Application of Laser Welding Technology in Ceramic Substrate Industry

Ultra short laser pulses for local welding (Source: Fraunhofer IOF）

With the accelerated evolution of electronic devices towards high power, high frequency, and miniaturization, ceramic substrates have become core materials in fields such as power semiconductors, 5G communications, and new energy vehicles due to their excellent thermal conductivity, insulation, and high temperature resistance. However, the high-strength connection between ceramic substrates and metal electrodes, precision packaging of complex structures, and long-term reliability in extreme environments have always been technological bottlenecks that constrain the development of the industry. In this context, laser welding technology, with its unique advantages of non-contact, high precision, and small heat affected zone, is gradually reshaping the process boundaries of ceramic substrate manufacturing and becoming a key engine for promoting industrial upgrading.

Technical principles
The essence of laser welding is to apply a high-energy density laser beam (usually fiber laser or semiconductor laser) to the surface of the material in a very short period of time, melt or vaporize local areas through photothermal effect, and then rapidly cool to form metallurgical bonding. Compared to traditional processes such as brazing and diffusion welding, the core breakthrough of laser welding lies in its high controllability of energy input - by adjusting parameters such as laser power, pulse width, and scanning speed, it can achieve precise processing from micro level solder joints to macroscopic structures.

Taking the welding of aluminum nitride (AlN) ceramics and copper electrodes as an example, due to the absorption rate of AlN for near-infrared laser (wavelength 1.06 μ m) being less than 10%, early processes were difficult to achieve effective connection. In recent years, research has shown that using short wavelength green laser (532 nm) can increase the absorption rate to over 30%. At the same time, combined with pulse modulation technology (pulse width 10-100 ns), it can suppress the generation of interface brittle compounds, making the joint shear strength exceed 200 MPa, which is nearly twice as high as traditional brazing. This progress directly promotes the reliability upgrade of silicon carbide (SiC) power modules in new energy vehicle motor controllers.

Application scenarios
In the field of power electronics, the application of laser welding has evolved from a single connection to multifunctional integration. For example, in the latest generation inverter module of a new energy vehicle factory, the laser welding process of AlN ceramic substrate and copper heat sink is used. By optimizing the circular scanning path and gradient energy input, the thermal resistance of the welding area is reduced by 40%, and the thermal cycle life is increased from the traditional process of 50000 times to 150000 times. This breakthrough significantly improves the stability of electric vehicles under extreme temperature fluctuations.

In the field of optical communication, the precision advantage of laser welding is more prominent. In the optical module production line of a certain communication company, laser welding is used for packaging aluminum oxide (Al ₂ O ∝) substrates and gold tin (AuSn) solder. Through the non thermal melting mechanism of femtosecond laser (pulse width<1 ps), the welding heat affected zone is controlled within 5 μ m, avoiding performance degradation of adjacent waveguide structures and increasing the device packaging yield from 85% to 99%. This technological path provides key support for the miniaturization of 800G/1.6T optical modules.

In addition, the value of laser welding in the field of ceramic substrate repair cannot be ignored. K Company has developed a machine vision based laser reprocessing system: micro cracks are located using a high-resolution infrared thermal imager, and the defect area is locally remelted using a low-power continuous laser (50 W) to restore the bending strength of the repaired Al ₂ O3 substrate to over 92% of its original value. At the same time, the repair time is shortened from 2 hours in traditional processes to 10 minutes, significantly reducing the scrap cost of high-end devices.

Technical challenges
Despite the significant advantages of laser welding, its large-scale application in the field of ceramic substrates still faces multiple challenges. The first and foremost constraint is the intrinsic properties of the material - the high brittleness and low fracture toughness of ceramics make it easy for thermal stress during welding to cause microcracks. Experiments have shown that the surface crack density of AlN substrates after laser welding can reach 10 ³/mm ², and the crack propagation rate can reach up to 10 ⁻⁴ m/s. To this end, the industry has explored two innovative solutions: one is to locally preheat the substrate (200-400 ℃) before welding, and suppress crack initiation by reducing the temperature gradient; The second is to use the "continuous+pulse" composite laser process, which uses continuous laser to preheat the substrate and pulse laser to complete precision welding, successfully reducing crack density by 70%.

Another major challenge comes from the compatibility of heterogeneous material interfaces. The difference in atomic structure between ceramics and metals leads to insufficient interfacial bonding. Taking aluminum oxide copper welding as an example, the interface porosity in traditional processes can reach 5%, which seriously affects the conductivity and thermal conductivity. The latest research introduces a nano silver transition layer (thickness 50-100 nm) and utilizes laser-induced transient liquid-phase diffusion to reduce the interface porosity to below 0.3%. The interface thermal resistance is optimized from 2.5 × 10 ⁻⁶ m ² · K/W to 8 × 10 ⁻⁷ m ² · K/W. This achievement provides new ideas for the heat dissipation design of high-power density devices.

In terms of process stability, laser spot drift (± 2 μ m) and power fluctuation (± 3%) are still bottlenecks that restrict the consistency of mass production. The adaptive welding system launched by IPG Photonics integrates a high-speed CCD camera and real-time power feedback module to dynamically adjust the laser focus position and output energy, controlling the welding position deviation within ± 0.5 μ m and improving power stability to 99.9%. The popularity of such intelligent devices is accelerating the penetration of laser welding from laboratories to industrial production lines.

Future Trends
From the perspective of technological evolution trends, ultrafast lasers and intelligent control will become the core breakthrough direction in the next stage. The cold processing characteristics of femtosecond laser can completely eliminate thermal stress. The German f research institute has achieved crack free welding of AlN ceramics with a speed of 20 mm/s and a heat affected zone of<1 μ m. At the same time, process optimization systems based on artificial intelligence, such as the LaserWeld AI module developed by ANSYS, can automatically match the optimal welding parameters within 10 minutes through machine learning algorithms, which is 100 times more efficient than traditional trial and error methods.

At the market level, according to Yole D é evelopment's prediction, the global market size of ceramic substrate laser welding equipment will grow from 860 million US dollars in 2023 to 2.2 billion US dollars in 2028, with a compound annual growth rate of 20.7%. The new energy vehicle and optical communication fields will contribute over 60% of the incremental demand. This trend requires equipment manufacturers and material suppliers to strengthen collaborative innovation, such as developing specialized ceramic metallization slurries, optimizing laser wavelength material absorption matching models, etc.

We need to focus on three major directions: first, to promote the cost reduction of short wavelength (green/ultraviolet) lasers. Currently, the price of 532 nm laser modules has dropped from $80000 in 2018 to $35000 in 2023; Secondly, participate in the formulation of international standards, such as the IEC's ongoing improvement of the "Quality Evaluation Standards for Ceramic Metal Laser Welding" (IEC 63209-2025); The third is to explore emerging application scenarios, such as laser sealing welding of hydrogen fuel cell ceramic bipolar plates, radiation resistant packaging for space probes, and other cutting-edge fields.

Source: Yangtze River Delta Laser Alliance