Types of PCB Drilled Holes

EMS - 13 November 2024 - 1:01 am

Common Types of PCB Drilled Holes

There are several types of PCB drilled holes, each serving a specific purpose. Here are the most common types:

Through Holes

Through holes are the most common type of PCB drilled holes. They are drilled completely through the PCB, from one side to the other. Through holes are used for mounting and soldering electronic components, such as resistors, capacitors, and Integrated Circuits (ICs). They also provide electrical connectivity between different layers of the PCB.

Advantages of Through Holes

Easy to manufacture
Suitable for mounting a wide range of components
Provide strong mechanical support
Allow for easy soldering and inspection

Disadvantages of Through Holes

Require more PCB real estate compared to other hole types
May increase the overall thickness of the PCB
Can limit the routing density on inner layers

Blind Vias

Blind vias are holes that start from one side of the PCB and terminate at an inner layer, without reaching the opposite side. They are used to interconnect the outer layer with one or more inner layers, providing a more compact and space-efficient design compared to through holes.

Advantages of Blind Vias

Save PCB real estate by reducing the number of through holes
Allow for higher routing density on inner layers
Reduce the overall thickness of the PCB
Improve signal integrity by minimizing the length of interconnects

Disadvantages of Blind Vias

More expensive to manufacture compared to through holes
Require specialized drilling equipment and processes
Limited to connecting only a few layers

Buried Vias

Buried vias are holes that start and end on inner layers of the PCB, without reaching either of the outer layers. They are used to interconnect different inner layers, providing a highly compact and space-efficient design.

Advantages of Buried Vias

Save even more PCB real estate compared to blind vias
Allow for the highest routing density on inner layers
Minimize the overall thickness of the PCB
Provide the best signal integrity by minimizing the length of interconnects

Disadvantages of Buried Vias

Most expensive to manufacture among all hole types
Require the most advanced drilling equipment and processes
Limited to connecting only inner layers

Microvias

Microvias are tiny holes, typically less than 150 microns in diameter, used for high-density interconnects (HDI) in advanced PCB Designs. They can be blind, buried, or even stacked, allowing for extremely compact and complex PCB layouts.

Advantages of Microvias

Enable the highest interconnect density in PCB design
Minimize the overall size and thickness of the PCB
Provide excellent signal integrity for high-speed applications
Allow for the use of advanced packaging techniques, such as chip-scale packaging (CSP)

Disadvantages of Microvias

Most expensive to manufacture among all hole types
Require state-of-the-art drilling equipment and processes
May have limited current-carrying capacity due to their small size

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PCB Drilled Hole Manufacturing Processes

The manufacturing process for PCB drilled holes depends on the type of hole and the required precision. Here are the most common manufacturing processes:

Mechanical Drilling

Mechanical drilling is the most common method for creating through holes and larger blind and buried vias. It involves using a high-speed drill bit to create holes in the PCB substrate. The drill bit is typically made of carbide or diamond-coated carbide for improved wear resistance and hole quality.

Advantages of Mechanical Drilling

Cost-effective for larger hole sizes
Suitable for a wide range of PCB materials
Provides good hole quality and consistency

Disadvantages of Mechanical Drilling

Limited to larger hole sizes (typically >200 microns)
May cause substrate damage or delamination if not properly controlled
Drilling speed is limited by the material and hole size

Laser Drilling

Laser drilling is used for creating smaller holes, such as microvias, and for drilling in hard-to-reach areas. It involves using a high-energy laser beam to vaporize the PCB substrate material, creating a precise and clean hole.

Advantages of Laser Drilling

Enables the creation of extremely small holes (<50 microns)
Provides excellent hole quality and consistency
Minimizes substrate damage and delamination
Allows for high-speed drilling of multiple holes simultaneously

Disadvantages of Laser Drilling

More expensive than mechanical drilling
Limited to certain PCB materials that are compatible with laser ablation
May require specialized post-processing to clean the holes

Plasma Drilling

Plasma drilling is an advanced method for creating microvias and other small holes in PCBs. It involves using a high-energy plasma arc to vaporize the PCB substrate material, creating a precise and clean hole.

Advantages of Plasma Drilling

Enables the creation of extremely small holes (<25 microns)
Provides excellent hole quality and consistency
Minimizes substrate damage and delamination
Allows for high-speed drilling of multiple holes simultaneously

Disadvantages of Plasma Drilling

Most expensive among all drilling methods
Limited to certain PCB materials that are compatible with plasma ablation
Requires specialized equipment and skilled operators

PCB Drilled Hole Design Considerations

When designing PCBs with drilled holes, several factors must be considered to ensure the manufacturability, reliability, and performance of the final product. Here are some key design considerations:

Hole Size and Tolerance

The hole size and tolerance should be carefully selected based on the component requirements and the manufacturing capabilities. Smaller holes may require more advanced drilling processes and tighter tolerances, which can increase the manufacturing cost.

Hole Type	Typical Size Range (mm)	Typical Tolerance (mm)
Through Hole	0.5 – 2.5	±0.1
Blind Via	0.2 – 1.0	±0.05
Buried Via	0.2 – 1.0	±0.05
Microvia	0.05 – 0.15	±0.02

Hole Placement and Spacing

The placement and spacing of holes should be optimized to ensure proper component fitting, minimize signal interference, and facilitate the routing of traces. The minimum hole spacing is determined by the PCB material, copper thickness, and manufacturing capabilities.

PCB Layer Count	Minimum Hole Spacing (mm)
1-2	0.8
4	0.6
6	0.5
8+	0.4

Pad Size and Shape

The pad size and shape should be selected based on the hole size, component requirements, and soldering process. Larger pads may improve solderability and mechanical strength, but they also consume more PCB real estate.

Hole Size (mm)	Recommended Pad Diameter (mm)
0.5	1.0
0.8	1.4
1.0	1.6
1.5	2.1
2.0	2.6

Drill Hit

The drill hit, or the location where the drill bit enters the PCB, should be carefully selected to minimize the risk of damage to the PCB substrate or neighboring components. The drill hit should be centered on the pad and avoid any sensitive areas.

Aspect Ratio

The aspect ratio, or the ratio of the hole depth to its diameter, should be kept within the manufacturing capabilities to ensure hole quality and reliability. Higher aspect ratios may require specialized drilling processes and increase the manufacturing cost.

Hole Type	Maximum Aspect Ratio
Through Hole	8:1
Blind Via	1:1
Buried Via	1:1
Microvia	0.75:1

FAQ

What is the difference between a through hole and a via?
A through hole is a hole that goes completely through the PCB, while a via is a hole that connects different layers of the PCB without necessarily going through the entire board. Vias can be blind (starting from an outer layer and ending at an inner layer) or buried (connecting only inner layers).
Can I use microvias in my PCB design?
Yes, microvias can be used in PCB designs that require high interconnect density and miniaturization. However, they are more expensive to manufacture and require advanced drilling processes, so they should be used only when necessary.
What is the minimum hole size that can be drilled in a PCB?
The minimum hole size depends on the drilling method and the PCB material. With mechanical drilling, the minimum hole size is typically around 0.2 mm. Laser and plasma drilling can achieve hole sizes as small as 0.05 mm or less.
How do I choose the appropriate pad size for a drilled hole?
The pad size should be selected based on the hole size, component requirements, and soldering process. A general rule of thumb is to use a pad diameter that is 0.5-0.8 mm larger than the hole diameter. However, the exact pad size may vary depending on the specific application and manufacturing capabilities.
What is the maximum aspect ratio for PCB drilled holes?
The maximum aspect ratio depends on the type of hole and the manufacturing process. For through holes, the maximum aspect ratio is typically 8:1. For blind and buried vias, the maximum aspect ratio is usually 1:1. Microvias have a lower maximum aspect ratio of around 0.75:1.

In conclusion, understanding the different types of PCB drilled holes and their manufacturing processes is essential for designing and manufacturing high-quality PCBs. By considering factors such as hole size, placement, pad size, and aspect ratio, designers can ensure the manufacturability, reliability, and performance of their PCB designs. As PCB technology continues to advance, new drilling methods and materials may emerge, enabling even smaller and more complex hole structures in the future.

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