With the rise and application of power devices, especially third-generation semiconductors, semiconductor devices are gradually developing in the direction of high power, miniaturization, integration, and multi-function, which also puts forward higher requirements for the performance of packaging substrates. Ceramic substrates have the characteristics of high thermal conductivity, good heat resistance, low thermal expansion coefficient, high mechanical strength, good insulation, corrosion resistance, radiation resistance, etc., and are widely used in electronic device packaging.

Among them, co-fired multi-layer ceramic substrates are gradually popularized and applied in high-power device packaging because they can be fired at one time for electrode materials, substrates, and electronic devices to achieve high integration.

Co-fired multi-layer ceramic substrates are made of many single-piece ceramic substrates through lamination, hot pressing, degumming, sintering and other processes. Since the number of layers can be made more, the wiring density is high, and the interconnect length can be as much as possible. Therefore, it can meet the requirements of the electronic whole machine for circuit miniaturization, high density, multi-function, high reliability, high speed and high power.

According to the temperature difference in the preparation process, the co-fired ceramic substrate can be divided into high-temperature co-fired ceramic (HTCC) multilayer substrate and Low-temperature co-fired ceramic (LTCC) multilayer substrate.

   (a) HTCC ceramic substrate products     (b) LTCC ceramic substrate products

So what is the difference between these two technologies?

In fact, the production process of the two is basically the same, and they all have to go through the preparation process of preparing slurry, casting green tape, drying green body, drilling via holes, screen printing and filling holes, screen printing circuits, lamination sintering, and finally slicing. However, the HTCC technology is a co-firing technology with a sintering temperature greater than 1000 °C. Usually, the debinding treatment is performed at a temperature below 900 °C, and then sintered at a higher temperature environment of 1650 to 1850 °C. Compared with HTCC, LTCC has a lower sintering temperature, generally lower than 950 °C. Due to the disadvantages of high sintering temperature, huge energy consumption, and limited metal conductor materials on HTCC substrates, the development of LTCC technology has been promoted.

typical multilayer ceramic substrate manufacturing process

The difference of sintering temperature first affects the choice of materials, and then affects the properties of the prepared products, resulting in the two products being suitable for different application directions.

Due to the high firing temperature, HTCC substrate can't be made of low melting point metal materials such as gold, silver and copper, but must be made of refractory metal materials such as tungsten, molybdenum and manganese. These materials have high manufacturing cost, and their low conductivity will cause signal delay and other defects, so they are not suitable for high-speed or high-frequency micro-assembly circuit substrates. However, due to the higher sintering temperature of the material, it has higher mechanical strength, thermal conductivity and chemical stability. At the same time, it has the advantages of extensive material sources, low cost and high wiring density. HTCC substrate has more advantages in the field of high-power packaging with higher requirements on thermal stability, mechanical strength, thermal conductivity, tightness and reliability of the substrate.

However, LTCC substrate can reduce the sintering temperature by adding amorphous glass, crystallized glass, low melting point oxide and other materials into ceramic slurry. Gold, silver, copper and other metals with high conductivity and low melting point can be used as conductor materials, which not only reduces the cost, but also can obtain good performance. Because of its low dielectric constant and high frequency and low loss, glass ceramics are very suitable for RF, microwave and millimeter wave devices. However, due to the addition of glass materials in ceramic slurry, the thermal conductivity of the substrate is low, and the low sintering temperature also makes its mechanical strength inferior to HTCC substrate.

Therefore, the difference between HTCC and LTCC is still a situation in which the performance changes, and each has its own advantages and disadvantages. It is necessary to select the appropriate products according to the specific application conditions.

difference between LTCC and HTCC

In a word, HTCC substrate will play an important role in electronic packaging for a long time because of its mature technology and cheap dielectric materials. However, in the future, with the continuous improvement of materials, the improvement of process control and the increasingly mature technology, LTCC's natural advantages will become more prominent, which is more suitable for the development trend of high frequency, high speed and high power. However, all kinds of substrate materials have their advantages and disadvantages, and the performance requirements of substrate materials are different due to the different requirements of specific application circuits. Therefore, all kinds of substrate materials will coexist and develop for a long time.