Printed Circuit Boards
Description and use of printed circuit boards, substrate, tracks, pads and vias; single, double and multilayer construction; through-hole and surface-mount components; conformal coating and ESD precautions.
Printed circuit boards, summary notes
- A printed circuit board is an insulating substrate carrying etched copper tracks that replace point-to-point wiring.
- Features: tracks (conductors), pads (component connection points), and vias (plated holes linking layers).
- Boards may be single-sided, double-sided or multilayer.
- Components are fitted either through-hole (THT), with leads passing through the board, or surface-mount (SMD), soldered directly to pads on the surface.
- Conformal coating protects against moisture, dust and vibration.
- ESD (electrostatic discharge) precautions are essential when handling boards, wrist straps, grounded mats and antistatic bags.
- ⚠ Exam trap: this is a Level 1 topic, recognition and purpose are examined, not detailed manufacturing processes.
Why must ESD precautions be observed when handling an avionics circuit board?
A static discharge far below the level a person can feel can puncture the thin oxide layers inside semiconductor devices, causing immediate failure or latent damage that shows up later in service.
PCB concept map
Printed Circuit Boards
Printed circuit boards quiz
Printed Circuit Boards, quiz
1. A multilayer PCB is used to:
Route more connections in a smaller areaIncrease the board weightReplace the need for components2. Conformal coating is applied to a PCB to:
Protect it from moisture and contaminationImprove its appearance onlyIncrease conductivity3. Surface-mount components are:
Soldered directly onto pads on the board surfaceFitted through holes and soldered on the far sideGlued without solder4. When handling a PCB containing MOS devices, the technician must:
Observe electrostatic-sensitive device (ESD) precautionsWarm the board first, so that any condensation is driven off before the devices are handledAvoid wearing gloves of any kind, since they insulate the hands and prevent charge draining away5. A plated hole that connects tracks on different layers of a PCB is called a:
ViaPadTrack6. Components soldered directly onto pads without leads passing through the board are:
Surface-mount (SMD)Through-hole (THT)Chassis-mounted7. ESD precautions are necessary when handling circuit boards because:
Static discharge can damage semiconductor devicesThe board may be hotThe copper corrodes quickly8. The base material of a printed circuit board is:
An insulating substrateA conducting sheetA magnetic core9. Which item on a PCB is used to attach a component's lead?
PadViaSubstrate10. A PCB with conductors on more than two levels is described as:
MultilayerDouble-sidedSingle-sided11. Appropriate storage for an unfitted avionics circuit board is:
An antistatic bagA sealed plastic food bagLoose in a metal toolbox