A 1200V Transfer Molded DIP-IPM

Transcription

1 A 1200V Transfer Molded DIP-IPM Eric Motto**, John Donlon**, Mitsutaka Iwasaki*,Kazuhiro Kuriaki*, Hiroshi Yoshida*, Kazunari Hatade* * Power Device Division, Mitsubishi Electric orp. Fukuoka Japan **Powerex Incorporated, Youngwood, PA USA Abstract This paper reports for the first time a 1200V transfer molded DIP-IPM with integrated HVI designed for control of small VA motors. By combining low cost transfer molded packaging with 1200V HVIs and fourth generation 1µm planar IGBTs the new series of modules allows significantly reduced cost and size compared to conventional designs. The new 1200V HVI uses field proven divided RESURF (REduced SURface Field) technology to provide robust level shifting and gate drive. I. INTRODUTION PU 15V DIP-IPM HVI Level Shift Gate Drive UV Prot. LVI Gate Drive UV Prot. O Prot. 3 Motor R SHUNT A Line Inverters for small A motors in general purpose industrial applications are required to meet stringent efficiency, reliability, size, and cost constraints. Presently, many of these small inverters utilize discrete IGBTs (Insulated Gate Bipolar Transistors) and free-wheel diodes in TO-220 or TO-247 packages along with HVIs (High Voltage Integrated ircuits) in their power stage. There are, however, several problems with this approach. One drawback is the high manufacturing cost associated with mounting and isolating multiple high voltage discrete components. In addition, relatively large and complex printed circuit designs are required to meet all of the spacing and layout requirements of the HVI and discrete power device combination. Another equally perplexing problem is maintaining consistent performance and reliability when the characteristics of the HVI drivers and IGBTs are not properly matched. An obvious solution to these problems is to use an Fig. 1 DIP-IPM Block Diagram integrated power device that contains all the required power silicon along with matched gate drivers in a single isolated base module. Unfortunately, the cost of integrated modules that rely on relatively expensive packages is prohibitive for many applications. A better approach, realized in the DIP- IPM (Dual-In-Line-Package Intelligent-Power-Module) described in this paper, is to assemble bare power chips and HVIs using a transfer molded lead frame design to maintain low cost and consistent, reliable performance. II. THE DIP-IPM ONEPT The concept of the DIP-IPM evolved from the conventional IPM (Intelligent Power Module). Intelligent power modules containing power semiconductors along 44mm 79mm Figure 2: 1200V DIP-IPM Package

2 AL wire IGBT, FWDi I u frame Al heat spreader 1 st Mold Resin 2nd Mold Resin reepage Distance Heat sink Figure 3: 1200V DIP-IPM Package with gate driving Is and protection functions have been widely accepted for general-purpose and high performance industrial motor drive applications ranging from 200W to more than 150kW [3, 5, 7]. The success of these IPM modules is the direct result of advantages gained through increased integration. Some of these advantages include the following: (1) Reduced design time and improved reliability offered by the factory tested, built-in gate drive and protection functions, (2) Lower losses resulting from simultaneous optimization of power chips and protection functions, (3) Smaller size resulting from the use of bare power die and control chips, and (4) Improved manufacturability resulting from lower external component count and isolated heat sink mounting surface. Unfortunately, in spite of these advantages, most integrated devices require relatively expensive IMS 1200V DIP-IPM Figure 4: 1200V DIP-IPM Application ircuit

3 P IN N IN High Voltage Level Shifters A One-Shot Pulse Logic A B D E F B Floating Supply D E (Insulated Metal Substrate) or DB (Direct Bond opper) based packages that tend to add considerable cost compared to transfer molded discrete components. To meet the demanding cost and size requirements of small, general purpose industrial inverters, Mitsubishi has developed a unique completely transfer-molded intelligent power device. The DIP-IPM offers the low cost of a discrete approach with the advantages of intelligent power modules. ompared to a discrete approach these devices offer high reliability, small size, and reduced manufacturing costs by integrating optimally matched power devices and HVI drivers in a single module. Fig. 1 presents a basic block diagram of the DIP-IPM in tegrated features, which include the power devices and custom control Is for gate drive and protection. The key to the DIP-IPM is the integration of HVIs to provide level shifting and gate drive for the high side IGBTs. This results in significant cost savings by enabling direct connection of all six IGBT control signals to the controller. The HVI also provides undervoltage lockout protection to allow simplified implementation of the required floating power supplies using bootstrap techniques. With just a few external components the entire three-phase power stage can operate from a single 15V control power supply. The DIP- IPM also utilizes a custom LVI (Low Voltage Integrated ircuit) to provide gate drive, overcurrent protection, and undervoltage lockout for the low side IGBTs. Incorporating the level shifting into the DIP -IPM reduces high voltage spacing requirements on the control PB R S Q Gate Drive +15 Gate Drive Fig. 5 High Voltage Level Shift F (P) (U,V,W) (N) al lowing a significant savings in circuit board space. The factory verified coordination of Is and power chips assures its reliability. All of these features are combined in a compact low cost transfer molded package that allows miniaturization of inverter designs. III. THE 1200V DIP-IPM PAKAGE The new 1200V DIP-IPM package is shown in f igure 2. This co mp act 44mm x 79mm package is used for four di fferent devices as summarized in Table 1. The DIP-IPMs are fabricated using a transfer molding process similar to a very large integrated circ uit. First, bare po wer chips and the custom HVI and LVI die are assembled on a lead frame. Ultrasonic bonding of large diameter aluminum wires makes electrical connections between the power chips and lead frame. Small diameter gold wires are bonded to make the signal level connections between the I die and lead frame. A cross-section of the 1200V DIP-IPM is shown in Fig. 3. In order to provide good thermal characteristics with the required 2500VRMS isolation the device is fabricated using a two-step injection molding process. In the first step, a thin layer of thermally conductive epoxy is formed between the lead frame and an aluminum block. The thin layer of epoxy and the aluminum block allow good heat transfer and provide electrical isolation between the power chips and heat sink. The integrated aluminum block provides the thermal characteristics needed for effective utilization of the power devices. A second injection-molding step then encapsulates the entire lead frame assembly to achieve the final form shown in figure 2. The two-step molding process allows fabrication of modules with IGBT ratings of up to 25A at elevated case temperatures. The module uses exclusively lead free solder and lead frame plating to meet environmental regulations. The transfer molded case has grooves in its bottom surface to provide 12.7mm of creepage distance between th e terminals and heatsink which is sufficient to satisfy both UL508 and IE664-1 standards. The transfer molded 1200V DIP-IPM is less expensive to produce than conventional hybrid m odules because it does no t require an IMS or ceramic substrate and plastic shell housing. The transfer molding process is also well suited for high volume, automated mass production, thus substantially reducing cost. TABLE V DIP-IPM Ratings Type Number Nominal IGBT Ratings (I /V ES ) Recommended Maximum O Trip Typical Inverter Ratings 460VA PS A/1200V 8.5A 3 KVA PS A/1200V 17A 5 KVA PS A/1200V 25A 7 KVA PS A/1200V 42A 10 KVA

4 Figure 6: Structure of high voltage LDMOSFET level shift Noise and breakdown prone overlapping signal interconnect n well n - well p - substrate (a) onventional IV. ELETRIAL HARATERISTIS OF THE DIP-IPM A schematic diagram showing the internal circuit along with typical external components for the 1200V DIP-IPM is shown in Fig. 4. The 1200V DIP-IPM contains the six IGBT/free-wheel diode pairs required for a three-phase motor drive. There is one LVI for the three low side IGBTs that provides the gate drive and protection functions. There are three HVI for the three high side IGBTs that provide gate drive, protection functions, and level shifting. (b) Divided RESURF A. Power hip Design The 1200V IGBT chips used in the DIP-IPM are fabricated using a fourth generation 1µm planar process to achieve high efficiency with low switching and conduction losses. All free-wheel diodes used in the DIP-IPMs are super fast/soft recovery shallow diffused types. These diodes have been carefully optimized to have soft recovery characteristics over a wide range of currents and temperatures in order to minimize EMI/RFI noise. The available ratings for the 1200V DIP-IPMs are summarized in Table I. The last column of the table lists Figure 7a: HVI using conventional level shifting structure Figure 7b: New HVI with 1200V level shift using divided RESURF structure High Voltage Floating ircuits High Voltage Level Shifters

5 typical inverter output ratings. Depending on overload requirements and PWM switching frequency the actual usable capability in a given application will vary. B. High Voltage Level Shift The main feature of the 1200V DIP-IPM is the high voltage level shifting provided by the integrated HVI. The built-in level shift eliminates the need for optocouplers and allows direct connection of all six control inputs to the PU/DSP. The omission of an isolated interface circuit results in significant savings. The detailed operation and timing diagram for the level sh ift function is shown in Fig. 5. The falling and rising edges of the p-side control signal (A) activate the one shot pulse logic which generates turn-on pulses (B, ) for the high voltage LDMOSFETs (Lateral Double Diffused Metal Oxide Semiconductor Field Effect Transistors). The LDMOSFETs translate the input signals up to a latching circuit (D, E) to set and reset the gate drive for the p-side IGBT (F). The latching circuit is fabricated on a floating junction isolated island that is referenced to the emitter of the high side IGBT in order to provide gate drive. The challenging part of high voltage I desi gn is the fa brication of microscopic high voltage LDMOSFETs and interconnects with low leakage current and immunity to noise and parasitic latching. In conventional high voltage integrated circuits (Figures 6a, 7a) separate high voltage LDMOSFETs are fabricated with their drains connected to the floating gate drive island by a bridge connection. In this structure, the high voltage bridge connection must pass over the ground potential substrate. The large voltage differential and high dv/dt present at this bridge becomes a major source of problems with voltage breakdown and noise injection. These problems become virtually unmanageable in the case of 1200V level shifting. To solve these problems Mitsubishi Electric developed a new high voltage I ontroller Fig V DIP-IPM Interface ircuit V 15V R 10K R V D U P, V P, W P, U N, V N, W N F O RPD (4k Typ.) GND DIP-IPM Gate Drive V th(off) =0.8V Min. V th (on) =2.6V Max. Fault Note: Dashed components optional noise filter structure called divided RESURF (REduced SURface Field) (Figures 6b, 7b). In the divided RESURF structure a proprietary process is used to fabricate the LDMOSFETs across the boundary of the floating gate drive island. By doing this, the high voltage bridge connection required in the conventional structure is eliminated. The result is an HVI process with robust high voltage level shifting capability. The divided RESURF process allowed the development of new HVIs with 1200V level shifting capability for use in the 1200V DIP-IPM.. Undervoltage Lockout The 1200V DIP-IPM is protected from failure of the 15V control power supply by a built in undervoltage lock out circuit. If the voltage of the control supply falls below the UV level specified on the data sheet, the low side IGBTs are turned off and a fault signal is asserted. In addition, the p-side HVI gate drive circuits have independent undervoltage lock out circuits that turn off the IGBT to protect against failure if the voltage of the floating power supply becomes too low. If the high side undervoltage lockout protection is activated the respective IGBT will be turned off but a fault signal is not supplied. D. Interface ircuit The 1200V DIP-IPM has seven microprocessor compatible input and output signals. The built in HVI level shifters allow all signals to be referenced to the common ground of the 15V control power supply. The signals are compatible with either 3.3V or 5V TTL/MOS logic in order to permit direct connection to a PWM controller as shown in Figure 4. The interface circuit between the PWM controller and the DIP-IPM can be made by either direct connections or optocouplers depending on the requirements of the application. Fig. 8 shows the internal structure of the DIP-IPMs control signals and a simplified schematic of a typical external interface circuit. On and off operations for all six of the DIP-IPM s IGBTs are controlled by the active high control inputs U P, V P, W P, U N, V N, W N. These inputs are pulled low internally with approximately 4kohm resistor. The controller commands the respective IGBT to turn on by pulling the input high. Approximately 1.8V of hysteresis is provided on all control inputs to help prevent oscillations and enhance noise immunity. The optional capacitor () and resistor (R), shown dashed in the figure, can be added to further improve noise filtering. These components may be required in some applications depending on the circuit layout and length of connections to the controller. The fault signal output (F O ) is in an open collector configuration. Normally, the fault signal line is pulled high to the 5V logic supply with a 10k resistor as shown in Fig. 8. When an overcurrent condition or improper control

6 power supply voltage is detected the DIP-IPM turns on the internal open collector device and pulls the fault line low. V. DIP-IPM SYSTEM ADVANTAGES The DIP-IPM contains all six of IGBT/free-wheel diode pairs required for a small motor drive in a fully isolated package. Mounting is accomplished with only two screws and no additional isolation material is required. The reduced manufacturing time and simplified assembly provided by the DIP-IPM will allow improvements in both cost and reliability of the finished system. Another advantage of the DIP-IPM is that the integrated HVI and LVI gate drive and protection functions are factory tested with the IGBTs as a subsystem. This eliminates uncertainty about the critical coordination of the electrical characteristics of these components. The result is better, more consistent system performance and reliability. VI. ONLUSION A new 1200V DIP-IPM consisting of a combination of power devices, low voltage Is and high voltage Is in a unique, low cost, transfer molded package has been presented. These devices have been optimized to simplify and miniaturize inverters for general purpose industrial applications. ompared to discrete semiconductors these new integrated modules offer improved manufacturability and increased reliability. REFERENES [1] G. Majumdar, et al. "A New Generation High Speed Low Loss IGBT Module", ISPSD, May 1992 [2] J Yamashita, et al. "A Study on the Short ircuit Destruction of IGBT's, ISPSD, May 1993 [3] G. Majumdar, et al. "A New Generation High Performance Intelligent Module" PIM Europe May 1992 [4] Powerex "IGBTMOD and Intellimod TM Application and Technical Data Book" Second Edition, PUB#9DB-200, 1998 [5] E. Motto, et al. "A New Generation of Intelligent Power Devices for Motor Drive Applications" IEEE IAS onference October 1993 [6] E. Motto "Protecting High urrent IGBT Modules From Over urrent and Short ircuits" HFP onference, May 1995 [7] John Donlon, et al. "A New onverter/inverter System for Windpower Generation Utilizing a New 600 Amp, 1200 Volt Intelligent IGBT Power Module" IEEE IAS onference October 1994 [8] E. Motto, et al. A New Intelligent Power Module With Microprocessor ompatible Analog urrent Feedback, ontrol Input, and Status Output Signals, 1996 IEEE IAS onference Proceedings [9] Eric R. Motto A New Ultracompact ASIPM with integrated HVASI 1997 Powersystems World conference proceedings [10] G. Majumdar et al. Novel Intelligent Power Modules for Low- Power Inverters 1998 IEEE PES Proceedings [11] S. Noda et al. A Novel Super ompact Intelligent Power Module 1997 PIM Europe conference proceedings [12] Eric R. Motto Application Specific Intelligent Power Modules A Novel Approach to System Integration in Low Power Drives Proceedings of the 1998 Powersystems World onference