What Is Laser Drilling?
Laser Drilling, or Laser Ablation creates precise holes on a printed circuit board (PCB) to establish connections between different copper layers. The sleek gadgets that we all are acquainted with consist of HDI boards that incorporate laser drilled microvias. Laser drilling techniques ensure accuracy even when dealing with the smallest of sizes.
As we know, laser stands for light amplification by stimulated emission of radiation. Laser drilling is the process that uses highly concentrated laser energy for drilling (ablating) a hole. It is completely different from drilling holes mechanically using a drill bit.
Also see term Laser Ablation
Why Laser Drilling Is Required in PCB Fabrication?
When using HDI technology for PCB design, plenty of microvias are included. These microvias that appear to be blind structures are small in sizes and require precision-controlled depth drilling. This precision can only be achieved using lasers.
Mechanical drilling is not suitable for microvias due to the following reasons:
- It is accompanied by drill vibration
- It cannot massively drill holes with less than 6mil (0.15mm) diameter
- It cannot achieve the precision-controlled depth drilling required for microvias
Lasers can drill 2.5 to 3mil vias on a thin flat FR4, FR5 and PTFE based rigid materials and polyimide based flexible materials. In the case of an unreinforced dielectric (with no fiberglass), it is possible to drill 1mil vias using lasers. Hence, laser drilling is recommended for drilling mirovias.
What Are the Advantages of Laser Drilling?
The advantages of using lasers are listed below:
- Non-contact process: It 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 offer high accuracy.
- High aspect ratio: the ratio between the drilled depth and the diameter of the hole. A typical microvia has an aspect ratio of 0.75:1.
- Multi-tasking: Laser machines used for drilling can also be used for other PCB fabrication processes, like cutting and flexible circuit depth controlled drilling.
What Is the Max Copper Thickness that Laser can Drill Through?
The minimum thickness of the target copper layer should be twice the thickness of the top copper layer to be penetrated. If given enough time, laser can drill through any copper thicknesses. If the copper thickness is thick, the finished laser-drilling holes will be hard to plated to planar with copper plating technique. The microvia’s dimple will be high, and the plated blind microvias quality will be bad, which will lead to low PCB production yield. So, if possible, try to design the microvia diameters to 3mil, 4mil and 5mil, rarely to 6mil. Smaller or bigger are not recommended.
Apart from a few challenges that may arise, we can surely say that lasers are the best choice to create microvias in circuit boards. Given the ever-increasing demand for reducing the board size and increasing the wiring density, laser-ablated microvias are crucial in PCB manufacturing. Creating diminished holes with extreme accuracy without affecting the integrity of the board is a difficult task. Laser drilling is the best way to manufacture such complex multilayer boards.