Ceramic Substrate Materials for System-in-Package (SiP) Applications

Ceramic Substrate Materials for System-in-Package (SiP) Applications

System-in-Package (SiP) technology integrates multiple passive and active components with different functions into a single package, forming a standardized module that delivers system-level or subsystem-level functionality. To meet market demands for increased system functionality, reduced size and weight, and lower overall cost, SiP has become one of the major development trends in advanced packaging.

1. Substrate Material Requirements for SiP

SiP substrates must exhibit excellent mechanical, dielectric, thermal, and electrical properties, while also being easy to form, process, and cost-efficient. Key requirements include:

①Low dielectric constant (Dk)

Signal transmission speed is strongly affected by the dielectric constant and propagation distance. A lower Dk enables faster signal propagation.

②Low dielectric loss (Df)

During electrical conduction and relaxation polarization, part of the electromagnetic energy converts into heat. Low dielectric loss significantly reduces thermal buildup within the substrate.

③High thermal conductivity

As chip density, power levels, and switching speeds increase, heat generation rises sharply. Higher thermal conductivity enables rapid heat dissipation from densely integrated chips.

④Suitable coefficient of thermal expansion (CTE)

CTE mismatch between the substrate and the chip generates thermal stress during operation, causing solder joint fatigue, delamination, or even chip damage. Substrate materials must closely match the CTE of the device.

⑤Excellent mechanical strength

High flexural strength and elastic modulus are required to minimize deformation during sintering, maintain dimensional accuracy, and ensure mechanical robustness during assembly and use.

2. Ceramic Substrate Materials for SiP

Ceramic substrates provide both mechanical support and electrical insulation in SiP modules. Traditionally, Al₂O₃ and BeO have been the dominant materials; however:

• Al₂O₃ suffers from low thermal conductivity and a CTE mismatch with Si.
• BeO offers outstanding performance but is expensive and highly toxic, limiting adoption.

Considering performance, cost, and environmental factors, these materials can no longer fully support modern high-performance semiconductor needs. As a result, AlN and LTCC materials have been widely developed in recent years.

①Aluminum Nitride (AlN)

Stacked SiP architectures generate increased heat density because heat sources are concentrated while radiator area does not grow proportionally. Heat coupling between stacked chips further intensifies thermal challenges. Embedded passive components also introduce additional thermal load. Therefore, choosing high-thermal-conductivity ceramic substrates is essential for SiP thermal management.

AlN is a wurtzite-structured ceramic featuring:

• Thermal conductivity up to 170 W/(m·K)
• CTE of 4.2×10^-6°C⁻¹, closely matched to Si, GaAs, and GaN
• High mechanical strength and excellent densification, ensuring hermeticity
• Low dielectric constant, enabling high-power and high-frequency operation

AlN is therefore one of the most preferred substrate and packaging materials for high-power, large-form-factor, and high-pin-count SiP devices.

②Low-Temperature Co-Fired Ceramics (LTCC)

LTCC technology uses thick-film materials and co-fires ceramic layers, electrodes, and embedded passive components in a single process, making it a key enabler of SiP integration. LTCC offers:

• Low dielectric loss and excellent high-frequency stability
• CTE compatibility with ICs
• Easy integration with chips
• High-density multilayer wiring and 3D passive structures

These advantages enable high-density, compact, and multifunctional system modules.

Key advantages of LTCC-based SiP:

① Multilayer interconnect capability

Greatly enhances system integration density.

② Embedded passive components and functional structures

Cavities, buried devices, and 3D passive networks reduce conductor length, lower interconnect parasitics, increase wiring density, and simplify external circuitry—improving assembly efficiency and lowering system cost.

③ Wide tunability of dielectric constants

By adjusting material compositions or co-firing different materials, LTCC substrates can be tailored for diverse RF, microwave, and mixed-signal applications.

Low firing temperatures allow the use of Au, Ag, and Cu conductors, minimizing interconnect loss—ideal for high-frequency and high-speed circuits.

④ Excellent thermal management

LTCC's thermal conductivity, together with via-fill structures, enhances vertical heat dissipation.

⑤ CTE compatibility

CTE values similar to Si, GaAs, and InP enable direct chip attach and reliable long-term performance.

3. Future Trends

As packaging density continues to rise and system functionality becomes increasingly diverse, the performance of single-phase materials is no longer sufficient. Future electronic packaging substrates will move toward multi-phase composite ceramics, combining complementary properties to meet the demands of next-generation semiconductor systems.