In the context of electronics, particularly concerning a Printed Circuit Board (PCB), the chassis is typically the external structure or enclosure that houses the PCB and other electronic components. It's not part of the PCB itself, but rather the framework or casing that protects and supports the electronics assembly.
Understanding the Chassis
A chassis provides a physical structure for the electronic device. It can be made from various materials, including metal, plastic, or a combination. For many electronic devices containing PCBs, especially those dealing with power or requiring shielding, the chassis is often metallic.
- Purpose:
- Physical protection for the sensitive components on the PCB.
- Structural support for the overall device.
- Mounting points for PCBs, connectors, and other parts.
- Thermal management (metal chassis can help dissipate heat).
- Electromagnetic Interference (EMI) shielding.
Chassis Ground and PCBs
A crucial aspect related to a metallic chassis, and relevant to the PCB it contains, is the concept of chassis ground.
As defined in the reference:
"A chassis ground refers to a ground connection that connects all of the metal parts to the earth ground."
This means that if the chassis housing the PCB is metallic, it is often intentionally connected to the safety earth ground.
Why is Chassis Ground Important?
Connecting the metal chassis to earth ground serves several vital functions:
- Safety: If a live wire accidentally touches the metal chassis, the current will flow directly to earth ground through this low-resistance path, tripping a circuit breaker or blowing a fuse. This prevents the chassis from becoming energized, which could cause a severe electric shock to anyone touching it.
- Noise Reduction: Connecting the chassis to ground can help reduce electrical noise and interference within the system and prevent it from radiating outwards. The chassis can act as a shield.
- Reference Point: It provides a common reference point for the electrical signals on the PCB, though this is distinct from the signal ground or power ground on the board itself.
Examples from the Reference
The reference provides clear examples of chassis grounds:
- An oven's metallic enclosure safely grounded to the earth.
- A vehicle's metallic body.
In both cases, the metal structure enclosing the electronics or electrical systems is connected to a ground reference. Similarly, a PCB mounted inside a metal computer case, a stereo receiver, or industrial equipment would typically be within a chassis that is chassis grounded.
Relationship Between PCB and Chassis
The PCB holds the electronic circuits and components. The chassis is the container for the PCB. The PCB is physically mounted to or within the chassis using standoffs, screws, or other mounting hardware.
| Feature | PCB (Printed Circuit Board) | Chassis |
|---|---|---|
| Primary Role | Holds and connects electronic components | Houses, protects, and supports the electronics |
| Material | Fiberglass, epoxy resin (e.g., FR-4) | Metal, plastic, etc. |
| Function | Provides electrical connections | Provides physical structure, shielding, safety |
| Location | Inside the device enclosure | The device enclosure itself or its framework |
| Grounding | Has internal signal/power ground planes/traces | Often connected to earth ground (chassis ground) |
In summary, the chassis is the protective enclosure or frame surrounding a PCB assembly, often a metallic structure connected to earth ground for safety and performance, as described by the concept of chassis ground.
