Via types (through-hole, blind, buried) in PCB Design - Full Explanation

Introduction

When designing printed circuit boards (PCBs), connecting different layers is essential for electrical signals to travel. Choosing the right type of via helps solve the problem of how to link these layers efficiently without wasting space or increasing manufacturing complexity.

Explanation

Through-hole vias

Through-hole vias are holes drilled all the way through the PCB from the top layer to the bottom layer. They connect every layer in between, allowing signals to pass through the entire board. These vias are the simplest and most common type, but they take up space on all layers they pass through.

Through-hole vias connect all layers by passing completely through the PCB.

Blind vias

Blind vias connect an outer layer of the PCB to one or more inner layers but do not go all the way through the board. They start on the surface and stop before reaching the opposite side. This saves space on the unused layers and helps keep the board compact.

Blind vias connect outer layers to inner layers without passing through the entire board.

Buried vias

Buried vias connect only inner layers inside the PCB and are not visible from the outside. They do not reach the outer surfaces, which helps maintain a clean board surface and allows for more complex layer connections inside. These vias require more advanced manufacturing steps.

Buried vias connect only inner layers and are hidden inside the PCB.

Real World Analogy

Imagine a multi-story building where people need to move between floors. Through-hole vias are like staircases that go from the ground floor all the way to the top floor. Blind vias are staircases that start on the ground floor but only go up a few floors, not reaching the top. Buried vias are hidden elevators inside the building that only connect middle floors without any doors on the ground or top floors.

Through-hole vias → Staircases going from the ground floor to the top floor, connecting all floors.

Blind vias → Staircases starting at the ground floor but stopping before the top floor.

Buried vias → Hidden elevators connecting only middle floors without access from outside.

Diagram

Diagram

┌───────────────┐
│ Top Layer     │
├───────────────┤
│ Inner Layer 1 │
├───────────────┤
│ Inner Layer 2 │
├───────────────┤
│ Bottom Layer  │
└───────────────┘

Through-hole via: │ drilled through all layers
Blind via:       │ drilled from top layer to inner layer 1
Buried via:      │ drilled between inner layer 1 and inner layer 2 only

A stack of PCB layers showing where through-hole, blind, and buried vias connect layers.

Key Facts

Through-hole via → A via that passes through all layers of the PCB from top to bottom.

Blind via → A via that connects an outer layer to one or more inner layers but does not go through the entire board.

Buried via → A via that connects only inner layers and is not visible from the outer surfaces.

PCB layer → A single conductive or insulating sheet within a multi-layer printed circuit board.

Via → A small hole in a PCB that allows electrical connection between different layers.

Common Confusions

Believing blind vias go through the entire PCB.

Believing blind vias go through the entire PCB. Blind vias only connect from an outer layer to inner layers and stop before reaching the opposite side.

Thinking buried vias are visible on the PCB surface.

Thinking buried vias are visible on the PCB surface. Buried vias are completely inside the PCB and do not appear on the outer layers.

Summary

Through-hole vias connect all layers by drilling through the entire PCB.

Blind vias connect outer layers to inner layers without passing through the whole board.

Buried vias connect only inner layers and remain hidden inside the PCB.

Practice

1.

Which type of via connects all layers of a PCB from top to bottom?

easy

A. Buried via

B. Blind via

C. Microvia

D. Through-hole via

Solution

1. Step 1: Understand via types

   Through-hole vias go through the entire PCB, connecting all layers.

2. Step 2: Compare with other vias

   Blind vias connect outer to inner layers only; buried vias connect only inner layers.

3. Final Answer:

   Through-hole via -> Option D

4. Quick Check:

   All layers connected = Through-hole via [OK]

Hint: Through-hole vias pass all layers top to bottom [OK]

Common Mistakes:

• Confusing blind vias with through-hole
• Thinking buried vias connect outer layers
• Assuming microvias connect all layers

2.

Which of the following is the correct DAX formula to count only blind vias from a table Vias with a column Type?

COUNTROWS(FILTER(Vias, Vias[Type] = "blind"))

easy

A. FILTER(Vias, Vias[Type] == "blind")

B. COUNTROWS(FILTER(Vias, Vias[Type] = "blind"))

C. SUM(Vias[Type] = "blind")

D. COUNT(Vias[Type] = "blind")

Solution

1. Step 1: Understand DAX counting syntax

   To count rows matching a condition, use COUNTROWS with FILTER.

2. Step 2: Check each option

   COUNTROWS(FILTER(Vias, Vias[Type] = "blind")) correctly filters rows where Type equals "blind" and counts them.

3. Final Answer:

   COUNTROWS(FILTER(Vias, Vias[Type] = "blind")) -> Option B

4. Quick Check:

   Correct DAX syntax for conditional count = COUNTROWS(FILTER(Vias, Vias[Type] = "blind")) [OK]

Hint: Use COUNTROWS with FILTER for conditional counts in DAX [OK]

Common Mistakes:

• Using COUNT instead of COUNTROWS for rows
• Using single equals (==) in DAX which is invalid
• Trying to sum boolean expressions directly

3.

Given the DAX measure:
BlindViaCount = COUNTROWS(FILTER(Vias, Vias[Type] = "blind"))
and the Vias table below:

Type
through-hole
blind
buried
blind
through-hole
blind

What is the value of BlindViaCount?

medium

A. 3

B. 2

C. 4

D. 1

Solution

1. Step 1: Identify rows with Type = "blind"

   From the table, rows 2, 4, and 6 have "blind" type.

2. Step 2: Count these rows

   There are 3 such rows matching the filter condition.

3. Final Answer:

   3 -> Option A

4. Quick Check:

   Count of "blind" rows = 3 [OK]

Hint: Count rows where Type equals "blind" to get 3 [OK]

Common Mistakes:

• Counting only first two blind vias
• Including buried or through-hole vias by mistake
• Misreading the table rows

4.

Identify the error in this DAX formula intended to count buried vias:
BuriedCount = COUNTROWS(FILTER(Vias, Vias[Type] == "buried"))

medium

A. FILTER syntax is incorrect without a comma

B. COUNTROWS cannot be used with FILTER

C. Using double equals (==) instead of single equals (=) in DAX

D. Buried vias cannot be counted with DAX

Solution

1. Step 1: Review DAX comparison operators

   DAX uses single equals (=) for comparisons, not double equals (==).

2. Step 2: Check the formula syntax

   The formula uses '==' which causes a syntax error in DAX.

3. Final Answer:

   Using double equals (==) instead of single equals (=) in DAX -> Option C

4. Quick Check:

   DAX comparison uses =, not == [OK]

Hint: Use single = for comparisons in DAX, not == [OK]

Common Mistakes:

• Using == from other languages in DAX
• Thinking COUNTROWS can't work with FILTER
• Misplacing commas in FILTER function

5.

You want to create a Power BI report showing the percentage of each via type (through-hole, blind, buried) in a PCB design. Which DAX measure correctly calculates the percentage of buried vias?

BuriedPercent = DIVIDE(CALCULATE(COUNTROWS(FILTER(Vias, Vias[Type] = "buried"))), COUNTROWS(Vias), 0)

hard

A. BuriedPercent = DIVIDE(CALCULATE(COUNTROWS(FILTER(Vias, Vias[Type] = "buried"))), COUNTROWS(Vias), 0)

B. BuriedPercent = COUNTROWS(FILTER(Vias, Vias[Type] = "buried")) / COUNTROWS(Vias)

C. BuriedPercent = SUM(Vias[Type] = "buried") / COUNTROWS(Vias)

D. BuriedPercent = CALCULATE(COUNT(Vias[Type] = "buried")) / COUNTROWS(Vias)

Solution

1. Step 1: Understand percentage calculation in DAX

   Percentage = count of buried vias divided by total vias, safely handling divide by zero.

2. Step 2: Analyze each option

   BuriedPercent = DIVIDE(CALCULATE(COUNTROWS(FILTER(Vias, Vias[Type] = "buried"))), COUNTROWS(Vias), 0) uses DIVIDE with CALCULATE and FILTER correctly, providing safe division.

3. Final Answer:

   BuriedPercent = DIVIDE(CALCULATE(COUNTROWS(FILTER(Vias, Vias[Type] = "buried"))), COUNTROWS(Vias), 0) -> Option A

4. Quick Check:

   Safe division with DIVIDE and correct filter = BuriedPercent = DIVIDE(CALCULATE(COUNTROWS(FILTER(Vias, Vias[Type] = "buried"))), COUNTROWS(Vias), 0) [OK]

Hint: Use DIVIDE with CALCULATE and FILTER for safe percentage [OK]

Common Mistakes:

• Using simple division without DIVIDE (risk divide by zero)
• Using COUNT instead of COUNTROWS for rows
• Trying to sum boolean expressions directly