Design for testability (DFT) in PCB Design - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding the Purpose of DFT

What is the primary goal of Design for Testability (DFT) in PCB design?

A To improve the aesthetic appearance of the PCB layout

B To reduce the cost of PCB components by using cheaper materials

C To make the PCB easier to test and diagnose faults after manufacturing

D To increase the speed of the PCB during normal operation

💡 Hint

Think about what helps engineers find problems quickly after the board is made.

DFT focuses on making the PCB easier to test and find faults, which helps reduce debugging time and improve quality.

❓ data_modeling

intermediate

DFT Test Point Coverage Calculation

You have a PCB with 100 nets. 80 nets have test points added for DFT. What is the test point coverage percentage?

A 80%

B 20%

C 50%

D 100%

💡 Hint

Coverage is the number of nets with test points divided by total nets, times 100.

Coverage = (80 / 100) * 100 = 80%. This means 80% of nets have test points for testing.

❓ visualization

advanced

Best Visualization for DFT Test Results

Which type of dashboard visualization best helps engineers quickly identify failing test points on a PCB?

A A line chart showing test duration over time

B A bar chart showing component costs

C A pie chart showing percentage of passed vs failed boards

D A heatmap showing test points colored by failure frequency

💡 Hint

Think about a visualization that highlights problem areas spatially on the PCB.

A heatmap visually shows which test points fail most often, helping engineers focus on problem areas quickly.

🔧 Formula Fix

advanced

Identifying a DFT Test Coverage Calculation Error

Given the formula Coverage = (TestedNets / TotalNets) * 100, a report shows 120% coverage. What is the most likely cause?

A TestedNets value is greater than TotalNets due to counting duplicates

B TotalNets value is zero causing division by zero

C The formula should be <code>(TotalNets / TestedNets) * 100</code>

D Coverage cannot exceed 100%, so the report software is faulty

💡 Hint

Think about how counting errors can cause coverage to exceed 100%.

If TestedNets is counted with duplicates or errors, it can exceed TotalNets, causing coverage over 100% which is invalid.

🎯 Scenario

expert

Optimizing DFT for Complex PCB Design

You are designing a complex PCB with limited space for test points. Which DFT strategy best balances test coverage and physical constraints?

A Use only visual inspection for testing to avoid adding test points

B Use boundary scan techniques to reduce physical test points while maintaining coverage

C Skip DFT to save space and rely on functional testing only

D Add test points to every net regardless of space constraints

💡 Hint

Consider methods that reduce physical test points but still allow thorough testing.

Boundary scan allows testing internal nets electronically, reducing the need for many physical test points and balancing space constraints with coverage.