Four-layer stack-up design in PCB Design - Cell-by-Cell Formula Trace

Concept Flow

[Identify Layers] → [List Materials] → [Note Thickness] → [Sum Thickness] → [Result: Total PCB Thickness]

This flow shows the steps to understand and calculate the total thickness of a four-layer PCB stack-up by identifying each layer, its material, thickness, and summing all thicknesses.

Formula

Total Thickness = SUM(C2:C5)

This formula adds the thickness values from cells C2 to C5 to calculate the total thickness of the PCB stack-up.

Step-by-Step Trace

Step	Operation	Layers Considered	Thickness Values (mil)	Sum Result (mil)
1	Start sum	None	-	0
2	Add Top Layer thickness	Top Layer	0 + 1.4	1.4
3	Add Prepreg thickness	Top Layer, Prepreg	1.4 + 4.0	5.4
4	Add Inner Layer thickness	Top Layer, Prepreg, Inner Layer	5.4 + 1.4	6.8
5	Add Core thickness	All layers	6.8 + 62.0	68.8

Final total thickness of the four-layer PCB stack-up is 68.8 mil.

Variable Tracker

Step	Variable	Value Before	Operation	Value After
1	Total Thickness	0	Initialize sum	0
2	Total Thickness	0	Add 1.4 (Top Layer)	1.4
3	Total Thickness	1.4	Add 4.0 (Prepreg)	5.4
4	Total Thickness	5.4	Add 1.4 (Inner Layer)	6.8
5	Total Thickness	6.8	Add 62.0 (Core)	68.8

Key Moments

Why do we add the thickness values of all layers?

What role does the Core layer play in the stack-up?

Why is the Prepreg layer important despite being thinner than the Core?

Sheet Trace Quiz - 3 Questions

What is the total thickness of the four-layer PCB stack-up?

A 66.8 mil

B 4.0 mil

C 68.8 mil

D 1.4 mil

Key Result

A four-layer PCB stack-up consists of Top Layer (signal), Prepreg (insulation), Inner Layer (ground plane), and Core (mechanical support). Total thickness is the sum of all layers' thicknesses.

Transcript

We start by identifying each layer in the PCB stack-up and noting its material and thickness. Then, we sum the thickness values from the Top Layer, Prepreg, Inner Layer, and Core to find the total PCB thickness. This total thickness is important for mechanical and electrical design considerations in PCB manufacturing.

Practice

1. What is the main purpose of using a four-layer stack-up in PCB design?

easy

A. To separate signal, power, and ground layers for better performance

B. To reduce the number of components on the board

C. To make the PCB physically larger

D. To increase the manufacturing cost

Solution

1. Step 1: Understand the role of layers in PCB

   Layers separate different electrical functions like signals, power, and ground to reduce interference.

2. Step 2: Identify the benefit of four-layer stack-up

   Four-layer stack-up improves noise control and signal integrity by proper separation.

3. Final Answer:

   To separate signal, power, and ground layers for better performance -> Option A

4. Quick Check:

   Layer separation = better PCB performance [OK]

Hint: Four layers separate signals, power, and ground clearly [OK]

Common Mistakes:

• Thinking it reduces components
• Assuming it makes PCB bigger
• Believing it increases cost only

2. Which of the following is the correct order of layers in a typical four-layer PCB stack-up from top to bottom?

easy

A. Signal - Power - Ground - Signal

B. Power - Signal - Ground - Signal

C. Ground - Signal - Power - Ground

D. Signal - Ground - Power - Signal

Solution

1. Step 1: Recall standard four-layer stack-up order

   Common order is Signal on top, then Ground, then Power, then Signal at bottom.

2. Step 2: Match options with standard order

   Signal - Ground - Power - Signal matches the typical order exactly.

3. Final Answer:

   Signal - Ground - Power - Signal -> Option D

4. Quick Check:

   Standard stack-up order = Signal - Ground - Power - Signal [OK]

Hint: Ground layer is usually just below top signal layer [OK]

Common Mistakes:

• Mixing power and ground layers
• Placing power on top
• Confusing bottom signal layer position

3. Given a four-layer PCB stack-up with layers: Top Signal, Ground, Power, Bottom Signal, which layer provides the best noise shielding for the top signal layer?

medium

A. Ground layer

B. Power layer

C. Bottom signal layer

D. Top signal layer itself

Solution

1. Step 1: Identify the layer adjacent to top signal

   The ground layer is directly below the top signal layer.

2. Step 2: Understand noise shielding role

   Ground layers provide a reference plane and shield signals from noise.

3. Final Answer:

   Ground layer -> Option A

4. Quick Check:

   Ground layer shields signals from noise [OK]

Hint: Ground layer next to signal layer shields noise best [OK]

Common Mistakes:

• Choosing power layer for shielding
• Confusing bottom signal as shield
• Thinking signal layer shields itself

4. A designer mistakenly places the power layer above the ground layer in a four-layer stack-up. What is the likely effect?

medium

A. Reduced manufacturing cost

B. Increased noise and reduced signal integrity

C. No effect on PCB performance

D. Improved noise shielding

Solution

1. Step 1: Understand layer order importance

   Ground layer next to signal layer provides best noise shielding.

2. Step 2: Effect of swapping power and ground layers

   Power layer above ground reduces shielding, increasing noise and hurting signal quality.

3. Final Answer:

   Increased noise and reduced signal integrity -> Option B

4. Quick Check:

   Wrong layer order = more noise [OK]

Hint: Ground layer must be closest to signal for shielding [OK]

Common Mistakes:

• Assuming no effect
• Thinking power layer shields noise
• Believing cost is affected

5. You need to design a four-layer PCB stack-up for a high-speed digital circuit requiring minimal crosstalk and good power distribution. Which stack-up arrangement is best?

hard

A. Ground - Signal - Power - Signal

B. Top Signal - Power - Ground - Bottom Signal

C. Top Signal - Ground - Power - Bottom Signal

D. Power - Ground - Signal - Signal

Solution

1. Step 1: Identify stack-up for noise control and power

   Ground layer next to top signal reduces crosstalk; power layer below ground helps stable power.

2. Step 2: Evaluate options for best layer order

   Top Signal - Ground - Power - Bottom Signal matches the ideal order: Signal, Ground, Power, Signal.

3. Final Answer:

   Top Signal - Ground - Power - Bottom Signal -> Option C

4. Quick Check:

   Proper layer order = minimal crosstalk and good power [OK]

Hint: Place ground layer just below top signal for best results [OK]

Common Mistakes:

• Swapping power and ground layers
• Placing power layer on top
• Ignoring signal layer placement