Chapter 1 Thermal management
I. Ultra-high thermal conductivity and high-frequency heat dissipation capabilities
1. High thermal conductivity materials are suitable for high power density
Aluminum nitride (AlN) ceramics: thermal conductivity 170-200 W/(m·K), suitable for GaN (gallium nitride) RF chips (heat flux density>300 W/cm²) at 28 GHz high frequency band, the chip junction temperature can be controlled below 85℃ (traditional FR4 substrate junction temperature>120℃).
Diamond copper substrate (DBC): thermal conductivity>2000 W/(m·K), used for heat dissipation of optical module lasers, reducing thermal resistance by 50%, and supporting high-speed optical communications above 100 Gbps.
2. Low dielectric loss and high-frequency stability
Silicon nitride (Si₃N₄) substrate: dielectric constant ε<8 (@10 GHz), loss tangent tanδ<0.001, reducing millimeter wave (28/39 GHz) signal transmission loss <0.3 dB/cm, ensuring the stability of 5G base station EIRP (equivalent isotropic radiated power).
Beryllium oxide (BeO) shell: dielectric constant tolerance ±0.02, meeting the strict requirements of Ka-band (26.5-40 GHz) phased array antenna T/R components for phase consistency.
2. Thermal shock resistance and long-term reliability
1. Extreme temperature cycle tolerance
AlN substrate passed 3000 times (-55℃ to +125℃) thermal cycle test, interface delamination area <1%, adapted to the long-term operation requirements of outdoor base stations (-40℃ to +85℃ environment).
Si₃N₄ ceramic bending strength>800 MPa, high temperature (600℃) strength retention rate>90%, supporting 10-year life of optical module laser in 85℃/85% RH hot and humid environment.
2. Hermetic packaging and environmental corrosion resistance
HTCC (high temperature co-fired ceramic) tube shell airtightness <1×10⁻⁹ Pa·m³/s, through MIL-STD-883K standard helium mass spectrometer leak detection, protect laser chip from water vapor erosion (humidity <500 ppm).
Surface metallization (such as Au/Sn solder) salt spray resistance test>1000 hours (ASTM B117), meet the corrosion protection needs of coastal base stations.
3. High-density integration and signal integrity
1. Three-dimensional heterogeneous integration technology
LTCC (low-temperature co-fired ceramic) substrate: supports more than 20 layers of wiring, line width/line spacing ≤50 μm, realizes RF front-end module (PA+LNA+filter) integration, and reduces volume by 60%.
TSV (through silicon via) ceramic substrate: vertical interconnection density>500 holes/cm², shortens high-frequency signal transmission path, and reduces delay by 30%.
2. Low thermal expansion coefficient (CTE) matching
AlN ceramic CTE4.5×10⁻⁶/℃, highly matched with GaAs/GaN chips (CTE 5-6×10⁻⁶/℃), interface stress <50 MPa, avoiding the risk of cracking during high-temperature welding (>300℃).
The copper layer thickness tolerance of the copper-ceramic composite substrate (AMB/DBC) is ±5%, ensuring the uniformity of heat distribution of the power amplifier (PA) at 40-60 W output.
IV. Lightweight and structural innovation
1. High-strength lightweight design
The density of the honeycomb structure Si₃N₄ ceramic substrate is <3.0 g/cm³ (traditional metal substrate>8 g/cm³), and the bending strength is >1000 MPa, which can reduce the weight of satellite-borne phased array antennas by 40%.
The ultra-thin AlN substrate (thickness 0.25 mm) has a withstand voltage of >3 kV, which is suitable for the 400G/800G high-speed requirements of compact optical modules (QSFP-DD packaging).
2. Multifunctional integrated packaging
Integrated microchannel heat dissipation ceramic substrate: channel width <100 μm, single-phase liquid cooling heat dissipation power >500 W/cm², supporting data center optical module CPO (co-packaged optics) technology.
Electromagnetic shielding ceramic shell: the shielding effectiveness of the nickel-gold layer on the surface is >60 dB (18 GHz), suppressing crosstalk in the millimeter wave band.
V. Technological evolution and industry standards
Material upgrade: Diamond-aluminum nitride composite substrate (thermal conductivity>600 W/(m·K)) has entered the pre-research stage, aiming to solve the heat dissipation bottleneck in the 6G terahertz band (>100 GHz).
Process breakthrough: Laser direct writing technology (LDT) achieves 2 μm line width patterning, supporting high-precision impedance matching of Sub-6 GHz Massive MIMO antenna arrays.
Application scenarios and technology trends
5G base stations and RF modules: Ceramic substrates are used for power amplifiers (PA) and filters to solve the heat dissipation bottleneck under high frequency and high power512.
Satellite communication and millimeter wave technology: Ceramic tube shells support stable operation in high-frequency and high-temperature environments, and are suitable for low-orbit satellites and high-speed data transmission systems513. Future direction: Combine AI algorithms to optimize thermal design (such as heat sink layout) and adapt to new generation semiconductor materials such as silicon carbide (SiC) to further improve heat dissipation efficiency and integration
Chapter 2 Electrical performance
I. High-frequency signal transmission optimization capability
1. Low dielectric loss and high-frequency stability
Aluminum nitride (AlN) and silicon nitride (Si₃N₄) ceramics have low dielectric constants (AlN: ε≈8.8@1 MHz; Si₃N₄: ε≈7.5@10 GHz), and the loss tangent (tanδ) can be as low as 0.001 or less, significantly reducing millimeter wave (28/39 GHz) signal transmission loss (<0.3 dB/cm), ensuring the high-frequency signal integrity of 5G base stations and satellite communications.
The HTCC (high temperature co-fired ceramic) shell adopts a multi-layer wiring design, and the dielectric constant tolerance is controlled at ±0.02, which meets the phase consistency requirements of the T/R components of the Ka-band (26.5-40 GHz) phased array antenna and reduces the risk of signal distortion.
2. High insulation and anti-interference performance
The insulation resistance of alumina (Al₂O₃) ceramics is as high as 10¹² Ω·cm, and the breakdown strength is >10 kV/mm, which effectively isolates the electromagnetic interference of high-power devices and is suitable for the packaging of 5G base station power amplifiers (PA).
The shielding effectiveness of the metallization process (gold plating, nickel plating) on the surface of the ceramic carrier board is >60 dB (@18 GHz), which suppresses the crosstalk of millimeter wave frequency band signals and improves the signal-to-noise ratio of the RF module.
2. High-density integration and signal integrity assurance
1. Three-dimensional heterogeneous integration technology
The vertical interconnection density of TSV (through silicon via) ceramic substrate is >500 holes/cm², which shortens the high-frequency signal transmission path and reduces the delay by 30%. It is suitable for CPO (co-packaged optics) technology of 400G/800G optical modules.
2. Thermal expansion coefficient (CTE) matching and mechanical stability
The CTE of AlN ceramics is 4.5×10⁻⁶/℃, which is highly matched with GaAs/GaN chips (CTE 5-6×10⁻⁶/℃), and the interface stress is <50 MPa, avoiding microcracks and electrical performance degradation caused by thermal mismatch during high-temperature welding.
The copper layer thickness tolerance of copper-clad ceramic substrates (such as DBC, AMB) is controlled at ±5%, ensuring the uniformity of current distribution of high-power devices (such as 40-60 W RF PA) and reducing impedance mutations caused by local overheating.
3. Environmental resistance and long-term reliability
1. Hermetic packaging and corrosion resistance
The airtightness of the HTCC shell is <1×10⁻⁹ Pa·m³/s (MIL-STD-883K standard), and the internal humidity is <500 ppm, which protects the laser chip from water vapor erosion and ensures the 10-year life of the optical module in a hot and humid environment.
2. Thermal shock resistance and high-frequency fatigue tolerance
The AlN substrate has passed 3000 (-55℃ to +125℃) thermal cycle tests, and the interface delamination area is <1%, ensuring the high-frequency performance stability of outdoor base stations under extreme temperature differences.
The bending strength of Si₃N₄ ceramics is >800 MPa, and the high temperature (600℃) strength retention rate is >90%, which is suitable for long-term operation of high-temperature RF devices (microwave transmission modules).
IV. Material innovation and process breakthroughs
1. Copper-clad ceramic substrate technology
The thermal conductivity of DBC (direct copper bonding) and AMB (active metal brazing) processes reaches 2000 W/(m·K) and >600 W/(m·K) respectively, supporting the high-frequency and high-power packaging requirements of third-generation semiconductor (SiC, GaN) devices, and the heat dissipation efficiency is more than 50 times higher than that of traditional FR4 substrates.
The bending strength of silicon nitride (Si₃N₄) AMB substrate is >1000 MPa, and the thermal expansion coefficient is 2.4×10⁻⁶/℃, making it the preferred material for automotive-grade IGBT modules and 6G terahertz devices.
2. Micron-level precision processing capabilities
Laser direct writing technology (LDT) achieves 2 μm line width patterning, meeting the high-precision impedance matching requirements of Sub-6 GHz Massive MIMO antenna arrays and reducing signal reflection losses.
The film thickness deviation of the high-precision thick film screen printing process is controlled within ±5%, ensuring the uniformity of the metallization coating of the electric vacuum ceramic shell and reducing the resistance fluctuation of high-frequency signal transmission.
Summary: The technical advantages of electrical performance make ceramic packaging the core of high-frequency and high-power communication equipment with the following advantages:
1. High-frequency optimization: low dielectric loss (Si₃N₄/AlN) combined with multi-layer wiring (LTCC/HTCC) supports the high-frequency requirements of millimeter wave and optical communications;
2. Reliable integration: CTE matching and three-dimensional interconnection technology (TSV) ensure signal integrity under high-density packaging;
3. Environmental tolerance: airtight packaging and anti-corrosion coating, adapt to the harsh environment of outdoor base stations and vehicle-mounted communications;
4. Material innovation: copper-clad ceramics (DBC/AMB) and silicon nitride substrates break through the bottlenecks of heat dissipation and mechanical strength, and promote the development of 6G and third-generation semiconductor technologies.
Chapter 3 Mechanical Strength and Reliability
I. Ultra-high Mechanical Strength and Fracture Toughness
1. Flexural Strength and Fracture Toughness
Silicon Nitride (Si₃N₄) Ceramics: Flexural strength > 800 MPa, fracture toughness > 7 MPa·m¹/², far exceeding alumina (about 300 MPa) and aluminum nitride (about 400 MPa), can inhibit crack propagation, and is suitable for long-term vibration environments of high-frequency and high-power devices (5G base station RF modules).
Alumina (Al₂O₃) Ceramics: Flexural strength > 300 MPa, combined with high hardness (Mohs hardness 9), suitable for scenes such as lithography machine support structures that need to withstand mechanical shock.
2. Three-dimensional structural reinforcement
Ceramic substrates with honeycomb structures (such as silicon nitride substrates) reduce density (<3.0 g/cm³) through porous design while maintaining flexural strength > 1000 MPa, meeting the lightweight and vibration resistance requirements of satellite-borne phased array antennas.
AMB (Active Metal Brazing) Process: A strong metallurgical bonding interface is formed through vacuum brazing, and the interface bonding strength is >100 MPa, which prevents the copper layer and the ceramic substrate from peeling off due to thermal stress.
2. Thermal Expansion Coefficient Matching and Thermal Shock Resistance
1. CTE Matching Reduces Interface Stress
The CTE of aluminum nitride (AlN) ceramic is 4.5×10⁻⁶/℃, which is highly matched with GaN chips (5-6×10⁻⁶/℃), and the interface thermal stress is <50 MPa, which prevents cracking during high-temperature welding (>300℃).
The CTE of silicon nitride (Si₃N₄) is 3.0×10⁻⁶/℃, which matches the silicon carbide (SiC) chip (4.0×10⁻⁶/℃), and the temperature cycle life is more than 3 times higher than that of traditional substrates, which can adapt to the extreme working conditions of fast charging and fast discharging of new energy vehicles.
2. Thermal shock resistance
The AlN ceramic shell has passed 3000 times (-55℃ to +125℃) thermal cycle test, and the interface delamination area is <1%, which meets the long-term reliability requirements of outdoor base stations (-40℃ to +85℃).
The strength retention rate of the HTCC (high temperature co-fired ceramic) shell at 600℃ is >90%, which is suitable for the high temperature working environment of microwave transmission modules.
III. Airtightness and environmental corrosion resistance
1. Ultra-high airtightness packaging
The airtightness of the HTCC shell is <1×10⁻⁹ Pa·m³/s (in line with MIL-STD-883K standard), and the internal humidity is controlled at <500 ppm, which protects the laser chip from water vapor erosion and ensures the 10-year life of the optical module in a hot and humid environment.
The high-precision thick film screen printing process achieves a metallized coating thickness deviation of ±5%, combined with the uniformity requirements of no pinholes and no burrs, to improve the reliability of airtight joints.
2. Corrosion resistance
Zirconia toughened alumina (ZTA) ceramics have a strength retention rate of >95% in acid and alkali corrosion environments, and are suitable for industrial communication equipment with strong chemical corrosion.
IV. Process innovation and reliability verification
1. Advanced process improves structural strength
AMB process: Active metal solder (Ti-Ag-Cu) is used to fill the interface micropores, so that the bonding strength between the silicon nitride substrate and the copper layer is >150 MPa, supporting thermal shock of high-voltage platforms above 800V.
Laser direct writing technology (LDT): Achieve 2 μm line width patterning, reduce line edge burrs, and improve the mechanical stability of high-frequency signal transmission.
2. Strict reliability test standards
The ceramic substrate has passed industry standard certifications such as Telcordia GR-468 (optical device reliability) and MIL-PRF-38534 (high reliability packaging) to ensure long-term operation in extreme environments.
The core advantages of mechanical strength and reliability can be summarized as follows:
1. Super strong damage resistance: high bending strength (Si₃N₄ >800 MPa) and fracture toughness (>7 MPa·m¹/²) support high-frequency vibration scenarios;
2. Thermal-mechanical collaborative design: CTE matching (AlN/Si₃N₄) and thermal shock resistance (3000 cycles) ensure structural integrity under extreme temperatures;
3. Environmental protection: airtightness (<1×10⁻⁹ Pa·m³/s) and corrosion resistance (salt spray >1000 hours) adapt to complex working conditions;
4. Process empowerment: AMB/LDT and other processes improve interface bonding strength and processing accuracy.
Chapter 4 Small size and integration
I. Multi-layer wiring and high-density interconnection technology
1. LTCC/HTCC process supports multi-layer 3D integration
Low temperature co-fired ceramic (LTCC): supports more than 20 layers of wiring, line width/line spacing can be as low as 50 μm, realizes three-dimensional heterogeneous integration of RF front-end modules (PA+LNA+filter), and the volume is reduced by 60% compared with traditional packaging.
High temperature co-fired ceramic (HTCC): The dielectric constant tolerance is controlled at ±0.02, which is suitable for Ka band (26.5-40 GHz) phased array antenna, meeting the stringent requirements of 5G millimeter wave communication for phase consistency.
2. Micron-level precision processing capability
Laser direct writing technology (LDT): realizes 2 μm line width patterning, supports high-precision impedance matching of Sub-6 GHz Massive MIMO antenna arrays, and reduces signal reflection loss.
DPC (direct copper plating) process: the surface roughness is only 0.03 μm, and the high-frequency characteristics are better than the traditional DBC substrate, which is suitable for the miniaturization design of 5G RF modules.
2. Material properties enable compact design
1. Low dielectric constant and high-frequency stability
The dielectric constant of aluminum nitride (AlN) ceramics is ε≈8.8@1 MHz, and that of silicon nitride (Si₃N₄) is ε≈7.5@10 GHz. The loss tangent (tanδ) is as low as below 0.001, which significantly reduces the transmission loss of millimeter wave signals (<0.3 dB/cm) and supports the miniaturization of 28/39 GHz high-frequency band devices.
The insulation resistance of alumina (Al₂O₃) ceramics reaches 10¹² Ω·cm, and the breakdown strength is >10 kV/mm, which ensures the electromagnetic isolation performance under high-density packaging.
2. Low coefficient of thermal expansion (CTE) matching
The CTE of AlN ceramics is 4.5×10⁻⁶/℃, which is highly matched with GaN/GaAs chips (5-6×10⁻⁶/℃), and the interface stress is <50 MPa, which avoids packaging failure caused by microcracks and supports ultra-thin substrate (thickness 0.25 mm) design.
The CTE of Si₃N₄ ceramics is only 3.0×10⁻⁶/℃, which is compatible with SiC chips (4.0×10⁻⁶/℃), and the temperature cycle life is increased by more than 3 times, which is suitable for the compact requirements of vehicle communication modules.
3. Advanced packaging structure and miniaturization
1. Surface mount packaging (SMD) technology
Ceramic quad leadless housing (CQFN): 50% smaller in volume and 60% lighter in weight than traditional packaging, supporting patch installation of high-speed AD/DA converters and RF microwave devices.
Ceramic ball array (CBGA): 40% higher in packaging density than PBGA, with air tightness of <1×10⁻⁹ Pa·m³/s, suitable for high-density integrated circuits such as CPU and FPGA.
2. Ultra-thin and lightweight design
The density of the honeycomb structure Si₃N₄ ceramic substrate is <3.0 g/cm³ (traditional metal substrate>8 g/cm³), and the bending strength is >1000 MPa, which meets the lightweight requirements of satellite-borne phased array antennas.
Ultra-thin AlN substrate (thickness 0.25 mm) withstands voltage >3 kV, adapts to the 400G/800G high-speed transmission requirements of QSFP-DD optical modules, and is 70% smaller in volume than traditional solutions.
IV. Multifunctional integration and system-level packaging (SiP)
1. Integrated integration of passive devices
LTCC technology can integrate passive components such as inductors, capacitors, antennas, etc. to form multi-layer filters and RF front-end modules, reduce the number of external components, and compress the volume by more than 50%.
Silicon nitride AMB substrate achieves strong bonding between copper layer and ceramic through active metal brazing (interface strength>150 MPa), supports direct integration of IGBT module and heat sink, and reduces the package volume by 40%.
2. Optoelectronic co-packaging (CPO) technology
Integrated microchannel heat dissipation ceramic substrate: channel width <100 μm, single-phase liquid cooling heat dissipation power>500 W/cm², supports chip-optical engine co-packaging of data center optical modules, and increases integration by 3 times.
The core advantages of miniaturization and integration are summarized as follows:
1. High-density interconnection: LTCC/HTCC multi-layer wiring and TSV technology achieve three-dimensional integration;
2. Material adaptability: low CTE and high-frequency characteristics support ultra-thin design;
3. Micro-package form: CQFN/CBGA and other surface mount structures optimize space utilization;
4. System-level integration: SiP and CPO technology integrate optoelectronic functional modules.
Chapter 5 Breakthrough Innovation
I. High-frequency signal transmission and low-loss performance breakthrough
1. Low dielectric loss and high-frequency stability
The dielectric constants of aluminum nitride (AlN) and silicon nitride (Si₃N₄) ceramics are as low as 8.8@1 MHz and 7.5@10 GHz, respectively, and the loss tangent (tanδ) can be as low as 0.001 or less, which significantly reduces the millimeter wave (28/39 GHz) signal transmission loss (<0.3 dB/cm), ensuring the high-frequency signal integrity of 5G base stations and satellite communications.
The HTCC (high temperature co-fired ceramic) shell adopts a multi-layer wiring design, and the dielectric constant tolerance is controlled at ±0.02, which meets the phase consistency requirements of the T/R components of the Ka-band (26.5-40 GHz) phased array antenna.
2. High-density interconnection and signal integrity
The LTCC (low temperature co-fired ceramic) substrate supports more than 20 layers of wiring, and the line width/line spacing can be ≤50 μm, realizing the miniaturization integration of the RF front-end module (PA+LNA+filter), reducing the volume by 60%, and reducing the impact of parasitic capacitance on high-frequency signals.
2. Subversive improvement of thermal management performance
1. Innovative application of ultra-high thermal conductivity materials
The thermal conductivity of aluminum nitride (AlN) ceramics reaches 170-200 W/(m·K), which is suitable for GaN RF chips (heat flux density>300 W/cm²), and the chip junction temperature is controlled below 85℃ (traditional FR4 substrate>120℃).
Silicon nitride (Si₃N₄) AMB substrate has a thermal conductivity of over 110 W/(m·K) and a bending strength of >600 MPa through active metal brazing process, supporting thermal shock of high-voltage platforms above 800V, becoming the core heat dissipation solution for new energy vehicles and 6G communication devices.
2. Advanced heat dissipation structure design
Integrated microchannel heat dissipation ceramic substrate: channel width <100 μm, single-phase liquid cooling heat dissipation power >500 W/cm², supporting chip-optical engine co-packaging (CPO) technology for data center optical modules.
DBC (direct copper bonding) and AMB processes: thermal conductivity reaches 2000 W/(m·K) and >600 W/(m·K) respectively, and the heat dissipation efficiency is more than 50 times higher than that of traditional substrates, adapting to the high power density requirements of third-generation semiconductors (SiC/GaN).
3. Technological breakthroughs in mechanical strength and reliability
1. Thermal shock resistance and extreme environmental tolerance
AlN ceramics have passed 3,000 (-55°C to +125°C) thermal cycle tests, with an interface delamination area of <1%, meeting the long-term operation requirements of outdoor base stations (-40°C to +85°C).
Si₃N₄ ceramics have a bending strength of >800 MPa and a high temperature (600°C) strength retention rate of >90%, which is suitable for extreme vibration and high and low temperature alternating environments of satellite-borne phased array antennas.
4. Miniaturization and integration leap
1. Three-dimensional heterogeneous integration technology
Ceramic quad-leadless package (CQFN): 50% smaller in volume and 60% lighter in weight than traditional packages, supporting patch installation of high-speed AD/DA converters and RF microwave devices.
Ceramic ball array (CBGA): 40% higher in packaging density than PBGA, with airtightness of <1×10⁻⁹ Pa·m³/s, suitable for high-density integrated circuits such as CPUs and FPGAs.
2. Ultra-thin and lightweight design
The density of the honeycomb structure Si₃N₄ ceramic substrate is <3.0 g/cm³ (traditional metal substrate is >8 g/cm³), and the bending strength is >1000 MPa, which meets the lightweight requirements of satellite-borne phased array antennas.
The ultra-thin AlN substrate (thickness 0.25 mm) has a withstand voltage of >3 kV, which is suitable for the 400G/800G high-speed transmission requirements of QSFP-DD optical modules, and the volume is 70% smaller than the traditional solution.
V. Disruptive innovation in materials and processes
1. Single crystal β-CaSiO3 substrate technology
The single crystal β-CaSiO3 substrate developed by Zefeng Semiconductor has a dielectric constant of <5 and a bending strength of >230 MPa, breaking through the performance bottleneck of traditional polycrystalline substrates and providing a new solution for 6G high-frequency communications.
This technology achieves compatibility of single crystal structure growth with LTCC process through chemical doping and sintering optimization. It has passed small and medium tests and will be applied to MEMS probe cards and ceramic substrates.
2. Micro-resistance conduction and packaging process breakthroughs
By connecting the upper and lower plates with oxygen-free copper pillars, the resistance loss is reduced by 50%, the conductivity efficiency is improved, and the miniaturization and high performance of electronic products are promoted.
The high-temperature ceramic shell packaging device adopts a precise positioning cavity design to eliminate manual errors and improve the yield of mass production. It is suitable for the automated packaging of high-frequency semiconductor devices.
Summary The advantages of breakthrough innovation are as follows:
1. High-frequency optimization: low dielectric loss (Si₃N₄/AlN) and multi-layer wiring (LTCC/HTCC) support millimeter wave and optical communication needs;
2. Thermal management leap: high thermal conductivity materials (AlN/Si₃N₄) and AMB/DBC processes solve the problem of thermal failure;
3. Reliability breakthrough: thermal shock resistance (3000 cycles) and hermetic packaging (<1×10⁻⁹ Pa·m³/s) adapt to extreme environments;
4. Integration revolution: three-dimensional heterogeneous integration (CQFN/CBGA) and single crystal substrate technology promote miniaturization;
5. Localization breakthrough: Fulehua, Zefeng and other companies have achieved mass production of silicon nitride substrates, breaking the foreign monopoly.
These technical indicator advantages support the performance leap in 5G/6G base stations, satellite communications, optical modules and other fields, and promote high-end semiconductor packaging technology to move upstream in the global value chain.
