Advanced reverse treated electrodeposited copper foil and copper clad laminate using the same

An advanced reverse treated electrodeposited copper foil and a copper clad laminate using the same are provided. The advanced reverse treated electrodeposited copper foil has an uneven micro-roughened surface. The micro-roughened surface has a plurality of copper crystals, a plurality of copper whiskers and a plurality of copper crystal groups, which are in a non-uniform distribution to form a non-uniformly distributed horizontal or vertical stripe pattern.

FIELD OF THE DISCLOSURE

The present disclosure relates to an electrodeposited copper foil and applications thereof, and more particularly to an advanced reverse treated electrodepo sited copper foil formed by a surface treatment and a copper clad laminate using the same. The surface treatment, which is also called an electroplating surface-roughening treatment of a copper foil, uses an electroplating technique to non-uniformly deposit fine granular copper crystals (hereinafter referred to as “copper crystals”) on a surface of the copper foil.

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, the copper foil substrate used needs to have a good insertion loss performance at high frequencies so as to transmit high-frequency signals without excessive loss. The insertion loss of the copper foil substrate is highly correlated with its surface roughness. The copper foil substrate has a good insertion loss performance when the surface roughness is decreased. However, the decrease of the surface roughness may reduce the peel strength between the copper foil and the substrate, thus affecting the defect rate of back-end products. Therefore, how a good insertion loss performance that can be provided while maintaining a peel strength at industry level standards has become a problem to be solved in the related field.

SUMMARY OF THE DISCLOSURE

In response to the above-referenced technical inadequacies, the present disclosure provides an advanced reverse treated electrodeposited copper foil that is adaptable to high frequency and high speed signal transmission and can meet the requirements of 5G applications without compromise of the characteristics required for a target application. For example, the electrodeposited copper foil cannot be reduced in peel strength. The present disclosure further provides a copper clad laminate using the advanced reverse treated electrodeposited copper foil, which can serve as a high frequency and high speed substrate.

In one aspect, the present disclosure provides an advanced reverse treated electrodeposited copper foil that has an uneven micro-roughened surface. The micro-roughened surface has a plurality of non-uniformly distributed copper crystals, in which different numbers of the copper crystals are stacked together to form respective copper whiskers, and different numbers of the copper whiskers are grouped together to form respective copper crystal groups. The copper crystals, the copper whiskers and the copper crystal groups form into a non-uniformly distributed horizontal or vertical stripe pattern that is observed from a scanning electron microscope image of the micro-roughened surface taken with a +35 degree tilt and under 1,000× magnification.

In another aspect, the present disclosure provides a copper clad laminate that includes a substrate and an advanced reverse treated electrodeposited copper foil. The advanced reverse treated electrodeposited copper foil is disposed on the substrate and has an uneven micro-roughened surface that is attached to a surface of the substrate. The micro-roughened surface has a plurality of non-uniformly distributed copper crystals, in which different numbers of the copper crystals are stacked together to form respective copper whiskers, and different numbers of the copper whiskers are grouped together to form respective copper crystal groups. The copper crystals, and the copper whiskers and the copper crystal groups, form into a non-uniformly distributed horizontal or vertical stripe pattern that is observed from a scanning electron microscope image of the micro-roughened surface taken with a +35 degree tilt and under 1,000× magnification. The stripe pattern is similar to a pattern of human hair as shown inFIG.24.

In certain embodiments, the micro-roughened surface has at least two smooth areas each having a length of 500 nm and a width of 500 nm and at least one rough area having a length of 1,000 nm and a width of 1,000 nm, which are observed from a scanning electron microscope image of the micro-roughened surface taken with a +35 degree tilt and under 10,000× magnification. In each of the smooth areas there are no copper crystals, copper whiskers and/or copper crystal groups, and in the at least one rough area there are at least six of the copper crystals, the copper whiskers and/or the copper crystal groups.

In certain embodiments, each of the copper whiskers has a topmost copper crystal.

In certain embodiments, the topmost copper crystals are each in the shape of a conoid, a rod or a sphere.

In certain embodiments, the number of the topmost copper crystal of the at least one rough area is at least 10% of the total number of the topmost copper crystal, which is observed under 10,000× magnification.

In certain embodiments, a surface roughness Rz (JIS94) of the micro-roughened surface is less than 2.3 μm.

In certain embodiments, the micro-roughened surface includes a plurality of peaks and a plurality of grooves among the peaks, and the copper crystals, the copper whiskers and the copper crystal groups are correspondingly formed on the peaks.

In certain embodiments, each of the grooves has a U-shaped or V-shaped cross-sectional profile.

In conclusion, the advanced reverse treated electrodeposited copper foil of the present disclosure has an apparent uneven surface profile resulted from a plurality of non-uniformly distributed copper crystals, a plurality of copper whiskers respectively formed by different numbers of the copper crystals and a plurality of copper crystal groups respectively formed by different numbers of the copper whiskers. Therefore, the advanced reverse treated electrodeposited copper foil may achieve an increased signal integrity and a reduced insertion loss while maintaining good peel strength, to adapt to high frequency and high speed signal transmission so as to meet the requirements of 5G applications.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

It is generally recognized in the industry that, if a copper foil has a flatter surface profile, a copper clad laminate formed by the copper foil would have better signal integrity but may have a reduced peel strength. That is, when the copper foil has a flatter surface profile, it is difficult to provide a balance between the signal integrity and peel strength of the copper clad laminate. Therefore, the present disclosure provides an advanced reverse treated electrodepo sited copper foil having a particular surface profile different from the conventional electrodeposited copper foil. The particular surface profile is capable of increasing signal integrity and reducing signal transmission loss, while not reducing the peel strength of the resulting copper clad laminate.

It is worth mentioning that, the present invention uses a technical solution that is discarded due to the above-mentioned technology prejudice. The technical solution allows a copper foil surface to have a certain degree of unevenness, which directly results in the beneficial technical effect of further optimizing the electrical properties while maintaining good peel strength.

Referring toFIG.1andFIG.2, the advanced reverse treated electrodeposited copper foil11has an uneven micro-roughened surface110that is formed by an electroplating micro-roughening treatment. It is worth mentioning that, the micro-roughened surface110has a plurality of copper crystals111, a plurality of copper whiskers W and a plurality of copper crystal groups G which are in a non-uniform distribution, i.e., are non-uniformly deposited on a copper foil surface. Each of the copper whiskers W is formed by two or more copper crystals111stacked together, and different numbers of the copper crystals111are stacked together to form respective copper whiskers W. Each of the copper whiskers W has a topmost copper crystal111that can be in the shape of a conoid, a rod or a sphere. Each of the copper crystal groups G is formed by two or more copper whiskers W grouped together, and different numbers of the copper whiskers W are grouped together to form respective copper crystal groups G.

In certain embodiments, the average height of the copper whiskers W can be less than 3 μm, preferably less than 1.8 μm, and more preferably less than 1.6 μm. The average height of the copper crystal groups G can be less than 4 μm, preferably less than 3 μm, and more preferably less than 1.6 μm. In certain embodiments, each of the copper whiskers W can include up to fifty copper crystals111, preferably up to thirty copper crystals111, more preferably up to fifteen copper crystals111, and most preferably up to eight copper crystals111. In certain embodiments, the average outer diameter of the copper crystals111can be less than 1 μm, more preferably between 0.5 μm and 1 μm, and most preferably between 0.01 μm and 0.5 μm.

It is worth mentioning that, the advanced reverse treated electrodeposited copper foil11of the present disclosure has an apparent uneven surface profile, in which not only are the copper crystals111non-uniformly distributed, but also the copper whiskers W are respectively formed by different numbers of the copper crystals111, and the copper crystal groups G are also respectively formed by different numbers of the copper whiskers W. Therefore, the advanced reverse treated electrodeposited copper foil11of the present disclosure is capable of increasing signal integrity and suppressing insertion loss while maintaining good peel strength, so as to adapt to high frequency and high speed signal transmission. In contrast, on a surface of the conventional electrodeposited copper foil, a plurality of copper crystals are uniformly distributed, only a few of which are gathered together. In addition, a surface roughness Rz (JIS94) of the micro-roughened surface100is less than 2.3 μm, which can provide a reduction in line width and line spacing.

Referring toFIG.5,FIG.9andFIG.13, together withFIG.24, images of the micro-roughened surface110taken by a scanning electron microscope (S-3400N, manufactured by Hitachi, Ltd.) with a +35 degree tilt and under 1,000× magnification are shown. It is observed that the copper crystals111, the copper whiskers W and the copper crystal groups G form into an uneven and non-uniformly distributed horizontal or vertical stripe pattern that is similar to a pattern of human hair. Referring toFIG.8,FIG.12andFIG.16, images of the micro-roughened surface110taken by a scanning electron microscope (S-3400N, manufactured by Hitachi, Ltd.) with a +35 degree tilt and under 10,000× magnification are shown. It is observed that the micro-roughened surface110has at least two smooth areas110aeach having a length of 500 nm and a width of 500 nm and at least one rough area110bhaving a length of 1,000 nm and a width of 1,000 nm. In each of the smooth areas110athere are no copper crystals111, copper whiskers W and/or copper crystal groups G In the at least one rough area110bthere are at least six of the copper crystals111, the copper whiskers W and/or the copper crystal groups G The number of the topmost copper crystal111of the at least one rough area110bis at least 10% of the total number of the topmost copper crystal of the micro-roughened surface110. In addition, in each of the copper crystal groups G, the copper whiskers W respectively extend toward different directions to form a branch structure.

FIG.8shows that the micro-roughened surface110of the advanced reverse treated electrodeposited copper foil11at least has seven smooth areas110aand three rough areas110b.FIG.12shows that the micro-roughened surface110of the advanced reverse treated electrodeposited copper foil11at least has three smooth areas110aand four rough areas110b.FIG.16shows that the micro-roughened surface110of the advanced reverse treated electrodeposited copper foil11at least has five smooth areas110aand three rough areas110b.

Reference is again made toFIG.2, in which the micro-roughened surface110further includes a plurality of peaks112and a plurality of grooves113among the peaks112. The copper crystals111, the copper whiskers W and the copper crystal groups G are correspondingly formed on the peaks112. It is worth mentioning that each of the grooves113has a U-shaped or V-shaped cross-sectional profile, and a plurality of filling spaces114are located among the copper crystals111, the copper whiskers W and the copper crystal groups G.

Accordingly, when a resin-based composite material is pressed on the advanced reverse treated electrodeposited copper foil11of the present disclosure, the micro-roughened surface110can receive a greater amount of a resin material so as to increase the bonding strength of the copper foil relative to a resulting substrate. In certain embodiments, the average depth of the grooves113can be less than 1.5 μm, preferably less than 1.3 μm, and more preferably less than 1 μm. The average width of the grooves113can be between 0.1 μm and 4 μm, and preferably between 0.6 μm and 3.8 μm.

Reference is again made toFIG.1together withFIG.3. The advanced reverse treated electrodeposited copper foil11of the present disclosure can be obtained by performing a copper-electrodepositing micro-roughening treatment on a shiny side of a raw copper foil, in which the shiny side is formed into the micro-roughened surface110. The copper-electrodepositing micro-roughening treatment is preferably performed by a continuous-type electrodepositing apparatus that uses a production speed of 5-20 m/min, a production temperature of 20-60° C. and a predetermined current density. However, these are merely exemplary details, and are not intended to limit the scope of the present disclosure. In certain embodiments, the copper-electrodepositing micro-roughening treatment can be performed to form a matte side of a raw copper foil into the micro-roughened surface110. In addition, the copper-electrodepositing micro-roughening treatment can be performed by a batch-type electrodepositing apparatus.

As shown inFIG.3, the continuous-type electrodepositing apparatus2includes a feeding roller21, a receiving roller22, a plurality of electrolytic tanks23, a plurality of electrolytic roller assemblies24and a plurality of auxiliary roller assemblies25. The electrolytic tanks23are arranged between the feeding roller21and the receiving roller22to contain copper-containing plating solutions having the same or different compositions. Each of the electrolytic tanks23has a pair of electrodes231(e.g., platinum electrodes) arranged therein. The electrolytic roller assemblies24are respectively arranged above the electrolytic tanks23. The auxiliary roller assemblies25are respectively arranged in the electrolytic tanks23. The electrolytic roller assemblies24and the auxiliary roller assemblies25can drive a raw copper foil to sequentially pass through the plating solutions within the electrolytic tanks23. The electrodes231in each of the electrolytic tanks23and the corresponding electrolytic roller assemblies24are electrically connected to an external power source (not shown) for electrolyzing the corresponding plating solution, so as to allow the raw copper foil to have a desired effect.

The copper-containing plating solutions for the copper-electrodepositing micro-roughening treatment can contain a copper ion source, at least one metal additive and at least one non-metal additive. Specific examples of the copper ion source include copper sulfate and copper nitrate. Specific examples of the metal additive include cobalt, iron, zinc, and oxides and salts thereof. Specific examples of the non-metal additive include gelatin, organic nitrides, hydroxyethyl cellulose (HEC), polyethylene glycol (PEG), sodium 3-mercaptopropane sulphonate (MPS), Bis-(sodium sulfopropyl)-disulfide (SPS), and thiourea-containing compounds. However, these are merely exemplary details, and are not intended to limit the scope of the present disclosure.

In certain embodiments, the copper-electrodepositing micro-roughening treatment is divided into first and second stages, which respectively use two different copper-containing plating solutions (i.e., first and second copper-containing plating solutions). More specifically, the first stage applies a current density of 25-40 A/dm2to the first copper-containing plating solution having a copper ion concentration of 10-30 g/l, an acid concentration of 70-100 g/l, and a metal additive concentration of 150-300 mg/l. The second stage applies a current density of 30-56 A/dm2to the second copper-containing plating solution having a copper ion concentration of 70-100 g/l, an acid concentration of 30-60 g/l, and a metal additive concentration of 15-100 mg/l.

It should be noted that, the copper-electrodepositing micro-roughening treatment 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.

Referring toFIG.4, the present disclosure further provides a copper clad laminate1that includes a substrate12and two advanced reverse treated electrodeposited copper foils11disposed on the substrate12. Two micro-roughened surfaces110of the two advanced reverse treated electrodeposited copper foils11are respectively bonded to two opposite surfaces (not numbered) of the substrate. In an unillustrated embodiment, the copper clad laminate1can include only one advanced reverse treated electrodeposited copper foil11disposed on the substrate12. A micro-roughened surface110of the only one advanced reverse treated electrodeposited copper foil11is bonded to a surface of the substrate.

More specifically, the substrate12preferably has low dissipation factor (Df). The Df of the substrate12is 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. The substrate12can be made of a resin-based composite material (i.e., a preperg) that is obtained by curing a base material impregnated with a synthetic resin. Specific examples of the base material include a phenolic cotton paper, a cotton paper, a resin fiber fabric, a resin fiber non-woven fabric, 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, polyimide resin, cyanate ester resin, a bismaleimide triazine resin, a polyphenylene ether resin and a phenol resin. The synthetic resin can be formed into a single layer or multilayer structure. In certain embodiments, the substrate12may be made of an EM891, IT958G, IT150DA, 57040G, S7439G, MEGTRON 4, MEGTRON 6 or MEGTRON 7 material.

Reference is now made toFIG.19andFIG.20.FIG.19illustrates the insertion loss performances of 4 GHz and 8 GHz between the printed circuit boards of Example 1 and Comparative Example 1.FIG.20illustrates the insertion loss performances of 12.89 GHz and 16 GHz between the printed circuit boards of Example 1 and Comparative Example 1. The printed circuit board of Example 1 is manufactured from a plurality of advanced reverse treated electrodeposited copper foils (also called “RG311”) and a plurality of substrates that are obtained by a printed circuit board manufacturing process. Each of the advanced reverse treated electrodeposited copper foils has a surface roughness Rz (JIS94) less than or equal to 2.3 μm. Each of the substrates is made of a low loss prepreg (product name: S7439G, prepared by the S company). The advanced reverse treated electrodeposited copper foils are produced by a copper-electrodepositing micro-roughening treatment having six stages, which can be implemented by the continuous-type electrodepositing apparatus2as shown inFIG.3. The production conditions of the eleven stages are shown in Table 1. The surface profiles of the advanced reverse treated electrodeposited copper foils used in Example 1 are shown inFIG.5toFIG.16, and the related technical details are as mentioned above.

The printed circuit board of Comparative Example 1 is manufactured from a plurality of reverse treated copper foils (product name: RTF 3, prepared by the C company) and a plurality of substrates obtained by a printed circuit board manufacturing process. Each of the reverse treated copper foils has a surface roughness Rz (JIS94) less than or equal to 3.0 μm. Each of the substrates is made of a low loss prepreg (i.e., S7439G prepreg). The surface profile of the reverse treated copper foil used in Comparative Example 1 is shown inFIG.17andFIG.18, in which the copper crystals are formed in a uniform distribution.

It is observed fromFIG.19andFIG.20that, compared to the printed circuit board of Comparative Example 1, the insertion loss of the printed circuit board of Example 1 is reduced by 11.2% at 8 GHz and is reduced by 16.1% at 16 GHz. That is to say, the advanced reverse treated electrodeposited copper foil is capable of increasing signal integrity. Furthermore, the printed circuit board of Example 1 has a peel strength that is tested and meets the requirements for use.

TABLE 3Insertion loss improvement percentage of RG311relative to RTF-3, according to EMC526 prepergFrequencyExample 1Comparative Example 2(GHz)(RG311)(RTF-3)40.0%9.1%80.0%13.2%12.890.0%17.4%

TABLE 4Insertion loss improvement percentage of RG311relative to FT1-UP, according to EMC526 prepergFrequencyExample 1Comparative Example 3(GHz)(RG311)(FT1-UP)40.0%4.8%80.0%8.3%12.890.0%10.4%

Referring toFIG.21, which is to be read in conjunction with Table 2, the insertion loss performances of the printed circuit boards of Example 1 and Comparative Example 2 are shown. The printed circuit board of Comparative Example 2 is manufactured from a plurality of reverse treated copper foils (product name: RTF 3, prepared by the C company) and a plurality of substrates obtained by a printed circuit board manufacturing process. Each of the substrates is made of a low loss prepreg (i.e., EM526 prepreg). In the surface profile of the reverse treated copper foil used in Comparative Example 2, copper crystals are formed in a uniform distribution.

It is observed fromFIG.21that, compared to the printed circuit board of Comparative Example 2, the insertion loss of the printed circuit board of Example 1 is reduced by 13.3% at 8 GHz (i.e., (−0.76−(−0.66))/−0.76=13.3%) and is reduced by 17.4% at 12.89 GHz (i.e., (−1.15−(−0.95))/(−1.15)=17.4%). It is observed from Table 2 and Table 3 that, the advanced reverse treated electrodeposited copper foil is capable of increasing signal integrity.

Referring toFIG.22, the insertion loss performances of the printed circuit boards of Example 1 and Comparative Examples 1 and 3 are shown. The printed circuit board of Comparative Example 3 is manufactured from a plurality of hyper very low profile (HVLP) copper foil (product name: FT1-UP, prepared by the F company) and a plurality of substrates obtained by a printed circuit board manufacturing process. Each of the HVLP copper foils has a surface roughness Rz (JIS94) less than or equal to 2.0 tim. Each of the substrates is made of a low loss prepreg (i.e., EM526 prepreg).

It is observed fromFIG.22, Table 2 and Table 4 that, compared to the printed circuit boards of Comparative Examples 1 and 3, the insertion loss of the printed circuit board of Example 1 is reduced by 8.4% at 8 GHz and is reduced by 10.4% at 12.89 GHz. That is to say, the advanced reverse treated electrodeposited copper foil is capable of increasing signal integrity.

In conclusion, the advanced reverse treated electrodeposited copper foil of the present disclosure has an apparent uneven surface profile resulted from a plurality of non-uniformly distributed copper crystals, a plurality of copper whiskers respectively formed by different numbers of the copper crystals and a plurality of copper crystal groups respectively formed by different numbers of the copper whiskers. Therefore, an increased signal integrity and a reduced insertion loss can be achieved, while maintaining good peel strength, to adapt to high frequency and high speed signal transmission so as to meet the requirements of 5G applications.