Board outline and dimensions in PCB Design - Cell-by-Cell Formula Trace

Sample Data

This data represents the dimensions of a PCB board: length, width, and margin for outline.

Cell	Value
A1	Length (mm)
B1	Width (mm)
A2	100
B2	50
A3	Margin (mm)
B3	5

Formula Trace

= (A2 + 2 * B3) * (B2 + 2 * B3)

Step 1: 2 * B3

Step 2: A2 + 2 * B3

Step 3: B2 + 2 * B3

Step 4: (A2 + 2 * B3) * (B2 + 2 * B3)

Cell Reference Map

     A      B
  +-------+-------+
1 |Length | Width |
  +-------+-------+
2 |  100  |  50   |
  +-------+-------+
3 |Margin |   5   |
  +-------+-------+

References:
- A2 (Length)
- B2 (Width)
- B3 (Margin)

The formula uses Length (A2), Width (B2), and Margin (B3) to calculate the total board area including margins.

Result

     A      B       C
  +-------+-------+---------+
1 |Length | Width |  Area   |
  +-------+-------+---------+
2 |  100  |  50   |  6600   |
  +-------+-------+---------+
3 |Margin |   5   |         |
  +-------+-------+---------+

The final result in cell C2 shows the total board area including margins: 6600 mm².

Sheet Trace Quiz - 3 Questions

What is the value of 2 * Margin (B3) in the formula?

A 5

B 10

C 15

D 20

Key Result

Calculate total board area by adding twice the margin to length and width, then multiply.

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