TWM560998U - Copper foil and circuit board assembly for high frequency signal transmission - Google Patents

Abstract

The present invention discloses a copper foil and a circuit board assembly for high frequency signal transmission. The copper foil includes a green foil layer, a roughened layer on the green foil layer, and a surface treatment layer on the roughened layer, wherein the thickness of the surface treatment layer and the green foil layer The thickness ratio is between 1.0 × 10 ^-5 and 3.0 × 10 ^-4 . Thereby, since the content of the non-copper metal element in the copper foil is lowered, the present invention can further reduce the circuit board assembly made of the copper foil under the high frequency signal without further reducing the surface roughness. Signal loss (Insertion Loss).

Description

Copper foil and circuit board assembly for high frequency signal transmission

The present invention relates to a copper foil and a circuit board assembly, and more particularly to a copper foil and a circuit board assembly for high frequency signal transmission.

The copper foil currently applied to the printed circuit board is formed by electroplating on the cathode wheel to form a raw foil, and then processed through a post-stage process to form a final product. The post-processing includes performing a roughening treatment on the rough surface of the original foil to form a plurality of copper tumors on the rough surface of the original foil, thereby increasing the bonding strength between the copper foil and the circuit substrate, that is, increasing the peel strength of the copper foil.

In recent years, the data processing speed and communication speed of electronic products have tended to be high-speed and high-speed. At present, most of the research points to the shape of the copper foil surface having a great influence on the transmission loss when transmitting high frequency signals. That is to say, the copper foil with a large surface roughness has a long propagation distance of the signal, which may cause signal attenuation or delay. On the other hand, as the frequency of transmission increases, the skin effect of the transmitted signal flowing on the surface of the circuit is more pronounced, that is, the current in the conductor is concentrated on the surface of the conductor. Therefore, the greater the thickness, the higher the signal loss.

Therefore, the industry is currently working to reduce the surface roughness of copper foil to reduce transmission loss, and meet the needs of high-frequency signal transmission. However, due to current limitations in the process, it has been difficult to further reduce the surface roughness of the copper foil. In addition, the surface roughness of the copper foil is too low, although the transmission loss of the high-frequency signal can be reduced, but the bonding strength between the copper foil and the circuit substrate is lowered, thereby causing the copper foil to be easily peeled off from the circuit substrate and reducing the printing. Board reliability.

The technical problem to be solved by the present invention is to provide a low-resistance copper foil and a circuit board assembly for high-frequency signal transmission in view of the deficiencies of the prior art.

One of the technical solutions adopted by the present invention is to provide a copper foil for high frequency signal transmission, comprising a green foil layer, a roughening layer on the green foil layer, and a roughening treatment. a surface treatment layer on the layer, wherein a ratio of a thickness of the surface treatment layer to a thickness of the green foil layer is between 1.0 × 10 ^-5 and 3.0 × 10 ^-4 .

Another technical solution adopted by the present invention is to provide a circuit board assembly including a substrate, at least one circuit layer on the substrate, and an adhesive layer connected between the substrate and the circuit layer, wherein the circuit layer is the above Copper foil for high frequency signal transmission.

Another technical solution adopted by the present invention is to provide a circuit board assembly including a substrate and at least one circuit layer on the substrate, wherein the circuit layer is the above-mentioned copper foil for high frequency signal transmission.

The beneficial effect of the present invention is that the ratio of the thickness of the surface treatment layer to the thickness of the green foil layer is between 1.0×10 ^-5 and 3.0×10 ^-4 , the purity of the copper foil is improved, and the grain size of the green foil is controlled. In order to reduce the grain boundary, the copper foil impedance is reduced. Thereby, the copper foil provided by the present embodiment can increase the conductivity of the copper foil without further reducing the surface roughness. Therefore, when the copper foil of the present embodiment is applied to a wiring board assembly for transmitting high frequency signals, it can have a lower electrical loss. In addition, since the surface roughness of the copper foil is maintained at a constant value, the bonding strength between the copper foil and the substrate is not sacrificed because the electrical loss is reduced.

In order to further understand the features and technical contents of the present invention, please refer to the following detailed description of the present invention and the accompanying drawings. However, the drawings are provided for reference and description only, and are not intended to limit the present invention.

1‧‧‧ copper foil

10‧‧‧ Raw foil layer

10a‧‧‧Smooth face

10b‧‧‧Rough surface

11‧‧‧ roughening layer

110‧‧‧ copper tumor

12‧‧‧Surface treatment layer

S1‧‧‧ pressed surface

P1, P2‧‧‧ circuit board assembly

2‧‧‧Substrate

1’‧‧‧Line layer

3‧‧‧Adhesive layer

T‧‧‧ total thickness

T‧‧‧roughening layer thickness

1 is a partial cross-sectional view showing a copper foil of the present embodiment.

2 is a partially enlarged schematic view of the copper foil of FIG. 1 in a region II.

Figure 3 is a cross-sectional view showing the circuit board assembly of the present embodiment.

4 is a cross-sectional view showing a circuit board assembly of another embodiment of the present creation.

The following is a description of an embodiment of the present disclosure relating to "copper foil applied to high frequency signal transmission and circuit board assembly" by a specific embodiment. The copper foil for high frequency signal transmission provided by the present embodiment can be applied to a printed circuit board (PCB) or a flexible printed circuit board (FPC). The aforementioned high frequency signal generally refers to a high frequency signal having a frequency of 8 GHz or higher.

Please refer to FIG. 1 and FIG. 2 . Fig. 1 is a partial cross-sectional view showing a copper foil of the present embodiment. 2 is a partial enlarged view of the copper foil of FIG. 1 in a region II. The copper foil 1 of the present embodiment includes a green foil layer 10, a roughened layer 11 on the green foil layer 10, and a surface treatment layer 12 on the roughened layer 11.

It should be noted that the green foil layer 10 is formed by an electroplating process, and the green foil layer 10 has a smooth surface 10a and a rough surface 10b opposite to the smooth surface 10a. The smooth surface 10a generally refers to the side of the green foil layer 10 that contacts the cathode wheel (not shown) during the plating process, and the rough surface 10b is the surface where the green foil layer 10 contacts the electrolyte.

In the present embodiment, the copper foil size of the green foil layer 10 is between 0.1 and 10 μm. It should be noted that the higher the purity of the copper foil 1 and the better the conductivity, the lower the loss during high-frequency signal transmission. However, the process and cost of obtaining the high-purity copper foil 1 are very high.

In the present embodiment, the impedance of the copper foil 1 is further reduced by optimizing the microstructure of the green foil layer 10, that is, controlling the copper grain size of the green foil layer 10. In detail, the grain boundary in the raw foil layer 10 can hinder or hinder electron transfer. Therefore, the less the grain boundary of the green foil layer 10, the better the electrical surface of the copper foil 1 will be. Since the grain interface is negatively correlated with the grain size, the larger the grain size, the less the grain boundary. Therefore, in the present embodiment, the grain size of the green foil layer 10 is controlled to be between 0.1 and 10 μm, preferably between 2 and 5 μm, and the copper foil 1 resistance value can be further increased to help lower the height. Frequency signal transmission loss.

After the process of the green foil layer 10 is completed, the rough surface 10b of the green foil layer is subjected to a roughening surface treatment, and the roughened surface layer 11 is formed on the rough surface 10b. The aforementioned roughening surface treatment includes a plurality of roughening treatments and curing treatments. The roughening treatment and the curing treatment mean that the green foil layer 10 is placed in an electrolytic solution having copper ions and sulfate ions for electroplating so that copper atoms are deposited on the rough surface 10b of the green foil layer 10 to form a plurality of copper. tumor.

In the present embodiment, the roughening treatment layer 11 is an arsenic-free roughening treatment layer. That is, an additive which is completely free of arsenic is used in the electrolytic solution used in performing the roughening treatment and the curing treatment. In an embodiment, the thickness t of the roughened layer 11 is approximately between 0.1 and 2 μm.

As shown in FIG. 2, the roughened layer 11 after the roughening treatment and the curing treatment includes a plurality of copper tumors 110. Each of the copper tumors 110 extends in a long axis direction that is not parallel to the rough surface 10b.

In addition, the shape of the copper tumor can be adjusted by controlling the composition of the electrolyte such as the concentration of copper ions, the concentration of sulfuric acid or the composition of the additive, or the magnitude of the current density. For example, the concentration of copper ions can be lowered, and the current density and the time of the roughening treatment can be controlled so that the copper grows in a direction substantially perpendicular to the rough surface 10b of the green foil layer 10 when crystallizing, and the copper is restricted. Grow in the horizontal direction. According to this, the long axis of the copper tumor 110 of the roughened layer 11 located on the rough surface 10b of the green foil layer 10 can be substantially the thickness direction of the parallel raw foil layer 10.

It should be noted that due to the high resistance of arsenic, if the arsenic content in the copper foil is too high, the impedance value of the copper foil is also increased. Therefore, the roughened layer 11 of the copper foil 1 of the present embodiment is an arsenic-free roughening layer, which can further reduce the impedance value of the copper foil 1, and is advantageous for application in high-frequency signal transmission.

Please refer to Figure 1 again. After the roughening and solidification treatment of the copper foil 1, other subsequent treatments may be performed to form the surface treatment layer 12 on the roughened layer 11 to adjust the heat resistance or corrosion resistance of the copper foil 1. The foregoing surface treatments are, for example, heat and chemical resistance treatment, chromate treatment, silane coupling treatment, and groups thereof. One can be selected by a person skilled in the art according to actual needs.

Therefore, the material constituting the surface treatment layer 12 is a metal element or an alloy. In an embodiment, the material constituting the surface treatment layer 12 may be selected from the group consisting of zinc, chromium, nickel, and combinations thereof.

Although the surface treatment layer 12 can protect the copper layer (the raw foil layer 10 and the roughing treatment layer 11) from being oxidized, and in the process of etching the copper foil 1 to form a wiring, the protective copper layer is not corroded by the acid-base syrup. However, the material constituting the surface treatment layer 12 has a higher resistance value than copper, and the impedance of the copper foil 1 is increased. Therefore, the thickness of the surface treatment layer 12 needs to be controlled within a certain range so that the impedance of the copper foil 1 is low enough to reduce transmission loss, but to protect the copper layer from oxidation or corrosion.

Since the thickness of the surface treatment layer 12 is positively correlated with the content of the non-copper metal element, the content of the non-copper metal element (e.g., zinc, chromium, nickel) can be controlled by controlling the thickness of the surface treatment layer 12. In the present embodiment, the thickness ratio of the surface treatment layer 12 to the thickness of the green foil layer 10 is between 1.0 × 10 ^-5 and 3.0 × 10 ^-4 to lower the impedance of the copper foil 1. In an embodiment, the total thickness T of the copper foil 1 is between 6 and 400 μm, and the thickness of the surface treatment layer 12 is between 10 and 50 Å.

In one embodiment, the material constituting the surface treatment layer includes zinc, chromium, and nickel, and has a zinc content of 50 to 175 ppm, a nickel content of 20 to 155 ppm, and a chromium content of 20 to 70 ppm in the copper foil 1. In one embodiment, the sum of the zinc content, the nickel content, and the chromium content in the copper foil 1 does not exceed 400 ppm.

It should be noted that if the total content of non-copper elements contained in the copper foil 1, such as arsenic, zinc, chromium, nickel, etc., is higher, the impedance value of the copper foil 1 is affected. The roughened layer 11 of the copper foil 1 of the present embodiment does not contain an arsenic element, and the ratio of the thickness of the surface treated layer 12 to the total thickness of the copper foil 1 is low, so that the non-copper element contained in the copper foil 1 can be The total content is reduced. Accordingly, the copper foil 1 of the present embodiment can have a lower impedance. When the copper foil 1 of the present embodiment is applied to transmit a high frequency signal, it can have a low transmission loss.

That is, by reducing the surface roughness of the copper foil 1 compared to the prior art To reduce transmission loss, the present embodiment reduces transmission loss by adjusting the microstructure of the green foil layer 10 and increasing the purity of the copper foil 1 as much as possible. Therefore, the surface roughness of the copper foil 1 of the presently-created embodiment does not need to be continuously lowered, and the effect of lowering the transmission impedance can also be achieved.

Please refer to Figure 3. Figure 3 is a cross-sectional view showing the circuit board assembly of the present embodiment. The copper foil of the present embodiment can be applied to different circuit board assemblies P1 such as a rigid printed circuit board (PCB), a flexible printed circuit board (FPC), and the like, but the present invention is not limited thereto.

In the embodiment of Fig. 1, the circuit board assembly P1 includes a substrate 2, a wiring layer 1', and an adhesive layer 3 connected between the substrate 2 and the wiring layer 1'. The wiring layer may be a copper foil 1 directly as described above or an electric circuit formed by etching the copper foil 1 described above.

The substrate 2 may be a high-frequency substrate such as an epoxy resin substrate, a polyoxyxylene resin substrate (PPO) or a fluorine-based resin substrate, or a polyimide, an ethylene terephthalate or a polycarbonate. A substrate composed of a liquid crystal polymer or a material such as polytetrafluoroethylene.

In the present embodiment, the copper foil 1 has a pressing surface S1, and the ten-point average roughness of the pressing surface S1 may be between 0.5 μm and 3 μm, preferably between 2 μm and 3 μm. When the copper foil 1 and the substrate 20 are joined by the adhesive layer 22, the pressing surface S1 faces the substrate 20.

Referring to FIG. 4, a cross-sectional view of a circuit board assembly of another embodiment of the present invention is shown. The wiring board assembly P2 of this embodiment includes a substrate 20 and a wiring layer 1'. Similar to the embodiment of Fig. 3, the wiring layer 1' may be the above-described copper foil 1, or the above-described copper foil 1 formed by etching.

Unlike the embodiment of Fig. 3, in the present embodiment, the substrate 20 can be directly bonded to the wiring layer 1' by heat pressing without additionally bonding the copper foil 1 through the adhesive layer 3. In the present embodiment, the substrate 20 may be made of a material such as a liquid crystal polymer or a glass fiber substrate (Pre-preg). Therefore, when press-bonding, the substrate 20 is directly bonded to the press-fit surface S1.

It should be noted that the copper foil 1 of the present embodiment was tested to have a resistance value of less than 0.16 ohm-gram/m ² after being heated at 200 ° C for 2 hours. Therefore, in the circuit board assemblies P1 and P2 of the present embodiment, since the surface roughness of the pressing surface S1 of the copper foil 1 does not need to be reduced to 2 μm or less, the electrical loss at the time of high-frequency signal transmission can be reduced. Therefore, the copper foil 1 and the substrate 2 or the adhesive layer 3 can have a high bonding strength, so that the bonding strength between the copper foil 1 and the substrate 2 can be sacrificed in order to reduce the high-frequency transmission loss in the prior art. The problem.

In addition, it should be noted that although the study found that the higher the conductivity of the copper foil, that is, the lower the resistance, is an important factor in determining the loss of the signal, no one is currently working to improve the conductivity of the copper foil. Therefore, the present invention has an advantageous effect of increasing the purity of the copper foil 1 by setting the thickness of the surface treatment layer 12 to the thickness of the green foil layer 10 to be between 1.0 × 10 ^-5 and 3.0 × 10 ^-4 . By controlling the grain size of the green foil layer 10 to reduce the grain boundary, the impedance of the copper foil 1 can be lowered.

Thereby, the copper foil 1 provided by the present embodiment can increase the conductivity of the copper foil 1 without continuing to lower the surface roughness. Therefore, when the copper foil 1 of the present embodiment is applied to the wiring board assemblies P1, P2 for transmitting high frequency signals, it can have a lower electrical loss. In other words, the present invention can further reduce the signal loss (Insertion Loss) of the circuit board assemblies P1 and P2 made of the copper foil 1 under the high frequency signal without further reducing the surface roughness. In addition, since the surface roughness of the copper foil 1 is maintained at a constant value, the bonding strength between the copper foil 1 and the substrate 2 is not sacrificed because the electrical loss is reduced.

The above disclosure is only a preferred and feasible embodiment of the present invention, and is not intended to limit the scope of the patent application of the present invention. Therefore, any equivalent technical changes made by using the present specification and the contents of the drawings are included in the application for this creation. Within the scope of the patent.

Claims (13)

A copper foil for high frequency signal transmission, comprising: a primary foil layer, a roughened layer on the green foil layer, and a surface treatment layer on the roughened layer, wherein The ratio of the thickness of the surface treatment layer to the thickness of the green foil layer is between 1.0 × 10 ^-5 and 3.0 × 10 ^-4 . The copper foil for high frequency signal transmission according to claim 1, wherein the raw foil layer has a copper grain size of between 0.1 and 10 μm. The copper foil for high frequency signal transmission according to claim 1, wherein the thickness of the roughened layer is between 0.1 and 2 μm, and the roughened layer is arsenic-free roughening treatment. Floor. The copper foil for high frequency signal transmission according to claim 1, wherein the roughening treatment layer comprises a plurality of copper tumors. The copper foil for high frequency signal transmission according to claim 1, wherein the surface treatment layer has a thickness of 10 to 50 Å, and the material constituting the surface treatment layer is selected from the group consisting of zinc, chromium, nickel, and combinations thereof. The group formed. The copper foil for high frequency signal transmission according to claim 1, wherein the material constituting the surface treatment layer comprises zinc, chromium and nickel, and the zinc content in the copper foil is 50 to 175 ppm, nickel The content is 20~155ppm, and the chromium content is 20~70ppm. The copper foil for high frequency signal transmission according to claim 6, wherein the sum of the zinc content, the nickel content, and the chromium content in the copper foil does not exceed 400 ppm. The copper foil for high-frequency signal transmission according to claim 1, wherein the copper foil has a pressing surface, and the ten-point average roughness of the pressing surface is between 0.5 and 3 μm. The copper foil for high frequency signal transmission according to claim 1, wherein the copper foil has an impedance value of less than 0.16 ohm-gram/m ² after being heated at 200 ° C for 2 hours. A circuit board assembly, the circuit board assembly comprising a substrate, at least one circuit layer on the substrate, and an adhesive layer connected between the substrate and the circuit layer, wherein the circuit layer is A copper foil for high frequency signal transmission as claimed in any one of claims 1 to 9. The circuit board assembly of claim 10, wherein the circuit board assembly is a rigid printed circuit board or a flexible printed circuit board. The circuit board assembly according to claim 10, wherein the substrate is a high frequency substrate, and the high frequency substrate is an epoxy resin substrate, a polyoxyxylene resin substrate or a fluorine resin substrate. A circuit board assembly comprising a substrate and at least one circuit layer on the substrate, wherein the circuit layer is applied to high frequency signal transmission as described in one of claims 1 to 9. Copper foil.