Laminated busbar industry knowledge popularization

 

The laminated busbar is an integrated multi-layer composite structure electrical connection component formed by alternately laminating multiple layers of conductive materials and insulating materials and then solidifying them by high temperature and high pressure hot pressing. Structurally, it is similar to a "highway" in a power distribution system, integrating multiple power terminals and input and output nodes into a flat, compact unit with low-impedance paths. The core value of the laminated busbar is that by tightly coupling adjacent conductive layers, the stray inductance in the loop can be significantly reduced - this parameter is often as high as hundreds of nanohenries in traditional wire harnesses, but can be reduced to the order of ten to tens of nanohenries in the optimized design of the laminated busbar. The reduction of stray inductance directly suppresses the peak voltage generated by power devices such as IGBT and MOSFET during high-speed turn-off, thereby effectively protecting power semiconductor devices from the risk of over-voltage breakdown. At the same time, the close contact between the conductive layer and the insulating layer will form a naturally distributed capacitance between adjacent conductors.

 

Although this distributed capacitance is small (usually several hundred picofarads to several nanofarads), it helps filter out common-mode noise in high-frequency switching scenarios and improves the system's anti-electromagnetic-interference capability. In addition, laminated busbars also have typical characteristics such as repeatable electrical performance (high batch consistency), low AC impedance (especially obvious advantages in high-frequency harmonic environments), good thermal conductivity (flat structure can fit the surface of the radiator), and simple and fast installation (reduces the number of contacts and screw tightening workload). Overall, laminated busbars are a systematic alternative to traditional wiring methods that are cumbersome, time-consuming and prone to wiring errors. They are especially suitable for modern power electronic systems with increasing power density. In the design of multi-layer composite structures, the thickness, width and insulation layer thickness of each layer of conductors need to be carefully calculated based on the voltage level, current effective value and switching frequency to ensure uniform electric field distribution and controllable hot spot temperature.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The core of the laminated busbar lies in the precise alternating lamination of conductive layers and insulating layers. The thickness tolerance of each layer of conductive material (copper or aluminum) is controlled within ±0.05mm to ensure uniform current density distribution. In multi-layer laminated busbars, the thickness of the insulation layer between adjacent conductive layers is not fixed, but is designed differently according to the voltage difference: for example, the thickness of the insulation layer between the positive and negative DC bus bars is usually 0.2–0.5mm, while the thickness of the insulation layer between the DC bus bar and the ground may be increased to 0.5–1.0mm to meet higher withstand voltage requirements. The shape design of the conductive layer also includes a lot of details: in order to reduce local electric field concentration, all sharp corners of the conductive layer need to be rounded, with a typical radius of not less than 1.5mm; in areas where welding or crimping terminals are required, the conductive layer will be locally thickened or reinforced to prevent mechanical stress from deforming the copper foil. After the multi-layer composite structure is laminated, the overall thickness consistency is controlled within ±0.1mm. This indicator directly affects the assembly fit of the busbar in the chassis.

 

Edge treatment is a key detail that determines the environmental resistance and long-term reliability of the laminated busbar. For open-edge structures, the cutting surface will expose the layered interface between the conductive layer and the insulating layer. Precision milling or grinding process is required to remove the adhesive burrs that overflow from the hot press and make the edges of all layers flush with a deviation of no more than 0.2mm. For edge-sealing structures, the edge-sealing adhesive needs to completely cover all exposed interfaces between the conductive layer and the insulating layer. The edge-sealing width is usually 3–8mm, and the edge-sealing thickness is about 0.3–0.8mm. The application methods of edge sealing adhesive include automatic spraying, dip coating or screen printing. After application, it needs to be pre-cured at 60-80°C for 30 minutes, and then fully cured at 120-150°C for 1-2 hours. The potting type structure is more complex: the entire laminated busbar is placed in a precision mold, and two-component polyurethane or epoxy resin is injected under vacuum conditions (vacuum degree ≤ 1mbar) to completely eliminate air bubbles. The thickness of the potting layer is generally 2–5mm, and it reaches a protection level of IP54 or above after complete curing. A qualified edge-sealing section observed under a microscope should have no visible pores, no delamination, no cracks, and no separation gap between the edge-sealing material and the insulating film.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The manufacturing process of laminated busbars involves multiple precision machining and hot pressing processes. The process parameter control and process inspection standards of each link will directly affect the electrical safety, mechanical strength and long-term operation reliability of the final product. The following is detailed one by one in the order of the typical process flow: First, raw materials are inspected upon arrival. Conductive layer copper or aluminum materials need to be measured for thickness tolerance (usually within ±0.05mm), hardness status and surface finish (no scratches, oil stains, oxidation spots). Insulating films need to be randomly tested for thickness, dielectric strength and thermal shrinkage, and adhesive films need to be checked for shelf life and bonding strength test piece data. Second, the conductive layer is cut and formed. According to the design graphics, laser cutting (high precision, no burrs, suitable for small batches or complex shapes), CNC stamping (high efficiency, suitable for mass production) or precision chemical etching (suitable for extremely thin copper sheets, no mechanical stress) processes can be used. The cut conductive layer must be deburred (roller brushing, magnetic polishing or high-pressure water deburring) to prevent sharp burrs from penetrating the adjacent insulating layer. For conductive layers that need to be bent, special molds must be used on a bending machine to form them in sequence. The bending radius is generally not less than 1.5 times the thickness of the material to avoid cracking of the copper material.

 

Third, surface treatment. The copper conductive layer is usually tin-plated (good solderability, moderate cost), nickel-plated (wear-resistant, high-temperature resistant, suitable for soldering or crimping terminals) or silver-plated (optimal conductivity, suitable for extremely high frequencies or extremely low contact resistance requirements). The aluminum conductive layer is anodized (to form an insulating oxide film) or sprayed with insulating powder. After surface treatment is completed, adhesion testing and contact resistance sampling inspection are required. Fourth, prepare the insulation layer. The insulating film is precisely cut (laser or die-cut) according to the designed shape, paying attention to removing material from the positioning holes and terminal lead-out areas. The adhesive film is also cut and pre-fixed on the surface of the conductive or insulating layer. In multi-layer stacked busbars, the thickness of the insulation layer may be different in different areas, which needs to be strictly distinguished during stack preparation. Fifth, layered assembly. According to the stacking sequence table, alternately place the conductive layer, insulating layer, adhesive film and positioning fixture in the hot pressing mold, and ensure that the terminal positions, positioning holes and mold pins are aligned one by one. This step requires a relatively clean environment (a class 10,000 clean room or a local class 100 laminar flow hood is recommended) to prevent dust particles from falling between the insulation layers and causing partial discharge.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

With its high power density, compact structure, low impedance characteristics and excellent long-term reliability, laminated busbars have been widely used in many industries with high requirements on electrical performance, space utilization and environmental adaptability. In the field of transportation, laminated busbars are widely used in the main circuit connections of rail transit traction converters, electronic control systems of new energy vehicles (including motor controllers, battery management system distribution boxes and on-board chargers), auxiliary power supply units of trams, and power busbars in traction locomotives. These applications generally face severe vibrations, wide temperature ranges (-40°C to 85°C or even higher), frequent thermal cycles, and strong electromagnetic interference environments. The multi-layer composite structure of the laminated busbar can effectively resist the above harsh conditions and at the same time improve the control stability of the traction system by reducing stray inductance.

 

In terms of energy conversion, laminated busbars are suitable for DC-side and AC-side connections of solar photovoltaic inverters, machine-side and grid-side power modules of wind power converters, battery cluster convergence units of energy storage systems, and DC bus distribution systems of industrial inverters. As photovoltaic and wind power systems develop towards higher voltage levels (1500V DC) and greater single-machine power, the low-impedance advantage of laminated busbars becomes more and more obvious, which can significantly reduce line losses and improve the overall system efficiency. In the communications and computer industry, the -48V power distribution system of communication base stations, the power distribution backplane of large data center servers, the backplane interconnection of network core routers, and medical imaging test equipment (such as the high-voltage power module of the CT rotating part and the output connection of the MRI gradient amplifier) ​​all use laminated busbars as key connection components. Their compact design releases valuable internal installation space while ensuring high-reliability signal and power transmission.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Based on the Mainframe BusBar structural drawings, electrical parameter tables, environmental grades and certification requirements provided by customers, we can complete turnkey development and batch delivery from edge treatment method selection, insulation film material comparison and recommendation, hot pressing process parameter debugging to a full set of electrical tests, helping customers achieve low failure rates, compact layout and long-term reliable operation in system-level integration.