Layer transition strategy in PCB Design - Cell-by-Cell Formula Trace

Concept Flow

Layer Transition Strategy Flow:

[Top Layer] --via--> [Inner1 Layer] --via--> [Inner2 Layer] --via--> [Bottom Layer]

Via Types:
- Through Via: connects Top to Bottom
- Blind Via: connects Top to Inner1 or Inner1 to Inner2 or Inner2 to Bottom

Costs:
Through Via = 5
Blind Via = 3

This flow shows how signals move through PCB layers using different via types. Through vias connect the top and bottom layers directly, while blind vias connect intermediate layers. Each via type has an associated manufacturing cost.

Formula

SUMX(FILTER(sample_data, sample_data[Start Layer] = "Top"), sample_data[Cost])

This formula sums the cost of all vias that start from the 'Top' layer by filtering rows where 'Start Layer' equals 'Top' and then summing their 'Cost' values.

Step-by-Step Trace

Step	Expression	Evaluates To	Explanation
1	FILTER(sample_data, sample_data[Start Layer] = "Top")	[Row 1, Row 2]	Filter rows where Start Layer is 'Top'. Rows 1 and 2 match.
2	SUMX([Row 1, Row 2], sample_data[Cost])	5 + 3 = 8	Sum the Cost values of filtered rows: 5 (Through Via) + 3 (Blind Via) = 8.

The final result is 8, the total cost of vias starting at the Top layer.

Variable Tracker

Variable	Value
Filtered Rows	Rows 1 and 2 (Start Layer = 'Top')
Costs in Filtered Rows	5 (Row 1), 3 (Row 2)
Sum of Costs	8

Key Moments

Which rows are selected when filtering for Start Layer = 'Top'?

What is the total cost calculated by the formula?

What does the SUMX function do in this formula?

Sheet Trace Quiz - 3 Questions

Which rows does the formula include when filtering Start Layer = 'Top'?

A Rows 4 and 5

B Only Row 2

C Rows 1 and 2

D All rows

Key Result

The layer transition strategy uses different via types to connect PCB layers. This example calculates the total cost of vias starting from the Top layer by filtering and summing costs.

Transcript

We start by filtering the data to find all vias that begin at the Top layer. This gives us two rows: one for a Through Via and one for a Blind Via. Next, we sum their costs, 5 and 3, to get a total cost of 8. This helps us understand the expense of using vias starting from the Top layer in PCB design.

Practice

1.

What is the main purpose of a layer transition strategy in PCB design?

easy

A. To decide the size of the PCB board

B. To select the color of the PCB layers

C. To plan how signals move between different PCB layers

D. To choose the type of solder used

Solution

1. Step 1: Understand the role of layer transitions

   Layer transitions manage how electrical signals pass from one PCB layer to another.

2. Step 2: Identify the main goal of the strategy

   The strategy ensures signal integrity and proper routing between layers.

3. Final Answer:

   To plan how signals move between different PCB layers -> Option C

4. Quick Check:

   Layer transition strategy = signal movement planning [OK]

Hint: Focus on signal movement between layers [OK]

Common Mistakes:

• Confusing layer transition with PCB color or size
• Thinking it relates to solder type
• Ignoring signal routing importance

2.

Which of the following via types is NOT typically used for layer transitions in PCB design?

easy

A. Surface mount via

B. Blind via

C. Buried via

D. Through-hole via

Solution

1. Step 1: Review common via types for layer transitions

   Through-hole, blind, and buried vias are standard for connecting layers inside PCBs.

2. Step 2: Identify the invalid via type

   Surface mount via is not a recognized via type for layer transitions; it refers to component mounting.

3. Final Answer:

   Surface mount via -> Option A

4. Quick Check:

   Surface mount via ≠ layer transition via [OK]

Hint: Recall via types used inside PCB layers [OK]

Common Mistakes:

• Confusing surface mount with via types
• Assuming all vias connect layers
• Ignoring buried via purpose

3.

Given a PCB with 4 layers, which via type would you use to connect only the top and second layers without passing through the entire board?

medium

A. Through-hole via

B. Blind via

C. Buried via

D. Microvia

Solution

1. Step 1: Understand via types and layer connections

   Through-hole vias connect all layers; buried vias connect inner layers only; blind vias connect outer to inner layers.

2. Step 2: Match via type to connection need

   To connect top and second layers only, a blind via is used because it does not go through the entire board.

3. Final Answer:

   Blind via -> Option B

4. Quick Check:

   Top to inner layer connection = Blind via [OK]

Hint: Blind vias connect outer to inner layers only [OK]

Common Mistakes:

• Choosing through-hole which connects all layers
• Confusing buried vias with blind vias
• Not knowing microvia specifics

4.

Identify the error in this layer transition plan: "Use buried vias to connect the top layer to the bottom layer in a 6-layer PCB."

medium

A. Buried vias require through-hole plating

B. Buried vias are too expensive for 6-layer PCBs

C. Buried vias cause signal loss on outer layers

D. Buried vias cannot connect outer layers

Solution

1. Step 1: Recall buried via function

   Buried vias connect only inner layers and do not reach outer layers like top or bottom.

2. Step 2: Analyze the plan's claim

   Connecting top to bottom layer with buried vias is impossible because buried vias do not extend to outer layers.

3. Final Answer:

   Buried vias cannot connect outer layers -> Option D

4. Quick Check:

   Buried vias = inner layers only [OK]

Hint: Buried vias never reach outer layers [OK]

Common Mistakes:

• Thinking buried vias connect all layers
• Confusing cost with functionality
• Assuming buried vias are through-hole

5.

You need to design a cost-effective layer transition strategy for a 10-layer PCB that minimizes signal interference and manufacturing cost. Which combination of vias is best?

hard

A. Use blind vias for outer to inner layers and buried vias for inner layers, minimizing through-hole vias

B. Use only through-hole vias for all layer transitions

C. Use only buried vias to connect all layers

D. Use microvias exclusively for all transitions

Solution

1. Step 1: Consider cost and signal quality factors

   Through-hole vias increase cost and can cause more interference; microvias are costly for many layers.

2. Step 2: Choose via types for efficient layer transitions

   Blind vias connect outer to inner layers; buried vias connect inner layers; minimizing through-hole vias reduces cost and interference.

3. Step 3: Evaluate options

   Use blind vias for outer to inner layers and buried vias for inner layers, minimizing through-hole vias balances cost and signal quality by using blind and buried vias appropriately and limiting through-hole vias.

4. Final Answer:

   Use blind vias for outer to inner layers and buried vias for inner layers, minimizing through-hole vias -> Option A

5. Quick Check:

   Balanced via use = cost & signal optimized [OK]

Hint: Mix blind and buried vias, limit through-hole [OK]

Common Mistakes:

• Using only through-hole vias increases cost
• Assuming buried vias connect outer layers
• Choosing microvias for all layers is expensive