ON Semiconductor AND9984 Assembly Guide

VE-Tract Dual Assembly Guide

AND9984

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.

Table 1.

NVG800A75L4DSC 750 V, 800 A, T2, HPS

NVG400A120L2SDSC 1200 V, 400 A, T2, HPS

Figure 1.

INTRODUCTION

In order to avoid unnecessary mechanical stress on the VE−Trac 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.

module, its control leads or the power terminals, it

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APPLICATION NOTE

Since the product is only the power module, it should be noted that this guide will use an example cooler design and Printed Circuit Board (PCB) to explain the assembly process. The user has the freedom to design their own coolers and PCBs 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 1 cooler

3. Apply TIM to the other side of the power module

4. Align 2 cooler

5. Secure 1 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.

half of the cooler to the 1st half of the

and 2nd halves of the cooler with the

half of the

Figure 2. VE−Trac Dual Power Module Showing

the Top and Bottom View

March, 2021 − Rev. 2

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 j 50 mm.

• Mating alignment feature must be included on the cooler

(see Figure 4).

1 Publication Order Number:

AND9984/D

AND9984

Table 2. SPECIFICATIONS FOR THE COOLER

Max. Cooler

Roughness Rz [mm]

Clamping Area

RED + BLUE AREA 10 50 10 760 7

BLUE AREA 10 50 10 760 5.4

per ISO 4287

Min. Cooler Flatness

[per 100 mm]

per ISO 1101

Max. Step [mm]

per ISO 4287

Minimum

Clamping

Force [N]

Maximum Clamping

Force [kN]

Figure 3. The Area Shown in Red is Where the Clamping Force Should Be Applied to Ensure Good Contact

In Figure 3 the cross sectional area where the clamping force should be applied is shown in red and blue. It’s important not to apply force on the DBC only (blue area), since it can crack the DBC and damage the module. You can also get cracked DBC if the specifications of the heatsink flatness is not met. The blue area shown in Figure 3 is the

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 shows the dimensions and spacing to be included for the alignment features.

area that should be actively cooled to ensure optimal thermal performance.

Figure 4. Alignment Feature to Be Included on the Bottom Half of the Cooler

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AND9984

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.

Figure 5. Different Acceptable Criteria of the Module DBC

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

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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 and flow rates. Reference design shown in Figure 6 should be considered as an example.

AND9984

Figure 6. Example Cooler for Use with the VE−Trac Dual

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

Rth,j−f vs. Flow rate, TF = 655C, 50/50 EGW

0,260

0,240

0,220

0,200

0,180

0,160

Rth,j−f (K/W)

0,140

0,120

0,100

02468101214

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.

FWD

IGBT

16 18

Flow Rate (LPM)

Figure 7. Thermal Performance Rth.j−f for IGBT and Diode at Coolant Temperature of 655C

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AND9984

Pressure Drop (mBar) vs. Flowrate (LPM)

Pressure Drop (mBar)

0.0 2.0 4.0 6.0

Flowrate (LPM)

Figure 8. Pressure Drop versus Flow Rate for the Reference Heatsink Coolant @ 655C

8.0 10.0 12.0

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 mm thickness. This material has been tested with the product and used in all thermal measurements shown on the product data sheet.

Table 3. CRITICAL PROPERTIES OF THE RECOMMENDED THERMAL INTERFACE MATERIAL (TIM)

Physical Properties

Thermal Conductivity W/m·K 6.5

Thermal Impedance @ No Shim °C.cm2/W 0.06

Specific Gravity g/cm

Volume Resistivity

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.

Unit Honeywell PTM7000

W·cm

2.7

2.1x10

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.

Figure 9. Recommended Size and Location of the TIM Pads for Bottom (left) and Top (right) Side

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

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material will have to be characterized to determine its performance and optimal method of use in assembly.

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