Development and application of IGBT module heatsink

1 Overview

The development of power electronic devices has gone through SCR, GTO, BJT, IGBT and so on. Is toward large capacity, high frequency, easy to drive, low loss, modular, points out the direction of development, compared with other power electronic devices, IGBT module heatsink has high reliability, simple drive, easy to protect, there is no buffer circuit and switching frequency is high, in order to achieve the high performance, have adopted many used in integrated circuit technology, such as extension technology, ion implantation, fine printing, etc. To improve the voltage resistance of the power MOSFET, it is necessary to increase the high-conduction resistance, thus hindering the application of the device in the high voltage and high-current range. In response to these defects, power IGBT(insulated gate bipolar transistor) devices were born in the 1980s and became practical in the early 1990s. In recent years, performance of IGBT module heatsink has been improved rapidly, rated current has reached hundreds of amperes, withstand more than 1500V, and continues to improve. As the IGBT device has the positive characteristics of PIN diode, the characteristics of the heatsink of the p-channel power IGBT module are not much different from that of the n-channel IGBT, which is very conducive to adopting complementary structure in the application, thus expanding its application in the field of ac and digital control technology.

At present, the application of power electronic devices in the field of medium-voltage high-power, the decision has been formed, IGCT, IGBT, IEGT innovative technology market, to compete with each other in high-power (1 mw), low frequency (1 KHZ) transmission areas, such as the field of electric traction locomotive decision, IGCT has a unique advantage, while under high carrier frequency, high chopping frequency, IGBT, IEGT have broad prospects for development, in the field of medium voltage high power inverter at present stage will be made by the four kinds of power electronic devices constitute its mainstream device.

The biggest advantage of IGBT is that it can withstand the current shock in both the conduction state and the short-circuit state. Its parallel connection is not a problem, because the shut-off delay itself is very short. Its series is also easy. Although IGBT module heatsink is commonly used in high power applications, its limited number of load cycles makes its reliability a problem. Its main failure mechanism is exposed cathode lead welding joint and low fatigue strength of welding joint. In addition, the defect of insulating material is also a problem.

Ten years ago, IGBT module heatsink appeared on the world stage of technology, although it embodies the essence of high voltage and large current thyristor manufacturing technology and large scale integrated circuit (lxi) micro-machining means of both, the performance of a very good combination, many people still hard to believe this device in the power field of vitality. Now, the cross-century IGBT shows significant progress in forming a new device application platform.

  1. Heatsink of intelligent MOS gate IGBT module

Owing to the improvement of IGBT’s high frequency performance, the drive circuit, protection circuit and fault diagnosis circuit can be integrated together to make an intelligent power module, which is normally triggered by voltage.

A new generation of power IGBT module heatsink chip has been developed by using the fine fabrication of loci and controlling the minority carrier life of the device. Compared with the first generation of IGBT, the off – state drop time and saturation voltage characteristics of the third generation are significantly improved.

IGBT is a composite device of a bipolar transistor (BJT) and MOSFET. It introduces the conductance modulation effect of BJT into the high-resistance drift region of VDMOS, greatly improving the device’s conductivity. Meanwhile, it also has the high input impedance of a MOSFET gate, which drives the device for voltage. The IGBT module heatsink can be applied to replace the traditional thyristor (SCR), shut-off thyristor (GTO), transistor (BJT) and other devices.

2.1 IGBT – the PIM

IGBT module heatsink module built-in rectifier module circuit, inverter main circuit and regenerative circuit to reduce losses as well as to reduce costs, this new module is called power integration module, referred to as PIM(PowerIntegratedModule). IGBT module is a kind of high-speed switch. The fourth generation of IGBT mainly adopts the following new technologies in the development.

(1) the FWD (FreeWheelingDiode) technology

A diode device with reduced forward voltage (VF) selected from the module. According to the test, in the 600V and 1200V series, the loss generated by the inverter carrier frequency of 10kHz was decreased by 20% compared with the old series.

(2) micro-refinement technology for etching module units

Since the width of the control pole (LH) has reached the optimal design, the saturation voltage VCE(SAT) between the collector and emitter can be reduced by 0.5v to decrease the switching loss.

(3) the NPT (NonPunchThrough) technology

The carrier life is controlled to reduce the dependence of switching loss on temperature. In this way, the switching loss during long – term use can be reduced.

IGBT module heatsink for this kind of high – speed switch requirements are nothing more than high – speed and flexible recovery. To forward voltage VF and recovery loss Err, a higher VF value is preferred in the design. However, when the selected high VF value works at the low frequency of the converter, the conduction time of FWD will be prolonged and the average loss will be increased, and the temperature rise of the converter will be increased at low speed and high torque. For this reason, the fourth generation IGBT module heatsink pays special attention to the design of the best electrode structure, thus improving the relationship between VF and Err, reducing the VF of FWD by 0.4v ~ 0.5v and reducing the total loss by 20%.

2.2 Features of P series NPT – IGBT modules

FUJIP IGBT is manufactured by NPT technology, which has more advantages than PT(PunchThrough)IGBT. It is especially suitable for inverter, ac servo system, UPS, welding power supply and other fields. Its remarkable features are as follows:

(1) the current rating is indicated at Tc=800℃.

(2) the VCE(SAT) of p-series IGBT is proportional to the temperature and easy to be connected in parallel.

(3) the temperature coefficient of switching loss is lower than that of Pt-igbt. When the junction temperature rises, the switching loss increases less than that of Pt-igbt. Therefore, p-series modules are more suitable for high-frequency applications.

(4)1400V series modules can be used in AC380V to 575V power conversion equipment.

(5) in the P series, especially the 1400V module has a larger safe working area than pt-igbt, and both RBSOA and SCSOA are rectangular. Its RBSOA can reach twice the rated current, and its SCSOA can reach ten times the rated current. Therefore, absorption circuit can be greatly simplified, at the same time, short – circuit capacity is also greatly improved.

(6) low loss, soft switch, whose dv/dt is only 1/2 of the ordinary module, greatly reduces EMI noise.

At present, IGBT has developed to the fourth generation, Siemens / EUPEC can supply IGBT module with current from 10A to 2.4 Ka and voltage range from 600V to 3.3 kv. Taking 1.2 ka / 3.3 kvigbt as an example, the grid emitter voltage is only 15V, the trigger power is low, the switching loss is small, di / dt. Du / DT are effectively controlled. The current development and application level of high-voltage IGBT module heatsink is: 600A ~ 800A / 6.5 kv, working frequency is 18kHz ~ 20kHZ The resistance of the junction type field effect transistor (JFET) located below the gate and sandwiched between the p-type base region is removed, which improves the contradiction between reducing the on-state voltage drop and increasing the frequency characteristic Because the IGBT chip with NPT structure has the temperature coefficient of positive resistance and is easy to be connected in parallel, this is the only way for IGBT module heatsink to be high power inductor packaging technology can ensure the long-term reliable operation of the system, large-capacity high-voltage IGBT module heatsink is suitable for flat-plate packaging structure. 3.1 Trench structures, same as all kinds of power semiconductor, the internal power of IGBT is a trade-off between reducing the on-state voltage drop and increasing the switching speed to reduce the switching time. In conventional IGBT, the MOS channel is a reminder to the surface of the silicon wafer. Its conduction current is made up of two parts: the MOS component IMOS and the thyristor component ISCR. In order to prevent Latch-up effect, the MOS component must dominate. The resistance RJFET, which is located below the gate and sandwiched between the p-type base region, is unavoidable in the current path. It is an obstacle to improve the frequency characteristic and reduce the on-state voltage drop. The fourth generation IGBT adopts a unique technology to make the trench structure, which removes the RJFET and moves the MOS trench perpendicular to the surface of the silicon wafer. The cell size can be reduced to 20%. This can improve the utilization of the silicon chip, decrease the on-state voltage drop, and create new possibilities for the improvement of its frequency parameters.

3.2 IGBT module heat sinks high voltage in 1993. EUPEC European Power Electronics Company introduced 3.2 kv / 1.3 Ka IGBT module, but it is composed of many IGBT chips in series and parallel. Can only be said to be a high-pressure development of an attempt. It has been thought that the voltage resistance of IGBT will not break through 2kV, because the IGBT below 1.2 kv is made of high resistance epitaxial silicon chip, the voltage should reach 1.5 kv, the thickness of epitaxial layer should exceed 180 m, it is hardly practical. In 1996, Japan Toshiba Company introduced 2.5 kv / 1kA IGBT, with the same high-power thyristor, GTO Tube flat-plate pressure-type packaging structure. It breaks through the restriction of epitaxial Wafer and is made of high resistant single crystal silicon with 110 crystal faces. The thickness of the silicon wafer is greater than 300 m and it has enough mechanical strength. In 1998, the single-tube IGBT with 4.5 kv withstand voltage was developed, but it is impossible to make the single-tube IGBT with high current.  the IGBT manufacturing process to do more than ten times fine lithography sets, after the corresponding number of high-temperature processing, graphics to a certain extent, the pass rate will decline sharply, or even zero. Therefore, the manufacture of high-power IGBT, must be parallel. Toshiba’s 2.5 kv 1kigbt is made up of 242.5 kv 80A IGBT chips in parallel, and 16 Fred chips in 2.5 kv 100A, which are ultra fast recovery diodes, in reverse, flyback diode. Realizing single-string multi-parallel structure is the only way IGBT to be high-power. The NPT structure is a prerequisite for IGBT to be freely connected in parallel. 3.3 Thunderbolt type IGBT module heatsink has been available for some time, the operating frequency of IGBT module heatsink is limited to less than 20 KHZ and can work up to 50 Khz in a soft-switching topology Many switching power supplies use higher frequencies and are basically power MOSFET’s. In 1998, based on the fourth generation technology, a new device named Thunderbolt IGBT was enhanced by Ir Warp Series and APT GT series. The rated voltage is 600V and the rated current is 0 ~ 100A. Its hard-switching operating frequency can reach 150 Khz, resonant inverter soft switching circuit can reach 300 Khz. Its switching characteristics are close to that of power Mosfet, and the current density is 2.5 times Mosfet, that is, the uniform current of its silicon area is greatly reduced, so the cost has been reduced.

3.4 Inverse conducting IGBT and bi-directional IGBT module heatsink, which are IGBT derived devices developed to meet the needs of different application circuits. 4. The structure of IGBT module heatsink is comparable to that of Mosfet. In terms of the equivalent circuit and working mechanism, IGBT can be considered as a Darlington transistor with Mosfet as input stages The output stage is a PNP transistor. The use of IGBT module should give particular attention to the following aspects. 4.1 anti-static countermeasures the VGE guarantee value of the heatsink of IGBT module is 20V, the danger of damage of the voltage exceeding the guarantee value is added to the IGBT module, so it is advisable to connect a resistor to 10kQ between grid and emitter. 4.2 drive circuit designs, strictly speaking, whether the full use of IGBT device performance, the key depends on the drive circuit design. IGBT drive circuit must be provided appropriate forward gate voltage, enough reverse gate voltage, enough input and output electrical isolation capability, as well as with gate voltage limiting circuit. 4.3 IGBT modules designed for protection circuits may be damaged due to abnormal phenomena such as over-current and over-voltage. Therefore, it is necessary in order to design over-voltage, over-current, over-heat and so on, which can match the characteristics of the device. 4.4 The heat dissipation design depends on the maximum junction temperature (Tj) allowed for IGBT modules. At this temperature, the loss of the device must be computed first, which causes the junction temperature to rise below the allowable value to select the heat sink. In the case of insufficient heat dissipation design, the device may be destroyed when the device is running at medium level. 4.5 Grid Series Resistance RC.

For IGBT module heatsink, increasing grid resistance can reduce the reverse recovery overvoltage of IGBT on flyback diode, and reduce the short-circuit impulse current in at state The increase of gate resistance will increase the loss of turn-on and turn-off and prolong the turn-off time. Therefore, the best way is tantamount to configure two series resistors, namely Rg on and RG off, in the actual design should consider the specific application requirements. If in the case of high voltage Diodes, recovery time is usually longer, Rg on should be 2-4 times larger than the recommended value of the product catalog. 5. In recent years, Toshiba Corporation of Japan has developed IEGT, which, like IGBT, has two structures: Plane Gate and groove. The former has been prepared successfully, and the product is coming out soon The latter is still in development. IEGT has the advantages of both IGBT and GTO: low saturation voltage drop, wide Safe operating area circuit capacity is only 1 / 10 of GTO. Low gate drive power is 2 orders of magnitude lower than GTO and high operating frequency. In addition, the device adopts the structure of the plate crimping electrode lead-out, which is expected to have higher reliability. Compared with IGBT module heatsink, IEGT structure is characterized by long gate length and high lateral resistance near the Gate Junction in the n long base region, so it is difficult to inject holes from the collector into the N long base region as in IGBT It flows smoothly laterally through the p region into the emitter and forms a hole accumulation layer in the region. In order to preserve the electrical neutrality of the region, the emitter must inject a large number of electrons into the N Long Base region via n channels. In this way, the carrier accumulates in the lung base region and forms the carrier distribution similar to GTO in the n base region. Thus the contradiction between high current and high voltage is solved. At present, the device has reached the level of 4.5kv/ 1kA.