With the rapid development of science and technology, social sectors in particular, composite materials, electronic materials, decorative materials, demand for electrolytic copper foil is increasing. Electrolytic copper foil has become a key material for PCBs that support and interconnect components in electronic products. It has been hailed as a "neural network" for signal transmission and communication of electronic products.

As the basic material of the electronics industry, electrolytic copper foil has been following the development of PCB technology, and PCB technology has been increasing with the rapid development of electronic products. The development of IT product technology has promoted the development of PCBs in the direction of multi-layer, thinning, high-density, and high-speed. Therefore, the development of electrolytic copper foil with higher performance, high quality, and high reliability has a very broad market prospect.

The application of ultrasonic in electroplating has been reported since the 1930s, but development has been slow, and it has not been developed rapidly until recently. Ultrasonic has a wide range of applications in the electroplating industry. Ultrasonic plating can not only improve the bonding strength between the coating and the substrate, but also refine the grains, improve the surface roughness of the coating, increase the current density, improve the current efficiency, and obtain better performance. Plating. Therefore, the application of ultrasonic waves in electrolytic copper foil will definitely affect the coating quality of copper foil, and open up a new field of application of ultrasonic technology. This paper will review the application of ultrasonic in the preparation of ultra-thin copper foil.

First, the working principle of ultrasound

Ultrasonic refers to a mechanical wave with a frequency range of 20 to 106 kHz. The wave velocity is generally about 1500 m/s and the wavelength is 10 to 0.01 cm. It is composed of a series of longitudinal and longitudinal longitudinal waves and propagates around the liquid medium. Ultrasonic waves have much greater energy than ordinary sound waves, and when the ultrasonic energy is high enough, ultrasonic cavitation occurs. Ultrasonic cavitation means that the microbubbles existing in the liquid vibrate under the action of the sound field, generate and grow in the negative pressure zone formed by the longitudinal propagation of the ultrasonic waves, and rapidly collapse and close in the positive pressure zone, resulting in a very short life at the collapse point. The phenomenon of local hot spots. The ultrasonic cavitation process is a process of concentrating the sound field energy and releasing it rapidly. The abnormal conditions such as high temperature and high pressure are abnormal, which provides a new and very special physics for chemical reactions that are difficult or impossible to achieve under normal conditions. Chemical environment.

Ultrasonic is used for electroplating. Its main functions are:

(1) Cleaning effect: The powerful shock wave can penetrate into the surface and gap of different electrode media to thoroughly clean the electrode surface.

(2) Hydrogen evolution: Electroplating is often accompanied by the generation of hydrogen. Hydrogen trapped in the coating reduces the performance of the coating. The evolved hydrogen easily causes spots and streaks, while ultrasonic cavitation causes hydrogen to enter the cavitation bubble or as an empty The nucleation accelerates the precipitation of hydrogen.

(3) Stirring effect: The high-speed micro-jet generated by ultrasonic cavitation strengthens the stirring effect of the solution, strengthens the transport capacity of ions, reduces the thickness and concentration gradient of the diffusion layer, reduces the concentration polarization, and accelerates the electrode process. , optimized plating operating conditions.

The cavitation effect of ultrasonic wave is easier to achieve uniform mixing of the medium compared with the traditional stirring technology, eliminating local concentration unevenness, increasing the reaction speed, stimulating the formation of a new phase, and also shearing the agglomerate. Ultrasonic cavitation is the physical basis for many ultrasound applications and is widely used in scientific research and industrial production.

Second, the type of ultrasound and the way of introduction

As an auxiliary experimental method, ultrasound can be roughly divided into two types: direct ultrasound and indirect ultrasound. Both types of ultrasound devices have their own advantages and disadvantages.

(a) direct ultrasound

This type of reactor is a probe system, also known as a horn system, also known as a horn-type sonochemical reactor, which is increasingly used in laboratory ultrasonic chemistry research. The device is such that the emitting end (also called the probe) of the horn driven by the ultrasonic transducer is directly immersed in the reaction liquid, so that the sound energy directly enters the reaction system without being transmitted through the reactor wall of the cleaning tank. This has the advantage of being able to deliver a large amount of energy directly to the reaction medium, modulated by varying the amplitude delivered to the transducer. However, there are some disadvantages in using the probe system, mainly the erosion and depression of the probe tip, which easily contaminates the reaction solution.

(2) Indirect ultrasound

This type of reactor is an ultrasonic bath, mainly used for cleaning reaction vessels and electrodes. A classic ultrasonic bath attaches the transducer to the bottom of the bath, and the transducer can also be immersed in the bath. Ultrasonic baths are convenient and inexpensive, and are widely used in ultrasonic chemistry research. The ultrasonic power used to reach the reaction vessel using indirect ultrasound is relatively small compared to direct ultrasound. In addition, since the power reaching the reaction medium is largely dependent on the position of the sample in the bath, the experimental reproducibility is relatively poor, and the result will also vary with the ultrasonic heating time of the bath during operation. A change has occurred.

(3) Ways of introducing ultrasonic waves

There are three main types of ultrasonic introduction: ultrasonic cleaning of the workpiece before electroplating; introduction of ultrasonic waves into the electroplating solution during electroplating; and introduction of ultrasonic waves on the electroplated cathode workpiece.

In fact, the simplest method of applying ultrasonic waves in the electroplating industry is to introduce the ultrasonic waves directly into the plating bath. In the electroplating process, the electroplating bath containing the electroplating solution is placed in the ultrasonic bath, which is indirect ultrasonic, which is convenient and inexpensive, and does not easily contaminate the reaction solution. In the ultrasonic process, the water level in the ultrasonic bath is required to be slightly higher than the liquid level of the plating solution in the plating bath to achieve better stirring effect.

Third, the application of ultrasonic in the preparation of ultra-thin copper foil

In recent years, China's electrolytic copper foil has developed rapidly, and its performance and variety have been updated to higher requirements, so that the development of electrolytic copper foil has a new trend, and its thickness is developing in a thin and ultra-thin direction. The production of ultra-thin copper foil requires carrier support, and the key to the production of ultra-thin copper foil is to solve the problem of peeling of the carrier layer and the copper foil layer. Therefore, a peeling layer is to be electroplated on the carrier copper foil in the peeling layer. On the ultra-thin copper foil plating. Many types of release layer, wherein the organic layer was preferably used together with the alloy layer as the release layer, to achieve a certain stripping effect. The introduction of ultrasonic waves during the plating of the alloy layer can effectively improve the quality of the coating and integrate other influencing factors to achieve better results.

The production of carrier ultra-thin copper foil is roughly determined by the following steps:

Ultrasonic waves are introduced during the plating of alloy layers and copper plating. The high-speed microjet generated by ultrasonic cavitation can enhance the stirring effect of the solution, enhance the transport capacity of ions, reduce the thickness and concentration gradient of the dispersion layer, and reduce the polarization of the solution. Accelerate the electrode process and optimize plating operating conditions.

(1) Application of ultrasonic waves in electroplating alloys

The ultrasonic plating alloy process has gradually developed with the development of the electroplating industry, and the types of alloys are also increasing.

Mahmood et al. studied the effect of 13kHz.350W, power-adjustable ultrasound on the electrodeposition of Ni-Co and Ni-Fe alloys. It is found that with the increase of ultrasonic power, the cobalt content in the Ni-Co alloy decreases, while the iron content in the Ni-Fe alloy increases. The hardness of both alloys increased significantly, the toughness of the coating also increased, and the tensile strength did not change significantly. Duda et al.1 studied the electrodeposition characteristics of Co-Ni alloys and studied the mechanism of the effects of ultrasonic vibration, temperature and alloying elements on the ion discharge kinetics in Co-Ni electrocrystallization. Walke et al. used ultrasonic technology to electroplate Ni-Fe alloys. The results show that ultrasonic can improve the hardness of the coating and increase the content of Fe in the coating. The ultrasonic wave with a frequency of 24.8 kHz is better than the effect of 37.9 kHz. However, the internal stress of the coating increases and is plated. When saccharin is added to the liquid, the internal stress can be reduced.

Seryanov et al. studied the Sn-Bi alloy plating applied to integrated circuit boards, and determined the optimal operating conditions, ultrasonic power and frequency range. Chen Huamao and others applied ultrasonic waves to tin - bismuth alloy plating, and tested and compared the plating solution and coating properties under the action of ultrasonic waves. The results show that the application of ultrasonic wave widens the current density and temperature range of electroplating. The surface of the prepared tin-bismuth alloy coating is dense and uniform, the crystal is fine, and the oxidation resistance, corrosion resistance and solderability are enhanced. Ultrasound accelerates the electrode. The process improves the bath performance and increases the cathode current efficiency and deposition speed.

There are many applications of ultrasonic waves in electroplating alloys, and there are many types of peeling layers and alloy layers for forming ultra-thin copper foils. Suzuki Yuuji et al. introduced the use of Ni-Mo alloys, Ni-Co alloys, Cr-Co alloys, and Ni-Cr. As a release layer, alloys also use Mo-Co, Mo-Ni, W-Ni, Mo-Co (first layer) + Mo-Co (second layer) as a release layer, in the process of electroplating, in order to make a solution The distribution of metal ions is more uniform, and mechanical agitation is generally used. Although mechanical agitation has a certain effect, the effect is not so obvious. Therefore, if an attempt is made to introduce ultrasonic waves in the electroplating alloy layer, the stirring effect is enhanced and the plating layer is improved. Quality, but also broaden the scope of application of ultrasonic technology.

(2) Application of ultrasonic wave in electroplating copper

As early as the 1930s, there were reports on the electro-deposition of ultrasonic metal copper. Studies on the introduction of ultrasonic waves into sulphate copper plating have found that ultrasonic waves not only accelerate the hydrogen evolution process, but also improve the current efficiency, and at higher current densities, bright coatings are also obtained.

R. Vasuoevan et al. studied the effect of ultrasonic vibration on the quality of electroplated copper layer at room temperature. It was found that ultrasonic vibration can increase the limiting current density, significantly improve the anode and cathode current efficiency, increase the brightness of the coating, and increase the microhardness by about 25%. Diffraction analysis shows that ultrasonic waves have a great effect on reducing the residual stress on the surface of the coating. The study also found that ultrasonic can not only accelerate the hydrogen evolution process, improve current efficiency, but also obtain a bright coating at higher current densities. M. C. Hsiao et al.'s research suggests that ultrasonic vibration is actually a millisecond-level pulse process that changes the crystal orientation of the acid copper plating layer and has a great effect on improving the physical and mechanical properties of the copper plating layer. Martins et al. used electromagnetism to electroplate copper on an iron base and found that the current efficiency, hardness of the electroplated copper layer, brightness, and adhesion to the substrate were significantly improved compared to mechanical agitation.

There are also related reports in China. Wang Yaqiong and others from Yangzhou University have made relevant research on ultrasonic electroplating copper. The research shows that the introduction of ultrasonic waves into the electrochemical deposition process of copper can significantly increase the cathode limit diffusion current density of copper electrodeposition. At the same electrode potential, the same electrode potential is 25 °C. The average limiting current density under ultrasonic action is 73.3 A/m ² , while the average limiting current density without ultrasonication is 5.2 A/m ² , and the average ultimate diffusion current density is increased by about 13 times, which greatly strengthens copper. The process of electrochemical deposition. The introduction of ultrasound during the electrochemical deposition of copper can change the orientation of the crystal plane of the electrodeposited copper, promote the formation of crystal nuclei, and also crack the normally developed crystals, thus significantly changing the particle size of the electrodeposited copper. Grain Refinement. It has been reported that the internal stress of the electroplated copper film can be effectively reduced by using ultrasonic technology without changing the original electroplating copper process, and the quality of the electroplated copper film can also be improved.

(III) The role of ultrasonic waves in the preparation of ultra-thin copper foil

Ultrasonic has achieved good results in electroplating alloy layers and electroplating copper. Ultrasonic cavitation is also used in the application of ultra-thin copper foil. Ultrasonic vibration and cavitation are equivalent to an unusually strong agitation of the bath. The usual agitation in the electroplating process, such as cathode movement, rotary agitation, mechanical agitation such as circulating flow, and manual agitation, can only reduce the thickness of the diffusion layer near the cathode to a certain extent, and the stirring effect cannot directly reach the electrode. The surface, and thus, a diffusion layer of a certain thickness near the surface of the electrode exists, and the solution in the diffusion layer is still stationary without convection. The effect of ultrasonic waves is different. The strong shock wave generated by cavitation acts on the diffusion layer near the electrode, which produces strong agitation. This effect reaches the surface of the electrode, making the diffusion layer almost non-existent, greatly improving the metal ions in the plating solution. The effective concentration accelerates the electrodeposition process. Therefore, when ultrasonic stirring is used, the current density can be increased, the concentration of metal ions in the vicinity of the cathode can be equalized, the metal ions in the vicinity of the cathode are not deficient, the concentration polarization is lowered, the brightness is increased, and the hydrogen on the surface of the cathode is easily escaped. Reduce burrs and pinholes to obtain a finer, uniform coating of crystalline particles. The application of ultrasonic waves in the preparation of ultra-thin copper foil makes the surface of the copper foil more flat, compact, uniform in thickness, and well bonded to the substrate, effectively improving the quality of the coating.

In addition, the introduction of ultrasonic waves can accelerate the growth rate of the crystal, prevent the occurrence of coalescence, and also change the structure of the crystal, thereby improving the performance of the crystalline product. Practice has shown that ultrasonic cavitation not only improves the plating speed and efficiency, but also improves the quality of the coating, which will play an increasingly important role in industrial production.

Fourth, the conclusion

Ultrasonic has a wide range of applications in the electroplating industry. Ultrasonic cavitation exerts a strong agitation effect on the plating solution, promotes the precipitation of hydrogen, accelerates the mass transfer process, and improves the plating speed and efficiency. On the other hand, the quality of the coating is improved, and its social and economic benefits are very obvious. But so far, the mechanism of the role of ultrasonic in electroplating is still not clear. The relationship between the power, frequency, intervention mode and shape of the electrode and the operating conditions and its influence on the coating have not yet been systematically studied. In-depth study. With the deepening of research on ultrasonic plating technology, ultrasonic technology will have broad application prospects.

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