Advanced electrodeposited copper foil and copper clad laminate using the same

An advanced electrodeposited copper foil and a copper clad laminate using the same are provided. The advanced electrodeposited copper foil has an uneven micro-roughened surface. As observed by a scanning electron microscope operated with a +35 degree tilt and under 1,000× magnification, the uneven micro-roughened surface has a plurality of production direction stripes formed by copper crystals.

FIELD OF THE DISCLOSURE

The present disclosure relates to an electrodeposited copper foil, and more particularly to an advanced electrodeposited copper foil and a copper clad laminate using the same.

BACKGROUND OF THE DISCLOSURE

With the development of information and electronic industries, high frequency and high speed signal transmission has become an integral part of modern circuit design and manufacture. In order to meet the high frequency and high speed signal transmission requirements of electronic products, a copper clad laminate (CCL) needs to be capable of preventing an excessive loss of a high frequency signal so as to achieve good signal integrity (SI). In general, the insertion loss of a copper foil in the copper foil substrate is highly correlated with the surface roughness of a surface-treated surface thereof. However, the peel strength of the copper foil conflicts with signal integrity. More specifically, when the copper foil has a flatter surface profile, it would achieve better signal integrity. When the copper foil has a rougher surface profile, it would achieve better peel strength. Therefore, it is necessary to develop a copper clad laminate that can provide a balance between signal integrity and peel strength in this technical field.

SUMMARY OF THE DISCLOSURE

In response to the above-referenced technical inadequacies, the present disclosure provides an advanced electrodeposited copper foil, which can be applied to the 5G field that requires high frequency and high speed transmission and can maintain properties required for a target application, such as the peel strength of an electrodeposited copper foil. The present disclosure further provides a copper clad laminate using the advanced electrodeposited copper foil, which can serve as a high frequency and high speed transmission substrate.

In one aspect, the present disclosure provides an advanced electrodeposited copper foil that has an uneven micro-roughened surface. As observed by a scanning electron microscope operated with a +35 degree tilt and under 1,000× magnification, the micro-roughened surface has a plurality of production direction stripes and a plurality of fine strips which are formed by copper crystals, and at least five of the fine strips each have a minimum included angle that is greater than 20 degrees relative to the production direction stripes.

In another aspect, the present disclosure provides a copper clad laminate that includes a substrate and an advanced electrodeposited copper foil. The advanced electrodeposited copper foil is disposed on the substrate and has an uneven micro-roughened surface that is bonded to a surface of the substrate. As observed by a scanning electron microscope operated with a +35 degree tilt and under 1,000× magnification, the micro-roughened surface has a plurality of production direction stripes and a plurality of fine strips which are formed by copper crystals, in which at least five of the fine strips each have a minimum included angle that is greater than 20 degrees relative to the production direction stripes.

In certain embodiments, as observed by the scanning electron microscope operated with a +35 degree tilt and under 10,000× magnification, the fine strips each have a length and a width which satisfy the following relationship:
50 nm≤width≤1000 nm; and
1.0 μm≤length≤10 μm.

In certain embodiments, as observed by the scanning electron microscope operated with a +35 degree tilt and under 10,000× magnification, the micro-roughened surface has at least ten first smooth areas each having a length of 250 nm and a width of 250 nm and at least one second smooth area having a length of 500 nm and a width of 500 nm, and no copper crystals are present in each of the first and second smooth areas.

In certain embodiments, different quantities of the copper crystals are stacked together to form respective copper whiskers, and different quantities of the copper whiskers are grouped together to form respective copper crystal groups. As observed by the scanning electron microscope operated with a +35 degree tilt and under 10,000× magnification, the copper crystals, the copper whiskers or the copper crystal groups have a median maximum diameter less than 550 nm.

In certain embodiments, each of the copper whiskers has a topmost copper crystal that is in the shape of a conoid, a rod or a sphere.

In certain embodiments, the micro-roughened surface has a surface roughness (Rz JIS B 0601-1994) less than 2.3 μm.

In certain embodiments, as observed by the scanning electron microscope operated with a +35 degree tilt and under 10,000× magnification, the number of the fine strips is three or more.

One of the beneficial effects of the present disclosure is that, the advanced electrodeposited copper foil and the copper clad laminate can increase signal integrity and suppress insertion loss, while maintaining good peel strength, to be adaptable to high frequency and high speed signal transmission so as to meet the requirements of 5G applications, by virtue of “the micro-roughened surface has a plurality of production direction stripes and a plurality of fine strips which are formed by copper crystals, and at least five of the fine strips each have a minimum included angle greater than 20 degrees relative to the production direction stripes.”

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

It is worth mentioning that, the present disclosure substantially uses a technical solution that is discarded due to a technical prejudice in the art, which allows a copper foil surface to have a certain degree of unevenness. The technical solution can directly achieve the beneficial technical effect of further optimizing electrical properties on the premise of maintaining good peel strength.

Referring toFIG. 1toFIG. 3, the present disclosure provides a copper clad laminate C that includes a substrate1and at least one advanced electrodeposited copper foil2disposed on the substrate1. In the present embodiment, the quantity of the advanced electrodeposited copper foil2is two, each of which has an uneven micro-roughened surface20that is bonded to a surface of the substrate1, but the present disclosure is not limited thereto. In other embodiments, the copper clad laminate C can include only one advanced electrodeposited copper foil2.

In order to reduce insertion loss, the substrate1can be formed from a material having a low dissipation factor (Df). The Df of the substrate1can be less than or equal to 0.015 at 10 GHz, preferably less than or equal to 0.010, and more preferably less than or equal to 0.005.

More specifically, the substrate1is formed from a resin-based composite material (i.e., a prepreg), which is obtained by the steps of impregnating a base material with a synthetic resin and then curing the impregnated base material. Specific examples of the base material include a phenolic cotton paper, a cotton paper, a fabric made of resin fibers, a non-woven fabric made of resin fibers, a glass board, a glass woven fabric and a glass non-woven fabric. Specific examples of the synthetic resin include an epoxy resin, a polyester resin, a polyimide resin, a cyanate ester resin, a bismaleimide triazine resin, a polyphenylene ether resin and a phenol resin. The synthetic resin can be formed into a single-layered or multi-layered structure. The resin-based composite material can be a mid loss, low loss, very low loss or ultra low loss material, which are well-known to people skilled in this art and are specifically exemplified by products of EM890, EM890(K), EM891(K), EM528, EM526, IT170GRA1, IT958G, IT968G, IT150DA, S7040G, S7439G, S6GX, TU863+, TU883 (A,SP), MEGTRON 4, MEGTRON 6, MEGTRON 7 and MEGTRON 8. However, these examples are not meant to limit the scope of the present disclosure.

Referring toFIG. 2andFIG. 3, the micro-roughened surface20of the advanced electrodeposited copper foil2is formed by a micro-roughening treatment of copper electrodeposition. It is worth mentioning that, the micro-roughened surface20has a plurality of copper crystals21, a plurality of copper whiskers W and a plurality of copper crystal groups G which are in a non-uniform distribution, i.e., being non-uniformly deposited on a copper foil surface. Each of the copper whiskers W is formed by two or more of the copper crystals21stacked together, and different quantities of the copper crystals21are stacked together to form the respective copper whiskers W. Furthermore, each of the copper whiskers W has a topmost copper crystal211that is in the shape of a conoid, a rod or a sphere, and preferably a sphere. Each of the copper crystal groups G is formed by two or more of the copper whiskers W grouped together, and different quantities of the copper whiskers W are grouped together to form the respective copper crystal groups G.

Referring toFIG. 5andFIG. 6, as observed by a scanning electron microscope (S-3400N, manufactured by Hitachi, Ltd.) operated at a +35 degree tilt and 3,000× magnification, the micro-roughened surface20has a plurality of production direction stripes20aand a plurality of fine strips20b. A reference line RL is defined by the production direction stripes20a, and the fine strips20beach have a minimum included angle β1-β9greater than 20 degrees relative to the reference line RL.

The reference line RL is defined as follows: acquiring images of the micro-roughened surface20as shown inFIG. 5andFIG. 6by a scanning electron microscope operated at a +35 degree tilt and respectively under magnification of 1,000× and magnification of 3,000×, with a sample being placed in the production direction (MD) (i.e., the extension direction of the production direction stripes20a); using an image analysis software (ImageJ software from the National Institutes of Health, available at on the Internet at https://imagej.nih.gov/ij/download.html) to draw a horizontal line HL at the bottom of the image under 1,000× magnification, and then draw extension lines of ten of the production direction stripes20aat different positions; acquiring the inclination angles α1-α10of the ten production direction stripes20arelative to the horizontal line HL to calculate an average value; and drawing a reference line RL according to the average value of the inclination angles α1-α10and based on the horizontal line HL. As shown inFIG. 5, the inclination angles α1-α10of the ten production direction stripes20aare respectively 92.79 degrees, 88.13 degrees, 89.51 degrees, 86.49 degrees, 85.74 degrees, 91.45 degrees, 85.88 degrees, 88.27 degrees, 79.62 degrees and 87.71 degrees, with the average value thereof being 87.56 degrees.

The inclination angles of the fine strips20bare measured by the following method: using the image analysis software (ImageJ software from the National Institutes of Health, http://rsb.info.nih.gov) to draw another horizontal line HL on the image under 3,000× magnification, and then draw a number of the reference lines RL that are parallel to each other based on the another horizontal line HL; and acquiring the minimum included angles β1, β2, β3, β4, β5, β6, β7, β8, β9of the fine strips20brespectively relative to the reference lines RL. As shown inFIG. 6, at least five of the minimum included angles β1, β2, β3, β4, β5, β6, β7, β8, β9of the fine strips20bare greater than 20 degrees. As used herein, the term “fine strip” means a strip having a length and a width which satisfy the following relationship: 50 nm≤width≤1000 nm and 1.0 μm≤length≤10 μm.

Referring toFIG. 7, as observed by a scanning electron microscope (S-3400N, manufactured by Hitachi, Ltd.) operated at a +35 degree tilt and 10,000× magnification, the micro-roughened surface20further has at least ten first smooth areas20ceach having a length of 250 nm and a width of 250 nm and at least one second smooth area20dhaving a length of 500 nm and a width of 500 nm, which are located between the production direction stripes20aand the fine strips20b.

It is worth mentioning that, different from the conventional electrodeposited copper foil, the micro-roughened surface20of the advanced electrodeposited copper foil2has a plurality of production direction stripes20aand a plurality of fine strips20bwhich are formed by copper crystals21, in which at least five of the fine strips20beach have a minimum included angle β1, β2, β3, β4, β5, β6, β7, β8, β9greater than 20 degrees. Furthermore, on the micro-roughened surface20, there are at least ten first smooth areas20ceach having a length of 250 nm and a width of 250 nm and at least one second smooth area20dhaving a length of 500 nm and a width of 500 nm. Therefore, the advanced electrodeposited copper foil2of the present disclosure can increase signal integrity and suppress insertion loss on the premise of maintaining good peel strength, so as to be adaptable to high frequency and high speed signal transmission. In addition, the micro-roughened surface20has a surface roughness (Rz JIS B 0601-1994) less than 2.3 μm, which can facilitate a reduction in line width and line spacing.

Reference is again made toFIG. 3, in which the micro-roughened surface20further includes a plurality of peaks22and a plurality of grooves23between the peaks22. The copper crystals21, the copper whiskers W and the copper crystal groups G are correspondingly formed on the peaks22. Each of the grooves23has a U-shaped or V-shaped cross-sectional profile. Accordingly, when the advanced electrodeposited copper foil2of the present disclosure is pressed on a resin-based composite material, the micro-roughened surface20can receive a greater amount of a resin material so as to increase the bonding strength between the copper foil and the resulting substrate.

Manufacturing Example

Referring again toFIG. 2, which is to be read in conjunction withFIG. 4, a method for manufacturing the advanced electrodeposited copper foil2of the present disclosure includes performing a micro-roughening treatment of copper electrodeposition on a matte side of a raw foil, in which the matte side is formed into a micro-roughened surface20. The micro-roughening treatment of copper electrodeposition can be performed by a conventional apparatus, such as a continuous-type electrodepositing apparatus or a batch-type electrodepositing apparatus, with a production speed between 5 m/min and 20 m/min, a production temperature between 20° C. and 60° C., and a predetermined current density. It is worth mentioning that, a steel brush can be used to scratch the matte side of the raw foil in advance to form non-directional grooves that form a stripe pattern, but the present disclosure is not limited thereto. In certain embodiments, the micro-roughening treatment of copper electrodeposition can also be performed on a shiny side of the raw foil to allow it to be formed into a micro-roughened surface20.

As shown inFIG. 4, a continuous-type electrodepositing apparatus3is used in the manufacturing example, and includes a feeding roller31, a receiving roller32, a plurality of electrolysis tanks33, a plurality of electrolyzing roller assemblies34and a plurality of auxiliary roller assemblies35. The electrolysis tanks33are arranged between the feeding roller31and the receiving roller32to contain copper-containing plating solutions having the same or different compositions. Each of the electrolysis tanks33has a pair of electrodes331(such as platinum electrodes) arranged therein. The electrolyzing roller assemblies34are arranged above the electrolysis tanks33, respectively. The auxiliary roller assemblies35are arranged in the electrolysis tanks33, respectively. The electrolyzing roller assemblies34and the auxiliary roller assemblies35can drive a raw foil to sequentially pass through the plating solutions within the electrolysis tanks33at a certain speed. The electrodes331of each of the electrolysis tanks33and the corresponding electrolyzing roller assembly34are jointly and electrically connected to an external power source (not shown) for electrolyzing the corresponding plating solution, so as to allow the copper foil to have a desired effect.

In practice, the copper-containing plating solutions each contain copper ions, an acid and at least one metal additive. The source of the copper ions can be copper sulfate, copper nitrate or a combination thereof. Specific examples of the acid include sulfuric acid, nitric acid or a combination thereof. Specific examples of the at least one metal additive include cobalt, iron, zinc, or a combination thereof. According to requirements, the copper-containing plating solutions can each contain at least one conventional additive such as a gelatin, an organic nitride, a hydroxyethyl cellulose (HEC), a polyethylene glycol (PEG), a sodium 3-mercaptopropane sulphonate (MPS), a bis-(sodium sulfopropyl)-disulfide (SPS), and a thiourea group-containing compound. However, the above-recited examples are merely exemplary and are not intended to limit the scope of the present disclosure.

The power supplied to the micro-roughening treatment of copper electrodeposition may be in a constant current form, a constant voltage form, a pulse wave form or a saw wave form, but it is not limited thereto. The conditions of the micro-roughening treatment of copper electrodeposition are as shown in Table 1.

It is worth mentioning that, the above-mentioned micro-roughening treatment of copper electrodeposition can be used to produce not only a reverse treated copper foil, but also a high temperature elongation (HTE) copper foil or a very low profile (VLP) copper foil.

Performance Verification of Copper Foil

An advanced electrodeposited copper foil is obtained by a micro-roughening treatment of copper electrodeposition with seven stages, and the processing conditions for each stage are shown in Table 1. A scanning electron microscope (SEM) (S-3400N, manufactured by Hitachi, Ltd.) is operated at a +35 degree tilt to obtain images (i.e.,FIG. 5,FIG. 6andFIG. 7), each showing a surface profile of the advanced electrodeposited copper foil.FIG. 5is a SEM image with 1,000× magnification,FIG. 6is a SEM image with 3,000× magnification, andFIG. 7is a SEM image with 10,000× magnification.

It can be observed fromFIG. 5andFIG. 6that, in the advanced electrodeposited copper foil of the present disclosure, the copper crystals21, the copper whiskers W and the copper crystal groups G form into an uneven (non-uniformly distributed) stripe pattern. Furthermore, more than five of the fine strips20beach have a minimum included angle β1-β9greater than 20 degrees relative to the reference line RL, as shown inFIG. 6. In addition, it can be observed fromFIG. 7that, in the surface profile of the advanced electrodeposited copper foil of the present disclosure, there are at least ten first smooth areas20ceach having a length of 250 nm and a width of 250 nm and at least one second smooth area20dhaving a length of 500 nm and a width of 500 nm.

Different types of prepregs are used with the advanced electrodeposited copper foils of the present disclosure to produce respective copper clad laminates, which are tested for insertion loss value. The results are shown in Table 2.

Test Example 11

Each of advanced electrodeposited copper foils of Examples 3-1 and 3-2 that are produced by the conditions of Example 1 as shown in Table 1, an electrodeposited copper foil according to Taiwan Patent Application No. 107133827 (product name: RG311, herein after referred to as “RG311”) and an electrodeposited copper foil produced by the C company (product name: RTF-3, herein after referred to as “RTF-3”) is laminated with a mid loss prepreg (product name: IT170GRA1) produced by the I company, so as to form a single-layered copper clad laminate after being cured, respectively. The RG311 has a surface roughness (Rz JIS B 0601-1994) that is less than 2.3 μm. The RTF-3 has a plurality of copper crystals that are apparently present in a uniform distribution on a copper foil surface thereof, as observed from an image obtained by a scanning electron microscope (S-3400N, manufactured by Hitachi, Ltd.) with a +35 degree tilt and under 10,000× magnification (as shown inFIG. 8). The peel strengths of the single-layered copper clad laminates all meet the practical requirements. The single-layered copper clad laminates are tested for signal integrity by the Delta-L test method provided by the Intel Corporation, and test conditions include a core thickness of 3 mils core (1 oz), 10 mils PP and 4.5 mils trace width. The results are shown in Table 3.

It can be seen from the test results shown in Table 3 that, at a frequency of 8 GHz, the insertion loss of the advanced electrodeposited copper foil is 17.63% to 22.1% less than that of the RTF-3 and is 6.2% to 10.67% less than that of the RG311. At a frequency of 16 GHz, the insertion loss of the advanced electrodeposited copper foil is 21.32% to 25.51% less than that of the RTF-3 and is 6.01% to 10.21% less than that of the RG311. Therefore, compared to the RTF-3 and the RG311, the advanced electrodeposited copper foil has better signal integrity.

Test Example 2

Each of advanced electrodeposited copper foils of Examples 4-1 and 4-2 that are produced by the conditions of Example 1 as shown in Table 1, an electrodeposited copper foil according to Taiwan Patent Application No. 107133827 (product name: RG311, herein after referred to as “RG311”) and an electrodeposited copper foil produced by the C company (product name: RTF-3, herein after referred to as “RTF-3”) is laminated with a mid loss prepreg (product name: IT985G) produced by the I company, so as to form a single-layered copper clad laminate after being cured, respectively. The RG311 has a surface roughness (Rz JIS B 0601-1994) that is less than 2.3 μm. The RTF-3 has a plurality of copper crystals that are apparently present in a non-uniform distribution on a copper foil surface thereof, as observed from an image obtained by a scanning electron microscope (S-3400N, manufactured by Hitachi, Ltd.) with a +35 degree tilt and under 10,000× magnification (as shown inFIG. 8). The peel strengths of the single-layered copper clad laminates all meet the practical requirements. The single-layered copper clad laminates are tested for signal integrity by the Delta-L test method provided by the Intel Corporation, and which test conditions include a core thickness of 3 mils core (1 oz), 10 mils PP and 4.5 mils trace width. The results are shown in Table 4.

It can be seen from the test results shown in Table 4 that, at a frequency of 8 GHz, the insertion loss of the advanced electrodeposited copper foil is 18.33% to 23.06% less than that of the RTF-3 and is about 18.33% less than that of the RG311. At a frequency of 16 GHz, the insertion loss of the advanced electrodeposited copper foil is about 21.07% less than that of the RTF-3. Therefore, compared to the RTF-3 and the RG311, the advanced electrodeposited copper foil has better signal integrity.

Test Example 3

Each of advanced electrodeposited copper foils of Examples 5-1 and 5-2 that are produced by the conditions of Example 1 as shown in Table 1, an electrodeposited copper foil according to Taiwan Patent Application No. 107133827 (product name: RG311, herein after referred to as “RG311”) and an electrodeposited copper foil produced by the M company (product name: HS1-M2-VSP, herein after referred to as “HS1-M2-VSP”, as shown inFIG. 9) is laminated with an ultra low loss prepreg (product name: IT968) produced by the I company, so as to form a single-layered copper clad laminate after being cured, respectively. The RG311 has a surface roughness (Rz JIS B 0601-1994) that is less than 2.3 μm. The peel strengths of the single-layered copper clad laminates all meet the practical requirements of use. The single-layered copper clad laminates are tested for signal integrity by the Delta-L test method provided by the Intel Corporation, and test conditions include a core thickness of 3 mils core (1 oz), 10 mils PP and 4.5 mils trace width. The results are shown in Table 5.

It can be seen from the test results shown in Table 5 that, at a frequency of 8 GHz, the insertion loss of the advanced electrodeposited copper foil is 16.04% to 19.73% less than that of the HS1-M2-VSP and is 7.31% to 11.00% less than that of the RG311. At a frequency of 16 GHz, the insertion loss of the advanced electrodeposited copper foil is 18.62% to 23.09% less than that of the HS1-M2-VSP and is 7.12% to 11.59% less than that of the RG311. Therefore, compared to the HS1-M2-VSP and the RG311, the advanced electrodeposited copper foil has better signal integrity.

One of the beneficial effects of the present disclosure is that, the advanced electrodeposited copper foil and the copper clad laminate can increase signal integrity and suppress insertion loss, while maintaining good peel strength, to be adaptable to high frequency and high speed signal transmission so as to meet the requirements of 5G applications, by virtue of “the micro-roughened surface has a plurality of production direction stripes and a plurality of fine strips which are formed by copper crystals, and at least five of the fine strips each have a minimum included angle greater than 20 degrees relative to the production direction stripes.” It should be noted that, the advanced electrodeposited copper foil is not limited to a reverse-treated electrodeposited copper foil, and can be applied to a copper foil having a surface roughness (Rz JIS B 0601-1994) less than 2.3 μm.

More specifically, different from the conventional electrodeposited copper foil, the advanced electrodeposited copper foil has a plurality of copper crystals that are present in a non-uniform distribution on a micro-roughened surface thereof, and the copper crystals are stacked or arranged into different types of copper whiskers and copper crystal groups. Furthermore, the copper whiskers and the copper crystal groups have no special directionality, as observed from a scanning electron microscope image of the micro-roughened surface taken with a +35 degree tilt and under 10,000× magnification. The copper crystals form into a stripe pattern, in which at least five of the fine strips each have a minimum included angle greater than 20 degrees, as observed from a scanning electron microscope image of the micro-roughened surface taken with a +35 degree tilt and under 1,000× magnification. As proved by the tests, the advanced electrodeposited copper foil of the present disclosure has better signal integrity.