Metal foil, carrier with metal foil provided therewith, and printed circuit board including same

Abstract

The present invention relates to a metal foil having a rough surface, a metal foil with a carrier including the metal foil, and a printed circuit board manufactured using the metal foil. The rough surface is formed naturally during the formation of the metal foil. By forming the rough surface, the metal foil can be provided with high adhesive strength to an insulating resin substrate, enabling the production of printed circuit boards with improved efficiency.

Description

[Technical Field]

[0001] The present invention relates to a metal foil having a rough surface, a carrier having the metal foil provided therewith, and a printed circuit board manufactured using the metal foil. [Background technology]

[0002] Printed circuit boards are typically manufactured by adhering a metal foil to an insulating resin substrate and etching the metal foil to form circuit wiring. High adhesive strength between the metal foil and the insulating resin substrate is required to prevent the metal foil from peeling off during circuit wiring.

[0003] Various proposals have been made to improve the adhesion between metal foil and insulating resin substrate. For example, the adhesive strength between metal foil and insulating resin substrate can be improved by roughening the surface of the metal foil to form irregularities on the surface, placing the insulating resin substrate on the irregular surface of the metal foil, and pressing the insulating resin substrate to adhere it to the metal foil. Specifically, Patent Document 1 discloses a method for improving the adhesion between copper foil and a resin layer by forming rough protrusions on the surface of the copper foil facing the resin layer through electrolysis, blasting, or oxidation-reduction.

[0004] However, this method has a problem in that further roughening of the metal foil reduces the manufacturing efficiency of printed circuit boards. Furthermore, forming irregularities on the surface of the metal foil can reduce the transmission efficiency of high-frequency signals. As the performance of portable electronic devices continues to improve, high-frequency signal transmission losses must be minimized to quickly process large amounts of information. However, the irregularities make the surface of the metal foil very rough, which becomes an obstacle to high-frequency signal transmission, resulting in inefficient high-frequency signal transmission. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Korean Patent Application Publication No. 2018-0019190 Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention aims to provide a metal foil that has high adhesive strength to an insulating resin substrate and can prevent a decrease in the transmission efficiency of high-frequency signals.

[0007] The present invention also aims to provide a metal foil with a carrier comprising the above metal foil.

[0008] The present invention also aims to provide a printed circuit board comprising the metal foil. [Means for solving the problem]

[0009] One aspect of the present invention provides a metal foil having a plurality of flat-topped protrusions.

[0010] Each of the plurality of protrusions may include a protruding portion having a truncated cone shape or a truncated polygonal pyramid shape, and a flat portion formed on an upper end of the protruding portion.

[0011] The protrusion may have a plurality of micro-protrusions formed on a surface of the protrusion.

[0012] The protrusions may have a surface roughness (Ra) of 0.05 to 0.3 μm.

[0013] The ratio of the height (b) of the protrusion to the length (a) of the base of the protrusion may be 0.4:1 to 1.5:1 (b:a).

[0014] The ratio of the length (c) of the flat portion to the length (a) of the base of the protrusion may be 0.1:1 to 0.7:1 (c / a).

[0015] The polygonal truncated pyramid shape may be selected from the group consisting of a pentagonal truncated pyramid shape, a hexagonal truncated pyramid shape, a heptagonal truncated pyramid shape, and an octagonal truncated pyramid shape.

[0016] The plurality of protrusions may be formed by electroless plating.

[0017] A further aspect of the present invention provides a metal foil with a carrier, comprising a carrier, a release layer formed on the carrier, and a metal layer formed on the release layer, wherein the metal foil is used as the metal layer.

[0018] Another aspect of the present invention provides a printed circuit board having a metal circuit layer, wherein the metal foil having circuit wiring formed thereon is used as the metal circuit layer. [Effects of the Invention]

[0019] By forming flat-topped protrusions on the surface of the metal foil of the present invention, the metal foil can have high adhesive strength to an insulating resin substrate, minimizing loss in high-frequency signal transmission. Because the protrusions are naturally formed on the metal foil of the present invention during the electroless plating process, there is no need for additional roughening to form irregularities on the metal foil, as is the case with prior art. Therefore, the use of the metal foil of the present invention enables highly efficient production of printed circuit boards. [Brief explanation of the drawings]

[0020] [Figure 1] FIG. 1 shows a portion of the surface of a metal foil according to one embodiment of the present invention. [Figure 2] FIG. 2 shows the shape of protrusions that can be formed on a metal foil according to one embodiment of the present invention. [Figure 3] FIG. 3 shows the results of Test Example 1. [Figure 4] FIG. 4 shows the results of Test Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0021] The technical terms and words used in this specification and claims should not be construed as being limited to their ordinary or dictionary meanings, but should be construed as meanings and concepts corresponding to the technical idea of ​​the present invention based on the principle that the inventor can appropriately define the concepts of technical terms so as to best express his or her invention.

[0022] When an element is referred to as being "on" another element, it is understood that the element may be directly on the other element, or there may be intervening elements. When an element and another element change position relative to each other, "on" may also be interpreted as "under."

[0023] The present invention will now be described in detail with reference to the accompanying drawings.

[0024] 1 , the metal foil 100 of the present invention has a plurality of flat-topped protrusions 10. The protrusions 10 may be metal crystal particles protruding vertically upward from the surface of the metal foil 100. Specifically, each of the plurality of protrusions 10 may have a protruding portion 11 and a flat portion 12.

[0025] The protruding portion 11 of the projection 10 is a portion that protrudes from the surface of the metal foil 100 and may have a truncated cone shape or a truncated polygonal pyramid shape. Specifically, as shown in FIG. 2, the protruding portion 11 has a truncated cone shape with a flat surface (side surface) or a truncated polygonal pyramid shape with angular surfaces. This shape can improve the fixation of the metal foil to the insulating resin substrate, thereby allowing the metal foil 100 to be bonded to the insulating resin substrate with high adhesive strength. More specifically, the protruding portion 11 may have at least one type of truncated polygonal pyramid shape selected from the group consisting of a truncated pentagonal pyramid shape, a truncated hexagonal pyramid shape, a truncated heptagonal pyramid shape, and a truncated octagonal pyramid shape.

[0026] Each of the protrusions 11 may have a plurality of micro-protrusions 11a to increase its surface area and thereby improve adhesion to the insulating resin substrate. By forming the micro-protrusions 11a, the surface roughness (Ra) of the protrusions 11 can be set to 0.05 to 0.3 μm, particularly 0.08 to 0.2 μm. Here, the surface roughness (Ra) of the protrusions 11 is defined as the surface roughness of the side surfaces of the protrusions 11 excluding the flat portions 12.

[0027] On the other hand, the ratio of the height (b) of each protrusion 11 to the length (a) of the base of the protrusion 11 may be within the range of 0.4:1 to 1.5:1 (b:a), particularly 0.6:1 to 1.2:1 (b:a). When the ratio (b:a) is within the above range, the adhesion between the metal foil 100 and the insulating resin substrate can be improved, and the loss of high-frequency signal transmission can be minimized.

[0028] The flat portion 12 of the protrusion 10 is the flat surface at the top end of the protrusion 11. The flat portion 12 may be the top surface of the protrusion 11 having a truncated cone shape or a truncated polygonal pyramid shape. According to the prior art, particles protrude from the surface of the metal foil at sharp or rounded angles, forming irregularities that make the surface of the metal foil very rough. While forming irregularities can improve adhesion to insulating resin substrates, it also results in a loss of high-frequency signal transmission. In contrast, the flat portion 12 that forms the top surface (top end) of the protrusion 10 allows the metal foil 100 of the present invention to have a relatively low surface roughness due to its flatness. The relatively low surface roughness minimizes the loss of high-frequency signal transmission. Specifically, the flat portion 12 may have a circular, elliptical, or polygonal shape. A flat surface formed by densely forming fine irregularities can also be considered to be included in the scope of the flat portion 12.

[0029] In each projection 10, the ratio of the length (c) of the flat portion 12 to the length (a) of the base of the protruding portion 11 may be within the range of 0.1:1 to 0.7:1, particularly 0.2:1 to 0.6:1. When the ratio (c:a) is within the above range, the adhesion between the metal foil 100 and the insulating resin substrate can be improved, and the loss of high-frequency signal transmission can be minimized. The length (c) of the flat portion 12 means the maximum length within the plane of the flat portion 12.

[0030] The unit area of ​​metal foil 100 (1 μm 2 The number of protrusions 10 per metal foil 100 may be 25 or less, particularly 5 to 20, and more particularly 7 to 15, taking into consideration the adhesion between the metal foil 100 and the insulating resin substrate, the transmission efficiency of high-frequency signals, the circuit wiring resolution of the metal foil 100, etc.

[0031] The protrusions 10 may be formed by electroless plating. Specifically, the protrusions 10 can be formed on the surface of the metal foil 100 by forming a metal seed foil by electroless plating and then continuously growing crystal grains on the metal seed foil. In the prior art, the irregularities are formed by additionally roughening the metal foil. In contrast, the multiple protrusions 10 naturally form a rough surface during the process of forming the metal foil 100 of the present invention. This eliminates the need for additional roughening, allowing for highly efficient formation of the metal foil 100 and / or manufacturing of printed circuit boards. In addition, electroless plating makes the metal foil 100 thinner and more porous than electroplating.

[0032] The composition of the electroless plating solution used to form the metal foil 100 is not particularly limited, and may contain a metal ion source and a nitrogen compound.

[0033] The metal ion source may specifically be a copper ion source selected from the group consisting of copper sulfate, copper chloride, copper nitrate, copper hydroxide, copper sulfamate, and mixtures thereof. The metal ion source may be present in a concentration of 0.5 to 300 g / L, particularly 100 to 250 g / L.

[0034] The nitrogen compound diffuses metal ions to form multiple protrusions 10 on the surface of the metal seed foil formed by the metal ion source. Specifically, the nitrogen compound may be selected from the group consisting of purine, adenine, guanine, hypoxanthine, xanthine, pyridazine, methylpiperidine, 1,2-di-(2-pyridyl)ethylene, 1,2-di-(pyridyl)ethylene, 2,2'-dipyridylamine, 2,2'-bipyridyl, 2,2'-bipyrimidine, 6,6'-dimethyl-2,2'-dipyridyl, di-2-furyl ketone, N,N,N',N'-tetraethylenediamine, 1,8-naphthyridine, 1,6-naphthyridine, terpyridine, and mixtures thereof. The nitrogen compound may be present at a concentration of 0.01 to 10 g / L, particularly 0.05 to 1 g / L.

[0035] The electroless plating solution may further contain one or more additives selected from the group consisting of a chelating agent, a pH adjuster, and a reducing agent.

[0036] Specifically, the chelating agent may be selected from the group consisting of tartaric acid, citric acid, acetic acid, malic acid, malonic acid, ascorbic acid, oxalic acid, lactic acid, succinic acid, potassium sodium tartrate, dipotassium tartrate, hydantoin, 1-methylhydantoin, 1,3-dimethylhydantoin, 5,5-dimethylhydantoin, nitriloacetic acid, triethanolamine, ethylenediaminetetraacetic acid, tetrasodium ethylenediaminetetraacetate, N-hydroxyethylenediaminetriacetic acid, pentahydroxypropyldiethylenetriamine, and mixtures thereof. The chelating agent may be present in a concentration of 0.5 to 600 g / L, particularly 300 to 450 g / L.

[0037] Specifically, the pH adjuster may be selected from the group consisting of sodium hydroxide, potassium hydroxide, lithium hydroxide, and mixtures thereof. The pH adjuster can adjust the pH of the electroless plating solution to 8 or higher, particularly 10 to 14, and more particularly 11 to 13.5.

[0038] Specifically, the reducing agent may be selected from the group consisting of formaldehyde, sodium hypophosphite, sodium hydroxymethanesulfinate, glyoxylic acid, borohydride compounds, dimethylamine borane, and mixtures thereof. The reducing agent may be present in a concentration of 1 to 20 g / L, particularly 5 to 20 g / L.

[0039] The conditions for electroless plating to form the metal foil 100 can be adjusted appropriately depending on the thickness of the metal foil 100. Specifically, the electroless plating temperature may be 20 to 60°C, particularly 25 to 40°C, and the electroless plating time may be 2 to 30 minutes, particularly 5 to 20 minutes.

[0040] The thickness of the metal foil 100 formed by electroless plating may be 5 μm or less, particularly 0.1 to 1 μm. The components of the metal foil 100 are not particularly limited and may be any known metal capable of forming a circuit layer of a printed circuit board. Specifically, the metal may be selected from the group consisting of copper, silver, gold, nickel, aluminum, and mixtures thereof.

[0041] The present invention also provides a metal foil with a carrier, which includes the above-mentioned metal foil. Specifically, the metal foil with a carrier includes a carrier, a release layer, and a metal layer, and the above-mentioned metal foil is used as the metal layer. The metal foil with a carrier will be described in detail below.

[0042] The carrier of the metal foil with a carrier according to the present invention serves to prevent deformation of the metal layer during transportation or use of the metal foil with a carrier. The carrier 300 is made of a metal such as copper or aluminum. Alternatively, the carrier 300 may be made of a polymer such as polyethylene terephthalate (PET), polyphenylene sulfide (PPS), or Teflon. The thickness of the carrier may be, specifically, 10 to 50 μm.

[0043] The release layer of the carrier-attached metal foil is designed to allow the carrier to be easily removed from the carrier-attached metal foil bonded to the insulating resin substrate. The release layer may have a single-layer structure or a multi-layer structure. Specifically, the release layer may have a single-layer structure containing a nitrogen-containing cyclic compound as an organic material and a metal selected from the group consisting of nickel, molybdenum, cobalt, phosphorus, manganese, and iron. Alternatively, the release layer may have a multi-layer structure in which an organic layer composed of a nitrogen-containing cyclic compound is bonded to an alloy layer containing one or more metals selected from the group consisting of nickel, molybdenum, cobalt, phosphorus, manganese, and iron. The release layer may have a thickness of 30 nm to 1 μm.

[0044] As the metal layer of the metal foil with a carrier, the above-mentioned metal foil is used, and therefore a detailed description thereof will be omitted.

[0045] The metal foil with a carrier of the present invention may further include an electrolytic metal layer formed on the metal layer to enhance the mechanical strength and electrical conductivity of the metal layer. The electrolytic metal layer may be composed of the same components as the metal layer, or may be composed of different components.

[0046] The metal foil with a carrier of the present invention may further include an anticorrosion layer formed on the metal layer to protect the metal layer from rust. For example, the anticorrosion layer may contain zinc or chromium.

[0047] The metal foil with a carrier of the present invention may further include a diffusion barrier layer formed between the carrier and the alloy layer of the release layer to improve its performance. For example, the diffusion barrier layer may contain nickel or phosphorus.

[0048] The metal foil with a carrier of the present invention may further include an oxidation barrier layer formed between the organic layer of the release layer and the metal layer. For example, the oxidation barrier layer may contain nickel or phosphorus.

[0049] The present invention also provides a printed circuit board manufactured using the metal foil. Specifically, the printed circuit board of the present invention comprises a metal circuit layer and an insulating resin layer. The metal circuit layer is derived from the metal foil, as described below.

[0050] The metal circuit layer of a printed circuit board is a layer on which circuit wiring is formed. The metal circuit layer is obtained by forming circuit wiring on the above-mentioned metal foil. The metal foil ensures the miniaturization and high resolution of the printed circuit board. Specifically, the printed circuit board of the present invention is manufactured by bonding an insulating resin substrate and a metal foil to form a laminate, and then etching the laminate to form circuit wiring on the metal foil. The metal foil is bonded to the insulating resin substrate with high adhesive strength and has a relatively small thickness, allowing fine, high-resolution circuit wiring to be formed on the metal foil. In addition, the circuit wiring formed on the metal foil has high adhesive strength to the insulating resin substrate.

[0051] There are no particular limitations on the method for forming the circuit wiring. For example, the circuit wiring may be formed by a subtractive method, an additive method, a full-additive method, a semi-additive method, or a modified semi-additive method.

[0052] The insulating resin layer of the printed circuit board is an insulating layer formed on a metal circuit layer. The insulating resin layer may be any suitable insulating resin substrate known in the art. Specifically, the insulating resin layer may be a resin substrate having a structure in which a known resin is impregnated into inorganic or organic fibers. For example, the resin substrate may be a prepreg.

[0053] The printed circuit board of the present invention may be manufactured using an insulating resin substrate, or may be manufactured by a coreless process that does not use an insulating resin substrate.

[0054] The present invention will be described in more detail with reference to the following examples. However, these examples are provided for illustrative purposes and are not intended to limit the scope of the present invention. It will be understood by those skilled in the art that various modifications and variations can be made without departing from the scope and spirit of the present invention. [Example]

[0055] [Example 1] A copper (Cu) foil carrier was bonded to a release layer (an alloy layer composed of nickel and molybdenum + an organic layer composed of sodium mercaptobenzotriazole) to fabricate a laminate. The laminate was then electrolessly plated in an electroless plating bath to form a 1 μm-thick metal foil (copper foil) on the release layer. The electroless plating solution used contained 190–200 g / L CuSO4·5H2O as the metal ion source, 0.01–0.1 g / L guanine as the nitrogen compound, 405–420 g / L potassium sodium tartrate as the chelating agent, NaOH as the pH adjuster, and 28% formaldehyde as the reducing agent. Electroless plating was performed at 30°C for 10 minutes.

[0056] [Comparative Example 1] A metal foil (copper foil) was formed in the same manner as in Example 1, except that electroless plating was carried out at 34°C for 20 minutes in an electroless plating solution containing 200 to 210 g / L of CuSO4·5H2O and NiSO4·6H2O as metal ion sources, 0.5 to 0.8 g / L of 2,2-bipyridine as a nitrogen compound, 405 to 420 g / L of potassium sodium tartrate as a chelating agent, and 28% formaldehyde as a reducing agent.

[0057] [Test Example 1] The surfaces and cross sections of the metal foils formed in Example 1 and Comparative Example 1 were analyzed with a scanning electron microscope (SEM) and an ion beam cross-section polisher (CP), and the results are shown in Figures 3 and 4.

[0058] Referring to Figures 3 and 4, the metal foil of the present invention in Example 1 had multiple flat protrusions on the top surface, while the metal foil of Comparative Example 1 had multiple angular protrusions on the top surface.

[0059] [Test Example 2] The adhesiveness of each of the metal foils formed in Example 1 and Comparative Example 1 was evaluated according to the following procedure. A SUS plate, kraft paper, a release film, an insulating resin substrate (DS-7409HG), the metal foil (including the release layer) formed in Example 1 or Comparative Example 1, kraft paper, and a SUS plate were laminated in this order and pressed under vacuum at a pressure of 3.5 MPa and a temperature of 200°C for 100 minutes to produce a laminate. After removing the kraft paper and the SUS plate from the laminate via the release layer, the peel strength between the metal foil and the insulating resin substrate was evaluated using the IPC-TM-650 test method (BMSP-90P peel tester, test speed: 50 mm / min, test angle: 90°). The results are shown in Table 1. [Table 1]

[0060] As can be seen from the results in Table 1, the peel strength between the metal foil and the insulating resin substrate of the laminate comprising the metal foil of the present invention in Example 1 was higher.

[0061] [Test Example 3] The high-frequency signal transmission performance of printed circuit boards equipped with the metal foils formed in Example 1 and Comparative Example 1 was evaluated by the following procedure. Copper foil (18 μm thick), an insulating resin substrate (DS-7402, 50 μm thick), and the metal foil formed in Example 1 or Comparative Example 1 were laminated in this order, and wiring (width: 40 μm, length: 10 cm) was formed on the metal foil using mSAP. An insulating resin substrate (DS-7402) and copper foil were laminated on the metal foil with the wiring formed, and through-hole processing was performed to manufacture a printed circuit board. The high-frequency signal transmission performance of the printed circuit board was measured using a PNA N5225A (KEYSIGHT). S 21 The parameters (dB) were measured from 10 MHz to 40 GHz, and the results are shown in Table 2. [Table 2]

[0062] The results in Table 2 show that the printed circuit board with the metal foil of Example 1 has better high frequency signal transmission performance. [Note] The present disclosure relates to the following aspects: <1> ~ <10> Also includes. <1> A metal foil having a plurality of flat-topped projections. <2> Each of the plurality of protrusions includes a protruding portion having a truncated cone shape or a truncated polygonal pyramid shape, and a flat portion formed on an upper end of the protruding portion. <1> The metal foil according to claim 1. <3> the protrusion has a plurality of microprotrusions formed on a surface of the protrusion; <2> The metal foil according to claim 1. <4> The protrusion has a surface roughness (Ra) of 0.05 to 0.3 μm. <2> The metal foil according to claim 1. <5> The ratio of the height (b) of the protrusion to the length (a) of the base of the protrusion is 0.4:1 to 1.5:1 (b:a). <2> The metal foil according to claim 1. <6> The ratio of the length (c) of the flat portion to the length (a) of the base of the protrusion is 0.1:1 to 0.7:1 (c / a). <2> The metal foil according to claim 1. <7> The polygonal truncated pyramid shape is selected from the group consisting of a pentagonal truncated pyramid shape, a hexagonal truncated pyramid shape, a heptagonal truncated pyramid shape, and an octagonal truncated pyramid shape. <2> The metal foil according to claim 1. <8> the plurality of protrusions are formed by electroless plating; <1> The metal foil according to claim 1. <9> a carrier, a release layer formed on the carrier, and a metal layer formed on the release layer; <1> ~ <8> 1. A metal foil with a carrier, wherein the metal foil according to any one of 1 to 3 above is used as the metal layer. <10> A printed circuit board having a metal circuit layer on which circuit wiring is formed. <1> ~ <8> 10. A printed circuit board, wherein the metal foil according to any one of 1 to 8 is used as the metal circuit layer. [Explanation of symbols]

[0063] 100: Metal foil 10: Protrusion 11: Protrusion 11a: Micro protrusion 12: Flat area

Claims

1. A metal foil having a plurality of flat-topped protrusions, each of the plurality of protrusions having a protruding portion having a truncated cone shape or a truncated polygonal pyramid shape, and a flat portion formed at an upper end of the protrusion, wherein the ratio of the length (c) of the flat portion to the length (a) of the base of the protrusion is 0.1:1 to 0.7:1 (c / a), and the protrusions have a surface roughness (Ra) of 0.05 to 0.3 μm.

2. The metal foil of claim 1 , wherein the protrusions have a plurality of microprotrusions formed on a surface of the protrusions.

3. 3. The metal foil according to claim 1, wherein the ratio of the height (b) of the protrusion to the length (a) of the base of the protrusion is 0.4:1 to 1.5:1 (b:a).

4. The metal foil according to any one of claims 1 to 3, wherein the polygonal truncated pyramid shape is selected from the group consisting of a pentagonal truncated pyramid shape, a hexagonal truncated pyramid shape, a heptagonal truncated pyramid shape, and an octagonal truncated pyramid shape.

5. The metal foil according to any one of claims 1 to 4, wherein the plurality of protrusions are formed by electroless plating.

6. A metal foil with a carrier, comprising: a carrier; a release layer formed on the carrier; and a metal layer formed on the release layer, wherein the metal foil according to any one of claims 1 to 5 is used as the metal layer.

7. A printed circuit board having a metal circuit layer, wherein the metal foil according to any one of claims 1 to 5 on which circuit wiring is formed is used as the metal circuit layer.

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