Copper foil soft connection industry knowledge

 

Copper foil soft connection is a high-current flexible conductive connection formed by solid-state pressure welding technology. It is usually superimposed and welded by multiple layers of high-purity copper foil. This product plays a key role in the fields of electronics, electricity and new energy, mainly achieving efficient and reliable conductive connections. Its core working principle is based on atomic diffusion: under the combined action of high temperature and external pressure, atoms on the contact surfaces of adjacent copper foils diffuse to each other and form new metallic bonds, thereby obtaining a solid-solid connection without using any solder or flux. Among them, Flexible Copper Busbar is widely used in situations where it is necessary to adapt to equipment vibration, thermal expansion and contraction, or where installation space is limited due to its excellent electrical conductivity (usually above 98% IACS) and excellent mechanical flexibility.

Compared with traditional soldering or tin soldering, this diffusion welding process completely avoids spatter, pores, voids, and the release of harmful substances from lead- or halogen-containing fluxes that may occur during the welding process, and has significant environmental protection and reliability advantages. In addition, since there is no introduction of a third material, the resistance of the connection interface is almost equal to the resistance of the copper matrix itself, which is critical for applications that require hundreds or even thousands of amperes of high current to pass through for a long time. Against the background of the current dual requirements of green manufacturing and high reliability in the global electronics industry, copper foil soft connections have become one of the ideal technical routes to replace traditional hard connections or braided wire connections.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The design of copper foil soft connections is based on the deep integration of the two seemingly contradictory properties of high conductivity and high flexibility. The raw materials generally use T2 or above grade copper tape (i.e., No. 2 pure copper and above), the copper content is not less than 99.95%, and the total impurity content is strictly controlled within 0.05% to ensure the best current carrying capacity. The thickness of a single piece of copper foil is one of the core parameters of the design, and the normal range is between 0.03mm and 1mm: the thinner the thickness, the better the overall flexibility and the smaller the bending radius after multiple layers are superimposed. However, correspondingly, the more layers that need to be superimposed, the higher the uniformity requirements for the welding process; conversely, thicker copper foil can provide higher structural stiffness and is suitable for scenarios that require shape maintenance. The shape and structure of the product can be highly customized according to the actual installation space and electrical direction. Common ones include straight, U-shaped, L-shaped, Z-shaped and special-shaped parts with a certain twist angle. In order to improve the corrosion resistance in harsh environments such as humidity, salt spray or industrial pollution, the contact surface (i.e., the welding end or the connection terminal part) can be surface treated as needed. For example, Tinned Copper BusBar refers to a product whose surface is evenly plated with a layer of pure tin. The tin layer can not only effectively isolate the contact between the copper matrix and the corrosive medium, but also reduce the contact resistance and prevent the formation of copper oxide.

In addition, nickel plating or silver plating are also suitable for high temperature environments or situations with extreme requirements on contact resistance. At the mechanical design level, engineers need to accurately specify key dimensional parameters such as the product's width (A), total thickness (B), mounting surface length (A1), bending angle and bending radius, and ensure that the flatness of the contact surface after welding usually does not exceed 0.1mm to ensure a tight fit with the device terminals. After molding is completed, the product usually needs to be polished to remove edge burrs, chemically cleaned to remove surface oxides, dried to remove residual moisture, and coated with PET or silicone insulating sleeves as needed to meet the safe creepage distance requirements under different voltage levels.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

According to the difference in welding heat source and connection mechanism, copper foil soft connections are mainly divided into two categories: pressure welding type and soldering type in actual production. Among them, the pressure welding type represents the most mainstream technical direction at present. Pressure welding Flexible BusBar uses polymer diffusion welding (also known as molecular diffusion welding or solid-state diffusion welding). This process uses low voltage and high current to generate Joule heat through the welding electrode, causing the area to be welded to quickly heat up to 0.6 to 0.8 times the melting point of copper (approximately 700°C to 900°C), while applying an axial pressure of tens to hundreds of MPa. Under this condition, the atoms on the copper foil contact surface gain enough energy to break through the energy barrier, diffuse with each other, and form a complete grain bonding layer, without any liquid phase transition occurring in the entire process. The most suitable copper foil thickness for this process is 0.05mm to 0.30mm, which can achieve one-time overall welding of dozens or even hundreds of layers of copper foil. When the product width (A) is greater than 90mm and the total thickness (B) is greater than 60mm, in order to ensure uniform pressure and temperature distribution at each point of the large-size contact surface, an additional layer of 1mm thick copper plate is often attached to both ends of the copper foil stack as a pressure equalizing and heat equalizing medium, and then pressure welding is performed.

When the product width exceeds 140mm and the total thickness exceeds 130mm, due to the limitations of the heating capacity and pressure uniformity of diffusion welding equipment, the silver-based brazing process is often used. The brazing type Flexible Copper Busbar pre-disposes silver, copper, phosphorus and other brazing materials between copper foil layers or at the ends, and melts the brazing material at a temperature slightly higher than the melting point of the brazing material (usually 650℃-800℃) to fill the interface gap, and forms a connection after cooling. Although brazing can achieve products with larger sizes or more complex shapes, it should be noted that the solder layer itself has a certain resistivity and may affect the annealing state of the copper foil at high temperatures. In addition, from a long-term reliability perspective, direct copper-to-copper connections formed by diffusion welding are superior to brazed joints in terms of thermal cycle stability, resistance to electromigration, and no risk of interface corrosion. Therefore, if conditions permit, the pressure welding process is the preferred manufacturing method for high-performance Copper BusBars.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Copper foil soft connections play an irreplaceable role in many industrial and transportation fields because of their high current-carrying capacity and flexible compensation function. In the field of new energy vehicles, it is an Automotive Copper Busbar that connects cells in series and parallel within the battery pack and between modules. Core components: On the one hand, its extremely low resistance (usually at the micro-ohm level) ensures that energy loss is minimized under hundreds of amps of charge and discharge current; on the other hand, the multi-layer copper foil structure can perfectly absorb the thickness expansion and contraction of the battery core during the charge and discharge process (amplitude is about 1%-3%), while withstanding the vibration and impact of the vehicle while driving, effectively avoiding terminal tearing or bolt loosening that may be caused by hard connections. In addition to the inside of the battery pack, this product is also widely used in the high-voltage interconnection of three electrical systems such as motor controllers (MCUs), high-voltage power distribution boxes (PDUs), on-board chargers (OBCs), and direct current converters (DCDC).

In the field of power equipment, copper foil soft connections are often used as flexible jumpers between generator outlet busbars and transformer bushings, which can compensate for alignment errors during installation and thermal elongation during equipment operation. They are also commonly used in high and low-voltage switchgear movable connections between circuit breakers and busbars to facilitate equipment extraction and maintenance. In high-current industrial scenarios such as electrolytic smelting and carbon production, a Copper Flexible Busbar may need to carry tens of thousands of amps of DC current while connecting multiple rectifier cabinets and electrolyzers. Its flexibility can adapt to factory foundation settlement or equipment thermal deformation.

In addition, in 5G communication base stations, the special structure of copper foil soft connections helps to weaken high-frequency electromagnetic interference; in magnetic resonance imaging (MRI) equipment, some ultra-precision special-shaped copper foil soft connections with flatness requirements as high as 0.02mm are used for cooling in low-temperature environments; in the field of rail transit, reinforced copper foil soft connections are used between traction converters and auxiliary power cabinets. Overall, the operating temperature range of copper foil soft connections is usually -40°C to +300°C, and by selecting appropriate plating (such as Tin Plated Copper Bus Bar, which preferentially corrodes the tin layer rather than the copper base in humid environments), the service life of the product in salt spray or acidic environments can be significantly extended.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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