Manufacturing constraints awareness in PCB Design - Cell-by-Cell Formula Trace

Sample Data

This table shows PCB components with their actual sizes and the maximum allowed sizes for manufacturing.

Cell	Value
A1	Component
B1	Size (mm)
C1	Max Allowed Size (mm)
D1	Status
A2	Resistor
B2	3.2
C2	3.5
A3	Capacitor
B3	4
C3	3.8
A4	IC Chip
B4	10
C4	10
A5	Connector
B5	12.5
C5	12

Formula Trace

=IF(B2<=C2, "OK", "Too Large")

Step 1: B2 <= C2

Step 2: TRUE

Step 3: IF(TRUE, "OK", "Too Large")

Cell Reference Map

    A       B       C       D
1 |Component|Size(mm)|MaxSize |Status
2 |Resistor |  3.2   |  3.5   |  ?  
3 |Capacitor|  4.0   |  3.8   |  ?  
4 |IC Chip  | 10.0   | 10.0   |  ?  
5 |Connector| 12.5   | 12.0   |  ?  

The formula in column D compares size in column B with max allowed size in column C for each component.

Result

    A       B       C       D
1 |Component|Size(mm)|MaxSize |Status
2 |Resistor |  3.2   |  3.5   |  OK 
3 |Capacitor|  4.0   |  3.8   |Too Large
4 |IC Chip  | 10.0   | 10.0   |  OK 
5 |Connector| 12.5   | 12.0   |Too Large

The Status column shows "OK" if the component size is within manufacturing limits, otherwise "Too Large".

Sheet Trace Quiz - 3 Questions

What does the formula check for each component?

A If the component size is less than or equal to the max allowed size

B If the component size is greater than the max allowed size

C If the component size equals zero

D If the max allowed size is less than the component size

Key Result

IF(actual_size <= max_allowed_size, "OK", "Too Large")

Practice

1. Which of the following is a common manufacturing constraint in PCB design?

easy

A. Color of the PCB silkscreen

B. Minimum trace width

C. Number of software licenses

D. Type of solder used

Solution

1. Step 1: Understand common PCB manufacturing constraints

   Manufacturing constraints include physical limits like trace width, spacing, and hole size.

2. Step 2: Identify the correct constraint from options

   Minimum trace width is a key constraint to ensure the PCB can be produced reliably.

3. Final Answer:

   Minimum trace width -> Option B

4. Quick Check:

   Manufacturing constraints = Minimum trace width [OK]

Hint: Think physical limits on PCB lines and holes [OK]

Common Mistakes:

• Confusing design preferences with manufacturing constraints
• Choosing cosmetic features like color
• Selecting unrelated options like software licenses

2. Which of these is the correct way to specify a minimum hole size constraint in a PCB design rule?

easy

A. MinHoleSize = 0.3mm

B. HoleSizeMin = 0.3mm

C. Min_Hole_Size = 0.3mm

D. MinimumHole = 0.3mm

Solution

1. Step 1: Recall standard naming conventions in PCB design rules

   Design tools often use concise, camel-case or Pascal-case names like MinHoleSize.

2. Step 2: Identify the exact syntax used for minimum hole size

   MinHoleSize = 0.3mm is the correct and common syntax for specifying this constraint.

3. Final Answer:

   MinHoleSize = 0.3mm -> Option A

4. Quick Check:

   Correct syntax = MinHoleSize = 0.3mm [OK]

Hint: Look for concise, standard naming without underscores [OK]

Common Mistakes:

• Using underscores instead of camel case
• Mixing words in unusual order
• Adding extra words not recognized by tools

3. Given a PCB design rule: MinTraceWidth = 0.15mm and a trace width of 0.1mm in the design, what will happen during manufacturing?

medium

A. The PCB will be manufactured without issues

B. The design software will ignore the rule

C. The trace width will automatically increase to 0.15mm

D. The trace may be too thin and cause manufacturing defects

Solution

1. Step 1: Compare trace width with minimum allowed

   The design trace width (0.1mm) is less than the minimum allowed (0.15mm).

2. Step 2: Understand manufacturing impact

   Traces thinner than minimum can cause defects like breaks or shorts during production.

3. Final Answer:

   The trace may be too thin and cause manufacturing defects -> Option D

4. Quick Check:

   Trace width below minimum = manufacturing risk [OK]

Hint: Check if design values meet or exceed minimum constraints [OK]

Common Mistakes:

• Assuming software fixes the trace width automatically
• Ignoring the importance of minimum trace width
• Thinking the rule is optional

4. A PCB design rule states MinSpacing = 0.2mm. The designer sets two traces 0.15mm apart. What is the error and how to fix it?

medium

A. Spacing too small; increase spacing to at least 0.2mm

B. No error; 0.15mm is acceptable spacing

C. Spacing too large; reduce spacing to 0.1mm

D. Rule syntax is wrong; change to Min_Spacing

Solution

1. Step 1: Identify the spacing violation

   The actual spacing (0.15mm) is less than the minimum required (0.2mm), causing a violation.

2. Step 2: Correct the spacing to meet the rule

   Increase the spacing between traces to at least 0.2mm to comply with manufacturing constraints.

3. Final Answer:

   Spacing too small; increase spacing to at least 0.2mm -> Option A

4. Quick Check:

   Spacing < minimum = increase spacing [OK]

Hint: Spacing must never be less than minimum rule [OK]

Common Mistakes:

• Thinking smaller spacing is better
• Ignoring rule syntax correctness
• Assuming no error if spacing is close

5. You must prepare a PCB design for a manufacturer who requires a minimum trace width of 0.2mm and minimum hole size of 0.4mm. Your design has traces at 0.15mm and holes at 0.35mm. What is the best approach to ensure manufacturability?

hard

A. Ignore the constraints since they are just recommendations

B. Submit the design as is and ask the manufacturer to adjust

C. Update the design to meet or exceed both minimums before submission

D. Increase only the hole size, leave trace width as is

Solution

1. Step 1: Compare design values with manufacturer constraints

   Trace width (0.15mm) and hole size (0.35mm) are both below required minimums (0.2mm and 0.4mm).

2. Step 2: Decide on corrective action

   To avoid production errors, update the design to meet or exceed both minimum constraints before sending to manufacturer.

3. Final Answer:

   Update the design to meet or exceed both minimums before submission -> Option C

4. Quick Check:

   Design meets constraints before submission = manufacturability [OK]

Hint: Always fix design to meet constraints before manufacturing [OK]

Common Mistakes:

• Relying on manufacturer to fix design errors
• Ignoring constraints thinking they are optional
• Fixing only one constraint and ignoring others