CAD CAD Specialist Electrical and Electronics Design 2 — Questions and Answers
Question 1: What is the purpose of a 'Design Rule Check' (DRC) in PCB CAD software?
- Verifies component values match the schematic BOM
- Checks that physical layout constraints such as clearances and trace widths are satisfied (Correct answer)
- Confirms that all components have 3D models assigned
- Validates the BOM against live supplier databases
Correct answer: Checks that physical layout constraints such as clearances and trace widths are satisfied
A DRC automatically verifies that the PCB layout meets specified manufacturing and electrical constraints — such as minimum clearances, trace widths, and annular ring sizes — before fabrication.
Question 2: In PCB design, what is a 'via'?
- A copper pour limited to the top copper layer
- A plated hole that electrically connects copper traces on different PCB layers (Correct answer)
- A non-electrical component mounting hole
- A fiducial mark used for automated optical inspection
Correct answer: A plated hole that electrically connects copper traces on different PCB layers
A via is a plated-through (or blind/buried) hole whose barrel wall is copper-plated, creating an electrical connection between traces on different PCB layers.
Question 3: Why is 'controlled impedance' important in high-speed PCB design?
- It minimizes the total number of vias required
- It matches trace impedance to source and load impedance to preserve signal integrity (Correct answer)
- It reduces overall board dimensions
- It prevents copper delamination during solder reflow
Correct answer: It matches trace impedance to source and load impedance to preserve signal integrity
Controlled impedance ensures that trace characteristic impedance matches the source and load, preventing signal reflections, ringing, and degradation at high frequencies.
Question 4: What does a 'copper pour' (flood fill) accomplish on a PCB layer?
- Adds a solder mask coating over exposed copper
- Fills unused board areas with copper connected to a net — typically ground (Correct answer)
- Increases the board's dielectric constant
- Creates thermal relief patterns around component pads
Correct answer: Fills unused board areas with copper connected to a net — typically ground
A copper pour fills unused PCB real estate with copper tied to a specified net (usually ground) to lower impedance, improve EMI shielding, and assist heat dissipation.
Question 5: In Gerber-based PCB fabrication output, what information does the NC drill file contain?
- Artwork for all copper layers in Gerber RS-274X format
- X,Y coordinates and diameters of all holes to be drilled (Correct answer)
- Silkscreen legend artwork for component identifiers
- Board outline dimensions in mechanical CAD format
Correct answer: X,Y coordinates and diameters of all holes to be drilled
The NC drill file (Excellon format) contains the x,y coordinates and tool-size codes for every hole — vias and component through-holes — that the CNC drill must produce.
Question 6: What is the primary purpose of a 'keepout zone' in PCB layout?
- Restricts component placement, copper routing, or both within a defined area (Correct answer)
- Marks recommended locations for fiducial alignment marks
- Defines the board outline path for the router
- Specifies areas where silkscreen ink is not allowed
Correct answer: Restricts component placement, copper routing, or both within a defined area
A keepout zone enforces design restrictions — preventing copper traces, component placement, or both — within an area to satisfy mechanical clearance, RF isolation, or regulatory requirements.
Question 7: Which PCB layer prevents solder from adhering to areas between pads during reflow soldering?
- Silkscreen (legend) layer
- Solder paste stencil layer
- Solder mask layer (Correct answer)
- Copper ground plane layer
Correct answer: Solder mask layer
The solder mask is a polymer coating applied over the PCB surface that covers all copper except the exposed pads, preventing solder bridges between adjacent pads.
CAD CAD Specialist Electrical and Electronics Design 2
What is the purpose of a 'Design Rule Check' (DRC) in PCB CAD software?