As a core heat dissipation and conductivity component in high-power electronic devices, the bonding degree between the charging pile copper substrate and the power device directly affects the heat conduction efficiency and electrical connection reliability. Microstructure fabrication technology allows for the creation of precise geometric features on or within the copper substrate, thereby optimizing the contact interface, reducing thermal resistance, and improving mechanical stability. This process requires systematic advancement across seven levels: surface morphology design, structural depth control, material compatibility, ensuring processing accuracy, multi-physics field synergistic optimization, reliability verification, and process compatibility.
Surface morphology design is the primary step in improving bonding degree. When traditional planar copper substrates contact power devices, the actual contact area is only 5%-15% of the theoretical value, resulting in low heat conduction efficiency. Microstructure fabrication allows for the fabrication of micron-level uneven structures on the copper substrate surface, such as arrayed micro pyramids, microgrooves, or micropillar arrays. These structures can penetrate the oxide layer or rough peaks on the device surface, increasing the actual number of contact points. For example, using laser processing technology to fabricate periodic microgrooves on the copper substrate surface can increase the contact area by 3-5 times, significantly reducing contact thermal resistance. Furthermore, biomimetic designs, such as flow channels mimicking the veins of a leaf, can further optimize the flow path of coolant within the copper substrate, improving heat dissipation uniformity.
Structural depth control is crucial for ensuring a perfect fit. The depth of the microstructure must match the surface roughness and coefficient of thermal expansion of the power device. If the structure is too deep, it may lead to localized stress concentration during device mounting; if it is too shallow, it cannot effectively fill interface gaps. For example, for high-power IGBT modules, the depth of the micropillar array on the copper substrate surface is typically controlled between 50-200 micrometers, which can accommodate the microscopic undulations of the device surface while avoiding structural damage caused by differences in thermal expansion. By employing a step-by-step processing strategy, first rapidly removing material with a large depth of cut, and then refining the bottom of the structure with a small depth of cut, sub-micrometer level control of depth accuracy can be achieved.
Material compatibility is fundamental to microstructure fabrication. The copper substrate must be compatible with the materials of the power device (such as ceramics, silicon, or metals) in terms of coefficient of thermal expansion, hardness, and chemical stability. For example, for gallium nitride (GaN) devices, the copper substrate needs to use a copper alloy with a low coefficient of thermal expansion (such as Cu-Mo or Cu-W) to reduce mechanical stress during temperature cycling. Simultaneously, the surface microstructure needs to be treated with electroless nickel plating or immersion gold to prevent increased contact resistance caused by copper oxidation. Some high-end applications also deposit a diamond film on the microstructure surface, utilizing its ultra-high thermal conductivity (above 2000 W/m·K) to further improve heat dissipation efficiency.
Ensuring machining accuracy is a prerequisite for the microstructure to function. CNC machining technology can achieve micron-level precision through digitally controlled tool paths. For thin-walled fin structures, a layered milling strategy is used to gradually remove material to prevent deformation; in the finishing stage, carbide-coated tools are used with low speed and high feed to achieve a surface roughness Ra < 0.2 microns. Furthermore, five-axis machining centers can engrave gradient fins on curved substrates to improve air convection efficiency; laser-assisted machining modules can create nanoscale textures on the copper substrate surface, enhancing the contact area with the thermal interface.
Multiphysics-based collaborative optimization is an advanced approach to improving bonding performance. During the microstructure design phase, simulation analysis (such as ANSYS or COMSOL) is needed to model the thermo-mechanical coupling field distribution and optimize structural parameters to balance heat dissipation and mechanical strength. For example, for silicon carbide (SiC) devices with high heat flux densities (>20kW/cm²), the copper substrate microstructure must simultaneously meet the requirements of high thermal conductivity (>400W/m·K) and low thermal stress (<50MPa). Topology optimization algorithms can generate biomimetic lightweight structures, reducing weight while increasing structural stiffness.
Reliability verification is crucial for ensuring long-term bonding stability. The copper substrate after microstructure fabrication must undergo environmental testing (such as temperature cycling from -40℃ to 150℃ and 500-hour salt spray testing) to verify its performance stability under extreme conditions. For example, in automotive electronics applications, the copper substrate must pass a 24G acceleration vibration test (compliant with ISO 16750 standards) to ensure that the microstructure does not detach or deform during long-term vibration. Furthermore, solder joint shear strength testing (>45MPa) verifies the reliability of the connection between the microstructure and the device.
Process compatibility is crucial for the successful fabrication of microstructures. Charging pile copper substrates typically require collaboration with other processes (such as chemical copper plating and pulse plating) to achieve localized thick copper or stepped copper thickness designs. For example, when fabricating a 10oz localized thick copper region, pulse plating technology is needed to control the microvia copper thickness deviation within ±10% to avoid current concentration burn-out issues caused by uneven copper distribution in the vias. Simultaneously, microstructure fabrication must be compatible with vacuum resin via plugging processes to ensure signal integrity is maintained at extreme temperatures ranging from -55℃ to 125℃.
