Industry knowledge analysis of copper foil diffusion soldering soft connection products

Copper foil diffusion welding soft connection is a flexible conductive connection made of multiple layers of extremely thin copper foils that are fused together at the ends through a diffusion welding process. The copper foils in the middle area remain separated from each other, so the overall body has good bending performance and vibration absorption capabilities. This product is usually in the shape of a flat belt or can be customized into three-dimensional shapes such as L-shaped, Z-shaped, or arc-shaped according to the installation space. The two ends are rigid connection areas processed by diffusion welding. Round holes, oblong holes, or square holes can be punched for bolt tightening. The middle part is a flexible area that can compensate for bending according to installation deviations. From a structural point of view, this feature of "rigidity at both ends and flexibility in the middle" distinguishes it from traditional solid copper bars - solid copper bars cannot absorb vibration and thermal expansion displacement, and soft connections appear to solve this problem. In engineering drawings, the product may appear under the name Copper Foil Flexible Laminated Copper Busbar, emphasizing its laminated structure and flexible features; when additional insulation protection is required, Copper Foil Flexible Busbar with Insulated Tube can be provided, that is, a high-temperature resistant insulating casing is coated in the flexible area; while Laminated Flexible Copper Busbars are a broader category, covering laminated flexible connection products of different thicknesses and different numbers of layers. In addition, the name Press Welding Foil Busbar directly points out its core manufacturing process, pressure welding, which is different from other connection methods such as brazing or ultrasonic welding.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The core material of copper foil soft connection is electrolytic copper foil or rolled copper foil, with copper content ≥99.95% and conductivity ≥97%IACS. The thickness of copper foil is usually 0.03mm to 0.3mm, which is selected according to different current carrying requirements and flexibility requirements - thinner copper foil (0.03~0.1mm) has better flexibility and is suitable for occasions that require frequent bending or severe vibration; thicker copper foil (0.1~0.3mm) has higher mechanical strength and is suitable for applications with larger current carrying but fewer bending times. Multiple layers of copper foil are laminated into one through diffusion welding. The number of layers ranges from dozens to hundreds. The total cross-sectional area determines the current carrying capacity of the soft connection. For Laminated Flexible Copper Busbars, the interface state between copper foils is crucial - if there is oil stain or oxide layer on the surface of the copper foil, metallurgical bonding cannot be formed during diffusion welding, which will lead to increased end resistance or even delamination during use. Therefore, high-quality soft connections place two requirements on copper foil raw materials: first, surface cleanliness, and second, thickness uniformity.

 

In actual production, the choice of copper foil supplier directly affects the quality stability of the final product. For outdoor or high-humidity environments that require additional protection, the Copper Foil Flexible Busbar with Insulated Tube is coated with a silicone rubber tube or polyolefin heat shrinkable tube in the flexible area. The insulated tube has a voltage rating ranging from 1kV to 35kV, and the color can be customized as required. For products such as Copper Foil Battery Busbar Connector, which are used to connect battery cores, the surface of the copper foil usually needs to be tin-plated or nickel-plated. The role of the plating has two aspects: one is to prevent the copper foil from oxidizing and turning black during long-term use, and the other is to reduce the risk of electrochemical corrosion when connecting to aluminum poles. In addition, after the end diffusion welding is completed, the connection area can be silver-plated as required to obtain lower contact resistance, which is especially suitable for internal connections of battery packs in high-current charging scenarios.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

After diffusion welding is completed, the end presents a dense metal block structure. When viewed from the side, the layered boundaries of the original copper foil completely disappear and are replaced by a uniform copper structure. The surface of the welding area is smooth and has no depressions, and the edges have no oxidation and discoloration. Use a magnifying glass to observe the boundary line between the welding zone and the flexible zone, and you can see a clear transition zone - a gradient from dense metal to loose lamination. There are no steps or gaps caused by stress concentration in the transition zone. After the end is punched, the hole wall is also in a dense state without delamination and peeling.

The layers of copper foil in the flexible area are arranged neatly, and there is no obvious gap between adjacent layers, but you can feel the relative sliding between the layers when you flick it with your fingers. Observed from the end face, the edges of the copper foil are well aligned, and there is no situation where a certain layer protrudes too far or indents too deeply. In the natural flat state, the flexible area droops in a natural arc without twisting or side bending. Bending the flexible area with your hands and then releasing it can restore it to its original shape without any trace of plastic deformation.

The mounting holes punched at the end are divided into round holes and oblong holes. The inner wall of the round hole is smooth, there are no burrs on the edge of the hole, and the resistance is even when trying to pierce the bolt. The long side direction of the oblong hole is consistent with the length direction of the soft connection, which is used to compensate for the hole distance deviation between the terminals of the two devices during installation. Both ends of the oblong hole are semicircular, and the transition is rounded without sharp corners. When frequent bolt tightening is required, a stainless steel retaining ring can be pressed into the hole. The retaining ring is tightly combined with the copper base without loosening or warping.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Copper foil diffusion soldering soft connections are widely used in electrical connection scenarios that need to compensate for relative displacement and absorb vibration. In the field of power transmission and transformation, between the high-voltage and low-voltage side bushings of large power transformers and switch cabinets, and between the busbar expansion joints and cable terminals of gas-insulated metal-enclosed switchgear (GIS), Flexible Copper Foil Soft Connectors for Electrical Transformers are standard configurations to solve the stress concentration on equipment terminals caused by thermal expansion and contraction. The transformer will produce temperature fluctuations due to load changes during operation. There is a difference between the thermal expansion of the oil tank and bushing and the thermal expansion of the connecting copper bar. If a rigid connection is used, this difference will produce a large push-pull force on the terminal. Long-term accumulation may cause oil leakage in the bushing or even insulation damage. The soft connection absorbs displacement through the deformation of the flexible zone, reducing the stress on the terminal to an acceptable range.

 

In the field of new energy, in electric vehicle battery packs and energy storage systems, Copper Foil Battery Busbar Connector is used to connect cell poles, modules, and between modules and high-voltage relays. Batteries will expand and contract in the thickness direction during charge and discharge cycles. At the same time, vibrations during vehicle driving also impose flexibility requirements on connectors. The laminated structure of soft connections can deform with the expansion and deformation of the battery core without causing fatigue fracture. In the field of industrial frequency conversion and rectification, since the replacement and maintenance of power modules require an operating gap between the laminated busbars of high-power thyristor rectifier cabinets and frequency converters and external terminal blocks, soft connections allow on-site personnel to maintain electrical connections after pulling out the equipment. In addition, in rail transit traction converters, Copper Foil Flexible Busbar Connectors are used to connect power modules and DC support capacitors, absorb shock vibrations during vehicle operation, and avoid loosening of solder joints or bolts.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

If you are looking for a reliable Copper Foil Flexible Connection solution for transformers, switch cabinets, battery packs or rectifier cabinets, our team of engineers can complete a structural assessment and quote and provide a solution after receiving drawings or samples.