Production method of etching resist pattern on metal surface

Abstract

To provide a method and a composition set for forming an etching resist mask on a metal surface.SOLUTION: The method comprises the steps of: applying a first liquid composition containing a first reactive component on a metal surface to form a primer layer; and applying a second liquid composition containing a second reactive component on a primer layer by image-like printing by a non impact printing process to generate the etching resist mask according to a prescribed pattern. When droplets of the second liquid composition come into contact with the primer layer, the second reactive component causes a chemical reaction with the first reactive component so as to solidify the droplets. A set includes: the first liquid composition containing a solidification reactive component; and the second liquid composition containing the etching resist reactive component. The solidification reactive component and the etching resist reactive component can cause the chemical reaction to form a two-component material which is insoluble to water and an acidic etching solution.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] Embodiments of the present invention relate to the manufacture of printed circuit boards by application of an etch resist mask using non-impact orientation such as inkjet printing. [Background technology]

[0002] Printed circuit boards (PCBs) are widely used in most electronic products. Manufacturing PCBs is considered cheaper, faster, and more accurate than using other wiring methods such as point-to-point configurations. Nevertheless, there is a continuing search for easier, more cost-effective manufacturing processes that maintain high quality and allow for the production of PCBs according to specific requirements, including the production of cost-effective small batches, larger batches with higher throughput, on-demand boards, boards with higher density wiring, boards with finer lines, and more.

[0003] Copper line patterning in the PCB manufacturing process is usually performed by applying an etch-resist photomask onto a copper layer laminated on an insulating material substrate, and then removing the exposed copper portion by an etching process, leaving only the desired copper lines as conductive paths (also called image patterning). The etch-resist pattern can also be applied by additive methods, for example by non-impact printing (e.g., inkjet printing) onto the copper layer. Conventional inkjet materials have relatively low viscosity, so when ink droplets hit a non-absorbing surface such as a copper surface, uncontrolled droplet diffusion usually occurs, along with other phenomena such as clustering, ink coalescence and extensive dot gain. Therefore, the printed patterns formed by inkjet printing technology may have poor details, uneven line widths, poor line edge smoothness, and may cause copper line quality degradation, such as short circuits between adjacent conductive lines and breaks in pattern lines. Summary of the Invention [Means for solving the problem]

[0004] An embodiment of the present invention includes a method for forming a metal pattern on a substrate, which may be characterized by the steps of: applying a chemical surface activation solution having an activator that chemically activates the metal surface on the metal surface bonded to the substrate; non-impact printing an etch-resist ink on the activated metal surface to generate an etch-resist mask according to a predetermined pattern, where at least one ink component in the etch-resist ink chemically reacts with the activated metal surface to immobilize droplets of the etch-resist ink; performing an etching process to remove unmasked metal portions not covered by the etch-resist mask; and removing the etch-resist mask.

[0005] In some embodiments, the metal pattern formed according to embodiments of the invention comprises metal lines having a width less than 50 μm. In some embodiments, the etch resist mask produced according to embodiments of the invention comprises lines having a width less than 50 μm. In some embodiments, the metal pattern formed according to embodiments of the invention comprises metal lines having a width less than 30 μm. In some embodiments, the etch resist mask produced according to embodiments of the invention comprises lines having a width less than 30 μm.

[0006] In some embodiments, the method further comprises removing the chemical surface activation solution from the metal surface with a solvent prior to printing. In some embodiments, the ink component that undergoes the chemical reaction is an anionic component. In some embodiments, the ink component that undergoes the chemical reaction with the activated metal surface is a polymer component selected from acrylates, phosphates, sulfonates, or mixtures thereof. In some embodiments, the activator comprises at least one of or mixtures of copper salts, ferric salts, chromium sulfate, persulfate, sodium chlorite, and hydrogen peroxide.

[0007] In some embodiments, the applying step comprises immersing the metal surface in a bath containing the chemical surface activation solution for about 10 to 60 seconds. In some embodiments, the applying step comprises spraying the chemical surface activation solution onto the metal surface. In some embodiments, the non-impact printing comprises inkjet printing.

[0008] The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the concluding portion of this specification, however the invention, together with its objects, features and advantages, both as to organization and method of operation, may best be understood by reference to the following detailed description taken in conjunction with the accompanying drawings.

[0009] It will be appreciated that for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn to scale. For example, dimensions of some elements may be greatly exaggerated relative to other elements for clarity. Further, where considered appropriate, the same reference numerals may be used in multiple figures to indicate corresponding or analogous elements. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a flow diagram of a method for fabricating an etch resist mask according to some embodiments of the present invention. [Figure 2A] FIG. 2A is a photograph of an exemplary etch resist mask printed over unactivated copper. [Figure 2B] FIG. 2B shows a photograph of an exemplary etch resist mask printed on an activated copper surface in accordance with an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be understood by those skilled in the art that the present invention may be practiced without these exact specific examples. In other instances, well-known methods, procedures, and components have not been described in detail so as not to obscure the present invention.

[0012] An embodiment of the invention relates to a method of forming or applying an etch resist mask on a metal layer by non-impact printing, such as inkjet printing, for example during the manufacture of a printed circuit board (PCB). A method of applying an etch resist mask on a metal surface according to an embodiment of the invention includes applying a first liquid composition comprising a first reactive component to the surface to form a primer layer, and then printing a second liquid composition comprising a second reactive component onto the primer layer to generate an etch resist mask according to a predetermined pattern. The method includes applying a chemical surface activation solution onto the metal surface to chemically activate said metal surface, followed by removing / washing the chemical surface activation solution from the surface, and printing (e.g. inkjet printing) an etch resist ink onto the activated surface. According to an embodiment of the invention, the reactive components of the etch resist ink undergo a chemical reaction with the activated surface when they strike the surface, immobilizing droplets of the liquid composition of the etch resist ink. The chemical reaction occurs when the droplets strike the activated surface, resulting in a chemical reaction with the activated surface. In some cases, the viscosity of the ink droplets can be increased dramatically (e.g., by one or two orders of magnitude) instantaneously.

[0013] In some embodiments, the reactive components in the etch-resist ink (ink components) may be etch-resist components, while in other embodiments the reactive components may be different from the etch-resist components. According to some embodiments, two or more reactive components of the etch-resist ink may undergo chemical reactions with components on the activated surface.

[0014] 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 form that is a metal layer surface. However, it should be understood that other metal surfaces, such as aluminum surfaces, stainless steel surfaces, gold surfaces, etc., are equally applicable to embodiments of the present invention.

[0015] Please refer to FIG. 1, which is a flow diagram of a method for manufacturing an etch resist mask according to some embodiments of the present invention. According to an embodiment of the present invention, as shown in box 110, the method may include the step of applying a chemical surface activation solution onto a metal surface on which an etch resist pattern is to be printed. In some embodiments, the chemical surface activation solution may be or include any etching solution capable of chemically activating a surface. A chemically activated surface may be defined as a surface that does not react with an etch resist ink material prior to surface activation, but reacts after surface activation to cause immobilization of the etch resist ink droplets. Surface activation solutions may include, for example, copper salts, ferric salts, chromium sulfate, persulfate salts, sodium chlorite, hydrogen peroxide, and the like. In some embodiments, applying the chemically activating solution may include immersing the surface in a bath containing the chemical surface activation solution, spraying the chemical surface activation solution onto the surface, or any other suitable method. In some embodiments, the method may include exposing the metal surface to the chemically activating solution (e.g., by immersion, spraying, etc.) for, for example, 10 seconds, 20 seconds, 30 seconds, 60 seconds, or more.

[0016] As shown in box 115, in some embodiments, the method may optionally include removing the chemical surface activation solution using, for example, an alcohol solution. For example, the method may include removing remnants of the chemical surface activation solution from the surface using ethanol. In some embodiments, removing the chemical activation solution from the surface may be accomplished using other alcohol solutions, such as, for example, propyl alcohol, isopropyl alcohol, acetone, or other liquids besides an alcohol solution.

[0017] As shown in box 120, in some embodiments, the method may include printing an etch-resist ink by non-impact printing (e.g., inkjet printing) onto the activated surface to generate an etch-resist mask according to a predetermined pattern. The etch-resist ink may include an etch-resist polymer component that chemically reacts with the activated surface to immobilize droplets of the etch-resist ink when they strike the activated surface. In some embodiments, another ink component, different from the etch-resist component, chemically reacts with the activated surface to immobilize droplets of the etch-resist ink when they strike the activated surface.

[0018] Non-limiting examples of etch resist polymer reactive components include acrylate, styrene acrylate, phosphate and sulfonate polymers with molecular weights (Mw) between 1000-17000.

[0019] In some embodiments, the etch-resist reactive polymer component may be water-soluble and may include a reactive anionic component. A non-exhaustive list of examples includes at least one anionic polymer with a pH greater than 7.0 (basic). The anionic polymer may be selected from acrylic and styrene-acrylic resins in the form of dissolved salts, sulfone resins in the form of dissolved salts (e.g., neutralized with sodium, ammonium or amine), and the like. Without intending to be bound by a particular theoretical mechanism, these resins may undergo a reaction with a reactive (activated) surface. For example, when a copper metal surface is activated to form copper cations on the copper and an acrylic polymer (contained in an etch resist ink) hits the surface, the anionic acrylate reacts with the copper ions to form a polymer matrix, which will dramatically increase the viscosity of the droplet.

[0020] In some embodiments, the ink component that chemically reacts with the surface-activating component to pin a droplet of the etch-resistant ink when it strikes the activated surface may be different from the etch-resistant component.

[0021] The masked copper plate may be further etched with a metal etch (e.g., an acid copper etch) solution to remove the exposed unmasked (non-masked) portions of the metal layer, as shown in box 130. The etch resist mask may then be removed to expose the substrate, i.e., the wiring pattern on the insulating substrate, as shown in box 140. EXAMPLES

[0022] An exemplary liquid composition (etch resist ink composition described herein) was printed on a FR4 copper clad substrate with a copper thickness of 18 μm using an Epson Stylus® 4900 inkjet printer. 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 etch resist ink was selectively printed according to a predetermined pattern onto either the activated or the passivated copper surface using inkjet printing technology. In the following description, % (w / w) is a measure of the concentration of a substance expressed as weight % relative to the weight of the composition. The copper was etched away from the exposed unmasked areas using an etchant bath containing an iron (II) chloride etchant solution of 42 Baume supplied by Amza [pernix 166]™. The etching was performed in Spray Developer S31™ supplied by Walter Lemmen GMBH at a temperature of 35° C. for 3 minutes. The etch resist mask was removed by immersing the FR4 copper substrate in a 1% (w / w) aqueous NaOH solution at a temperature of 25°C, followed by rinsing the FR4 copper substrate with water and air drying at 25°C.

[0023] Example 1 - An etch resist ink in the form of a liquid composition at room temperature was printed onto an untreated (passivated) copper FR4 board. The liquid composition was prepared with 10% propylene glycol (as a humectant), as well as 1% (w / w) 2-amino-2-methylpropanol, 0.3% (w / w) BYK348 supplied by BYK, and 2% (w / w) Bayscript® BA cyan. These substances were dissolved in water containing 24% Joncryl® 8085 styrene acrylic resin solution as an anionic reactive component. The etch resist composition was printed onto a FR4 copper clad substrate having a thickness of 18 μm using an Epson Stylus® 4900 inkjet printer to produce an etch resist mask.

[0024] The etch resist mask was visually inspected, and as shown in Figure 2A, the printed pattern exhibited very poor print quality, with very poor line definition accuracy, poor line breaks, and shorts between lines.

[0025] Example 2 - A liquid composition was prepared as detailed in Example 1. The surface of a FR4 copper clad board was activated by dipping (e.g., immersing) the copper clad in a 0.5% (w / w) aqueous CuCl2 solution for 30 seconds, followed by rinsing the copper board with industrial ethanol.

[0026] Using an Epson Stylus 4900 inkjet printer, The liquid composition was printed onto the treated copper plate and dried at 80° C. to produce an insoluble etch resist mask. The etch resist pattern exhibited high print quality with sharp edges, no line breaks, fine line widths down to 50 μm, and well-defined thin lines, as shown in FIG. 2B. Etching of the exposed copper and removal of the etch resist mask was performed as detailed in Example 1. The wiring pattern on the plate exhibited well-defined thin lines with sharp edges, no line breaks, and fine line widths down to 50 μm.

[0027] Example 3 - A liquid composition was prepared as detailed in Example 1. The copper surface was activated by immersion in a bath containing 20% ​​(w / w) FeCl3 aqueous solution for 10 seconds, followed by rinsing the copper plate with industrial ethanol.

[0028] The liquid composition was inkjet printed onto the coated copper substrate and dried at 80° C. to produce an insoluble etch resist mask, as in Example 2. The etch resist pattern exhibited well-defined thin lines with sharp edges, no line discontinuities, and line widths as fine as 50 μm. Etching of the exposed copper and removal of the etch resist mask was performed as detailed in Example 1. The wiring pattern on the board exhibited well-defined thin lines with sharp edges, no line discontinuities, and line widths as fine as 30 μm.

[0029] Example 4 - A liquid composition was prepared as detailed in Example 1. The surface of a FR4 copper clad board was activated by immersing the copper clad in a 1% (w / w) Na2S2O8 aqueous solution for 30 seconds, and then the copper board was washed with industrial ethanol.

[0030] Using an Epson Stylus 4900 inkjet printer, The liquid composition was printed onto the treated copper plate and dried at 80°C to produce an insoluble etch resist mask. The etch resist pattern exhibited high print quality with sharp edges, no line breaks, fine line widths down to 50 μm, and well-defined thin lines. Etching of the exposed copper and removal of the etch resist mask was performed as detailed in Example 1. The wiring pattern on the plate exhibited well-defined thin lines with sharp edges, no line breaks, and fine line widths down to 30 μm.

[0031] Some non-limiting examples of chemical surface activation components used in embodiments of the present invention, and their relative weight concentrations in surface activation solutions according to some embodiments of the present invention as well as suggested immersion times, are listed in Table 1 below.

[0032] [Table 1]

[0033] Some non-limiting examples of etch resist inks are listed in Table 2.

[0034] [Table 2]

[0035] While certain features of the invention have been described in this specification and drawings, numerous modifications, substitutions and changes of elements, and equivalents will occur to those skilled in the art. It is therefore to be understood that the appended claims are intended to cover all such modifications and changes that fall within the spirit of the invention.

Claims

1. A substrate, the substrate comprising: A metal portion is provided on the substrate. activating the metal portion of the substrate by applying an activator selected from the group consisting of copper salts, ferric salts, chromic sulfate, persulfate, sodium chlorite, hydrogen peroxide, and combinations thereof to the metal portion to form an activated metal portion; inkjet printing an ink containing a reactive component and no initiator onto the activated metal parts according to a predetermined pattern, such that when droplets of the ink contact the activated metal parts, the reactive component in the ink chemically reacts with the activated metal parts to immobilize the droplets of the ink and create a patterned resist; performing an etching process to remove areas of metal not covered by the resist; removing the resist.

2. 1. A method of treating a substrate, the method comprising: applying an activator selected from the group consisting of copper salts, ferric salts, chromic sulfate, persulfate, sodium chlorite, hydrogen peroxide, and combinations thereof to a metal portion of the substrate to activate the metal portion to form an activated metal portion; inkjet printing an ink containing a reactive component and no initiator onto the activated metal parts according to a predetermined pattern to create a patterned resist, whereby when droplets of the ink contact the activated metal parts, the reactive component in the ink chemically reacts with the activated metal parts to immobilize the droplets of the ink; performing an etching process to remove areas of metal not covered by the resist; and removing the resist.

3. The method of claim 2 , wherein the resist comprises a plurality of lines, each having a width less than 50 μm.

4. The method of claim 2 , wherein the resist comprises a plurality of lines, each having a width of less than 30 μm.

5. 3. The method of claim 2, wherein applying the activator to the metal part comprises applying an aqueous solution containing the activator to the metal part, and further comprising removing the aqueous solution from the activated metal part using a solvent prior to the inkjet printing.

6. The method of claim 2 , wherein the reactive component is an anionic component.

7. The method of claim 2 , wherein the reactive component is a polymer that includes an acrylate, a phosphate, a sulfonate, or any combination thereof.

8. 3. The method of claim 2, wherein applying the activator to the metal part comprises immersing the metal part in an aqueous solution containing the activator for 10 to 60 seconds.

9. The method of claim 2 , wherein applying the activator to the metal part comprises spraying the metal part with an aqueous solution containing the activator.

10. 1. A method of treating a substrate, the method comprising: applying an activator selected from the group consisting of copper, ferric salts, chromic sulfate, persulfate, sodium chlorite, hydrogen peroxide, and combinations thereof to the copper portion of the substrate to activate the copper portion to form an activated copper portion; inkjet printing an ink containing a reactive component and no initiator onto the activated copper parts according to a predetermined pattern to create a patterned resist, whereby when droplets of the ink contact the activated copper parts, the reactive component in the ink chemically reacts with the activated copper parts to immobilize the droplets of the ink; performing an etching process to remove areas of the copper portion not covered by the resist; and removing the resist.

11. The method of claim 10 , wherein the activator forms copper ions on the copper moieties.

12. The method of claim 10 , wherein the reactive component comprises an acrylate polymer.

13. The method of claim 10 , wherein the ink comprises a dye.

14. 11. The method of claim 10, wherein applying the activator to the copper parts comprises applying an aqueous solution containing the activator to the copper parts, and further comprising removing the aqueous solution from the activated copper parts with a solvent prior to the inkjet printing.

15. The method of claim 10 , wherein the acrylate polymer in the ink is in the form of a dissolved salt.

16. The method of claim 10 , wherein the ink further comprises an etch resist component.

17. 1. A method of treating a substrate, the method comprising: activating the copper portion of the substrate by applying an activator to the copper portion selected from the group consisting of copper salts, ferric salts, chromic sulfate, persulfate, sodium chlorite, hydrogen peroxide, and combinations thereof to form an activated copper portion; selectively printing an ink, containing reactive components in the form of dissolved salts and no initiator, onto the activated copper areas according to a predetermined pattern to produce a patterned resist, whereby when droplets of the ink contact the activated copper areas, the reactive components in the ink chemically react with the activated copper areas to immobilize the droplets of the ink; performing an etching process to remove areas of the copper portion not covered by the resist; and removing the resist.

18. 20. The method of claim 17, wherein applying the activator to the copper parts comprises applying an aqueous solution containing the activator to the copper parts, and further comprising removing the aqueous solution from the activated copper parts with a solvent prior to the inkjet printing.

19. The method of claim 17 , wherein the ink is an aqueous solution.

20. The method of claim 17 , wherein the ink has a pH greater than 7.0.

Images