Via size and drill diameter in PCB Design - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding the relationship between via size and drill diameter

In PCB design, the via size is closely related to the drill diameter. Which statement correctly describes this relationship?

A The drill diameter is always larger than the via size to ensure clearance.

B The drill diameter and via size are always equal for precision.

C The drill diameter is always smaller than the via size to allow for plating.

D The drill diameter is unrelated to the via size and can be any value.

💡 Hint

Think about how the plating process reduces the hole size.

The drill diameter is larger than the finished via size because plating adds copper thickness to the walls, reducing the final hole size.

🎯 Scenario

intermediate

Selecting drill diameter for a given via size

You need to design a via with a finished size of 0.4 mm. The plating thickness is 0.025 mm on each side of the hole. What drill diameter should you specify?

A 0.35 mm

B 0.30 mm

C 0.40 mm

D 0.45 mm

💡 Hint

Add twice the plating thickness to the finished via size.

Drill diameter = via size + 2 * plating thickness = 0.4 + 2*0.025 = 0.45 mm.

❓ dax_lod_result

advanced

Calculate average drill diameter per via size category

Given a dataset of vias with columns 'ViaSize' and 'DrillDiameter', which DAX measure correctly calculates the average drill diameter for each via size category?

PCB Design

Average Drill Diameter = AVERAGEX(VALUES(Vias[ViaSize]), CALCULATE(AVERAGE(Vias[DrillDiameter])))

A Average Drill Diameter = CALCULATE(AVERAGE(Vias[DrillDiameter]), ALLEXCEPT(Vias, Vias[ViaSize]))

B Average Drill Diameter = AVERAGEX(VALUES(Vias[ViaSize]), CALCULATE(AVERAGE(Vias[DrillDiameter])))

C Average Drill Diameter = AVERAGE(Vias[DrillDiameter])

D Average Drill Diameter = SUM(Vias[DrillDiameter]) / COUNTROWS(Vias)

💡 Hint

Use AVERAGEX over distinct via sizes to get average per category.

Option B uses AVERAGEX over distinct ViaSize values and calculates average DrillDiameter per group, correctly computing average per category.

❓ visualization

advanced

Best visualization to compare via sizes and drill diameters

You want to create a dashboard that shows the distribution of via sizes and their corresponding drill diameters across multiple PCB layers. Which visualization type is best suited for this purpose?

A Stacked bar chart showing total drill diameters per layer

B Pie chart showing percentage of each via size

C Scatter plot with Via Size on X-axis and Drill Diameter on Y-axis, colored by PCB layer

D Line chart showing drill diameter trends over time

💡 Hint

Consider how to show relationship between two numeric variables and categories.

A scatter plot effectively shows the relationship between via size and drill diameter, with color differentiating PCB layers.

🔧 Formula Fix

expert

Identify the error in drill diameter calculation measure

Consider this DAX measure intended to calculate the drill diameter for a given via size by adding plating thickness twice:

Drill Diameter = Vias[ViaSize] + 2 * Vias[PlatingThickness]

Why does this measure produce incorrect results when used in a report?

A It uses direct column references without aggregation, causing row context issues.

B It incorrectly multiplies plating thickness by 2 instead of adding.

C It should use SUM instead of subtraction for drill diameter calculation.

D It lacks a FILTER function to limit rows to the current via size.

💡 Hint

Think about how DAX handles row context in measures.

Measures cannot use direct column references without aggregation because they lack row context, leading to errors or incorrect results.

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