PCB Design 4

Question 1

What is the recommended placement strategy for bypass (decoupling) capacitors?

Accepted Answer

Place them as close as possible to the power pins of the IC they are decoupling

Answer

Decoupling capacitors must be placed as close as possible to the IC power pins to minimize the inductance of the loop between the capacitor and the IC, providing effective high-frequency filtering.

Question 2

What is 'impedance matching' and why is it important for high-speed PCB traces?

Accepted Answer

Designing the trace characteristic impedance to match the source and load impedance to prevent signal reflections

Answer

Impedance matching ensures the trace, source, and load all have the same characteristic impedance (e.g., 50Ω), preventing signal reflections that cause distortion and data errors.

Question 3

What is the purpose of 'thermal relief' connections to SMD pads on a copper pour?

Accepted Answer

To reduce the thermal mass at the pad, making soldering easier by preventing the pour from acting as a heat sink

Answer

Thermal relief connects a pad to the copper pour through narrow spokes, reducing the thermal conductivity to the pour so the soldering iron can heat the pad to soldering temperature without the pour draining heat away.

Question 4

What is a 'ground plane split' and when should it be used with caution?

Accepted Answer

Dividing the ground plane into separate sections (e.g., analog and digital GND) to isolate noise domains

Answer

A split ground plane separates analog and digital ground sections to prevent digital switching noise from coupling into sensitive analog circuitry, but must be implemented carefully to avoid return current discontinuities.

Question 5

What does 'BGA fanout' refer to in PCB design?

Accepted Answer

The routing strategy of connecting BGA ball pads to the rest of the circuit using escape vias and traces

Answer

BGA fanout is the process of routing escape traces from the dense BGA ball grid pads outward using vias (often microvias) to access inner rows of pads and connect to the rest of the PCB.

PCB - Design Practice Test

PCB - Design Practice Test

PCB Design 4