Via size and drill diameter in PCB Design - Real Business Scenario

Scenario Mode

👤 Your Role: You are a PCB design analyst at an electronics manufacturing company.

📋 Request: Your manager wants a report showing the relationship between via sizes and drill diameters used in recent PCB designs to optimize manufacturing costs and reliability.

📊 Data: You have a dataset listing various PCB designs with columns for Via Size (in mils), Drill Diameter (in mils), and Quantity used in each design.

🎯 Deliverable: Create a dashboard that summarizes average drill diameter by via size category and total quantity used, with a visualization that helps identify optimal via and drill size combinations.

Sample Data

PCB Design	Via Size (mils)	Drill Diameter (mils)	Quantity
Design A	12	10	150
Design B	15	13	200
Design C	12	11	180
Design D	20	18	120
Design E	15	14	160
Design F	20	19	140
Design G	12	10	170
Design H	15	13	190

1

Step 1: Load the PCB design data into your BI tool.

Import the table with columns: PCB Design, Via Size (mils), Drill Diameter (mils), Quantity.

Expected Result

Data table with 8 rows loaded correctly.

2

Step 2: Create a calculated measure to find the average Drill Diameter for each Via Size.

Average Drill Diameter = AVERAGE('Table'[Drill Diameter (mils)]) grouped by 'Table'[Via Size (mils)]

Expected Result

Average drill diameters calculated per via size: 12 mils -> 10.33, 15 mils -> 13.33, 20 mils -> 18.5

3

Step 3: Create a calculated measure to find the total Quantity used for each Via Size.

Total Quantity = SUM('Table'[Quantity]) grouped by 'Table'[Via Size (mils)]

Expected Result

Total quantities per via size: 12 mils -> 500, 15 mils -> 740, 20 mils -> 260

4

Step 4: Build a bar chart visualization with Via Size on the X-axis and two bars per via size: one for Average Drill Diameter and one for Total Quantity (use secondary axis for quantity).

Configure chart: X-axis = Via Size (mils), Y-axis left = Average Drill Diameter, Y-axis right = Total Quantity

Expected Result

Bar chart shows average drill diameter and total quantity side by side for each via size.

5

Step 5: Add data labels to the bars for clarity and ensure color contrast for accessibility.

Enable data labels on both bars; use distinct colors with good contrast.

Expected Result

Chart clearly shows numeric values on bars, easy to read and interpret.

Final Result

Via Size (mils) | Avg Drill Diameter | Total Quantity
-----------------------------------------------------
12               | ########## 10.33   | ########### 500
15               | ############ 13.33 | ############### 740
20               | ############## 18.5| ####### 260

Bar chart with two bars per via size: left bar (avg drill diameter), right bar (total quantity).

✓Via size 15 mils has the highest total quantity used, indicating it is the most common.

✓Average drill diameter increases with via size as expected.

✓Via size 20 mils has the largest drill diameter but lower quantity, suggesting it is less common but used for specific needs.

Bonus Challenge

Create a drill-down feature in the dashboard to see individual PCB designs contributing to each via size category.

Show Hint

Use drill-through or filter actions in your BI tool to link from via size summary to detailed design rows.

Practice

1. What does the term via size in PCB design usually refer to?

easy

A. The length of the trace connected to the via

B. Only the drill hole diameter

C. The thickness of the PCB

D. The total diameter including drill hole and annular ring

Solution

1. Step 1: Understand via size components

   Via size includes the drill hole plus the annular ring around it.

2. Step 2: Define via size

   Via size = drill diameter + 2 x annular ring width.

3. Final Answer:

   The total diameter including drill hole and annular ring -> Option D

4. Quick Check:

   Via size = drill + 2xannular ring [OK]

Hint: Via size always includes drill plus annular ring twice [OK]

Common Mistakes:

• Confusing drill diameter with via size
• Ignoring annular ring width
• Thinking via size is PCB thickness

2. Which of the following formulas correctly calculates the via size if the drill diameter is D and annular ring width is R?

easy

A. Via size = D + 2 * R

B. Via size = D + R

C. Via size = 2 * (D + R)

D. Via size = D - 2 * R

Solution

1. Step 1: Recall the via size formula

   Via size equals drill diameter plus twice the annular ring width.

2. Step 2: Apply formula to variables

   Via size = D + 2 x R.

3. Final Answer:

   Via size = D + 2 * R -> Option A

4. Quick Check:

   Via size = drill + 2xannular ring [OK]

Hint: Remember annular ring counts twice around drill [OK]

Common Mistakes:

• Adding annular ring only once
• Multiplying drill diameter incorrectly
• Subtracting annular ring width

3. If a PCB designer uses a drill diameter of 0.3 mm and an annular ring width of 0.1 mm, what is the total via size?

medium

A. 0.4 mm

B. 0.6 mm

C. 0.5 mm

D. 0.7 mm

Solution

1. Step 1: Identify given values

   Drill diameter D = 0.3 mm, annular ring R = 0.1 mm.

2. Step 2: Calculate via size

   Via size = D + 2 x R = 0.3 + 2 x 0.1 = 0.3 + 0.2 = 0.5 mm.

3. Final Answer:

   0.5 mm -> Option C

4. Quick Check:

   0.3 + 2x0.1 = 0.5 mm [OK]

Hint: Add drill plus twice annular ring width [OK]

Common Mistakes:

• Adding annular ring once only
• Mixing units or decimal points
• Choosing closest but incorrect option

4. A PCB design rule states the minimum annular ring width is 0.15 mm. A designer sets drill diameter to 0.4 mm and via size to 0.55 mm. What is wrong?

medium

A. Via size is too small for the annular ring requirement

B. Drill diameter is too large

C. Annular ring width is too large

D. Via size is correctly set

Solution

1. Step 1: Calculate required via size

   Minimum annular ring R = 0.15 mm, drill D = 0.4 mm, so via size = 0.4 + 2x0.15 = 0.7 mm.

2. Step 2: Compare with given via size

   Given via size is 0.55 mm, which is less than required 0.7 mm.

3. Final Answer:

   Via size is too small for the annular ring requirement -> Option A

4. Quick Check:

   Via size < required minimum [OK]

Hint: Check if via size ≥ drill + 2xannular ring [OK]

Common Mistakes:

• Ignoring minimum annular ring width
• Assuming drill diameter can be changed
• Thinking via size can be smaller than drill

5. A PCB manufacturer requires a minimum annular ring width of 0.12 mm and a maximum drill diameter of 0.5 mm. If a designer wants a via size of 0.8 mm, what is the largest drill diameter they can use?

hard

A. 0.56 mm or less

B. 0.56 mm

C. 0.56 mm or more

D. 0.56 mm exactly

Solution

1. Step 1: Write the via size formula

   Via size = drill diameter + 2 x annular ring width.

2. Step 2: Substitute known values and solve for drill diameter

   0.8 = drill + 2 x 0.12 -> drill = 0.8 - 0.24 = 0.56 mm.

3. Step 3: Check manufacturer max drill diameter

   Max drill diameter allowed is 0.5 mm, but calculated drill is 0.56 mm, which is too large.

4. Step 4: Interpret largest drill diameter possible

   Designer must use drill diameter ≤ 0.5 mm to meet manufacturer limit, so largest drill diameter is 0.5 mm, less than 0.56 mm.

5. Final Answer:

   0.56 mm -> Option B

6. Quick Check:

   Drill ≤ 0.5 mm and via size = 0.8 mm [OK]

Hint: Solve via size formula, check max drill limit [OK]

Common Mistakes:

• Ignoring max drill diameter limit
• Assuming drill can be larger than max allowed
• Confusing annular ring with drill diameter