[Guide]LTCC technology is a new type of multilayer substrate process technology that appeared in the mid-1980s. It uses a unique material system, so its sintering temperature is low, and it can be co-fired with metal conductors, thereby improving the performance of Electronic devices. Beginning in the 1990s, NEC, Fujitsu, IBM, Murata and other companies in Japan and the United States successfully introduced LTCC technology into communication commercial applications. LTCC began to develop towards mobile communications and high-frequency microwave applications. Today, let’s talk about its applications.
(Image source: Forty-third Institute of China Electric Power)
According to the role of the product in the circuit, LTCC products can be roughly divided into four types: LTCC components, LTCC package substrates, LTCC functional devices and LTCC integrated modules.
Components produced using LTCC technology are widely used in mobile communication equipment and other fields. For example: mobile phones, WLAN, Bluetooth, power amplifiers, automotive electronics, etc. Since the 1990s, related LTCC products have gradually been applied, and their popularization and application are mainly attributed to the rapid development of the aerospace and communications fields. There are many types of products, including filters, duplexers, baluns, couplers, transceiver switch function modules, power dividers, and common mode chokes.
Application in high-density packaging
1. Used in aviation, aerospace and military fields
LTCC technology was first applied in aviation, aerospace and military electronic equipment. The Space System/LoralInc. of the United States Loral Corporation uses LTCC technology to develop satellite control circuit components. It uses 9 layers of conductors, the metal line width and line spacing are 125 µm, and the green material is DuPont’s A951. The product has passed harsh aerospace calibration tests. American companies such as Raytheon, Westinghouse and Honeywell all have LTCC design and manufacturing technology, and have developed a variety of LTCC components or systems that can be used in electronic devices such as missiles, aviation and aerospace.
2. Used in MEMS, actuators, sensors and other fields
LTCC can form a three-dimensional structure by embedding capacitors, inductors, etc., so as to greatly reduce the circuit volume. Therefore, in high-performance devices such as drivers of radio frequency circuits and high-frequency switches, three-dimensional structure circuits have been widely used to meet the current requirements for the volume and performance of such circuits.
3. Application in automotive electronics and other fields
With the development of automobile electronic technology, the control of modern cars has begun to enter the electronic and information age, but the general circuit system cannot be completely installed in the cab. In addition, many control circuits must be placed together with the controlled system. Located under the hood, and the temperature near the general engine is 130-500 ℃, so the circuit board must be able to withstand high temperature and high humidity working environment, and it must have high working reliability. Because LTCC has many excellent characteristics, it has been listed as an important technology for making automotive electronic circuits abroad. Delco Electronics, a subsidiary of General Motors in the United States, used LTCC technology to produce engine control modules, and Magneti Marelli’s Electronics of Italy produced automotive fuel valve control modules, including MOSFET and power MOS device integration.
The filters and duplexers in early communication products were mostly bulky dielectric filters and duplexers. The filters on GSM and CDMA mobile phones have been replaced by surface acoustic filters or embedded in the module substrate, while the filters on PHS mobile phones and cordless phones are mostly small, low-priced, and LC filters made of LTCC. Bluetooth and wireless network cards use LC filters from the beginning.
The filter made by LTCC includes three kinds of band-pass, high-pass and low-pass filters, and the frequency ranges from tens of MHz to 5.8 GHz. LC filter has its unparalleled advantages in terms of volume, price and temperature stability, and it is not difficult to understand that it has been receiving extensive attention.
The above-mentioned radio frequency devices produced by LTCC have a history of several years abroad and in Taiwan Province of my country. Japan’s Murata, Toko, TDK, and Shuangxin Electric, my country’s Taiwan Province’s Huaxin Technology, ACX, and South Korea’s Samsung are all in mass production. And sales. The mainland of my country only saw from exhibitions and web pages in 2003 that CSG Electronics and another company started to develop similar products.
Module base board
Modularization of electronic components has become an indisputable fact in the industry, especially LTCC is the preferred method. The available module substrates are LTCC, HTCC (high temperature co-fired ceramic), traditional PCB such as FR4 and PTFE (high performance polytetrafluorohexene) and so on. The sintering temperature of HTCC is above 1500℃, and the matching refractory metals such as tungsten, molybdenum/manganese and other conductive properties are poor, and the sintering shrinkage is not as easy to control as LTCC. The dielectric loss of LTCC is an order of magnitude lower than that of RF4. The loss of PTFE is low, but the insulation is poor. LTCC has better control accuracy than most organic substrate materials. There is no organic material that can be compared with the high-frequency performance, size and cost of LTCC substrates.
Research on LTCC module substrates in foreign countries and Taiwan Province of my country is in full swing, and there are already many commercial production and applications of LTCC modules. There are more than ten manufacturers of mobile phone antenna switch modules (ASM), including Murata, Mitsubishi Electric, Kyocera, TDK, Epcos, Hitachi, and Avx. In addition, there are Bluetooth modules from companies such as NEC, Murata and Ericsson, power amplifier modules from companies such as Hitachi, etc., all made of LTCC technology.
Because of its compact structure, strong resistance to mechanical shock and thermal shock, the LTCC module has received great attention and wide application in military and aerospace equipment, and its application in automotive electronics will be very extensive in the future.
Application in antenna
1. 5G array antenna
As the frequency of 5G communication rises, antennas and radio frequency modules will be smaller and more integrated. When the operating frequency is greater than or equal to 30 GHz, the antenna size will be reduced to a millimeter level or even smaller. At this time, the antenna design will be changed from the existing single antenna to an array antenna. LTCC is expected to become the core integrated technology of 5G antennas.
2. Ultra-wideband LTCC antenna
The multi-layer patch structure of LTCC can effectively broaden the bandwidth of the antenna to prepare ultra-wideband antennas with a relative bandwidth of ≥20%. At the same time, LTCC can also integrate the receiving chip and ultra-wideband antenna into the LTCC module, providing single-module design and manufacturing solutions for the development of ultra-wideband transceiver devices for ultra-large-scale integrated circuits.
3. Wifi/Bluetooth antenna
Wifi and Bluetooth devices have short communication distances, low transmit and receive power, and low requirements for antenna power and transmit and receive characteristics. However, they have higher requirements on the area and cost of the antenna occupied by the PCB. LTCC technology is expected to be widely used in Wifi/Bluetooth antennas.
4. GPS antenna
GPS ceramic antennas are divided into block ceramic antennas and multilayer ceramic antennas, and LTCC antennas are classified as multilayer ceramic antennas. The development of mobile communication equipment makes GPS antennas develop in the direction of miniaturization, multi-frequency bands and anti-interference. Utilizing the high dielectric constant and high Q value of ceramic materials can effectively reduce the size of the antenna; combined with the characteristics of the LTCC multilayer structure, it can reduce the size while keeping the antenna bandwidth and gain unaffected, realizing the multi-frequency GPS antenna Design and production.
5. Multi-band LTCC antenna
LTCC antennas can achieve multi-frequency antennas through a variety of technical means. In addition to the method of loading adjustable capacitance in a single antenna structure and loading branches of different lengths, multiple antenna structures are often used to design LTCC multi-frequency antennas. The zigzag antenna can be multi-layered, each layer of antenna can achieve a resonant frequency; the helical antenna can be coiled with different lengths of spirals to achieve a multi-helical structure; the patch antenna can be between different layers, using multiple resonant patches The structure constitutes multi-frequency resonance. With this feature of the LTCC antenna structure, dual-frequency/multi-frequency GPS and Wifi antennas can be designed and manufactured.
6. RFID antenna
LTCC has the characteristics of high dielectric constant, low loss, stable performance and easy to achieve hybrid integration, which can meet the miniaturization and high gain requirements of RFID micro chip antennas, and has the advantages of good omnidirectionality, impedance matching, and long reading distance. , Make the application prospect of RFID broader.
7. NFC antenna
Ferrite diaphragms for NFC antennas are usually prepared by LTCC technology. The ferrite green tapes made by multi-layer casting are stacked into ferrite diaphragms with a certain thickness. The patch-type NFC antennas that have emerged in recent years can use LTCC technology for interlayer coil winding and multi-layer structure design, make full use of the space of the ferrite chip, and effectively reduce the size of the antenna.
8. Integrated package antenna
Packaged antenna technology is an integrated antenna solution developed in the past 20 years to adapt to the emergence of system-level wireless chips. It integrates the antenna with the radio frequency transceiver system to form a standard surface mount device. LTCC is currently the mainstream technical solution for packaging antennas. The antenna can be integrated into an antenna-chip system to achieve a higher level of integration of the entire system and improve system performance, such as increasing gain and broadening bandwidth.
Yu Chengcheng, etc. Low-temperature co-fired ceramic technology development and industry status analysis
Zhang Xiaohui et al. Research progress of low-temperature co-fired ceramic materials
Yang Bangchao, etc. New progress in low-temperature co-fired ceramics (LTCC) technology
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