While providing traditional materials for automotive electronics, Heraeus has developed new materials such as DCB (Direct Copper Bonding), sintered silver paste and Die Top System, which are systematically matched materials for high-power IGBT modules. Testing services.
introduction
More than a century ago, the advent of fuel cars changed our lives and made travel easier and more convenient. Today, more than a century later, global warming and environmental pollution have become issues of concern. In order to effectively curb the speed of air pollution, new energy vehicles have been put on the agenda by countries instead of fuel vehicles. Sale time.
New energy vehicles have entered an explosive phase in recent years, and IGBT: Insulated Gate Bipolar Transistor (IGBT) modules have become the darlings of the market.
IGBT introduction
IGBT is a composite full-control voltage-driven power semiconductor device composed of a bipolar transistor (BJT) and an insulated gate field effect transistor (MOS). It has the advantages of low driving power and fast switching speed of MOSFET devices, The extreme type device has the advantages of reduced saturation voltage and large capacity, so it is very suitable for application in alternating current systems of 600V and above. It generally appears in the form of IGBT modules, or integrated gate drive and protection circuits inside the module are called intelligent power Module (IPM: Intelligent Power Module).
With the continuous development of technology and the full use of energy, the required devices need to have higher power density, higher operating temperature, lower power loss and faster switching speed. At present, silicon (Si) materials are The main power devices have been unable to meet higher demands. The third-generation wide band gap semiconductor power devices represented by silicon carbide (SiC) and gallium nitride (GaN) materials have begun to be used in electric vehicles and other fields. In addition to the higher performance and switching frequency of automotive IGBT modules, a series of changes in environmental factors such as load, climate, and vibration must be considered. In addition, the state has stipulated that the service life of automotive IGBT modules is not less than 15 years. This requirement puts forward the requirements for the IGBT module itself in addition to the performance of the chip, and also puts higher requirements on its packaging materials.
Heraeus Electronics
Heraeus is a family-owned company with a history of more than 160 years. Trust and reliability are the basis of our cooperation with customers. Heraeus Electronics is an expert in materials and matching material solutions in the field of electronic packaging materials. In the field, our bonding wires, solder paste, tin wires, SMT glue, bonding pads and electronic pastes have been well known in the industry. Now we are committed to ensuring that our customers can meet their requirements for rapid innovation and development. While providing traditional materials to automotive electronics, Heraeus has developed a new material DCB (Direct Copper Bonding), sintering suitable for today's power semiconductor module packaging Silver paste and Die Top System and test services for systematic matching of high power IGBT modules.
The future has come and we are ready.
1 welding material
The main role of the soldering material in the power module is to bond the chip to the DCB, DCB and the heat sink. The main soldering materials in the industry are solder paste and solder pads.
The advantage of solder paste is that it is suitable for large-scale batch production. Generally, it is a vacuum reflow soldering process, which requires nitrogen or nitrogen-hydrogen mixed gas for protection. Especially on small-sized chips, the effect is very good, and chip drift will not occur. Because of the presence of flux in the solder paste, the effective soldering area after soldering is ≥85%, and the cleaning process needs to be increased after soldering.
There is no flux in the solder material, so no-clean is one of the highlights of this material. Usually it is a vacuum welding process that requires formic acid or nitrogen-hydrogen mixed gas for auxiliary welding. The welding quality is better and the effective welding area is ≥95%. However, its external dimensions and thickness need to be prefabricated in advance according to the chip size and process requirements, which has poor flexibility and is not suitable for large-scale and flexible rapid production.
Lead-free is the future trend, especially in electric vehicles. Lead-free applications have become the focus. Heraeus has also introduced solutions for lead-free solder materials, including InnoLot high-reliability alloys for PCB and DCB substrates. It can make the body electronics still show its excellent performance in high temperature environment; Heraeus mAgic series sintered materials are more suitable for high-power applications of DCB substrates (pressurized process) and other lead frame packages (voltage-free process).
Compared with other solder pastes, Heraeus mAgic has a wider process window and no-cleaning characteristics, which can shorten the time of online process development; a new model has been developed that can be directly pressure-sintered on the surface of bare copper substrates, which not only increases Its sintering reliability, but also reduces the increased material cost due to plating precious metals; higher melting temperature and fatigue strength can be more adapted to extreme environments (-55 ℃ -250 ℃); higher thermal conductivity and lower Low resistivity can give full play to the performance of the device and extend its life by more than 10 times, which can fully meet the high requirements of automotive electronics.
2 interconnect materials
Wire bonding technology is a technology that enables chips and chips, chips and DCB to achieve electrical interconnection and information communication through metal wires. Because of its simple process and low cost, it is currently the mainstream interconnection technology for power modules. For some modules with simple internal structure (such as: MOSFET, Rectifier Module), it is better to use aluminum ribbon or copper bridge interconnection. However, for automotive IGBT modules, because of their high internal structure density and relatively complicated circuit design, the use of bonding wire interconnections in the design process will be more flexible.
Heraeus high-purity aluminum wires are resistant to corrosion and are particularly suitable for interconnection applications in body electronics and power electronics and other special environments.
Heraeus bonded copper wires have high current carrying capacity, good temperature resistance, and excellent resistance to power cycling, making them ideal for use in SiC and GaN chip devices.
Heraeus not only produces bonded aluminum wires and bonded copper wires, but also develops aluminum-clad copper wires that perform better than bonded aluminum wires and are more widely used than bonded copper wires. For details, please see the performance comparison of bonding wires of different materials in the table below to select more suitable interconnect materials. (As shown in Table 4 and Figure 3)
3 ceramic copper-clad substrate
There are many ceramic copper cladding technologies in the market. In power modules, direct copper cladding technology DCB and active metal brazing technology AMB (Active Metal Brazed) are mainly used. According to different requirements of the end application, you can choose the appropriate ceramic copper cladding technology and A combination of ceramics and copper with different thicknesses to match its performance.
Heraeus Condura.classic (DCB) substrate uses alumina as the insulating layer; Heraeus Condura.extra (DCB) substrate uses ZTA (toughened alumina) ceramic as the insulating layer; Heraeus Condura.prime (AMB) The substrate uses a silicon nitride ceramic as an insulating layer.
Different types of ceramic substrates can be selected according to the actual application of the market segment and the technical requirements of the device (as shown in Tables 5 and 6).
4 metal substrate
The metal substrate is a unique metal composite product of Heraeus Electronics. The technology is to use two or more metals to rub each other's metal layers under a certain pressure to produce high-temperature softening and finally produce intermetallic compounds, which makes the metal substrate different. Functional surface, mainly used for bonding pads in automotive electronic hybrid circuits.
Metal composite technology has a history of more than 50 years in Heraeus, and now it exerts its superior performance in power modules again. Copper-aluminum composite materials are used for the lead terminals of power modules, so that they have excellent electrical conductivity and thermal conductivity. The reliability of the bonding point is increased on the basis of the rate. The product has no other chemical elements involved in the entire manufacturing and application process, and fully complies with RoHS standards.
5 Die Top System
The technology of silicon power devices has been developed to the extreme. The chip junction temperature has been increased from 150 ° C to 175 ° C. Today's SiC devices have increased the chip junction temperature to 200 ° C. However, while increasing the chip junction temperature and power density, the package has been improved. Reliability and putting it into application will be the main work in the future.
In IGBT modules, bond wire fatigue and solder layer fatigue are the main causes of module failure. Through power cycle test analysis of IGBT modules, it is found that bond wire fatigue is the primary cause of IGBT module failure, but through comprehensive comparative test analysis It was found that the use of different interconnect materials and solder materials in the module again showed different results. (As shown in Figures 6 and 7)
As can be seen from the above figure, the reliability of materials can be superimposed on each other. A single upgrade of the material inside the module cannot effectively solve the overall life of the module, so the system can ensure the fatigue failure of the interconnecting materials and welding materials to ensure that The reliability and ruggedness of automotive electronics at extreme temperatures, and a more reliable systemized material packaging solution were proposed by Heraeus-Die Top System.
Heraeus DTS uses Heraeus mAgic's sintering technology to bond the chip to the Heraeus Condura substrate, which improves the current-carrying and heat-dissipation capabilities while increasing the reliability of the bonding. The chip surface interconnections can use Heraeus bonding Copper wire instead of aluminum wire. Because copper wire bonding requires a harder metal surface on the chip to avoid chip failure during the bonding process, sintering technology is used to sinter a layer of copper foil on the surface of the chip (gold or silver) to achieve copper on the chip surface. Wire bonding process (as shown in Figure 8).
Through power cycle comparison tests, it is found that the reliability life of modules using Die Top System materials is 67 times that of traditional modules.
As a material and matching material solution expert in the field of electronic packaging materials, Heraeus Electronics has the advantage of providing customers with high-quality materials and more professional technical services, helping customers shorten new product development cycles and optimizing process technology. And reduce production costs. Generally, our competitors only have one or two materials. In addition to providing customers with a single material, Heraeus can also help customers provide matching systematic materials, packaging process solutions and reliability testing services for their products. .