onsemi VE-Trac Family Traction Inverters Installation Guide

onsemi VE-Trac Family Traction Inverters

Product Information

The VE-Tract Dual is a family of modules designed for power converters. This assembly guide provides specifications and requirements for the dual side cooler, printed circuit boards, terminal connections, and assembly.

Key Features:

• Designed for power converters
• Ensures good thermal and electrical performance
• Allows freedom to design custom coolers and PCBAs

roduct Usage Instructions

1. Apply thermal interface material (TIM) to one side of the power module.
2. Align and place the power module on the first half of the cooler.
3. Apply TIM to the other side of the power module.
4. Align the second half of the cooler to the first half of the cooler.
5. Secure the first and second halves of the cooler with the power modules in between.
6. Secure the PCB to the cooler or bracket.
7. Solder the PCB to the power modules.

Heatsink/Cooler Requirements

In order to effectively dissipate the power dissipated in the module, the cooler must meet certain requirements:

• The cooler must ensure that the maximum rated operating temperature of the module is not exceeded.
• The cooler must have a surface flatness within ±50 mm.
• The cooler must have a clamping force within the specified range.
• The cooler must provide full coverage of the Direct Bond Copper (DBC) area on the power module.
• The cooler should have a raised contact area that only contacts the blue area of the power module for optimal thermal performance.
• The cooler should include module alignment features to control module orientation and spacing.

For detailed dimensional specifications and requirements, please refer to the product data-sheet.

This document is intended to be a guide to assemble all VE−Trac Dual family of modules. It covers the specifications and requirements for a dual side cooler, printed circuit boards, terminal connections and assembly.

Applies to the following parts:

• NVGxxxA75LxDSxx
• NVGxxxA120LxDSxx

INTRODUCTION

In order to avoid unnecessary mechanical stress on the VE−Trac module, its control leads or the power terminals, it is important to follow the recommended specifications and assembly order to install the power module into the end application power converter. Proper assembly also ensures good thermal and electrical performance for the power module assembly. Since the product is only the power module, it should be noted that this guide will use an example reference cooler design and Driver Printed Circuit Board Assembly (PCBA) to explain the assembly process. There are different types of VE−Trac Dual modules, but they only differ in terminal configurations (See Figure 2) and the body of the package remains unchanged. These differences can be in the bending of the power terminals or signal pins, lead length, press−fit or solder pins for signal leads, terminal plating finish or terminals with or without screw holes. In this document the DSC variant is used as an example to explain the assembly process, but most of the information applies to all variants.

Please consult the data sheet of the specific product for details and dimensional differences.

The user has the freedom to design their own coolers and PCBAs to meet their end application requirements. But the assembly order and certain specific requirements should be followed.

Recommended mounting order for the assembly:

1. Apply TIM to one side of the power module
2. Align and place power module on 1st half of the cooler
3. Apply TIM to the other side of the power module
4. Align 2nd half of the cooler to the 1st half of the cooler
5. Secure 1st and 2nd halves of the cooler with the power modules in between
6. Secure PCB to cooler or bracket
7. Solder PCB to power modules

HEATSINK/COOLER REQUIREMENTS

Power dissipated in the module must be effectively removed from the module without exceeding the maximum rated operating temperature of the module as specified in its data sheet. In this section the general requirements for the cooler is explained and in the following section the assembly process is explained using an example reference cooler.

General Specifications for the Cooler

• Dual side liquid cooling is necessary to enable the full capability of the power module.
• It is necessary to use a thermal interface material between the power module top and bottom area of the Direct Bond Copper (DBC) to the cooler surface. It’s necessary to ensure full coverage of the DBCs to the cooler.
• The specified flatness for the module for top and bottom clamping area (see Figure 3) is specified as Max. Surface flatness 50 m.
• Mating alignment feature must be included on the cooler (see Figure 4).

Table 1. SPECIFICATIONS FOR THE COOLER

Clamping Area

| Max. Cooler Roughness Rz [µm] per ISO 4287| Max. Cooler Flatness [µm per 100 mm]

per ISO 1101

| ****

Max. Step [µm] per ISO 4287

| Minimum Clamping Force [N]| Maximum Clamping Force [kN]
---|---|---|---|---|---
RED + BLUE AREA| 10| 50| 10| 760| 7
BLUE AREA| 10| 50| 10| 760| 5.4

In Figure 3 the area where the clamping force should be applied is shown in red and blue. It is possible to apply force on the DBC only (blue area) at reduced levels. The limits for each area are defined in the table above. You can get a cracked DBC if the specifications for the heatsink flatness is not met. If the cooler contact area is warped or has a burr, it can exert a large force in a small area and quickly exceed the force limits defined in Table 2. The blue area shown in Figure 3 is the area that should be actively cooled to ensure optimal thermal performance. We recommend using a 1 mm raised contact area on the cooler that only contacts the blue area for a more consistent performance.
The cooler should also include the module alignment features as shown in Figure 4. This protrusion feature has a mating feature on the power module to control the module orientation and spacing between the modules. Figure 4 also shows the dimensions and spacing to be included for the alignment features.

DBC Appearance

The cooling surfaces (DBC) as shown in Figure 3 can sometimes appear to be discolored, scratched or pitted. The discoloration is due to the copper on the DBC getting oxidized due to prolonged exposure to air. The oxide layer is thin (1.8 – 14 nm) and forms non−uniformly, resulting in various shades of colors. The contribution of the copper oxide layer to the thermal performance of the module is so small that it has no effect on the Rth.j−f (junction to fluid) of the module.

Other common issues seen on the DBC include scratches and pitting. This can occur due to handling during assembly or assembly rework. Figure 5 shows some examples of these common issues and acceptable criteria for each type. Copper oxide layer, scratches and pits within the acceptable criteria have no impact on the electrical, thermal or isolation voltage capability of the power module.

Reference Cooler Design and Performance

The reference cooler design can be used as a guide by customers to develop their own cooler designs. There is no specific requirement to use this design for the cooler. The thermal data shown in the data sheet for VE−Trac Dual products are all measured using this reference cooler. The cooler can be designed in different ways as long as the minimum requirements described in the previous section are met and the proper trade−off consideration is given to the thermal resistance/impedance, pressure drop, flow rates and cost. Reference design shown in Figure 6 should be considered as an example.

The reference cooler uses a simple pin−fin design and is optimized for thermal performance, pressure drop and cost. The data shown below in Figure 7 and Figure 8 should be considered as typical performance of the cooler with three 750 V, 800 A VE−Trac Dual modules assembled using the recommended thermal interface material and the assembly process described later in the document. All measurements were performed using 50/50 Ethylene Water Glycol mix at 65°C as the coolant. The maximum static withstand pressure of the reference heatsink is 4 Bar.

Thermal Interface Material (TIM)
Use of an effective Thermal Interface Material is crucial to achieving the best thermal performance. For VE−Trac Dual assemblies we recommend using the Honeywell PTM7000 die cut Phase Change Material at 200 m thickness. This material has been tested with the product and used in all thermal measurements shown on the product data sheet.

Table 2. CRITICAL PROPERTIES OF THE RECOMMENDED THERMAL INTERFACE MATERIAL (TIM)

The PTM7000 is also available in paste form to be used with automated dispensing machines. Please refer to the supplier for additional information on its handling and use.

Figure 9 shows the size and positioning of the die cut PTM7000 pad placement on the top and bottom cooling areas of the VE−Trac power modules.

It is possible to use other TIM materials from other suppliers in either pad or paste form. However, the new

REFERENCE COOLER ASSEMBLY

The reference cooler described in the previous section is used as example to explain the recommended assembly process of the half−bridge VE−Trac Dual modules into a material will have to be characterized to determine its performance and optimal method of use in assembly.
3−phase power stack i.e. three power modules integrated with a cooler. The complete assembly process is described in the following steps:

STEP 1: Cooler placement in Jig

The bottom side cooler plate in inverter and placed in a jig. We refer to this side of the cooler plate as the bottom half, since it is contact with bottom side of the power module. The recommended jig design is described below in detail. The purpose of the jig is to securely hold the bottom half of the cooler plate while the power stack is being assembled.

STEP 2: TIM Application and Module placement

The TIM pads are aligned and placed as shown in Figure 9 to the bottom side (smaller DBC) of the power modules. The power module with the TIM is then inverted and placed on the bottom cooler plate in the jig using the alignment features on the module and the cooler plate to ensure proper orientation and placement.

STEP 3: TIM Application, O−ring and Cooler

The TIM pads are aligned and placed as shown in Figure 9 to the top side (larger DBC) of the power modules. Two O−rings are placed as shown to seal the coolant flowing between the top and bottom cooler halves. The top cooler half is then visually aligned using the eight mounting holes and placed on top of the three power modules as shown above.

The O−ring design for the reference cooler is shown below in Figure 11:

For automotive applications it is typical to use double or triple edge seal O−rings. In the above example a single edge seal O−ring is shown as an example for the reference heatsink. There are other heatsink designs that do not use O−rings, but is instead welded or braized.

STEP 4: Securing the Cooler Halves

The stack assembly is now inverted bottom side up and secured using the eight screws. Heatsink secured using an ISO 4762 M4 x 0.7 mm Thread X 16 mm long Stainless Steel Socket Head Cap Screw in combination with a DIN 7980 M4 stainless steel split lock washer. The screws are fastened in the order shown above in a 3 step torque sequence. First torque each screw in order shown to 10%of the recommended torque value of 1 Nm. Second step is to torque each screw in order to 75% of recommended torque. The complete assembly is then cured in an oven at 65°C for 30 minutes as recommended by the TIM supplier. Once cured and removed from the
oven, the screws are immediately torqued in order shown to the final recommended torque value of 1 Nm. The process can be different for different types of TIM and heatsink designs.

POWER TERMINAL CONNECTIONS

There are limited options to connect the module power terminals to bus bars. The oxygen free copper power terminals are tin-plated and well-suited for screw-type fastening. There are many terminal versions for the VE−Trac Dual family with some designed for fastening and some versions designed for a welding process.

Terminal Connection Options
The power terminal connections should be made to bus bars are shown in Figure 12. An isolator with captured nuts (see Figure 19) is used between the module terminal and heatsink or chassis. The power module terminals go over the isolator and the captive nuts and the bus bars over that and a screw is used to fasten the bus bars to the module terminals.

Hardware shown:
Screw – DIN 439B M6 x 1 mm thread Thin Hex nut Nut – ISO 7380 M6 x 1 mm thread x 8 mm long

Limitations
The mounting process should result is a system that will limit the forces acting on the power terminals when secured to the bus bars. Figure 13 shows the maximum allowed forces and their axis on the module power terminal.

PRINTED CIRCUIT BOARD (PCB) GUIDELINES
The general recommendation for the plated through holes for the control pins are shown in Table 3 and Figure 14 shows the recommended drill hole pattern. Depending on the design of the PCB there are different methods to solder the control pins to the PCB. Wave soldering or hand soldering are the general practice for through−hole type (THT) components.

Table 3. SPECIFICATIONS FOR PLATED THROUGH HOLES ON PCB FOR THE SOLDERABLE MODULE CONTROL PINS

#| Description| Min.| Typ.| Max.| ****

---|---|---|---|---|---
1| Initial hole diameter (mm)| 1.95| 2.00| 2.15
2| Copper thickness in via (µm)| 25| −| −
3| Metallization (Sn) in via (µm)| 10| −| −
4| Final hole diameter (mm)| −| 1.85| −
5| Annular ring (µm)| 200| −| −
6| PCB Thickness (mm)| 0.8| 1.6| −

Manual Soldering

The recommended conditions for manual soldering are listed in Table 4. Considering the glass transition temperature (Tg) of the package mold resin and the thermal withstand capability of internal chips, the temperature of the terminal root part should be kept below 150°C. Iron tip should touch the lead terminal keeping certain distance from the package mold body. Manual soldering is not recommended for mass production as it may be difficult to control the amount of solder applied and the time and temperature of the soldering step.

Table 4. SPECIFICATIONS FOR MANUAL SOLDERING CONDITIONS

Parameter

| Single Side Circuit Board| Double/Multi − layer Circuit Board
---|---|---
Iron tip temperature| 385 ± 10°C| 420 ± 10°C
Soldering time| 2 – 6 seconds| 4 – 10 seconds

Wave Soldering

Assembles are placed on a carrier belt and run the soldering process to contact the wave solder. The wave soldering process typically uses a thermal profile which consists of four stages: solder fluxing, preheating zone, solder wave and cooling zone. Solder flux is either sprayed or foamed into the components. Then goes to the preheating zones, normally by convention, where the flux is activated. The assembly then goes to wave soldering and slowly cooled down. Key elements such as preheat ramp rate, conveyor speed, peak temperature and time forms a wave solder profile. Wave soldering profile should be optimized in the assembly site since it strongly depends on the equipment condition and the material type used in application. A typical soldering profile and conditions is illustrated in Figure 15 and recommended specifications are shown in Table 5 for different solder types.

Preheat: Preheat is required to avoid any possible thermal stress due to overheating. Preheat temperatures and the preheating time should be set according to the flux specification. Too high a temperature and too long a duration may break down the flux activation systems which can cause unintentional shorts. On the other hand, too low a preheat temperature setting may cause skips or unwanted residues left on the PCB. Ramp up rate between 1~4°C per second is suggested in the preheat zone.
Wave soldering: Dual−wave soldering is the most common method. The 1st wave which has turbulent wave crest ensures wetting of all the landing pads, allowing the molten solder to find its way to all joints on the PCB. The 2nd wave, which has a laminar flow, drains the excess solder from the board after the 1st wave thus removing the solder bridges. It is recommended that maximum soldering temperature up to 260°C for 10 sec is maintained to establish a good quality of the solder joint and to avoid package damage by thermal shock.
Cooling: Gradually cool the processed board down. A cool down rate between 1 − 5°C/s is recommended in general.

Table 5. RECOMMENDED WAVE SOLDERING CONDITIONS

Profile Feature| SnPb Eutectic Assembly| Pb − Free Assembly
---|---|---
Average ramp up rate| ~200°C/sec| ~200°C/sec
Preheat ramp up rate| Typical 1 − 2, max 4°C/sec| Typical 1 − 2, max 4°C/sec
Final preheat temp.| ~130°C| ~130°C
Peak wave soldering temperature| max 235°C, max 10 sec| max 260°C, max 10 sec
Ramp down rate| 5°C/sec max| 5°C/sec max

Solder Inspection

Monitoring the soldering quality is essential, since abnormal solder joints are potential risks for failures. IPC−A−610 (DE) standard specifies the soldering quality criteria for soft soldering. For the examination of a solder joint, visual or X−ray inspection and automatic optical inspection are suitable evaluation methods.
Figure 16 shows the recommended final position of a 4−layer PCB (1.6 mm) relative to the edge of the power module. The minimum recommended space from the edge of the module to the PCB surface is 10 mm spacing. Moving it closer will likely bend the control pins. Likewise, the maximum distance between the module edge and PCB surface should be 18.38 mm. It is generally recommended that the distance between the PCB and the module edge be kept as short as possible for optimal performance.

SYSTEM ASSEMBLY REQUIREMENTS

The VE−Trac Dual represents a new standard for packaging power modules for high power applications. It offers many possibilities for designing more compact power converters, but there are certain minimum requirements that must be met to ensure optimal performance.

Creepage and Clearance Requirements
The creepage and clearance distances are summarized in the Table 6 for the VE−Trac Dual package attached to the G3 reference cooler. The module offers basic isolation, pollution degree 2 and a Comparative Tracking Index (CTI) value > 600.

Table 6. CREEPAGE AND CLEARANCE

Table 6 summarizes the creepage and clearance distances between the various pins of the module and also between the G3 reference cooler and different module pins. Figure 17 illustrates the various distances noted in Table 6. However, the actual minimum requirements for creepage and clearance should be calculated based on the maximum operating voltage and the required specifications in the compliance standard. In some cases the spacing may not be enough to meet a certain standard and it may be necessary to achieve a higher level of creepage and clearance. This is a common issue when using screws and nuts to fasten the power terminals to external bus bars.

In order to increase the creepage and clearance between the cooler and the pins it is necessary to use an isolator. The issue is illustrated in Figure 18. The addition of the screw and nut has reduced the distance between the high potential power terminal and the grounded metal cooler.
There are several methods to overcome this clearance issue depending on your cooler design. However, one of the methods is discussed as an example. This method captures the nuts in a floating isolator as shown in the figure below.

DC Link, Current Sensor and Gate Driver Integration
Another critical design area that can also impact performance of the converter system is the mechanical integration of the DC link capacitor. The goal is to minimize the parasitic inductance between the power module and the bus capacitor. High parasitic inductance will impact the switching losses of the power modules. Again, there are multiple options for integrating a DC link and far less critical is the integration of the output current sensors. Two example methods are illustrated.
The first example is the Horizontal Integration Concept − It integrates the DC bus capacitor (from SBE) below the power stack (power modules + cooler). The DC link uses a laminated bus structure to connect the power terminals on the module to the bus capacitor as shown in Figure 20. It uses a 3−pak, off the shelf hall−effect current sensor from LEM (HAH3DR 900−S00) with copper AC bus bars. This concept positions the gate driver board over the power stack and cable harness to connect the driver output to a daughter board that is soldered on to the power module. This design primarily meant for evaluation and offers flexibility and ease in probing signals during evaluations. The front isometric view of the horizontal concept (Figure 21) shows how the phase current sensor is integrated with the power stack. It also shows how the module interface board is connected to the power module and then a cable is used to connect the interface board to the driver board on top of the power module cooler.

Another example (Figure 22) of the horizontal integration concept is the compact evaluation kit for the DSB variant that is available for purchase from onsemi. This design uses far lesser parts and a single PCBA.

The last example is the Vertical Integration Concept and it is suited for paralleling the VE−Trac Dual modules to develop high power converters. This concept orients the power modules vertically and allows the modules to be stacked in multiples of three to create a compact and scalable high power inverter. Figure 23 illustrates this concept in more detail with the parallel integration of 6 (2 modules per phase) VE−Trac Dual modules. It uses a single large PCB for driver and controller and the power stack is attached via screws to the PCB. The large DC bus capacitor from SBE is located behind the stack with DC link snubber capacitors attached very close to the paralleled power modules. In this example concept hall−effect current sensors from LEM (HAH1DRW 1100−S) are directly attached to the AC bus bars..

VISUAL MARKINGS

The product has a number of visual markings to enable traceability of the materials. It’s important to link the traceability from the chip to the inverter to maintain an effective traceability chain.

Traceability and Identification
The Figure 24 and Table 7 below together describe the all the visual indicators on the module and provide an explanation of the markers. All the 2D codes are 3.78 x 3.78 mm in size. Some of the modules include the temperature sensor calibration information in a 2D code. This data is used to remove temp sense offset error in the sensing circuit. The code includes the temp sense voltage reading for high side (HS) and low side (LS) switch in the half−bridge module. The temperature is coded in degree centigrade with a 10x multiplier (eg. 25.2°C is coded as 252). The temperature sensor reading is coded in mV. The bias current for the temp sensor can vary for different products within the family, so consult the specific product data sheet for the correct value.

Table 7. EXPLANATION OF MARKINGS

Temp1 x 10 + T−sense voltage HS + LS ; Temp2 x 10 + T−sense Voltage HS + LS Example: 25222342236;150211381318 25.2°C 2234 mV 2236 mV ; 150.2°C

1138 mV 1318 mV

2D Code 3| P/N + Last 3 digit of LOT number + Trace code (3.78 x 3.78 mm)
Site and Date Code| Assembly location (XX) and date code (YWW)
Lot Code| Last 3 digits of lot number
P/N Number Cont.| Remaining characters of product part number
P/N Number| First 7 Characters of product part number

Storage and Shipping
Transporting and storing the modules requires care to avoid extreme shock, vibration and environments. The recommended storage conditions for the module according to IEC 60721−3−1, class 1K2 should be followed and storage time should not exceed two years from manufactured date code. Below is a summary of the recommended storage parameters:

Table 8. STORAGE SPECIFICATIONS

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onsemi, , and other names, marks, and brands are registered and/or common law trademarks of Semiconductor Components Industries, LLC dba “onsemi” or its affiliates and/or subsidiaries in the United States and/or other countries. onsemi owns the rights to a number of patents, trademarks, copyrights, trade secrets, and other intellectual property. A listing of onsemi’s product/patent coverage may be accessed at www.onsemi.com/site/pdf/Patent−Marking.pdf. onsemi reserves the right to make changes at any time to any products or information herein, without notice. The information herein is provided “as−is” and onsemi makes no warranty, representation or guarantee regarding the accuracy of the information, product features, availability, functionality, or suitability of its products for any particular purpose, nor does onsemi assume any liability arising out of the application or use of any product or circuit, and specifically disclaims any and all liability, including without limitation special, consequential or incidental damages. Buyer is responsible for its products and applications using onsemi products, including compliance with all laws, regulations and safety requirements or standards, regardless of any support or applications information provided by onsemi. “Typical” parameters which may be provided in onsemi data sheets and/or specifications can and do vary in different applications and actual performance may vary over time. All operating parameters, including “Typicals” must be validated for each customer application by customer’s technical experts. onsemi does not convey any license under any of its intellectual property rights nor the rights of others. onsemi products are not designed, intended, or authorized for use as a critical component in life support systems or any FDA Class 3 medical devices or medical devices with a same or similar classification in a foreign jurisdiction or any devices intended for implantation in the human body. Should Buyer purchase or use onsemi products for any such unintended or unauthorized application, Buyer shall indemnify and hold onsemi and its officers, employees, subsidiaries, affiliates, and distributors harmless against all claims, costs, damages, and expenses, and reasonable attorney fees arising out of, directly or indirectly, any claim of personal injury or death associated with such unintended or unauthorized use, even if such claim alleges that onsemi was negligent regarding the design or manufacture of the part. onsemi is an Equal Opportunity/Affirmative Action Employer. This literature is subject to all applicable copyright laws and is not for resale in any manner.

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