onsemi SiC E1B Modules User Guide
Scope
onsemi has pioneered the introduction of SiC JFETs in a cascode configuration with gate drive compatibility to Si MOSFETs, IGBTs, and SiC MOSFETs, based on the 5 V threshold voltage and wide gate operating range of ±25 V.
These devices are inherently very fast switching, with excellent body diode characteristics. onsemi has combined the advantageous SiC JFET based power device with an industry standard power module package, E1B, to further enhance power density, efficiency, cost-effectiveness, and ease of use for industrial power systems.
This application note introduces mounting guideline (PCB and heatsink) for onsemi’s latest E1B power module packages (half-bridge and full bridge).
IMPORTANT: Snubbers are strongly recommended for SiC E1B modules due to their intrinsic fast-switching speed. Also, snubber greatly reduces turn-off switching loss making SiC E1B modules extremely attractive in ZVS (zero voltage turn-on) soft-switching applications such as phase-shifted full-bridge (PSFB), LLC, etc.
This product is recommended for use with solder pin attach and phase change thermal interface materials, and not recommended for implementations using press fit and application of thermal grease. Please refer to mounting guidelines and user guide documents associated with this product for detailed information.
This application note also provides resource links to simulation models, assembly guidelines, thermal characteristics, reliability, and qualification documents.
Resource and Reference
- SiC E1B Modules Technical Overview
- SiC E1B Modules Mounting Guideline
- SiC Cascode JFET & Module User Guide
- SiC E1B Modules DPT EVB User Guide
- onsemi SiC Module Link: SiC Modules
- EliteSiC Power Simulator
- onsemi SiC power solution central hub
- Origins of SiC JFETs and Their Evolution Towards the Perfect Switch
E1B Module Information
The primary cause of power semiconductor module failure is improper mounting. Poor mounting will result in elevated or excessive junction temperature, which will significantly limit the module’s operational lifetime. As a result, proper module installation is critical to achieving reliable heat transfer from SiC device junction to the cooling channel.
The E1B modules are designed to be soldered to a printed circuit board (PCB) and attached to a heat sink with pre-assembled screws and washers, as shown in Figure 1 and Figure 2. More extensive information on dimensions and tolerances for designing hardware for these systems can be found in the module datasheets.
Figure 1. Module Mounting Screw Location (Top View)
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Figure 2. Module Mounting with PCB and Heatsink (Assembly Exploded View)
Recommended Mounting Sequence
onsemi recommends following mounting sequence for better thermal performance and lifetime of SiC E1B module:
- Solder the module pin to the Printed Circuit Board (PCB)
- Mount the PCB onto the module
- Mount the module to the heat sink
With pre-assembled screw (combine screw, washer, and lock washer), fasten the module onto the heat sink using limiting torque. It should be noted that the size and surface of the heatsink must be considered throughout the soldering process, as proper heat transfer between the module backside and the heatsink interface is critical to the overall performance of a package in a system (see Figure 2).
- Solder the Module Pin to PCB
The Solderable pins used on the E1B module have been checked and qualified by onsemi for standard FR4 PCBs.
If the PCB requires a reflow soldering process for other components, it is recommended to reflow the PCB before mounting the module to avoid exposure to high temperatures.
A typical wave soldering profile is shown in Figure 4 and Table 1.
If other handling techniques are used in the manufacture of printed circuit boards, additional testing, inspection, and certification is required.
PCB Requirement
FR4 PCB with a maximum thickness of 2 mm.
Refer to IEC 61249−2−7:2002 to check if PCB material meets the standard requirements.
User to determine the optimum conductive layers for proper design of PCB stack layers but need to ensure multi layer PCBs follows IEC 60249-2-11 or IEC 60249-2-1
If the customer will consider a double−sided PCBs refer to IEC 60249-2-4 or IEC 60249-2-5
Solder Pin Requirement
Key factors for achieving solder joints with high reliability is the PCB design.
The plated-through hole diameters on the PCB must be manufactured according to the soldering pin dimension (see Figure 3).
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If the PCB hole design is not correct, potential problems can occur.
If the final hole diameter is too small, it may not be properly inserted and will cause the pins to break and damage the PCB.
If the final hole diameter is too large, it may not result in good mechanical and electrical performance after soldering. Solder quality should refer to IPC-A-610.
The recommended parameters for wave soldering process temperature profiles are based on IPC-7530, IPC-9502, IEC 61760-1:2006.
Figure 3. Module Mounting to PCB Prior Mounting to a Heat Sink
Figure 4. Typical Wave Soldering Profile (Reference EN EN 61760-1:2006)
Table 1. TYPICAL WAVE SOLDERING PROFILE (Reference EN EN 61760-1:2006)
| Profile Feature | Standard SnPb Solder | Lead (Pb) Free Solder | |
| Preheat | Temperature min. (Tsmin) | 100 °C | 100 °C |
| Temperature typ. (Tstyp) | 120 °C | 120 °C | |
| Temperature max. (Tsmax) | 130 °C | 130 °C | |
| Temperature max. (Tsmax) | 70 seconds | 70 seconds | |
| Δ Preheat to max. Temperature | 150 °C max. | 150 °C max. | |
| D Preheat to max. Temperature | 235 °C − 260 °C | 250 °C − 260 °C | |
| Time at Peak Temperature (tp) | 10 seconds max5 seconds max each wave | 10 seconds max5 seconds max each wave | |
| Ramp-down Rate | ~ 2 K/s min ~ 3.5 K/s typ ~5 K/s max | ~ 2 K/s min ~ 3.5 K/s typ ~5 K/s max | |
| Time 25 °C to 25 °C | 4 minutes | 4 minutes | |
Mounting PCB onto Module
When the PCB is soldered directly on the top of the module, the mechanical stresses are present especially on the solder joint. To reduce these stresses, an additional screw can be utilized to fix the PCB into the four standoffs of the module, see Figure 5.
The modules are compatible with the self-tapping screws (M2.5 x L (mm)), depending on PCB thickness.
The length of the thread entering the standoff hole should have a minimum of Lmin 4 mm and a maximum of Lmax 8 mm. It is recommended to use an electronically controlled screwdriver or electric screwdriver to ensure better accuracy.
Figure 5. PCB Mounting on E1B Module: (a) E1B PCB Mounting Hole with Standoff, and (b) Maximum Screw Thread Engagement Depth
PCB Mounting Requirement
The standoff holes depth of 1.5 mm serves as a screw entry guide only and should not apply any force.
Key factor is the amount of torque allowed for the pre-tightening and tightening process:
- Pre-tightening = 0.2 ~ 0.3 N.m
- Tightening = 0.5 N.m Max
Figure 6. PCB Mounting on E1B Module: Vertical Alignment of Self-tapping Screw (a) Aligned, and (b) Misaligned.
Mounting Module to Heatsink
Heatsink Requirement
The surface condition of heatsink is a vital factor on the entire heat transfer system and must be in full contact with the heatsink. The module substrate surface and the heat sink surface must be uniform, clean, and free of contamination before mounting. This is to prevent voids, to minimize the thermal impedance and maximize the amount of power that can be dissipated within the module and attain the target thermal resistance based on datasheet. The heatsink’s surface qualities are required to attain a good thermal conductivity as per DIN 4768−1.
- Roughness (Rz): ≤10 m
- Flatness of the heatsink based on a length of 100 mm: ≤50 m
Thermal Interface Material (TIM)
Thermal interface material used between module case and heatsink is key to achieve reliable and high-quality thermal performance. Thermal grease or thermal paste is not recommended for a baseplate-less module like E1B.
Without a thick copper baseplate serving as a heat spreader, the thermal grease pump−out effect (by thermal expansion and contraction of TIM layer between module case and heatsink during power cycling or temperature cycling) exacerbates void formation in the TIM layer and has significant negative impact on power cycling lifetime of the module.
Instead, TIM using phase change material is strongly recommended for E1B modules. Figure 7 shows the power cycling results for the 1200 V 100 A half-bridge module (UHB100SC12E1BC3N) using two different methods, thermal grease vs phase change material. The horizontal axis shows the number of cycles. The vertical axis shows device VDS during Tj_rise at 100 °C. The red curve shows power cycling with thermal grease. The blue curve shows power cycling with phase change material. The red curve can only go to 12,000 cycles before thermal runaway happened due to thermal resistance degradation from thermal grease pump-out effect. For the same E1B module using phase change material for heatsink TIM significantly improves power cycling beyond 58,000 cycles.
Figure 8 shows power cycling test conditions and setup Figure 7. E1B Module Power Cycling Performance with Different TIM for Heatsink: Thermal Grease vs Phase Change Material
Figure 8. E1B Module Power Cycling Test (a) Setup, and (b) Test Conditions
| Setup | Description |
| DUT | UHB100SC12E1BC3N |
| Heating method | Constant DC current |
| Tj rise | 100 °C |
| Water cool heat sink temp | 20 °C |
| Heating time per cycle | 5 s |
| Cooling time per cycle | 26 s |
| TIM (phase change) | Laird TPCM 7200 |
Typically, after mechanical mounting, phase change material should be baked in oven to allow TIM to change its phase to further fill microscopic voids between module case and heatsink and reduce thermal resistance from module case to heatsink. In the above example shown in Figure 7 and Figure 8, thermal resistance from device junction to water is reduced from 0.52 °C/W to 0.42 °C/W after 1 hour baking at 65 °C. Please consult TIM supplier for detailed instructions.
NOTE: Any different phase change material type should be evaluated and tested additionally by the customer by following instructions from a TIM (phase change material) vendor to ensure optimal performance
Mounting Module to Heatsink
The mounting procedure is also an important factor to guarantee an effective contact of module and heatsink with phase change material in between. Note that heatsink and the module should not touch across the entire area to avoid a localized separation between the two components. Table 2 summaries mounting guidelines for heatsink attachment.
Table 2. onsemi SiC E1B MODULE HEATSINK MOUNTING RECOMMENDATIONS
| Heatsink Mounting | Description |
| Screw size | M4 |
| Screw type | DIN 7984 (ISO 14580) flat socket head |
| Depth of screw in heatsink | > 6 mm |
| Spring lock washer | DIN 128 |
| Flat washer | DIN 433 (ISO 7092) |
| Mounting torque | 0.8 N.m to 1.2 N.m |
| TIM | Please change material, such as Laird Tpcm |
Other Mounting Considerations
The overall system of the mounted module should be considered. If the module is properly attached to the heat sink and circuit board, the overall performance of the product will be achieved.
Appropriate measures must be taken to minimize vibration too since the PCB is soldered only to the module.
Weak soldered terminals must be avoided. Individual pins can only be loaded perpendicular to the heat sink with maximum pressure, tension, and adequate distance between the PCB and heatsink needs to be evaluated by the customer’s application.
To minimize the mechanical stress on the PCB and module, specially when the PCB has heavy component it is recommended to use space post, see Figure 9.
Figure 9. E1B Module PCB and Heatsink Mounting with Space Post
The recommended dimension (X) between the space post and edge of the PCB mounting hole is ≤ 50 mm.
In case multiple modules are mounted on the same PCB, the height variation between modules can result in mechanical stresses on the solder joint. To minimize stress, the recommended height (H) of the space posts is 12.10 (±0.10) mm.
Clearance and Creepage Requirement
The mechanical spacing of the assembly between the module and PCB must meet the clearance and creepage distance required by IEC 60664-1 Revision 3. Figure 10 shows the illustration.
The minimum clearance is the distance between the screw head and the bottom surface of the PCB must have adequate distance to prevent electrical conductivity in this area.
Alternatively, additional insulation measures, such as PCB slot, coating or special potting may need to be implemented to meet appropriate clearance and creepage distance standards.
Figure 10. Clearance between Screw and PCB
The screw type determines the minimum clearance gap between it and the PCB. With a pan head screw in accordance with ISO7045, a lock washer in accordance with DIN 127B and flat washer DIN 125A, and the clamp that is shown in Figure 10, the distance will be 4.25 mm. Typical clearance and creepage is available in the datasheet. Further details on module clearance or creepage distance may contact the application support or sales and marketing.
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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.
ADDITIONAL INFORMATION
TECHNICAL PUBLICATIONS:
Technical Library: www.onsemi.com/design/resources/technical−documentation
onsemi Website: www.onsemi.com
ONLINE SUPPORT: www.onsemi.com/support
For additional information, please contact your local Sales Representative at www.onsemi.com/support/sales
Documents / Resources
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onsemi SiC E1B Modules [pdf] User Guide AND90340-D, SiC E1B Modules, SiC E1B, Modules |