Designing an aerospace PCB demands precision and adherence to specific DFA rules. This guide outlines 5 important design for assembly practices, focusing on component placement, clearance requirements, and thermal considerations.
By integrating these tips into your design, you can create reliable boards that meet strict aerospace standards and simplify the assembly process.
1. Do not place components on the opposite side of a BGA
BGAs are sensitive and require special attention during PCB design. Avoid placing components on the opposite side of a BGA and ensure clearance of at least 2-4 mm from BGAs to other components.
This reduces thermal stress during rework, ensures uniform heat distribution, and provides easy access to the BGA during repairs.
2. Provide at least 20 mil of component courtyard clearance for BGAs
Courtyard clearance is the additional spacing around components to prevent collisions with adjacent parts during assembly. This clearance is important for automated assembly machines to operate without obstruction.
Sensitive devices, like BGAs, should have a courtyard clearance of 20 mil to accommodate their specific manufacturing requirements.
Non-sensitive components such as resistors can have 10 mil of courtyard clearance to avoid interference during the assembly process.
3. Place components 50 to 75 mil away from the board edge
Components should be placed 50 to 75 mil away from the board edges. When components are placed too close to the board edge, it can lead to mechanical damage or misalignment during depanelization.
4. Maintain a minimum clearance of 4 mm between SMT connectors and PTHs
To avoid interference and potential electrical short, maintain a minimum distance of 4 mm between SMT connectors and plated-through holes.
A 4 mm clearance ensures solder masks and traces are not compromised during assembly and prevents mechanical strain during reflow soldering. This spacing allows technicians to access the connectors and plated-through holes without damaging adjacent parts.
5. Use a minimum of 4 spokes around thermal relief pads
Thermal relief pads play a crucial role in balancing heat distribution during soldering. The 4-spoke configuration ensures even heat flows, reducing thermal stress on the pad and component.
Proper spoke width ensures mechanical stability while maintaining effective thermal performance. Each spoke should have a width equal to 1/3 to 1/2 of the pad diameter.
Implementing these 5 design for assembly principles is critical for robust aerospace PCBAs. From ensuring proper component spacing to managing thermal dynamics, each guideline plays a significant role in enhancing the PCB’s functionality, reliability, and ease of assembly.
By following these best practices, you can reduce errors, simplify assembly, and achieve a high-quality end product that meets the demands of modern aerospace applications.