Automotive PCB Design

In the current automotive landscape, digitization has taken precedence, with an array of electronic features incorporated into vehicles, ranging from driver assistance systems to safety and convenience enhancements like backup cameras. This shift has resulted in numerous advantages, as it transfers a considerable portion of operational and safety responsibilities from drivers to the automotive systems themselves. These technologies heavily rely on circuit boards that facilitate monitoring, control, and drive for the mechanical systems, enabling various automotive functionalities. For this reason, adhering to essential automotive PCB design guidelines is crucial to meet the intelligent operational requirements of these advanced automotive systems.

There’s a variety of aspects that go into automotive PCB design, from thermal to layout to safety considerations.

Essential Automotive PCB Design Standards

For automotive PCBs, designing for safety is paramount. As such, numerous automotive standards focus on the components and materials utilized, the quality of design and manufacturing, and the testing requirements for AV electronics boards and devices. It is absolutely essential for all stakeholders involved to be well-informed about these standards and diligently adhere to them to ensure the highest level of safety and reliability in autonomous vehicle technology. Below are some essential standards to be aware of.

Automotive PCB Design Standards and Regulations

IPC-6012D Section	IPC-6012DA Description	Fabrication/Assembly Step(s)
3.3	Introduces inspection procedures for uncovering defects in the printed circuit boards (PCBs)	Visual/Automated Optical Inspection (AOI)
3.3.4	Specifies tolerances for lifted lands, pad, and plated through-hole (PTH) separation	Hole drilling, plating
3.4.1	Establishes tolerances for drill hole sizes in the PCBs	Hole drilling, plating
3.4.3	Specifies limitations on bow and flex in the PCBs	Solder reflow
3.5	Defines quality standards for conductors in the PCBs and guides the inspection process	PCB Stackup, AOI
3.5.4.2.1	Details land quality standards and tolerance for defects in the PCBs	Etching, visual/AOI
3.6.2.1	Specifies quality standards for plated through-holes (PTHs) in the PCBs	Hole drilling, soldering
3.7.3	Provides guidelines for solder mask thicknesses in the PCBs	Solder masking
3.9	Outlines cleanliness quality control measures for fabrication and assembly of PCBs	Fabrication and assembly quality control, finishing, Resistivity of Solvent Extract (ROSE) testing is required
3.9.1	Specifies requirements for board cleanliness prior to solder masking	Fabrication quality control, and ionic testing is recommended
3.9.2	Directs the implementation of cleanliness testing after solder masking, soldering, and finishing	Fabrication and assembly quality control, solder masking, soldering, finishing

IPC-6012DA Design Tips for Board Fabrication

IPC standards encompass specifications and guidelines applicable to circuit boards across diverse industries. One of the most important standards, the IPC-6012DA addendum to IPC-6012D, focuses on “ensuring the reliability of printed boards that must withstand the demanding vibration and thermal cycling environments of electronic interconnects within the automotive industry.” By adhering to these standards, engineers can gain assurance in their designs. Furthermore, contract manufacturers (CM) employ the manufacturing processes to ensure that the electronics and PCBs produced can reliably operate in the distinct and challenging automotive environment.

IPC-6012D Standards for Automotive vehicle design

Regulation	Description	Key Area of Application	Governing Organization
AEC-Q100	Establishes failure test qualifications for integrated circuits	Ensuring reliability of integrated circuits	Automotive Electronics Council (AEC)
AEC-Q101	Sets failure test qualifications for discrete semiconductors	Ensuring reliability of discrete semiconductors	Automotive Electronics Council (AEC)
AEC-Q102	Defines failure test qualifications for discrete optoelectronic semiconductors	Ensuring reliability of optoelectronic semiconductors	Automotive Electronics Council (AEC)
AEC-Q104	Specifies failure test qualifications for multichip modules	Ensuring reliability of multichip modules	Automotive Electronics Council (AEC)
AEC-Q200	Outlines failure test qualifications for passive components	Ensuring reliability of passive components	Automotive Electronics Council (AEC)
IATF 16949	Sets guidelines and requirements for quality management systems (QMS) in the automotive industry	Ensuring high-quality product design and development	International Automotive Task Force (IATF)
IPC-6011	Establishes generic performance specifications for PCBs	Ensuring standardization in PCB design and manufacturing	IPC – Association Connecting Electronics Industries
IPC-6012DA	Defines tolerances and test procedures for rigid PCBs used in automotive systems	Ensuring reliability of rigid PCBs in automotive applications	IPC – Association Connecting Electronics Industries
IPC-6013D	Specifies performance specifications for flex and rigid-flex PCBs	Ensuring reliability of flex and rigid-flex PCBs	IPC – Association Connecting Electronics Industries
SAE J3016_201401	Classifies automated driving systems	Classifying vehicle types for automation	Society of Automotive Engineers (SAE)

Below are some of the IPC-6012 design tips for board fabrication:

Perform preconditioning before assessing the board for bow and twist, following IPC-TM-650 guidelines. This preconditioning is conducted after the soldering process to identify cracks, open circuits, and short circuits.
Verify that the drill holes meet the size and quality requirements specified in IPC-6012DA and align with the aspect ratios supported by your contract manufacturer's (CM) equipment.
Maintain hole position accuracy within the allowed tolerance of 100 microns.
Specify via holes with a minimum drill size to achieve a sufficient aspect ratio.
Ensure that the hole wall separation does not exceed 40% of the dielectric thickness.

Ensure that the solder mask specifications comply with the tolerances specified in IPC-6012DA.
Prioritize cleanliness before applying the solder mask, with a contamination level up to 0.75 g/cm2 of sodium chloride equivalent.
Maintain a minimum drill hole size to achieve a good aspect ratio.
Inspect solder mask parameters to ensure compliance with IPC-6012DA requirements.
Make sure that the land and spacing specifications in your design adhere to the tolerances outlined in IPC-6012DA.

High Voltage Considerations

As we’ve mentioned, safety is of utmost importance when designing automotive systems, especially when designing EVs. One of the key factors to address is the presence of high voltages and currents. Vehicle system operations involve the use of high voltage, high current, or both for a variety of different electronic control units (ECUs). This necessitates the use of circuit boards that can efficiently handle, process, convert, and distribute electrical parameters at multiple levels. However, it is essential to be cautious, as high-voltage boards in automotive applications can be prone to surface tracking issues caused by arcing. Similarly, high current boards may face problems due to creeping and clearance distances not meeting standard requirements.

Automotive PCB Component Placement Design Tips

Component orientation and placement play a crucial role in determining a board’s reliability, manufacturability, and overall performance. To optimize the assembly process, consider the following approaches when placing components:

Group similar components in the same direction, which facilitates efficient routing and soldering operations during assembly.
For wave soldering, ensure that components are oriented parallel to the direction of the wave to prevent solder bridging and open circuits.
Provide ample space between inductors on the board and align them at right angles to minimize crosstalk.
Prioritize placing larger and more significant components first to streamline the assembly process.

Separate analog and digital components into different sections of the board to avoid interference between the two.
Segregate component placement based on specific design requirements and functionalities.
Avoid positioning tall components, such as electrolytic capacitors, adjacent to shorter ones to prevent the risk of loose solder junctions.
Optimize heat dissipation on the board by keeping high-power components as far away as possible from other components, ensuring efficient cooling.

Lead Placement

Proper lead placement is also crucial to prevent undesirable magnetic coupling and the potential generation of mutual inductance. To ensure effective lead placement, consider the following points.

Avoid positioning leads in close proximity to each other to minimize any undesired coupling effects.
Select a return current path near the main current path, preferably in an area with minimal radiation, to reduce the current loop area.
Implement a comprehensive grounding strategy beneath the leads, as this can significantly improve the board's overall performance.

Thermal Management for Automotive PCB Design

Another critical aspect that demands attention is the thermal profile. In both high voltage and high current boards, there is a reliance on high-power components that generate significant amounts of heat. Furthermore the high voltage and current conditions may cause hot spots to arise on the board. Thus, effective management of thermal resistance becomes crucial in automotive designs to ensure the safety and reliability of the system.

To effectively manage heat dissipation for components absorbing more than 10 mW or conducting over 10 mA, employ the following techniques for improved temperature control:

Techniques for improved temperature control in automotive PCBs

Implement heatsinks for high-power components to efficiently dissipate excess heat.
Enhance thermal conductivity by selecting copper planes and signal vias as thermal vias.
Opt for metal core or polyimide material for the board, as they offer improved thermal characteristics.
Utilize metal thermal pads beneath hot areas on the board.

Separate analog and digital components into different sections of the board to avoid interference between the two.
Prefer high Tg (glass transition temperature) boards, as the operating environment tends to raise the PCB temperature frequently.
Incorporate solid-filled vias to transfer heat from thermal pads to ground planes.
Employ multiple ground and power planes and establish direct coupling to heat sources through thermal vias to reduce operating temperatures.

Grounding Tips for Automotive PCBs

Implementing proper grounding rules is also crucial when designing automotive systems. To ensure effective grounding, all internal grounds should connect to a single point. Each PCBA (Printed Circuit Board Assembly) must have a single ground connection, and in the case of multiple boards, all ground connections should converge to a single point. For larger electronic systems, it is advisable to establish a single ground connection for each internal system, where all internal board grounds meet.

When implementing grounding techniques in your automotive design, consider the following guidelines:

Grounding techniques for automotive PCB design

Chassis Grounding

Since vehicles do not have direct contact with earth ground, it becomes essential to utilize chassis grounding techniques. This involves bonding all internal metallic elements of the system to a common point. For metallic enclosures, the enclosure itself can serve as this point. However, for other electronics systems like those with plastic enclosures, a chassis ground may not be present.

When it comes to chassis grounding, there should be only one connection from the chassis ground to the electronic system(s) that it serves as the safety ground for. Whether using the enclosure or mains neutral as the chassis ground, having a single connection enhances safety and reliability.

Preventing EMI Through Grounding

Proper grounding techniques are also essential to prevent electromagnetic interference in your automotive PCB design. Below are some recommendations to ensure effective grounding:

Establish a single-point ground connection for each automotive board to centralize and optimize the grounding system.
Create a continuous grounding region with extremely low impedance to minimize the risk of signal interference and enhance overall circuit performance.
Use a thru-hole array to connect the ground to the filling wire terminals, ensuring reliable and efficient grounding throughout the design.
Always connect copper-coated cables to the ground to maintain a robust and stable grounding network, further mitigating the potential for electromagnetic interference.

RF Guidelines for Radiating PCBs

For automotive PCBs that require a receiver, transmitter, or other wireless capabilities, it is crucial to address challenges with radiating and wireless components. Incorporate the following tips into your design.

Employ extremely linear active or front-end devices to ensure high-performance signal processing.
Pay careful attention to the efficiency of the radio frequency front end, considering current usage and power dissipation for better energy management.
Select a high-performance RF filter that effectively reduces insertion loss, temperature drift, and interferences, ensuring enhanced signal quality.
Utilize components that integrate transmit, receive, and filtering capabilities into a single unit, streamlining the design and optimizing space utilization for improved overall performance.

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