Electrolytic copper foil special for high-frequency and high-speed circuit and preparation method of electrolytic copper foil

Abstract

The invention belongs to the technical field of copper foil manufacturing, and particularly relates to a special electrolytic copper foil for a high-frequency high-speed circuit and a preparation method thereof. The method comprises the following steps: 1) taking a raw copper foil for pretreatment to obtain a pretreated copper foil; 2) preparing a copper sulfate-sulfuric acid system electrolyte, and placing the pretreated copper foil in the electrolyte for electro-deposition to obtain an intermediate copper foil; 3, the intermediate copper foil is subjected to heat treatment, and the electrolytic copper foil special for the high-frequency high-speed circuit is obtained.Performance optimization of the electrolytic copper foil can be effectively and efficiently achieved through simple operation, the high-frequency signal transmission loss of the electrolytic copper foil is greatly reduced, cost is low, operation is easy, and industrial popularization is facilitated.

Description

Technical Field

[0001] The present invention belongs to the technical field of copper foil manufacturing, and in particular relates to an electrolytic copper foil specially used for high-frequency and high-speed circuits and a preparation method thereof. Background Art

[0002] Printed circuit boards, as materials for mounting chips and semiconductor components, will face even more pressing demands in the high-frequency, high-speed era. Electronic copper foil, one of the three main components of PCBs (Printed Circuit Boards), has been called the "neural network of communication" and will also face stricter requirements. Therefore, the development of high-performance electrolytic copper foil materials has become a research topic of great concern to copper foil manufacturers worldwide. For high-frequency, high-speed PCB circuits, resistance increases at high frequencies, and the vast majority of current is concentrated on the surface of the circuit, a phenomenon known as the "skin effect" of the conductor. The higher the frequency, the shallower the skin depth. At 1 GHz, the skin depth is 2 μm, while at 10 GHz, the skin depth is only 0.66 μm. In addition to macroscopic roughness, actual grains also form a special "rough layer." This "rough layer" does not necessarily exhibit a large surface roughness (Ra), and may even exhibit an extremely low roughness of Ra ≤ 0.3. However, it contains abundant grain boundaries, resulting in a huge microscopic "roughness." When signals are transmitted only in the "rough layer," they will inevitably produce severe signal "standing waves" and "reflections" due to the effects of grain boundaries, causing severe signal loss or even complete distortion. Therefore, the surface roughness of copper foil has a significant impact on the transmission of high-frequency signals.

[0003] Therefore, how to simultaneously coordinate and improve the macro-roughness Ra and micro-roughness (grain boundary density) of the copper foil surface is an extremely important research direction. Summary of the Invention

[0004] In order to solve the problems of excessive loss rate of high-frequency and high-speed signal transmission and even severe signal distortion when the existing electrolytic copper foil is directly used in PCB applications, the present invention provides an electrolytic copper foil specially used for high-frequency and high-speed circuits, and a preparation method of the electrolytic copper foil.

[0005] The main objectives of the present invention are:

[0006] 1. It can be effectively used for the performance optimization of electrolytic copper foil;

[0007] 2. The method is simple and efficient, and can significantly reduce the high-frequency signal transmission loss of electrolytic copper foil.

[0008] To achieve the above objectives, the present invention adopts the following technical solutions.

[0009] A method for preparing electrolytic copper foil specially used for high-frequency and high-speed circuits.

[0010] The method comprises:

[0011] 1) Pre-treating a raw copper foil to obtain a pre-treated copper foil;

[0012] 2) preparing a copper sulfate-sulfuric acid system electrolyte, placing the pretreated copper foil in the electrolyte for electrodeposition to obtain an intermediate copper foil;

[0013] 3) The intermediate copper foil is heat-treated to obtain an electrolytic copper foil specially used for high-frequency and high-speed circuits.

[0014] As a preference,

[0015] Step 1) The pretreatment includes pickling;

[0016] The pickling solution used in the pickling process is an 8-12 wt% sulfuric acid aqueous solution;

[0017] The pickling process is to place the raw foil in the pickling solution and soak it for 10 to 15 seconds.

[0018] As a preference,

[0019] Step 2) Dynamically controlling the copper ion concentration and sulfuric acid concentration in the copper sulfate-sulfuric acid system electrolyte;

[0020] The copper ion concentration is dynamically controlled at 10 to 30 g / L;

[0021] The sulfuric acid concentration is dynamically controlled at 100-150 g / L.

[0022] As a preference,

[0023] Step 2) The current density of the electrodeposition process is controlled to be 1.0 to 2.5 A / cm 2 ;

[0024] In step 2), the electrodeposition process controls the thickness of the electrodeposited layer to be 0.65 to 1.15 μm.

[0025] As a preference,

[0026] Step 2) The electrodeposition process controls the thickness of the electrodeposited layer to be 0.65 to 0.80 μm.

[0027] As a preference,

[0028] In step 3), the heat treatment process is performed at a temperature of 80 to 150° C. and a heat preservation time of 5 to 10 hours.

[0029] An electrolytic copper foil specially used for high-frequency and high-speed circuits.

[0030] The present invention develops a method for preparing electrolytic copper foil for high-frequency and high-speed circuits with low signal transmission loss. Before the surface treatment of the raw foil (curing, alloying, and silane treatment), a thin layer of coarse copper particles is deposited on the treated surface using a high current density to reduce surface grain boundaries. After the surface treatment, low-temperature annealing is used to increase grain growth and reduce grain boundaries, thereby reducing electron scattering, thereby achieving the purpose of reducing signal loss when used at high frequencies and high speeds.

[0031] However, although the technical solution of the present invention can grow a coarse grain layer with low-density grain boundaries, thereby reducing the signal standing wave and signal reflection phenomenon at the microscopic level, it should be noted that the growth of the coarse grain layer will also change the roughness Ra of the copper foil surface. The roughness Ra value also has a significant impact on high-frequency signal transmission. When the Ra value is too large, the signal loss rate will also increase dramatically. Therefore, the present invention also requires strict control of the electrodeposition process. This process not only requires the control and allocation of the electrolyte system and the current density of the electrodeposition process, but also a very important factor, namely the thickness of the electrodeposited layer. Although the skin depth of high-frequency signals is theoretically very small, in order to comprehensively improve the signal transmission capability of the electrolytic copper foil, it is theoretically known that the electrodeposited layer is beneficial to reducing signal transmission loss. In the early stage of the research and development of the present invention, a long time of electrodeposition was carried out to increase the thickness of the electrodeposited layer. However, as the research deepened, the researchers also found that as long as the thickness of the larger electrodeposited layer is ensured to be within about 1.15 μm, although the grain boundary density can still be kept relatively low, the actual surface roughness Ra will gradually increase, resulting in an increase in the actual electrical signal loss rate. Therefore, for the technical solution of the present invention, the thickness of the electrodeposited layer also needs to be strictly controlled.

[0032] In addition, the present invention also combines a unique low-temperature heat treatment. Low-temperature heat treatment can promote the recrystallization and grain growth of the surface grains of the copper foil, thereby reducing the grain boundary density and optimizing the electrical conductivity and surface stability of the copper foil in high-frequency and high-speed signal transmission. This is because the copper particles formed by electrodeposition are coarse, but still have subgrain boundaries and dislocation defects. During the heat treatment process, copper atoms obtain diffusion energy at low temperatures (80-150°C), and through grain boundary migration and dislocation annihilation, the grains are further coarsened (the grain size can be increased to 5-10μm), significantly reducing the number of grain boundaries per unit area. In addition, the electrodeposited layer is prone to surface micro-protrusions (Ra value rebound) due to residual stress release during subsequent processing (such as pressing and etching). Heat treatment makes the copper particles more densely bonded through stress relaxation and surface atomic rearrangement, reduces the surface roughness Ra, and promotes chemical bonding between the copper foil and subsequent surface treatment layers (such as alloying layer, silane coupling agent), enhancing adhesion by reducing the interfacial oxygen content.

[0033] The beneficial effects of the present invention are:

[0034] The present invention can effectively and efficiently optimize the performance of the electrolytic copper foil through simple operations, greatly reduce the high-frequency signal transmission loss of the electrolytic copper foil, and is low-cost, simple and easy to operate, and convenient for industrial promotion. DETAILED DESCRIPTION

[0035] The present invention is further described in detail below with reference to specific embodiments. Those skilled in the art will be able to implement the present invention based on these descriptions. Furthermore, the embodiments of the present invention described below are generally only a portion of the embodiments of the present invention, rather than all of the embodiments. Therefore, all other embodiments derived by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0036] Unless otherwise specified, the raw materials used in the examples of the present invention are all commercially available or available to those skilled in the art; unless otherwise specified, the methods used in the examples of the present invention are all methods known to those skilled in the art.

[0037] Example 1

[0038] A method for preparing electrolytic copper foil specially used for high-frequency and high-speed circuits.

[0039] The method comprises:

[0040] 1) taking a standard electrolytic copper foil (STD-ED) raw foil and immersing it in a 10 wt % sulfuric acid aqueous solution for 15 seconds for pretreatment to obtain a pretreated copper foil;

[0041] 2) Prepare a copper sulfate-sulfuric acid system electrolyte, place the pretreated copper foil in the electrolyte for electrodeposition, and dynamically control the copper ion concentration at 10-30 g / L, the sulfuric acid concentration at 100-150 g / L, and the current density at 2.0 A / cm 2 , the thickness of the electrodeposited layer is 0.80 μm, and an intermediate copper foil is obtained;

[0042] 3) The intermediate copper foil is heat-treated at 120° C. for 8 hours to obtain an electrolytic copper foil specifically for high-frequency and high-speed circuits.

[0043] The performance of the copper foil before and after treatment was characterized, including the main grain boundary density, surface roughness Ra and signal loss (10 GHz and 45 GHz).

[0044] The grain boundary density characterization depth depends on the thickness of the electrodeposited layer controlled in step 2), and the grain boundary density characterization test is performed on the surface of the copper foil before and after treatment within this thickness range.

[0045] The characterization test results are shown in the following table.

[0046]

[0047] The above characterization results clearly demonstrate that the performance of the electrolytic copper foil has been significantly improved after treatment using the technical solution of the present invention. While maintaining a substantially unchanged surface roughness Ra, the grain boundary density on the copper foil surface has been significantly reduced, resulting in a sharp decrease in signal loss. Furthermore, characterization of the thickness of the electrodeposited copper foil before and after heat treatment revealed a thickness change of ≤2%, indicating that the electrodeposition has formed a stable and dense deposited layer.

[0048] Example 2

[0049] A method for preparing electrolytic copper foil for high-frequency and high-speed circuits is based on the preparation process of Example 1. The operation process of this example is the same as that of Example 1, and only the control strategy of the copper ion concentration during the electrodeposition process is adjusted, as shown in the following table.

[0050] Sample No. Copper ion concentration control strategy S1 Same as Example 1, the copper ion concentration is dynamically controlled at 10-30 g / L S201 The copper ion concentration is dynamically controlled at 10-20 g / L S202 The copper ion concentration is dynamically controlled at 20-30 g / L S203 The copper ion concentration is controlled at 5-40g / L S204 The initial concentration of copper ions in the equal amount of electrolyte is 30g / L, and the electrodeposition process is completely consumed until it stops spontaneously.

[0051] For the field of electrodeposition, it is usually a fixed concentration electrodeposition operation, or similar to S204, to ensure that the copper ion content is sufficient to complete the electrodeposition target. However, it is different for the technical solution of the present invention. For example, the S204 sample has an electrodeposition thickness of only about 0.33 μm (and therefore the signal loss performance of S204 is not characterized because there is no actual lateral comparison value), and for S1 (ie, Example 1), copper ions are supplemented twice, that is, the control of the copper ion concentration of the present invention actually implies a condition, that is, the initial copper ion content is not enough to complete the formation of the electrodeposited layer of the entire target thickness, that is, the initial content is insufficient, and copper ions need to be supplemented at least twice during the electrodeposition process (in the form of copper salts, conventional methods), so as to ensure that dynamic changes can be formed during the electrodeposition process. This is because the copper ion concentration also affects the grain size of the growing deposited layer. Therefore, the dynamic change trend of copper ions actually has a significant impact on the microscopic characteristics of the electrodeposited layer.

[0052] The same performance characterization as in Example 1 was performed on samples S1 to S203, and the characterization results are shown in the following table.

[0053]

[0054] In the table: The change rate of the electrodeposited layer thickness refers to the change rate of the electrodeposited layer thickness on the copper foil surface before and after heat treatment.

[0055] From the characterization results in the table above, it can be clearly seen that S201 uses a lower dynamic concentration of copper ions, which leads to a significant increase in grain boundary density, while S202 uses a higher dynamic concentration of copper ions, and the grain boundary density decreases, but the surface roughness Ra increases significantly, which all leads to a significant deterioration of signal loss. In addition, the thickness change rate of the electrodeposited layer of the S202 sample increases before and after heat treatment, indicating that its deposition density and stability are not good. Similarly, for the S203 sample, when the copper ion concentration is dynamically controlled within a larger range, the surface roughness and deposition stability density are significantly reduced, resulting in a sharp increase in signal loss. As for the S204 sample, it uses a relatively natural electrodeposition process, which is equivalent to the first cycle of at least three cycles of ion concentration changes (i.e., at least two supplements) in the electrodeposition process of the technical solution of the present invention. Its deposition effect is actually relatively good, the grain boundary density is still relatively controllable, and the deposition stability and density are better. However, due to the small thickness of the deposited layer, there is no actual signal loss detection characterization and lateral comparison value.

[0056] Example 3

[0057] A method for preparing electrolytic copper foil for high-frequency and high-speed circuits is based on the preparation process of Example 1. The operation process of this example is the same as that of Example 1, and only the current density and thickness of the electrodeposited layer during the electrodeposition process are adjusted, as shown in the following table.

[0058]

[0059]

[0060] The above samples were subjected to the same technical characterization as in Example 1, and the characterization results are shown in the following table.

[0061]

[0062] It is obvious from the table above that with the increase of current density and / or electrodeposited layer thickness, the actual surface roughness Ra will begin to increase significantly, resulting in a gradual increase in signal loss. However, when the current density is low, it will also lead to an increase in grain boundary density, which will also increase signal loss to a certain extent. Therefore, the current density and electrodeposited layer thickness also need to be controlled, usually between 1.0 and 2.5 A / cm 2 , 0.65~1.15μm, can play a good optimization effect, but the best current density range, after many experiments, should be controlled at about 1.5~2.0A / cm 2 , and the thickness of the electrodeposited layer should be optimally controlled at 0.65-0.80 μm.

[0063] Example 4

[0064] A method for preparing electrolytic copper foil for high-frequency and high-speed circuits is based on the preparation process of Example 1. The operation process of this example is the same as that of Example 1, and only the control strategy of the heat treatment process is adjusted, as shown in the following table.

[0065] Sample No. Heat treatment condition control strategy S1 Same as Example 1, heat treatment at 120°C for 8h S401 Heat treatment at 70℃ for 8h S402 Heat treatment at 80℃ for 8h S403 Heat treatment at 150℃ for 8h

[0066] The above samples were subjected to the same technical characterization as in Example 1, and the characterization results are shown in the following table.

[0067]

[0068] From the above characterization results, it can be seen that the technical effects of heat treatment at different temperatures are slightly different. From the comparison of S1 and S401, it can also be seen that appropriate heat treatment can further significantly reduce the grain boundary density and significantly optimize the surface roughness, thereby comprehensively improving the use effect of copper foil in high-frequency and high-speed circuits.

Claims

1. A method for preparing electrolytic copper foil for high-frequency and high-speed circuits, characterized in that: The method comprises: 1) Pre-treating raw copper foil to obtain pre-treated copper foil; 2) preparing a copper sulfate-sulfuric acid system electrolyte, placing the pretreated copper foil in the electrolyte for electrodeposition to obtain an intermediate copper foil; 3) Heat-treating the intermediate copper foil to obtain electrolytic copper foil specifically for high-frequency and high-speed circuits.

2. The method for preparing a special electrolytic copper foil for high-frequency and high-speed circuits according to claim 1, characterized in that: Step 1) the pretreatment includes pickling; The pickling solution used in the pickling process is an 8-12 wt% sulfuric acid aqueous solution; The pickling process is to place the raw foil in the pickling solution and soak it for 10 to 15 seconds.

3. The method for preparing a special electrolytic copper foil for high-frequency and high-speed circuits according to claim 1, characterized in that: Step 2) Dynamically controlling the copper ion concentration and sulfuric acid concentration in the copper sulfate-sulfuric acid system electrolyte; The copper ion concentration is dynamically controlled at 10 to 30 g / L; The sulfuric acid concentration is dynamically controlled at 100-150 g / L.

4. The method for preparing a special electrolytic copper foil for high-frequency and high-speed circuits according to claim 1 or 3, characterized in that: Step 2) The current density of the electrodeposition process is controlled to be 1.0-2.5 A / cm 2 ; In step 2), the electrodeposition process controls the thickness of the electrodeposited layer to be 0.65 to 1.15 μm.

5. The method for preparing a special electrolytic copper foil for high-frequency and high-speed circuits according to claim 4, characterized in that: In step 2), the electrodeposition process controls the thickness of the electrodeposited layer to be 0.65 to 0.80 μm.

6. The method for preparing a special electrolytic copper foil for high-frequency and high-speed circuits according to claim 1, characterized in that: In step 3), the heat treatment temperature is controlled to be 80-150° C. and the holding time is 5-10 h.

7. An electrolytic copper foil specially used for high-frequency and high-speed circuits produced by the method according to any one of claims 1 to 6.

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