 7.0. The anionic polymer may be selected from acrylic resins and styrene-acrylic resins in their dissolved salt form, sulfonic acid resins in their dissolved salt form, such as those neutralized with sodium, ammonium, or amine, and the like. Without wishing to be bound by any particular theoretical mechanism, the aforementioned resins may undergo a reaction with reactive (activated) surfaces. For example, a copper metal surface is activated to form copper cations on top of the copper, and when the acrylic polymer (present in the etch-resistant ink) is to strike the surface, the anionic acrylate may react with the copper ions to form a polymer matrix in the droplet, which will significantly increase the droplet viscosity.

[0027] In some implementations, the ink component that undergoes a chemical reaction with the surface-activated component to fix the droplets of the anti-etching ink upon impact with the activated surface may be different from the anti-etching component.

[0028] As shown in box 130, the masked copper plate can be further etched using a metal etching solution (e.g., acidic copper etching) to remove exposed, unmasked portions of the metal layer. As shown in box 140, the etch-resistant mask can then be removed to expose the substrate, i.e., the line pattern on the insulating plate. Example

[0029] Using an Epson Stylus 4900 inkjet printer, an exemplary liquid composition (such as the anti-etching ink composition described herein) was printed onto an FR4 copper-clad laminate with a copper thickness of 18 micrometers. In some tests, the copper was first chemically activated by applying a chemical surface-activating solution to activate the copper surface. The liquid composition of the anti-etching ink was selectively printed onto the activated or unactivated copper surface according to a predetermined pattern using inkjet printing technology. In the description below, % (w / w) is a measure of the concentration of the substance as a percentage of weight relative to the weight of the composition. The exposed areas of the copper that were not masked were etched away using an etchant bath containing a ferric chloride etchant solution with a strength of 42 Baume provided by Amza (PERMIX166). Etching was performed at a temperature of 35°C for 3 minutes in a Spray Developer S31 provided by Walter Lemmen GMBH. The anti-etching mask was peeled off by immersing the etched board in a 1% (w / w) aqueous solution of NaOH at a temperature of 25°C, followed by washing the FR4 copper board with water and air drying at 25°C.

[0030] Example 1 - An etch-resistant ink in liquid composition form at room temperature was printed onto the top of an untreated (unactivated) FR4 copper clad laminate. The liquid composition was prepared with 10% propylene glycol (as a humectant), 1% (w / w) 2-amino-2-methylpropanol, 0.3% (w / w) BYK 348 supplied by BYK, and 2% (w / w) Bayscript BA cyan. These materials were dissolved in water containing a 24% Joncryl 8085 styrene-acrylic resin solution. Using an Epson Stylus 4900 inkjet printer, the etch-resistant composition was printed onto the top of an FR4 copper-clad laminate with a copper thickness of 18 micrometers to create an etch-resistant mask.

[0031] Visually inspect the etch-resistant mask. For example... Figure 2A It is evident that the printed pattern exhibits very poor printing quality, with extremely poor edge definition and severe short circuits between lines.

[0032] Example 2 - The liquid composition was prepared as detailed in Example 1. The surface of the FR4 copper-clad laminate was activated by immersing (e.g., dipping) the copper-clad laminate in a 0.5% (w / w) aqueous solution of CuCl2 for 30 seconds, followed by cleaning the copper-clad laminate with technical ethanol.

[0033] Using an Epson Stylus 4900 inkjet printer, the liquid composition was printed onto the top of a treated copper plate and dried at 80°C to produce an insoluble etch-resistant mask. Figure 2B As can be seen, the resist pattern exhibits high print quality with well-defined boundaries and line widths as low as 50 micrometers, including sharp edges and no breaks. Etching of the exposed copper and removal of the resist mask are performed as detailed in Example 1. The wiring pattern on the board exhibits well-defined lines with widths as low as 50 micrometers, including sharp edges and no breaks.

[0034] Example 3 - The liquid composition was prepared as detailed in Example 1. The copper surface was activated by immersing the FR4 copper-clad laminate in a bath containing a 20% (w / w) FeCl3 aqueous solution for 10 seconds, followed by washing the copper plate with technical ethanol.

[0035] Similar to Example 2, the liquid composition was inkjet printed onto the coated copper plate and dried at 80°C to produce an insoluble resist mask. The resist pattern exhibited high print quality with well-defined boundaries and fine lines as low as 50 micrometers, containing sharp edges and no breaks. Etching of the exposed copper and removal of the resist mask were performed as detailed in Example 1. The wiring pattern on the board exhibited a well-defined pattern with fine lines as low as 30 micrometers in width, sharp edges, and no breaks.

[0036] Example 4 - The liquid composition was prepared as detailed in Example 1. The copper surface was activated by immersing the FR4 copper-clad laminate in a 1% (w / w) aqueous solution of Na2S2S8 for 30 seconds, followed by cleaning the copper plate with technical ethanol.

[0037] Using an Epson Stylus 4900 inkjet printer, the resist liquid composition was printed onto a treated copper substrate and dried at 80°C to produce an insoluble resist mask. The resist pattern exhibited high print quality with well-defined boundaries and fine lines down to 50 micrometers, containing sharp edges and no breaks. Etching of the unmasked copper and removal of the resist mask were performed as detailed in Example 1. The wiring pattern produced by the etching and stripping process exhibited a well-defined pattern with fine lines down to 30 micrometers in width, sharp edges, and no breaks.

[0038] Table 1 below lists some non-limiting examples of chemical surface-activating components used in embodiments of the invention, their relative weight concentrations in the surface-activating solution, and recommended immersion times.

[0039] Table 1

[0040] Activator Concentration (w / w%) Immersion time (seconds) <![CDATA[CuCl2 (or any divalent copper salt)]]> 0.5-1 30 <![CDATA[Na2S2S8 (or any persulfate)]]> 0.5-1 30 <![CDATA[H2O2]]> 10 30 <![CDATA[FeCl3]]> 20 10 <![CDATA[HCrO4 / H2SO4]]> 5 30 <![CDATA[NaClO2]]> 5 60

[0041] Table 2 below lists some non-limiting examples of etch-resistant inks.

[0042]

[0043]

[0044] Although certain features of the invention have been illustrated and described herein, many modifications, substitutions, variations, and equivalents will now occur to those skilled in the art. Therefore, it will be understood that the appended claims are intended to cover all such modifications and variations, all of which fall within the true spirit of the invention.

Claims

1. A method of forming a metal pattern on a substrate, the method comprising: applying an aqueous solution comprising an inorganic activator to a metal surface to activate the metal surface of the substrate; inkjet printing an etch resist ink on the metal surface after chemically activating the metal layer; reacting components of the etch resist ink with ions of the metal surface to produce an etch resist mask; performing an etching process to remove portions of the metal layer not covered by the etch resist mask; and removing the etch resist mask to form a metal pattern.

2. The method of claim 1, wherein the metal pattern formed by performing the etching process comprises a plurality of metal lines, each metal line of the plurality of metal lines having a width of less than 50 microns.

3. The method of claim 1, wherein the etch resist mask produced by inkjet printing comprises lines having a width of less than 50 microns.

4. The method of claim 1, wherein the metal pattern formed by performing the etching process comprises metal lines having a width of less than 30 microns.

5. The method of claim 1, further comprising, prior to printing, removing the aqueous solution comprising the inorganic activator from the activated surface of the metal layer using a solvent.

6. The method of claim 1, wherein the components of the etch resist ink that undergo a reaction with the activated surface of the metal layer are polymeric components comprising acrylate, phosphate, sulfonate, or mixtures thereof.

7. The method of claim 1, wherein the inorganic activator comprises one or more materials selected from the group consisting of copper salts, iron salts, chromic-sulfuric acid, persulfate salts, sodium chlorite, and hydrogen peroxide.

8. The method of claim 1, wherein applying the aqueous solution comprises immersing the metal surface in a bath of the aqueous solution for 10-60 seconds or spraying the aqueous solution onto the metal surface.

9. The method of claim 1, wherein the etch resist ink further comprises a dye.

10. The method of claim 1, wherein the metal surface comprises copper and the ions of the metal surface comprise copper cations.

11. A method of forming a metal pattern on a substrate, the method comprising: applying an aqueous solution comprising an inorganic activator selected from the group consisting of copper salts, iron salts, chromic-sulfuric acid, persulfate salts, sodium chlorite, and hydrogen peroxide to a metal surface to activate the metal surface of the substrate; inkjet printing an ink comprising acrylate, phosphate, sulfonate, or mixtures thereof onto the metal surface after chemically activating the metal layer; reacting components of the ink with copper ions of the metal surface to produce an etch resist; performing an etching process to remove portions of the metal layer not covered by the etch resist; and removing the etch resist to form a metal pattern.

12. The method of claim 11, wherein the metal pattern formed by performing the etching process comprises metal lines having a width of less than 30 microns.

13. The method of claim 11, wherein the ink further comprises a dye.

14. A method of forming a metal pattern on a substrate, comprising: applying an activation solution comprising an inorganic activator to a metal surface to chemically activate the metal surface of the substrate; chemically activating the metal layer, printing an etch resist ink in a masking pattern onto the metal surface using inkjet printing; reacting components of the etch resist ink with ions of the metal surface to produce an etch resist mask; performing an etching process to remove portions of the metal layer not covered by the etch resist mask; and removing the etch resist mask to form a metal pattern.

15. The method of claim 14, wherein the metal pattern comprises lines each having a width of less than 50 microns.

16. The method of claim 14, wherein the etch resist mask comprises lines each having a width of less than 50 microns.

17. The method of claim 14, wherein the metal pattern comprises lines each having a width of less than 30 microns.

18. The method of claim 14, further comprising, prior to printing, removing the activation solution from the substrate.

19. The method of claim 14, wherein the components of the etch resist ink are polymeric components comprising acrylate, phosphate, sulfonate, or mixtures thereof.

20. The method of claim 14, wherein the inorganic activator comprises a material selected from the group consisting of copper salts, iron salts, chromic sulfate, persulfate salts, sodium chlorite, and hydrogen peroxide.

21. The method of claim 14, wherein the etch resist ink comprises a dye.

22. The method of claim 14, wherein the metal surface comprises copper and the ions comprise copper cations.

23. A method of forming a metal pattern on a substrate, comprising: chemically activating a metal surface of the substrate by applying an activation solution comprising one or more materials selected from the group consisting of copper salts, iron salts, chromic sulfate, persulfate salts, and sodium chlorite onto the metal surface; chemically activating the metal layer, printing an etch resist ink in a masking pattern onto the metal surface using inkjet printing; reacting components of the etch resist ink with ions of the metal surface to produce an etch resist mask; performing an etching process to remove portions of the metal layer not covered by the etch resist mask; and removing the etch resist mask to form a metal pattern.

24. The method of claim 23, wherein the etch resist ink comprises a reactive polymer.

25. The method of claim 24, wherein the etch resist ink further comprises a material selected from the group consisting of surfactants, humectants, and dyes.

26. The method of claim 25, wherein the metal surface comprises copper and the ions comprise copper cations.

27. The method of claim 23, wherein the metal pattern comprises lines each having a width of less than 30 microns.

28. The method of claim 24, wherein the reactive polymer is selected from the group consisting of acrylic resins, styrene-acrylic resins, and sulfonic resins.

29. The method of claim 23, wherein the activation solution comprises copper chloride or iron chloride.

30. The method of claim 29, wherein the etch resist ink comprises a styrene-acrylic resin.

31. The method of claim 30, wherein the etch-resistant ink further comprises a surfactant, a humectant, and a dye.

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