Learn About IGBT Modules
01 what is IGBT
IGBT (Insulated Gate Bipolar Transistor), an insulated gate bipolar transistor, is a composite fully-controlled voltage-driven power semiconductor device composed of BJT (bipolar transistor) and MOS (insulated gate field effect transistor), with both The advantages of both high input impedance of MOSFET and low turn-on voltage drop of GTR. The saturation voltage of GTR is low, the carrying current density is large, but the driving current is large; the driving power of MOSFET is small, the switching speed is fast, but the conduction voltage drop is large, and the current carrying density is small. The IGBT combines the advantages of the above two devices, with low driving power and low saturation voltage. It is very suitable for the conversion system with a DC voltage of 600V and above, such as AC motors, frequency converters, switching power supplies, lighting circuits, traction drives and other fields.
02 Composition of IGBT module
The IGBT module is a modular semiconductor product that is packaged by IGBT (insulated gate bipolar transistor chip) and FWD (freewheeling diode chip) through a specific circuit bridge; the packaged IGBT module is directly applied to inverters, UPS uninterruptible power supply and other equipment.
03 Characteristics and market of IGBT module
IGBT modules have the characteristics of energy saving, convenient installation and maintenance, and stable heat dissipation; most of the current market sales are such modular products, and the so-called IGBT also refers to IGBT modules; There will be more and more in the market; IGBT is the core device of energy conversion and transmission, commonly known as the "CPU" of power electronic devices, as a national strategic emerging industry, in rail transit, smart grid, aerospace, electric vehicles and new energy It is widely used in equipment and other fields.
04 Manufacturing process and flow of IGBT module
Screen printing➔Automatic placement➔Vacuum reflow soldering➔Ultrasonic cleaning➔Defect inspection (X-ray)➔Automatic wire bonding➔Laser marking➔Shell plastic sealing➔Shell potting and curing➔Terminal forming➔Functional testing
IGBT module packaging is to integrate and package multiple IGBTs together to improve the service life and reliability of the IGBT module. Smaller size, higher efficiency and higher reliability are the market demand for IGBT modules. Development and application of module packaging technology. At present, the popular IGBT module packaging forms include lead type, solder pin type, flat type, and disc type. , DP70, etc.
The IGBT module has 3 connection parts: the aluminum wire bonding point on the silicon wafer, the welding surface of the silicon wafer and the ceramic insulating substrate, and the welding surface of the ceramic insulating substrate and the copper base plate. The failure of these joints is caused by the stress and thermal deterioration of the materials caused by the mismatch of the thermal expansion coefficients of the two materials at the interface.
There are many IGBT module packaging technologies, but they can be summarized as thermal management design, ultrasonic terminal welding technology and high reliability soldering technology:
(1) In terms of heat dissipation management design, the chip layout and size were optimized by adopting the thermal simulation technology of the package, so that under the same ΔTjc condition, the output power was successfully achieved by about 10% higher than the original.
(2) Ultrasonic terminal welding technology can directly weld the copper pads and copper bonding wires connected by soldering together. Compared with the soldering method, this technology not only has a high melting point and high strength, but also has no difference in linear expansion coefficient, and can obtain high reliability.
(3) High reliability soldering technology. Ordinary Sn-Ag soldering will lose 35% strength after 300 temperature cycles, while Sn-Ag-In and Sn-Sb soldering will not lose strength after the same cycle. These technologies are "with high high temperature reliability."
IGBT module packaging process:
First welding ➔ first bonding wire ➔ second welding ➔ second bonding wire ➔ assembly ➔ upper shell, coating sealant ➔ curing ➔ filling silicone gel ➔ aging screening. These processes are not solidified. It depends on the specific module. Some may not require multiple welding or bonding wires, while others may require it, and some may have other processes. The above are just some main processes, and there are other auxiliary processes, such as plasma treatment, ultrasonic scanning, testing, marking and so on.
The role of IGBT module packaging The IGBT module packaging uses colloidal isolation technology to prevent explosions during operation; the second is that the electrode structure uses a spring structure, which can alleviate the cracks on the substrate during installation and cause cracks in the substrate; the third is The bottom plate is processed and designed so that the bottom plate is in close contact with the radiator, which improves the thermal cycle capability of the module.
The mid-point design is selected for the bottom plate design, and its amplitude will disappear under our specified installation conditions to achieve a better connection with the radiator. We will see later in the installation process that it plays a role in the installation process. Product performance, in the process of applying IGBT, the turn-on process is relatively gentle to the IGBT, and the turn-off process is relatively harsh. Most of the damage is from shutdowns that exceed ratings.