US20240229275A1

US20240229275A1 - Nano-twinned copper foil, electronic element and methods for manufacturing the same

Info

Publication number: US20240229275A1
Application number: US18/456,923
Authority: US
Inventors: Chih Chen; Guan-You SHEN
Original assignee: National Yang Ming Chiao Tung University NYCU
Current assignee: National Yang Ming Chiao Tung University NYCU
Priority date: 2023-01-05
Filing date: 2023-08-28
Publication date: 2024-07-11
Also published as: TWI850951B; TW202428386A

Abstract

A nano-twinned copper foil is provided, which comprises: plural twinned grains, wherein at least part of the plural twinned grains are formed by stacking plural nano-twins along a [111] crystal axis. The nano-twinned copper foil has a first surface and a second surface opposite to the first surface, and 80% or more of areas of the first surface and the second surface respectively exposes (111) planes of the nano-twins. In addition, the present invention further provides a method for manufacturing the aforesaid nano-twinned copper foil, an electronic element comprising the same, and a method for manufacturing the electronic element.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefits of the Taiwan Patent Application Serial Number 112100392, filed on Jan. 5, 2023, the subject matter of which is incorporated herein by reference.

BACKGROUND

Field of the Disclosure

The present invention relates to a nano-twinned copper foil, an electronic component comprising the same and a method for preparing the same. More specifically, the present invention relates to a nano-twinned copper foil with the (111) preferred direction on both surfaces, an electronic component comprising the same, and a method for preparing the same.

Description of Related Art

High-power components will generate a lot of heat during operation with the temperature even higher than 300° C. If the heat cannot be dissipated in time, it may cause component failure or issues related to its reliability. Therefore, various bonding layers and thermal interface materials have been developed to solve this problem. However, currently developed bonding layers and thermal interface materials still have drawbacks.
For example, the material used in the traditional chip bonding layer is solder, and it has become a challenge for solder to withstand high temperature of 300° C. in need of removing lead from the solder, and reliability problems caused by intermetallic compounds are also a big issue. In addition, if sintered copper or silver is used as the bonding layer and thermal interface material, its porous structure will lead to an increase in thermal resistance. Sintering performed under the condition of high temperature and long time period and expensive material increase the cost. Furthermore, although the bonding can be achieved at low temperature and low cost when using polymer as the bonding layer and thermal interface material, its thermal conductivity is about 2 orders of magnitude lower than that of metal, and it needs to overcome the problem of high temperature resistance, large difference in thermal expansion coefficient, etc, and the heat dissipation coefficient is also low.
Therefore, there is an urgent need to develop a novel bonding layer and thermal interface material in order to solve the above problems.

SUMMARY

The object of the present invention is to provide a nano-twinned copper foil, both surfaces of the nano-twinned copper foil with the (111) preferred direction, and thus it may be applied to the bonding of the electronic components.
A nano-twinned copper foil provided in the present invention comprises: plural twinned grains, wherein at least part of the plural twinned grains are formed by stacking plural nano-twins along a [111] crystal axis; wherein the nano-twinned copper foil has a first surface and a second surface opposite to the first surface, and 80% or more of areas of the first surface and the second surface respectively exposes (111) planes of the nano-twins. In addition, the first surface and the second surface of the nano-twinned copper foil of the present invention further have low roughness.
In addition to the excellent performance in the mechanical strength and electrical properties for the nano-twinned copper foil of the present invention, both of the front and back surfaces of the nano-twinned copper foil of the present invention are surfaces having (111) preferred direction surfaces, even both of the back and front surfaces have low roughness. The nano-twinned copper foil of the present invention acts similar to a double-sided tape in order to bond, using the property of high diffusion rate of the (111) plane, two substrates at low temperature and/or in a short time. Compared with copper or silver sintering-bonding, using the nano-twinned copper foil of the present invention for bonding may produce fewer holes on the bonding surface, and the obtained electronic components may have lower electrical resistance or thermal resistance. Therefore, the nano-twinned copper foil of the present invention may be applied to the bonding between the backside metallization of a high power component and the direct copper bond (DCB) substrate as well as the bonding between the DCB substrate and the heat dissipation fin; also, it may be applied to the bonding between the thermal interface material and heat dissipation copper pipes.
In one embodiment, the roughness of the first surface and the second surface of the nano-twinned copper foil may be less than or equal to 20 nm, for example, may be respectively in a range from 0.1 nm to 20 nm, 0.5 nm to 20 nm, 1 nm to 20 nm, 2 nm to 20 nm, 3 nm to 20 nm, 4 nm to 20 nm, or 5 nm to 20 nm.
In one embodiment, more than 80% of the volume of the nano-twinned copper foil may include plural twinned grains. In one embodiment, for example, 80% to 99%, 80% to 95%, 85 to 95%, or 90% to 95% of the volume of the nano-twinned copper foil may include plural twinned grains. However, the present invention is not limited thereto.
In one embodiment, at least part of the plural twinned grains of the nano-twinned copper foil may be columnar twinned grains, wherein the columnar twinned grains may be formed by stacking plural nano-twins along a [111] crystal axis within ±15 degrees, and the angle included between the stacking direction of the at least part of the plural twinned grains and the thickness direction of the nano-twinned copper foil is in a range from 0 degree to 20 degrees. In one embodiment, more than 80% (for example, 80% to 99%, 80% to 95%, 85 to 95%, or 90% to 95%) of the plural twinned grains are columnar twinned grains. When the columnar twinned grains grow to the surface of the nano-twinned copper foil, more than 80% of the area of the surface may expose the (111) plane of the nano-twins; and, the surface of the nano-twinned copper foil may have a preferred direction of (111).
In one embodiment, more than 80% of the areas of the first surface and the second surface of the nano-twinned copper foil may respectively expose the (111) plane of the nano-twins. In other words, both the first surface and the second surface of the nano-twinned copper foil may have a (111) preferred direction. In one embodiment, the (111) plane of the nano-twins exposed on the first surface and the second surface of the nano-twinned copper foil may respectively occupy the total area in a range from, for example, 80% to 100%, 85% to 100%, 90% to 100%, 90% to 99.5%, 90% to 99%, 95% to 99%, or 97% to 99%. However, the present invention is not limited thereto. Herein, the preferred direction of the first surface and the second surface of the nano-twinned copper foil may be measured by an electron backscatter diffraction (EBSD).
In one embodiment, when the twinned grain of the nano-twinned copper foil has a significant ratio of thickness to diameter for the twinned grain (for example, the thickness is significantly greater than the diameter), the twinned grain is a columnar twinned grain.
In one embodiment, at least part of the twinned grains may be connected to each other. For example, 50%, 60%, 70%, 80%, 90% or more than 95% of the twinned grains may be connected to each other interconnected.
In one embodiment, the thickness of the nano-twinned copper foil may be adjusted according to the needs. In one embodiment, the thickness of the nano-twinned copper foil may be, for example, in a range from 10 μm to 500 μm, 10 μm to 400 μm, 10 μm to 300 μm, 10 μm to 200 μm, or 10 μm to 100 μm. However, the present invention is not limited thereto.
In one embodiment, the diameters of the twinned grains (such as columnar twinned grains) may be in a range from 0.1 μm to 50 μm, respectively. In an embodiment of the present invention, the diameter of the twinned grains (such as columnar twinned grains) may be, for example, in a range from 0.1 μm to 45 μm, 0.1 μm to 40 μm, 0.1 μm to 35 μm, 0.5 μm to 35 μm, 0.5 μm to 30 μm, 1 μm to 30 μm, 1 μm to 25 μm, 1 μm to 20 μm, 1 μm to 15 μm or 1 μm to 10 μm. However, the present invention is not limited thereto. In one embodiment, the diameter of the twinned grains (such as columnar twinned grains) may be a length measured in a direction substantially perpendicular to the twin direction of the twinned grains. In details, the diameter of the twinned grains (such as columnar twinned grains) may be a length (such as maximum length) measured in a direction substantially perpendicular to the stacking direction of the twin planes of the twinned grains (that is, the direction in which the twin plane extends).
In one embodiment, the thickness of the twinned grains (such as columnar twinned grains) may be respectively in a range from 0.1 μm to 500 μm respectively. In one embodiment, the thickness of the twinned grains (such as columnar twinned grains) may be, for example, in a range from 0.1 μm to 500 μm, 0.1 μm to 400 μm, 0.1 μm to 300 μm, 0.1 μm to 200 μm, 0.1 μm to 100 μm, 0.1 μm to 80 μm, 0.1 μm to 50 μm, 1 μm to 50 μm, 2 μm to 50 μm, 3 μm to 50 μm, 4 μm to 50 μm, 5 μm to 50 μm, 5 μm to 40 μm, 5 μm to 35 μm, 5 μm to 30 μm or 5 μm to 25 μm. In one embodiment, the thickness of the twinned grains (such as columnar twinned grains) may be a thickness measured in the twin direction of the twinned grains. In details, the thickness of the twinned grains (such as columnar twinned grains) may be a thickness (such as maximum thickness) measured in the stacking direction of the twin planes of the twinned grains.
In the present invention, the so-called “twin direction of the twinned grains” refers to the stacking direction of twin planes in twinned grains, wherein the twin planes of the twinned grains may be substantially perpendicular to the stacking direction of the twin planes.
In the present invention, a section of the nano-twinned copper foil may be used to measure the angle included between the twin direction of the twinned grains and the thickness direction of the nano-twinned copper foil. Similarly, a section of the nano-twinned copper foil may also be used to measure the thickness of the nano-twinned copper foil, the diameter and thickness of the twinned grains, and other characteristics. Alternatively, the surface (for example, the first surface or the second surface) of the nano-twinned copper foil may also be used to measure the diameter and thickness of the twinned grains. In the present invention, the measurement method is not particularly limited, and the measurement may be performed by scanning electron microscope (SEM), transmission electron microscope (TEM), focus ion beam (FIB) or other suitable means.
In addition to the nano-twinned copper foil described above, the present invention further provides a method for preparing the aforementioned nano-twinned copper foil, comprising the following steps: providing an electroplating device, comprising an anode, a cathode, a plating solution and a power supply, wherein the power supply is connected to the cathode and the anode respectively, and the cathode and the anode are immersed in the plating solution; performing an electroplating process by using the power supply to grow a nano-twinned copper layer on the cathode; and removing the cathode and polishing a surface (lower surface) of the nano-twinned copper layer to obtain the nano-twinned copper foil as described above, wherein the surface is the surface of the nano-twinned copper foil that is in contact with the cathode before removing the cathode.
In one embodiment, the cathode may comprise: a substrate; and a titanium-tungsten bonding layer disposed on the substrate, wherein the nano-twinned copper layer is formed on the titanium-tungsten bonding layer. The substrate may be a silicon substrate, a glass substrate, a quartz substrate, a metal substrate, a plastic substrate, a printed circuit board, a III-V material substrate or a laminated substrate; and the substrate may have a single-layer or multi-layer structure.
In one embodiment, the titanium-tungsten bonding layer may comprise a titanium-tungsten alloy represented by the following formula (I):
Ti_xW_100-x (I)
wherein, x ranges from 5 to 20. In one embodiment, the titanium-tungsten alloy is Ti₁₀W₉₀. When using the titanium-tungsten alloy shown in formula (I) as the titanium-tungsten bonding layer, the nano-twinned copper layer may be effectively separated from the cathode (including the substrate and the titanium-tungsten bonding layer). In contrast, the nano-twinned copper layer and the cathode (including the substrate and the bonding layer) may not be effectively separated when using titanium bonding layer. In one embodiment, the nano-twinned copper layer may be separated from the cathode (including the substrate and the titanium-tungsten bonding layer) by tearing off the cathode, thereby obtaining the nano-twinned copper foil.
In one embodiment, the thickness of the titanium-tungsten bonding layer may be in a range from 100 nm to 200 nm. When the thickness of the titanium-tungsten bonding layer is less than 100 nm, it is difficult to grow twinned grains with a (111) preferred direction. When the thickness of the titanium-tungsten bonding layer is greater than 200 nm, it is difficult to separate the nano-twinned copper layer from the cathode (including the substrate and the titanium-tungsten bonding layer).
In one embodiment, a step may be further comprised before removing the cathode: polishing another surface (upper surface) of the nano-twinned copper layer away from the cathode.
In one embodiment, a step may be further comprised before removing the cathode or after removing the cathode and before polishing the surface (lower surface) of the nano-twinned copper layer: forming a protective layer on the other surface (upper surface) of the nano-twinned copper layer away from the cathode. The protective layer will be removed after polishing the surface (lower surface) of the nano-twinned copper layer.
In one embodiment, the polishing of the two surfaces (i.e., upper and lower surfaces) of the nano-twinned copper layer may also be performed in the same polishing process.
In one embodiment, the plating solution may comprise a copper salt and an acid. Examples of copper salts in the plating solution may include, without limitation, copper sulfate, copper methanesulfonate, or combinations thereof. Examples of acids in the plating solution may include, without limitation, hydrochloric acid, sulfuric acid, methylsulfonate acids or combinations thereof. In addition, the plating solution may further include an additive, for example, gelatin, a surfactant, a lattice modifying agent or a combination thereof.
In one embodiment, direct current electroplating, pulse electroplating, or alternate use of direct current electroplating and pulse electroplating may be used to form the nano-twinned copper layer.
In one embodiment, direct current electroplating may be used to prepare the nano-twinned copper layer. The current density of direct current electroplating may be in a range, for example, from 0.5 ASD to 30 ASD, 1 ASD to 30 ASD, 2 ASD to 30 ASD, 2 ASD to 25 ASD, 2 ASD to 20 ASD, 2 ASD to 15 ASD or 2 ASD to 10 ASD. However, the present invention is not limited thereto.
In addition to the aforementioned nano-twinned copper foil, the present invention further provides the application to the electronic components using the same and the method for preparing the same.
The electronic component of the present invention comprises: a first substrate; a second substrate; and a bonding unit disposed between the first substrate and the second substrate, wherein the bonding unit is the nano-twinned copper foil as described above.
The method for preparing an electronic component of the present invention comprises the following steps: providing a first substrate and a second substrate; disposing a bonding unit between the first substrate and the second substrate, and bonding the first substrate and the second substrate by using the bonding unit to form an electronic component, wherein the bonding unit is the nano-twinned copper foil as described above.
In the electronic component of the present invention, when using the nano-twinned copper foil provided by the present invention to perform the bonding of the first substrate and the second substrate, it achieves excellent bonding quality with almost no gaps at low temperature and in a short time since the two surfaces of the nano-twinned copper foil of the present invention have a highly (111) preferred direction and low roughness.
In one embodiment, the first substrate and the second substrate may be respectively a metal substrate, wherein the material of the metal substrate may comprise at least one selected from the group consisting of copper, silver, gold, palladium, nickel and platinum.
In on embodiment, the first substrate and the second substrate may be respectively a substrate on which a metal layer is formed, wherein the substrate may be a silicon substrate, a glass substrate, a quartz substrate, a plastic substrate, a ceramic substrate or a circuit board, and the material of the metal layer may comprise at least one selected from the group consisting of copper, silver, gold, palladium, nickel and platinum.
In one embodiment, the device for bonding is subject to no particular limitation, for example, the bonding may be performed with grips. In addition, bonding may be optionally performed by means of pressurization. The pressure applied in the pressurization is subject to no limitation, preferably, the pressure is a low pressure. For example, the bonding is performed at a pressure of about 5 MPa to 50 MPa.
In one embodiment, the bonding may be performed at elevated temperature, wherein the bonding temperature is subject to no limitation, provided that the purpose of bonding may be achieved without affecting the structures of the first substrate and the second substrate. For example, the bonding may be performed at a low temperature of 150° C. to 400° C., 150° C. to 350° C., or 200° C. to 350° C. In addition, the bonding time is subject to no limitation, provided that the bonding between the first substrate and the second substrate may be completed. For example, the bonding time may be 0.5 hour to 5 hours, 0.5 hour to 4 hours, 0.5 hour to 3 hours, 0.5 hour to 2 hours or 0.5 hour to 1 hour.
The details of one or more embodiments are set forth in the accompanying drawing and the description below, and other features of the present invention will be apparent.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A to FIG. 1B are schematic cross-sectional views of the nano-twinned copper foil prepared in Example 1 of the present invention.

FIG. 2 is an image of a focus ion beam of the nano-twinned copper foil according to Example 1 of the present invention.

FIG. 3A and FIG. 3B are diffraction images of the electron backscatter diffraction for the upper surface and the lower surface of the nano-twinned copper foil according to Example 1 of the present invention, respectively.

FIG. 4A and FIG. 4B are atomic force microscope images of the upper surface and the lower surface of the nano-twinned copper foil according to Example 1 of the present invention, respectively.

FIG. 5A to FIG. 5B are schematic cross-sectional views of the electronic component prepared according to Example 2 of the present invention.

FIG. 6A to FIG. 6B are the ion and electron images of the focus ion beam for the electronic component according to Example 2 of the present invention, respectively.

FIG. 7A to FIG. 7B are the ion and electron images of the focus ion beam of the electronic component according to Example 3 of the present invention, respectively.

DETAILED DESCRIPTION OF EMBODIMENT

Different embodiments of the present invention are provided in the following description. These embodiments are meant to explain the technical content of the present invention, but not meant to limit the scope of the present invention. A feature described in an embodiment may be applied to other embodiments by suitable modification, substitution, combination, or separation.
It should be noted that, in the present specification, when a component is described to have an element, it means that the component may have one or more of the elements, and it does not mean that the component has only one of the element, except otherwise specified.
In the present specification, except otherwise specified, the feature A “or” or “and/or” the feature B means the existence of the feature A, the existence of the feature B, or the existence of both the features A and B. The feature A “and” the feature B means the existence of both the features A and B. The term “comprise(s)”, “comprising”, “include(s)”, “including”, “have”, “has” and “having” means “comprise(s)/comprising but is/are/being not limited to”.
Moreover, in the present specification, when an element is described to be arranged “on” another element, it does not essentially means that the elements contact the other element, except otherwise specified. Such interpretation is applied to other cases similar to the case of “on”.
Moreover, in the present specification, a value may be interpreted to cover a range within ±10% of the value, and in particular, a range within ±5% of the value, except otherwise specified. A range may be interpreted to be composed of a plurality of subranges defined by a smaller endpoint, a smaller quartile, a median, a greater quartile, and a greater endpoint, except otherwise specified.

Example 1—Preparation of Nano-Twinned Copper Foil

FIG. 1A to FIG. 1B are schematic cross-sectional views of the nano-twinned copper foil prepared in the present embodiment. As shown in FIG. 1A, a silicon substrate 11 on which a titanium-tungsten bonding layer 12 was formed was used as a cathode in the present embodiment, wherein the titanium-tungsten bonding layer 12 comprised Ti₁₀W₉₀and had a thickness of 100 nm.
The plating solution used in the present embodiment was prepared from copper sulfate pentahydrate crystals. A total of 196.54 g of copper sulfate pentahydrate (containing 50 g/L of copper ions) was provided, added with 1.5 ml of additives, 100 g of sulfuric acid (96%), and 0.1 ml of hydrochloric acid (12N), and the mixture was stirred with a stir bar until the copper sulfate pentahydrate was uniformly mixed in 1 liter of the solution. The stir bar at the bottom of the plating tank rotated at 1200 rpm to maintain the uniformity of ion concentration, and electroplating was performed at room temperature under atmospheric pressure. The hydrochloric acid added in the plating solution enabled the copper target (acting as the anode) to be dissolved normally in the electroplating tank in order to balance the concentration of the copper ions in the plating solution. Herein, the power supply (Keithley 2400) was controlled by a computer, and direct current electroplating was used, and the forward current density was set to 6 ASD (A/dm²). A nano-twinned copper metal layer 13 with the thickness of about 20 μm was formed on the titanium-tungsten bonding layer 12 after electroplating for about 20 minutes.
Then, an upper surface 13 a of the nano-twinned copper metal layer 13 was polished, wherein the composition of the electrolytic polishing solution was 100 ml of phosphoric acid together with 1 ml of acetic acid and 1 ml of glycerin. Meanwhile, a test piece to be electropolished was clamped at the anode, applied with a voltage of 1.75 V for 10 minutes to achieve the effect of electropolishing. The thickness of the test piece after electropolishing was about 17 μm, and the roughness of the upper surface 13 a of the nano-twinned copper metal layer 13 could be reduced to less than 20 nm.
After the upper surface 13 a of the nano-twinned copper metal layer 13 was polished, a protective layer (not shown) was formed on the upper surface 13 a of the nano-twinned copper metal layer 13; and, the protective layer could be a polymer layer. Then, as shown in FIG. 1B, the silicon substrate 11 and the titanium-tungsten bonding layer 12 were removed, and the lower surface 13 b of the nano-twinned copper metal layer 13 was polished to remove the copper seed layer and transition layer. Herein, the lower surface 13 b of the nano-twinned copper metal layer 13 could be polished by electropolishing which was applied to the upper surface 13 a of the nano-twinned copper metal layer 13. The thickness of the test piece after electropolishing was about 10 μm, and the roughness of the lower surface 13 b of the nano-twinned copper metal layer 13 could be reduced to less than 20 nm.
The nano-twinned copper foil of the present embodiment could be obtained through the preparation process above. The nano-twinned copper foil of this embodiment was subjected to electron backscatter diffraction (EBSD), focus ion beam (FIB) and atomic force microscope (AFM) to analyze the surface preferred direction and microstructure, respectively.
FIG. 2 is an image of a focus ion beam of the nano-twinned copper of the present embodiment. FIG. 3A and FIG. 3B are diffraction charts of the electron backscatter diffraction for the upper surface and the lower surface of the nano-twinned copper foil of the present embodiment, respectively. FIG. 4A and FIG. 4B are atomic force microscope images of the upper surface and the lower surface of the nano-twinned copper foil of the present embodimen, respectively.
As shown in FIG. 2 , the measurement results of the focused ion beam showed that most of the grains in the nano-twinned copper foil had twins at a high density. More than 95% of the volume of the nano-twinned copper foil contained columnar twinned grains. The angle between more than 95% of the twin direction of the twinned grains and the thickness direction of the nano-twinned copper foil was in a range from about 0 degree to 10 degrees, and the angle between more than 95% of the twin direction of the twinned grains and the surface of the substrate was in a range from about 80 degrees to 90 degrees, indicating that the twin plane of the twinned grains was substantially parallel to the surface of the substrate. In addition, more than 95% of the twinned grains in the nano-twinned copper foil had the thickness ranging from 1 μm to 10 μm. Furthermore, no transition layer was found at the bottom of the nano-twinned copper foil, ensuring that the transition layer was removed, and leaving a nano-twinned structure with a high (111) preferred direction.
As shown in FIG. 3A and FIG. 3B, the measurement results of the electron backscatter diffraction showed that almost all of the volume (more than 95% of the volume) of the nano-twinned copper foil prepared in the present embodiment were columnar twinned grains connecting to each other, and the diameter of the columnar twinned grains was in a range from about 0.5 μm to 3 μm. In addition, the twinned grains were formed by the nano-twins stacking along the [111] direction of the crystal axis, and the twin planes of the nano-twins were substantially parallel to the cathode surface (that is, the stacking direction of the nano-twins is substantially parallel to the thickness direction of the nano-twinned copper foil). In addition, after calculation, the proportions of the (111) planes of the nano-twins on the upper surface and the lower surface of the nano-twinned copper foil were respectively 100% and 99.6%, representing that both of the upper and lower surfaces of the nano-twinned copper foil had the (111) preferred direction.
As shown in FIG. 4A and FIG. 4B, the measurement results of the atomic force microscope showed that the nano-twinned copper foil prepared in the present embodiment had a roughness of 18.9 nm and 7.7 nm respectively for the upper and lower surfaces, representing that the nano-twinned copper foil of the present embodiment had an extremely low roughness.
The above-mentioned experimental results showed that all the upper and lower surfaces of the nano-twinned copper foil of the present embodiment had a (111) preferred direction and a roughness less than 20 nm, representing that the nano-twinned copper of the present embodiment facilitated subsequent bonding of electronic components.

Example 2—Preparation of Electronic Components

FIG. 5A to FIG. 5B are schematic cross-sectional views of the electronic components prepared in the present embodiment. As shown in FIG. 5A, a first substrate 21 and a second substrate 22 were provided; a bonding unit 23 was disposed between the first substrate 21 and the second substrate 22, and the first substrate 21 and the second substrate 22 were bonded by the bonding unit 23 to form the electronic component of the present embodiment, as shown in FIG. 5B.
In the present embodiment, the first substrate 21 and the second substrate 22 were respectively silicon substrates with a copper seed layer disposed thereon, and the surfaces thereof had a roughness of 3.1 nm and near 100% of (111); and, the bonding unit 23 was the nano-twinned copper foil prepared in Example 1. Herein, the bonding was performed by bonding the surface having the copper seed layer to the bonding unit 23. In addition, in the present embodiment, the bonding was performed at 250° C. and 35 MPa for 1 hour. The ion and electron images of the focus ion beam for the electronic component obtained after the bonding were shown in FIG. 6A and FIG. 6B.
As shown in FIG. 6A and FIG. 6B, the bonding unit 23 was well bonded to the copper seed layer 211 on the first substrate and the copper seed layer 221 on the second substrate, and almost no gaps was found from the upper and lower bonding surfaces of the bonding unit 23 (as indicated by arrows).

Example 3—Preparation of Electronic Components

The preparation method of the electronic component of the present embodiment was the same as that of Example 2, except that the first substrate 21 and the second substrate 22 used in the present embodiment were respectively copper substrates, and the surfaces thereof had a roughness of 48 nm and extreme low ratio of (111) for 2.7%; and, the bonding was performed at 300° C. and 30 MPa for 30 minutes. The ion and electron images of the focus ion beam for the electronic component obtained after the bonding were shown in FIG. 7A and FIG. 7B.
As shown in FIG. 7A and FIG. 7B, the copper substrates used in the first substrate 21 and the second substrate 22 had a relatively large roughness and a very low (111) ratio, so the small gaps on the upper and lower bonding surfaces of the bonding unit 23 (as indicated by arrows) were inevitable under the bonding condition of low temperature and short time. However, most of the bonding remained excellent bonding quality without gaps.
The results of Example 2 and Example 3 showed that using the nano-twinned copper foil prepared in Example 1 to perform the bonding led to excellent boding quality whether the bonding surface of the substrate to be bonded had a low roughness or high (111) ratio.
In summary, regarding the nano-twinned copper foil proved in the present invention, 80% or more of the areas of the two surfaces respectively exposes the (111) plane of the nano-twins and even have roughness less than 20 nm, so it can be applied to the bonding of the high-power components and the bonding of thermal interface materials and heat pipes, thereby reducing the thermal budget of the process.

Claims

1. A nano-twinned copper foil, comprising:

plural twinned grains, wherein at least part of the plural twinned grains are formed by stacking plural nano-twins along a [111] crystal axis;

wherein the nano-twinned copper foil has a first surface and a second surface opposite to the first surface, and 80% or more of areas of the first surface and the second surface respectively exposes (111) planes of the nano-twins.

2. The nano-twinned copper foil of claim 1, wherein more than 80% of the volume of the nano-twinned copper foil comprises the plural nano-twins.

3. The nano-twinned copper foil of claim 2, wherein the at least part of the plural twinned grains are columnar twinned grains.

4. The nano-twinned copper foil of claim 2, wherein diameters of the plural twinned grains respectively range from 0.1 μm to 50 μm.

5. The nano-twinned copper foil of claim 2, wherein thicknesses of the plural twinned grains respectively range from 0.1 μm to 500 μm.

6. The nano-twinned copper foil of claim 2, wherein the at least part of the plural twinned grains are connected to each other.

7. The nano-twinned copper foil of claim 1, wherein an angle included between a stacking direction of the plural nano-twins and a thickness direction of the nano-twinned copper foil ranges from 0 degree to 20 degrees.

8. The nano-twinned copper foil of claim 1, wherein a thickness of nano-twinned copper foil ranges from 10 μm to 500 μm.

9. The nano-twinned copper foil of claim 1, wherein roughnesses of the first surface and the second surface are respectively less than or equal to 20 nm.

10. A method for preparing a nano-twinned copper foil, comprising the following steps:

providing an electroplating device, comprising an anode, a cathode, a plating solution and a power supply, wherein the power supply is connected to the cathode and the anode respectively, and the cathode and the anode are immersed in the plating solution;

performing an electroplating process by using the power supply to grow a nano-twinned copper layer on the cathode; and

removing the cathode and polishing a surface of the nano-twinned copper layer to obtain the nano-twinned copper foil of claim 1, wherein the surface of the nano-twinned copper foil is in contact with the cathode before removing the cathode.

11. The method of claim 10, wherein the cathode comprises:

a substrate; and

a titanium-tungsten bonding layer disposed on the substrate, wherein the nano-twinned copper layer is formed on the titanium-tungsten bonding layer.

12. The method of claim 10, wherein the titanium-tungsten bonding layer comprises a titanium-tungsten alloy represented by the following formula (I):

Ti_xW_100-x (I)

wherein, x ranges from 5 to 20.

13. The method of claim 10, wherein a thickness of the titanium-tungsten bonding layer ranges from 100 nm to 200 nm.

14. The method of claim 10, wherein the substrate is a silicon substrate.

15. The method of claim 10, further comprising a step: polishing another surface of the nano-twinned copper layer away from the cathode before removing the cathode.

16. An electronic component, comprising:

a first substrate;

a second substrate; and

a bonding unit disposed between the first substrate and the second substrate, wherein the bonding unit is the nano-twinned copper foil of claim 1.

17. The electronic component of claim 16, wherein the first substrate and the second substrate are respectively a metal substrate or a substrate on which a metal layer is formed, wherein a material of the metal substrate or the metal layer comprises at least one selected from the group consisting of copper, silver, gold, palladium, nickel and platinum.

18. A method for preparing an electronic component, comprising the following steps:

providing a first substrate and a second substrate;

disposing a bonding unit between the first substrate and the second substrate, and bonding the first substrate and the second substrate by using the bonding unit to form an electronic component, wherein the bonding unit is the nano-twinned copper foil of claim 1.

19. The method of claim 18, wherein the first substrate and the second substrate are respectively a metal substrate or a substrate on which a metal layer is formed, wherein a material of the metal substrate or the metal layer comprises at least one selected from the group consisting of copper, silver, gold, palladium, nickel and platinum.