In July 2026, the power semiconductor industry experienced another round of price increases. Infineon adjusted its prices for the second time, with nearly 20 manufacturers following suit, extending delivery cycles to 40-50 weeks. Behind this phenomenon is the explosive growth of third-generation SiC/GaN semiconductors in fields such as new energy vehicles, AI data center HVDC power supplies, and energy storage PCS. Taking 800V new energy vehicles as an example, the market penetration rate of SiC power modules has exceeded 60%, while the demand for high-power-density power supplies in AI data centers is driving the rapid evolution of SiC technology towards higher current and higher junction temperatures.
However, the high-reliability packaging of SiC power modules is becoming a key bottleneck in the industry chain. The thermal conductivity of traditional soldering processes is approximately 50 W/m·K, with a temperature limit of only 220℃, which can no longer meet the requirements of SiC modules for junction temperatures >175℃ and process temperatures >350℃. Silver sintering technology, with its thermal conductivity >200 W/m·K and temperature resistance >350℃, is becoming the mainstream process choice for high-reliability interconnects in SiC power modules.
I. Core Principles of Silver Sintering
Silver sintering is essentially a solid-state diffusion bonding process. Unlike the liquid-phase reflow of soldering, silver sintering utilizes nano-silver particles (or micro-silver particles) under low-temperature (220-250℃) and high-pressure (20-40MPa) conditions to form a dense metallic bonding layer through atomic diffusion between particles and neck growth mechanisms.
Stage 1: Particle rearrangement. Under pressure, silver particles undergo physical contact and rearrangement, eliminating initial porosity.
Stage 2: Neck growth. Atoms at the contact points of adjacent particles diffuse along grain boundaries, forming "necks," rapidly increasing the bonding strength between particles.
Stage 3: Pore elimination. Continuous diffusion causes grain growth and porosity contraction, ultimately resulting in a dense silver sintered layer. After sintering, the thermal conductivity of the silver layer is purely metallic, eliminating the thermal resistance of the intermetallic compound (IMC) layer in traditional solders. The thermal conductivity reaches 200-250 W/m·K, 4-5 times higher than the 50 W/m·K of SnAg solder.
Reliability Verification: After more than 2000 temperature cycling tests (-55℃~200℃), the shear strength of the silver sintered layer remains >15MPa, far exceeding the 1000-cycle requirement of the automotive-grade AEC-Q101 standard. This characteristic makes silver sintering the preferred interconnect technology for electric vehicle main drive power modules and high-reliability aerospace applications.
II. Process Challenges and Key Technologies
1. Sintering Uniformity Control
Uniform sintering of large-area chips (>20×20mm) is the primary challenge. The rheological properties of the silver paste, the uniformity of pressure transmission, and the temperature field distribution all affect the final void ratio. 1. A density difference exceeding 10% between the chip edge and center will lead to thermomechanical stress concentration, accelerating fatigue failure of the interconnect layer.
2. Interface Metallization Layer Matching
The difference in the coefficient of thermal expansion (CTE) between the chip's back metallization layer (typically Ag, Al, or TiN) and the sintered silver layer must be precisely compensated through process windows. Taking the Ag/silver sintering/Ni-Au-DBC system as an example, the CTEs are 17, 19, and 7 ppm/℃, respectively. Thermal stress at the interface needs to be mitigated through pressure curve optimization.
3. Void Rate Control
<5% in the sintered layer (tested according to IPC-A-610), but in actual production, void rate control for large-area chips is a core challenge. Current mainstream solutions include:
Step-by-step pressure loading: A two-stage pressure curve involving low-pressure preheating followed by high-pressure sintering.
Nano silver paste formulation optimization: Reduces sintering activation energy and improves densification kinetics.
Online X-Ray inspection: 100% X-Ray void rate detection, providing real-time feedback on process status.
4. Ceramic substrate synergy
Interface matching between DBC (Direct Copper Clad) and AMB (Active Metal Brazing) ceramic substrates and the silver sintered layer is equally crucial. AMB silicon nitride substrates, with their excellent thermal expansion matching (CTE approximately 2.5ppm/℃), are rapidly replacing the traditional AlN-DBC solution in SiC power modules, improving module power cycle life.
III. The final link in PCBA end-to-end reliability
The silver sintering process not only solves the interconnection problem from chip to substrate, but also concerns the end-to-end reliability of power module packaging → PCBA assembly.
After the SiC power module completes sintering and interconnection, its electrical connection to the PCB, thermal management design, and mechanical fixing all need to be considered in terms of system-level reliability:
Heat Dissipation Design: An efficient thermal path needs to be designed beneath the silver sintered layer, optimizing the complete thermal resistance chain from chip junction temperature to ambient temperature.
Substrate Layout: The stack-up structure of the DBC/AMB ceramic substrate and the PCB needs to be subjected to thermomechanical simulation.
Soldering Process Window: The reflow soldering temperature profiles of the module and the PCB need to match the temperature limit of the silver sintered layer.
Concrete Coating: The coating process of the power module needs to consider the surface compatibility of the silver layer.
