Why is laser drilling required for circuit boards?
When using HDI technology for PCB designing, plenty of microvias are included. These microvias that appear to be blind structures are small in size and require precise controlled depth drilling. This precision can only be achieved using lasers.
Why mechanical drilling cannot be used for microvias?
Mechanical drilling is not suitable for microvias due to the following reasons:
- Mechanical drilling is accompanied by drill vibration.
- It cannot drill holes with less than 6 mil diameter (approximately).
- It cannot achieve the precisely controlled depth drilling required for microvias.
How small of a hole can a laser drill?
Lasers can drill 2.5 to 3-mil vias on a thin flat glass reinforcement. In the case of an unreinforced dielectric (with no glass), it is possible to drill 1-mil vias using lasers. Hence, laser drilling is recommended for drilling microvias.
What are the advantages of laser drilling?
The advantages of using lasers are listed below:
- Non-contact process: Laser drilling is a non-contact process and hence the damage induced on the material by drilling vibration is eliminated.
- Precise control: We can control the beam intensity, heat output, and duration of the laser beam. This helps to create different hole shapes and offers high accuracy.
- High aspect ratio: One of the most important parameters of a drilled hole on a circuit board is the aspect ratio. It is the ratio between the drilled depth and the diameter of the hole. Since lasers can create holes with very small diameters, they provide a high aspect ratio. A typical microvia has an aspect ratio of 0.75:1.
- Multi-tasking: Laser machines used for drilling can also be used for other manufacturing processes like welding, cutting, etc.
Different methods of laser drilling
Single-pulse/shot laser drilling
As the name suggests, in single-pulse laser drilling, a single shot of laser beam is fired at the material to create the required hole. In this method, both the source of the laser and the work material is kept static.
Percussion laser drilling
In percussion drilling, a series of laser pulses are shot at the work material repeatedly. During this process, there is no relative motion between the laser beam and the workpiece. This form of laser drilling effectively creates deeper and precise holes with smaller diameters as compared to single-shot laser drilling.
Trepanning is the process in which a laser beam is guided around a predefined locus. This locus is the center of the via to be drilled. It is used in situations where the diameter of the via to be cut is larger than the laser beam diameter. The accuracy of the via is determined by the movement of the beam.
Helical laser drilling
Helical laser drilling is a method in which the laser beam follows a helical path for movement while rotating about its own axis with respect to the workpiece. A dove prism controls the movement of the laser beam.
Which lasers are suitable for drilling small holes?
There are different types of laser machines available that can be used for a variety of purposes. These purposes can be hole creation, etching, depaneling, etc. Out of these, only those machines which can accurately create small holes on the type of materials used for circuit boards should be used as PCB drilling machines.
What is a PCB drilling machine?
A PCB drilling machine drills holes with high precision and accuracy based on the provided data. This data includes the exact position, number, and other parameters of the holes to be drilled.
Types of laser drilling machines
Different types of machines for laser processing are available depending on their operating principles. The most commonly used machines for drilling microvias are CO2 and Nd:YAG lasers. Excimer lasers are also available and are used in the etching of polymers. They are not suitable for the removal of metals.