Three Types Of Vias In PCB: Through Holes, Blind Holes And Buried Holes

Definition:
A via that goes through all layers of a PCB, from the top layer to the bottom layer. This is the most traditional and widely used type of via, which goes through layers 1-2-3-4 in a four-layer board.

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Manufacturing process:
Mechanical drilling is usually used, with a hole diameter of 0.2mm; high-density boards use laser drilling, with a hole diameter of up to 0.1mm. Electroplating is required to form a conductive path to support the installation of plug-in components and inter-layer signal transmission.

Features and Applications:

· Advantage:The process is mature and the cost is low, which is suitable for large current/mechanical fixing requirements (such as screw holes);

· Shortcoming:/strong>It occupies vertical space, affects wiring density, and high-speed signals may cause interference due to overly long routing;

· Typical Applications:General circuit board and power device mounting area.

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Design points:
The aperture needs to meet electrical (current carrying capacity) and mechanical (pad size) requirements, and the solder mask treatment needs to prevent tin bead contamination.

Definition:
A non-penetrating hole that only connects the surface layer to the inner layer, usually from the top layer to the second layer or the bottom layer to the second to last layer. For example, a short via extending from the surface layer to the inner layer.

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Manufacturing process:

· Laser blind via：The precision reaches ±0.025mm, which is suitable for HDI high-density interconnection boards;

· Mechanical blind hole：The cost is lower but the depth accuracy is limited (tolerance ±0.05mm).
Drilling copper plating must be completed before lamination, and depth control needs to consider the material expansion coefficient and plating uniformity.

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Features and Applications:

· Advantage:Save surface space, shorten signal paths (reduce impedance by about 30%), and improve high-frequency signal integrity;

· Shortcoming:The drilling accuracy requirement is high (depth ≤ 6 times of the hole diameter), and the defective rate affects the cost;

· Typical applications:Space-sensitive scenarios such as mobile phone motherboards, RF circuits, and ultra-thin devices.

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Design Standards：
IPC-6012 Class 3 requires a blind hole depth-to-diameter ratio of ≤1:1 and a plating thickness of ≥0.8mil (20μm) to ensure reliable connection.

Definition:
The inner layer vias are completely hidden inside the multilayer board, connecting any two non-surface inner layers (such as L2-L5) and are not visible from the outside.

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Manufacturing process:
Adopt layered lamination technology: first partial lamination + drilling copper plating, and finally integrate into a complete board. Multiple precise alignments are required (alignment deviation ≤15μm).

Features and Applications:

· Advantage:Maximize surface space release to achieve ultra-fine wiring (line width/spacing up to 3/3 μm) and eliminate through-hole shadow effect;

· Shortcoming:The process complexity is extremely high (cost increased by more than 40%), and rework is almost impossible;

· Typical applications:Large CPU substrates, optical modules, automotive radar PCBs and other high-density multi-layer boards.

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Manufacturing Difficulties:
The inner hole diameter tolerance needs to be controlled within ±10%, and plasma cleaning is required after drilling to prevent residual glue from affecting the adhesion of the coating.

type

Penetration

Process complexity

cost

Applicable scenarios

Through Hole

Full-thickness penetration

Low

Low

Traditional circuit, power/ground signal

Blind Via

One-side penetration

Medium

Medium to high

HDI Board、High frequency and high speed design

Buried Via

Inner layer interconnection

High

Very high

Ultra-high density board, special fields