How does laser drilling work in PCB?

Laser drilling creates precise holes on PCBs to establish connections between different layers. The fashionable gadgets we are all familiar with consist of HDI boards that contain laser-drilled holes. The laser drilling technology ensures precision even when dealing with the smallest of dimensions.

As we all know, Laser stands for Light Amplification by Stimulated Emission of Radiation. Laser drilling is the process of drilling (vaporizing) holes using highly concentrated laser energy. It is completely different from mechanical drilling using a drill.

What is Circuit Board Drilling?

Circuit board drilling is the process of drilling holes in a PCB for any of the following purposes:

Placement of components

To achieve interconnection between different layers

These are achieved through various types of vias, namely, through-hole vias, micro-vias, blind vias, and buried vias. When it comes to vias for electrical interconnection between layers, blind vias are preferred over through-hole vias. Blind vias increase the space available for routing compared to through-holes. This is shown in the following figure.

What circuit boards need laser drilling?

When using HDI technology for PCB design, a large number of microvias are included. These microvias that seem to be blind structures are very small in size and require precise control of the depth of drilling. This precision can only be achieved using lasers.

Why can't mechanical drilling be used for microvias?

Mechanical drilling is not suitable for microvias due to the following reasons:

1. Mechanical drilling is accompanied by drill bit vibration.

2. It cannot drill holes smaller than 6 mil in diameter (approximately).

3. It cannot achieve the precise controlled depth drilling required for microvias.

How small can a laser drill?

A laser can drill 2.5 to 3 mil vias in thin, flat glass reinforcements. In the case of unreinforced dielectrics (no glass), a 1 mil via can be drilled with a laser. Therefore, it is recommended to use laser drilling to drill micro holes.

What are the advantages of laser drilling?

The advantages of using laser are as follows:

鈼廚on-contact process: Laser drilling is a non-contact process, so damage to the material caused by drilling vibration is eliminated.

鈼廝recise Control: We can control the beam intensity, heat output, and duration of the laser beam. This helps create different hole shapes and provides high precision.

鈼廐igh Aspect Ratio: One of the most important parameters for drilling holes in circuit boards is the aspect ratio. It is the ratio of the drilling depth to the hole diameter. Since lasers can create holes with very small diameters, they offer a high aspect ratio. A typical microvia has an aspect ratio of 0.75:1.

鈼廙ulti-tasking: The laser machine used for drilling can also be used for other manufacturing processes such as welding, cutting, etc.

How to make micro holes with laser?

As we can see from the above picture, the laser beam is projected onto the material using beam shaping technology. The material absorbs the beam energy which breaks the chemical bonds. This process of removing material from the surface by irradiating it with a laser beam is called laser ablation. These vapors will generate recoil pressure which exerts a downward force on the remaining molten material.

The recoil pressure will force the molten material out of the hole. The ejection of molten material is called melt jetting. The absorption rate depends on the type of material used. Usually, we use non-homogeneous materials such as FR4 to make circuit boards.