Solder mask expansion in PCB Design - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to set the solder mask expansion value to 0.1 mm.

PCB Design

solder_mask_expansion = [1]

Drag options to blanks, or click blank then click option'

A0.1

B1.0

C0.01

D10

Attempts:

3 left

💡 Hint

Common Mistakes

Using too large a value like 10 mm

Using zero which disables expansion

The solder mask expansion is typically set in millimeters. Here, 0.1 mm is a common value to ensure proper coverage.

2fill in blank

medium

Complete the code to calculate the adjusted pad size by adding solder mask expansion.

PCB Design

adjusted_pad_size = pad_size [1] solder_mask_expansion

Drag options to blanks, or click blank then click option'

A-

B/

C*

D+

Attempts:

3 left

💡 Hint

Common Mistakes

Using subtraction which reduces size

Using multiplication or division which changes scale incorrectly

To get the adjusted pad size, you add the solder mask expansion to the original pad size.

3fill in blank

hard

Fix the error in the code to correctly apply solder mask expansion only if the expansion is positive.

PCB Design

if solder_mask_expansion [1] 0:
    apply_expansion()

Drag options to blanks, or click blank then click option'

A<=

B>

C==

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<=' which includes zero and negatives

Using '==' which only checks zero

The expansion should be applied only if the solder mask expansion value is greater than zero.

4fill in blank

hard

Fill both blanks to create a dictionary comprehension that maps pad names to their adjusted sizes only if expansion is positive.

PCB Design

adjusted_sizes = {pad: size [1] solder_mask_expansion for pad, size in pads.items() if solder_mask_expansion [2] 0}

Drag options to blanks, or click blank then click option'

A+

B-

C>

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using '-' which subtracts expansion

Using '<' which checks for negative values

The dictionary comprehension adds the expansion to each pad size only if the expansion is greater than zero.

5fill in blank

hard

Fill all three blanks to create a dictionary comprehension that maps pad names in uppercase to their adjusted sizes only if expansion is positive and size is above 0.5 mm.

PCB Design

adjusted_sizes = [1]: size [2] solder_mask_expansion for pad, size in pads.items() if solder_mask_expansion [3] 0 and size > 0.5

Drag options to blanks, or click blank then click option'

Apad.upper()

B+

C>

Dpad.lower()

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'pad.lower()' instead of uppercase

Using '-' instead of '+' for addition

Using '<' instead of '>' for positive check

This comprehension converts pad names to uppercase, adds expansion to sizes, and filters pads with positive expansion and size greater than 0.5 mm.

Practice

1. What is the main purpose of solder mask expansion in PCB design?

easy

A. To adjust the size of mask openings around pads

B. To change the thickness of the PCB substrate

C. To increase the number of layers in the PCB

D. To modify the copper trace width

Solution

1. Step 1: Understand solder mask expansion function

   Solder mask expansion changes the size of openings around pads to control soldering quality.

2. Step 2: Identify the correct purpose

   Adjusting mask openings prevents solder bridges or insufficient coverage during assembly.

3. Final Answer:

   To adjust the size of mask openings around pads -> Option A

4. Quick Check:

   Solder mask expansion = Adjust mask openings [OK]

Hint: Think about mask openings size control [OK]

Common Mistakes:

• Confusing mask expansion with PCB thickness
• Mixing mask expansion with copper trace width
• Assuming it changes PCB layers

2. Which of the following is the correct way to specify a solder mask expansion value to increase the mask opening size by 0.05 mm?

easy

A. solder_mask_expansion = -0.05

B. solder_mask_expansion = 0

C. solder_mask_expansion = 0.05

D. solder_mask_expansion = +0.00

Solution

1. Step 1: Understand sign convention for expansion

   Positive values increase mask opening size; negative values decrease it.

2. Step 2: Choose the positive value for increasing size

   0.05 mm positive value means mask opening grows by 0.05 mm.

3. Final Answer:

   solder_mask_expansion = 0.05 -> Option C

4. Quick Check:

   Positive value increases opening size [OK]

Hint: Positive value means bigger opening [OK]

Common Mistakes:

• Using negative value to increase size
• Using zero which means no change
• Confusing plus sign usage

3. Given a pad size of 1.0 mm and a solder mask expansion of -0.1 mm, what will be the effective mask opening size?

medium

A. 0.8 mm

B. 1.1 mm

C. 1.0 mm

D. 0.9 mm

Solution

1. Step 1: Understand the effect of negative expansion

   Negative expansion reduces the mask opening size by the given amount.

2. Step 2: Calculate effective mask opening

   1.0 mm pad size minus 0.1 mm expansion = 0.9 mm opening.

3. Final Answer:

   0.9 mm -> Option D

4. Quick Check:

   Pad size + expansion = opening size [OK]

Hint: Add expansion (negative) to pad size [OK]

Common Mistakes:

• Adding negative expansion instead of subtracting
• Ignoring sign of expansion
• Using pad size without adjustment

4. A designer sets solder mask expansion to 0.0 mm but notices solder bridging on the PCB. What is the most likely error?

medium

A. Expansion value is too small, should be positive

B. Expansion value is too large, should be negative

C. Expansion value syntax is incorrect

D. Expansion value has no effect on solder bridging

Solution

1. Step 1: Analyze effect of zero expansion

   Zero expansion means mask opening matches pad size exactly, no extra clearance.

2. Step 2: Understand solder bridging cause

   Without extra clearance (positive expansion), solder can bridge between pads.

3. Final Answer:

   Expansion value is too small, should be positive -> Option A

4. Quick Check:

   Positive expansion prevents bridging [OK]

Hint: Use positive expansion to avoid bridging [OK]

Common Mistakes:

• Thinking zero expansion is enough
• Assuming negative expansion prevents bridging
• Ignoring solder mask role

5. A PCB has pads of 0.8 mm size. To ensure no solder bridging but avoid excessive mask exposure, the designer wants the mask opening to be 0.9 mm. What solder mask expansion value should be set?

hard

A. -0.1 mm

B. 0.1 mm

C. 0.9 mm

D. -0.9 mm

Solution

1. Step 1: Calculate required expansion

   Desired opening (0.9 mm) minus pad size (0.8 mm) = 0.1 mm expansion.

2. Step 2: Confirm sign of expansion

   Since opening is larger than pad, expansion must be positive 0.1 mm.

3. Final Answer:

   0.1 mm -> Option B

4. Quick Check:

   Opening - pad size = positive expansion [OK]

Hint: Expansion = desired opening - pad size [OK]

Common Mistakes:

• Using negative expansion when opening is larger
• Confusing pad size with opening size
• Setting expansion equal to opening size