Lithium battery pack in electric vehicle
Virtually all gasoline-powered automobiles utilize a 12V DC battery for electric power. All of the electrical and electronic systems in the vehicle are supplied by this source. Therefore, the variation in voltage level for electronics is limited. Electric vehicles, on the other hand, which typically use Lithium-Ion batteries, have a wide range of voltage operation. In most cases, this range is hundreds of volts. The range and potential high voltage required for electrical vehicle operation affect how your boards are made.
First, let’s take a look at the operational voltages for electric vehicles and then discuss how your PCBA development process can accommodate these electrical vehicle voltage levels.
Operational Voltages for Electric Vehicles
Although electric vehicles or EVs predate the invention of combustion engine vehicles, EVs, including hybrid EVs (HEVs) and plug-in HEVs (PHEVs), can be thought of as combustion engine automobiles where all non-electric operations have been converted to electric control. There are many advantages to this transformation. The most notable, of course, is the favorable ecological impact, as automobiles are a major contributor to global warming. Additionally, there is lessened noise pollution, the ability to recycle used electronics, and compatibility with our electric energy grid system.
Fortunately, the conversion of gasoline or diesel engine to electric vehicle design and development only affects a few major systems, as even combustion vehicles utilize electronics for monitoring, control, and accessories. The major EV systems and their corresponding voltage levels are as follows.
Electric Vehicle Voltage Levels and Major Systems
|200V-300V DC or 400V-800V DC||Internal Charging|
|48V DC||Battery Management System (BMS)|
The list above is not exhaustive in terms of the electronic systems that comprise an EV; however, it is representational of the major systems and the ranges of voltages for which electronics and circuit boards must be developed. One of the factors that can impact your PCBA design and development process is indeed the voltage level(s); therefore, your process should be able to accommodate each of the various electric vehicle voltage levels listed above.
How to Adapt PCBA Development for Various Electric Vehicle Voltage Levels
It is well-known that the best PCBA development is based on an open, symbiotic relationship with the builder of your boards. The effectiveness of this white box approach is directly proportional to the degree of integration of your design intent with your contract manufacturer’s (CM’s) DFM rules and guidelines. Equally important for automotive systems development is agility. Agility or the flexibility to quickly identify and adapt to a wide range of design and manufacturing specifications is also key for optimal EV system boards and electronics.
As shown in the previous section, EV systems have a range of voltages within which PCBAs may be required to operate and specific levels may be defined by the auto manufacturer and/or be model and/or year specific. Although the span of voltage levels that EV boards may need to be developed to operate at is hundreds of volts, there are guidelines that can be instituted to ensure your development process will incorporate the necessary considerations for the best board development for any system.
Essential Considerations for Targeted EV PCBA Development
- Perform thermal simulations
Knowing the thermal dissipation and distribution patterns for your board aid you in layout design and stackup choices. Dissipation can be determined from initial prototype testing, if available. However, for first designs, the best way to gather this information is by performing thermal simulation during design.
- Follow clearance and creepage standards
One of the biggest threats to your boards once deployed is high voltage arcing. In addition to testing to assess your board’s resistance to arcing, you should follow all applicable clearance and creepage standards.
- Include protection circuitry
In most cases, HV means high currents and high-voltage transients. This is most likely to be true for charging and BMS systems. Nevertheless, including protection circuitry (such as fuses, circuit breakers, and even redundancy) for lower voltage levels is also a good idea to protect board operation and components. For example, using fuses at the input followed by Reverse Schottky diodes can be used to guard against overcurrent and overvoltage.
- Effectively use chassis and other grounding techniques
Good grounding should be a focus of every design. For EVs, chassis grounding techniques come into play as vehicles are not attached to the grid. It is also important to use specific components. Using HV (1 kV or higher) rated capacitors in parallel with large resistors (e.g. 5-10 MΩ) around the mounting holes connecting “Chassis_GND” to “GND” is usually the standard practice.
- Design for electromagnetic compatibility
EV PCBAs or adjacent ones are likely to be emitters of radiation. Therefore, it is critical to balance the EM effects felt on nearby boards or achieve the best electromagnetic compatibility possible.
- Choose materials based on the thermal profile
For most applications, general FR4 is a good choice; however, it may not the best option if your board will be subjected to high temperatures that are a part of the automotive environment. Selecting the right material for your design may involve trade-offs. For example, you may opt to decrease board thickness from 62 mil to 31 mil to improve vertical thermal conductivity. This may preclude FR4 and necessitate more exotic dielectrics which in turn increases cost and possibly turn-around time.
- Optimize the usage of your CM’s tolerances
Target the process window centers of CM-specified PCB tolerances maximize your board’s construction and securing of components.
As safety is the overriding consideration for all automotive system development, it is imperative that you not only choose well; in terms of components, but also test and verify.
Designing, building, and testing (DBT) of PCBAs for EVs require that your process is flexible enough to cover a wide range of board types and specifications. The list above highlights guidelines that will go a long way in ensuring that your development process meets the safety, high quality, and reliability standards that EV deployment demands. And your CM is a major contributor. At Tempo Automation, the industry leader in fast, high-quality PBCA manufacturing for prototypes and low-volume production, we will work closely and transparently with you to make sure your boards reflect your design intent and meet our equipment capabilities.
And to help you get started on the best path, we furnish information for your DFM checks and enable you to easily view and download DRC files. If you’re an Altium user, you can simply add these files to your PCB design software.
|Tempo's Custom AV & EV Automotive PCBA Manufacturing Service