Board outline and dimensions in PCB Design - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of the board outline in PCB design?

The board outline defines the physical shape and size of the PCB. It shows where the edges of the board will be cut, helping manufacturers know the exact dimensions.

beginner

Which units are commonly used to specify PCB board dimensions?

PCB dimensions are commonly specified in millimeters (mm) or inches. Designers choose based on regional standards or project requirements.

intermediate

Why is it important to keep clearance between the board outline and components?

Clearance ensures components do not extend beyond the board edges, preventing damage during manufacturing or assembly and ensuring proper fit in enclosures.

intermediate

How do you represent the board outline in PCB design software?

The board outline is usually drawn as a closed shape on a specific mechanical or edge layer. This shape guides the fabrication process for cutting the board.

advanced

What could happen if the board outline dimensions are incorrect?

Incorrect board outline dimensions can cause the PCB to not fit in its intended case, interfere with mounting holes, or cause manufacturing errors.

What does the board outline in PCB design define?

A The type of components used

B The electrical connections between components

C The color of the PCB solder mask

D The physical shape and size of the PCB

The board outline defines the physical shape and size of the PCB, guiding where the board will be cut.

Which layer is typically used to draw the board outline in PCB software?

A Silkscreen layer

B Copper layer

C Mechanical or edge layer

D Solder mask layer

The mechanical or edge layer is used to draw the board outline as a closed shape.

Why should components not extend beyond the board outline?

A To prevent damage during manufacturing and ensure fit

B To avoid electrical shorts

C To reduce weight

D To improve signal quality

Components extending beyond the board outline can be damaged or cause fitting issues.

What units are commonly used for PCB board dimensions?

A Pixels

B Millimeters or inches

C Centimeters only

D Feet

Millimeters and inches are standard units for PCB dimensions.

What is a risk of incorrect board outline dimensions?

A PCB not fitting in its enclosure

B Faster signal transmission

C Lower manufacturing cost

D Improved thermal performance

Incorrect dimensions can cause the PCB to not fit properly in its case or mounting.

Explain why the board outline is critical in PCB design and what it represents.

Think about how the board fits in the final product and how it is made.

Describe the importance of clearance between components and the board outline.

Consider what happens if parts stick out beyond the board edges.

Practice

1. What is the primary purpose of the board outline in PCB design?

easy

A. To define the physical shape and size of the PCB

B. To specify the electrical connections between components

C. To list the components used on the PCB

D. To set the color of the PCB surface

Solution

1. Step 1: Understand the role of board outline

   The board outline defines the physical boundaries of the PCB, including its shape and size.

2. Step 2: Differentiate from other PCB elements

   Electrical connections and component lists are separate from the outline, which is purely about shape and size.

3. Final Answer:

   To define the physical shape and size of the PCB -> Option A

4. Quick Check:

   Board outline = physical shape and size [OK]

Hint: Board outline means PCB shape and size, not electrical details [OK]

Common Mistakes:

• Confusing board outline with electrical schematics
• Thinking board outline sets component placement
• Assuming board outline controls PCB color

2. Which of the following is the correct way to specify a rectangular board outline with width 100mm and height 50mm in a PCB design file?

easy

A. Outline: Rectangle(100mm, 50mm)

B. Outline: Circle(100mm, 50mm)

C. Outline: Polygon(100mm, 50mm)

D. Outline: Rectangle[50mm, 100mm]

Solution

1. Step 1: Identify correct shape and syntax

   A rectangle with width 100mm and height 50mm is correctly specified as Rectangle(100mm, 50mm).

2. Step 2: Eliminate incorrect options

   Circle cannot have two dimensions like width and height; Polygon requires multiple points; brackets [] are not standard syntax here.

3. Final Answer:

   <code>Outline: Rectangle(100mm, 50mm)</code> -> Option A

4. Quick Check:

   Rectangle(width, height) syntax correct [OK]

Hint: Rectangle needs width first, then height in parentheses [OK]

Common Mistakes:

• Using Circle instead of Rectangle for rectangular shapes
• Swapping width and height values
• Using brackets instead of parentheses

3. Given a board outline defined as a polygon with points (0,0), (100,0), (100,50), (0,50), what is the total perimeter of the board in millimeters?

medium

A. 250 mm

B. 300 mm

C. 200 mm

D. 150 mm

Solution

1. Step 1: Calculate lengths of each side

   The polygon is a rectangle: sides are 100mm and 50mm. Perimeter = 2*(width + height) = 2*(100 + 50) = 300mm.

2. Step 2: Verify calculation

   Sum of all sides: 100 + 50 + 100 + 50 = 300mm total perimeter.

3. Final Answer:

   300 mm -> Option B

4. Quick Check:

   Perimeter = 2*(100+50) = 300 mm [OK]

Hint: Perimeter of rectangle = 2*(width + height) [OK]

Common Mistakes:

• Adding only two sides instead of all four
• Confusing perimeter with area
• Misreading coordinates order

4. You defined a board outline as a polygon with points (0,0), (100,0), (100,50), but the PCB manufacturer says the outline is invalid. What is the most likely problem?

medium

A. The dimensions are too large

B. The points are not in clockwise order

C. The outline is not a closed shape

D. The outline uses incorrect units

Solution

1. Step 1: Check polygon closure

   The points given do not return to the starting point (0,0), so the polygon is open, not closed.

2. Step 2: Understand manufacturer requirements

   Manufacturers require the board outline to be a closed shape to define the PCB boundary properly.

3. Final Answer:

   The outline is not a closed shape -> Option C

4. Quick Check:

   Closed outline needed for valid PCB shape [OK]

Hint: Ensure last point equals first to close the outline [OK]

Common Mistakes:

• Assuming order of points causes invalidity
• Blaming size instead of shape closure
• Ignoring unit specification issues

5. You need to design a PCB that fits exactly inside a case with internal dimensions 120mm x 80mm x 10mm (length x width x height). Which approach ensures the board outline and dimensions are correct?

hard

A. Set board outline to 120mm x 80mm and add 10mm height to outline

B. Set board outline to 130mm x 90mm to allow extra space

C. Ignore board outline and focus only on component placement

D. Set board outline to 120mm x 80mm and verify height clearance separately

Solution

1. Step 1: Match board outline to case internal length and width

   The board outline must fit inside the case, so width and length should be exactly 120mm and 80mm.

2. Step 2: Handle height separately

   Height is not part of the 2D board outline but must be checked for component clearance.

3. Final Answer:

   Set board outline to 120mm x 80mm and verify height clearance separately -> Option D

4. Quick Check:

   Outline matches length and width; height checked separately [OK]

Hint: Outline = length & width; height is checked separately [OK]

Common Mistakes:

• Adding height to 2D outline dimensions
• Making board larger than case internal size
• Ignoring outline and focusing only on components