The Co-Fired Ceramic Fabrication Process

Key Takeaways

• Co-fired ceramic fabrication is a packaging technique to create monolithic electrical devices with two main types: low-temperature co-fired ceramic (LTCC) and high-temperature co-fired ceramic (HTCC).

• LTCC technology enables the integration of passive components into compact modules, ideal for RF and microwave applications. 

• HTCC is preferred for high-power applications, offering high thermal conductivity and structural strength that can withstand operating temperatures up to 1000°C.

Illustration of the Chip Packaging Process

The co-fired ceramic fabrication process is a packaging method for multi-chip integrated circuits (MCIC). The process is divided into two sub-groups: low-temperature co-fired ceramics (LTCC) and high-temperature co-fired ceramics (HTCC). 

Co-fired ceramic devices are monolithic, microelectronic devices where the entire ceramic support structure and internal components are fired in a kiln at the same time. Typical devices include capacitors, inductors, resistors, transformers, and hybrid circuits. 

Co-Fired Ceramic Fabrication Procedure

The Co-Fired Ceramic Fabrication Process

The co-fired ceramic fabrication process is a multilayer approach. Active and passive electronic components such as filters, digital and controlled impedance RF interconnects, and RLC elements (R = resistor, L = inductor, and C = capacitor) are embedded within the surface layers, facilitating the fabrication of a monolithic structure with increased functionality-to-size ratio, performance, and reliability. 

The two main types of co-fired ceramic fabrication processes are:

1. Low-temperature co-fired ceramic (LTCC) can embed passive elements in its structure by screen-printing. Thick-film conductors constitute the largest percentage of printed elements.  Inductors are formed by printing conductor windings on ceramic tape, while resistors are screen-printed and can be laser-trimmed for precise resistance values. Transformers, similar to inductors, have integrated cores and windings for improved coupling and durability.

2. High-temperature co-fired ceramic (HTCC) uses raw ceramic substrate material, which has higher structural strength, thermal conductivity, chemical stability, and wiring density, making it more suitable for high-performance processors.

Types of Co-Fired Ceramic Fabrication

High-Temperature Co-Fired Ceramic (HTCC) Fabrication Process

High-temperature co-fired ceramics (HTCC) involve printing metal heat-resistant pastes, such as tungsten, molybdenum, and manganese, onto a ceramic green body made of alumina (92-96%). The assembly is sintered at high temperatures (1500-1600°C) to form a solid structure.

HTCC offers advantages such as corrosion and high-temperature resistance, long life, high efficiency, energy saving, uniform temperature, good thermal conductivity, and fast thermal compensation. However, its high sintering temperature restricts the use of low melting point metals, leading to potential signal delay issues. While not ideal for high-speed or high-frequency microassembly circuits, HTCC is well-suited for high-power microassemblies due to its high structural strength, thermal conductivity, and chemical stability.

HTCC Classification Based on Ceramic Materials 

Low-Temperature Co-Fired Ceramic  Fabrication Process

LTCC is the cost-effective and upgraded version of HTCC, with firing temperatures in the range of 700–960°C. LTCC devices are some of the most rapidly developed integral passive devices. They provide a solution to the integration of passive components into a multilayered ceramic module by interconnecting components in layers. 

Two main components of a typical LTCC materials system include LTCC sheets and integrated passives. Integrated passives are the electronic components of the multilayer circuits such as conductors, resistors, capacitors, and inductors, which are screen-printed on LTCC layers. 

LTCC Sheets

From a general perspective, LTCC sheets are thick layers prepared by precisely spreading (tape-casting) a glass-ceramic slurry on polymeric carriers at varying thicknesses. Glass-ceramic are polycrystalline solids containing residual glass phase, which are derived from the controlled crystallization of glasses. This material is ideal due to its low dielectric constant for successful signal transmission, high dielectric strength, low dissipation factors particularly at high frequencies, well-matched thermal coefficient of expansion (TCE) to that of printed components, flexibility in design and fabrication, and low firing temperatures.

LTTC Applications

LTCC technology is advantageous for RF and high-frequency applications, allowing for multiple layers with distinct functionalities, such as high permittivity and low dielectric loss, which are beneficial in mobile telecommunication devices, wireless local networks, and in-car radars.  Additionally, the integration of thick-film passive components and 3D mechanical structures has led to the development of sophisticated LTCC sensors and microsystems.

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