Mechanical Drilling vs. Laser Drilling

 

In order to establish continuity between the top and bottom or to intermediate layers on the printed circuit board(PCB), holes need to be drilled through or partially drilled in the laminate. These holes connect traces and pads of different layers. In PCB manufacturing, drilling is one of the costly and time-consuming processes because even though a small error can cause a considerable loss. Mechanical drilling and laser drilling are two technologies used to drill holes in the PCB manufacturing process.

Mechanical drilling uses a rotating drill bit to drill through different types of laminate materials. The drill bit is usually made of micro-granule cemented carbide, allowing repeated use for the drill bit. It can also be resharpened for repeated use but usually up to 3 times. The first advantage of using mechanical drilling is that no matter the number of holes are drilled, the drill bit can still create high-quality and consistent holes. Furthermore, the ends of the holes have no taper. Therefore, all holes are completely drilled through the substrate, keeping the knee of the wall clean without bevels. Compared to other methods, the drilling speed of mechanical drilling is much faster. However, every hole drilled by mechanical drilling needs to be deburred to remove elevated copper ends left during the drilling process. Sometimes, the deburring process may take a longer time than schedules. Also, mechanical drilling is not suitable for microvias. Because mechanical drilling cannot drill holes smaller than 6 mils in diameter, it cannot precisely control the drilling depth required for microvias.

Laser drilling utilizes a high-density laser beam to create microvias on PCB. UV and CO2 are two types of lasers commonly used in laser drilling. By beam shaping technology, the laser beam is projected onto the material surface, which absorbs beam energy to break chemical bonds. The released steam will generate a recoil pressure, applying a downward force on the remaining molten material as well as forcing the molten material to flow out of the hole. Compared to mechanical drilling, laser drilling is able to ablate through various substrate materials using different diameters that cannot be obtained by mechanical drilling. As a non-contact technique, laser drilling requires less processing and tool selection than mechanical drilling. However, laser drilling also has the following disadvantages. If there is no metal stop layer, it is hard to obtain accurate depth control, and it will cause tapering resulting from the large aspect ratio. Laser drilling will carbonize the cutting edges leading to a black or burnt appearance.

Aspect ratio (AR) is an indicator of effective plating copper in a hole. Copper plating on the inner wall is a laborious job, as the diameter of the hole decreases and the depth of the hole increases. Our company can achieve an aspect ratio of 16:1 for plated through holes (PTH) and 0.9:1 for microvias. The formula of aspect ratio is:

AR= Depth of the hole / Diameter of the drilled hole

 

 

If you have any questions about mechanical drilling and laser drilling for PCB, please contact our engineers:

 

Reference:

https://www.protoexpress.com/blog/no-chilling-when-it-comes-to-pcb-drilling/

https://blog.epectec.com/pcb-mechanical-drilling-vs-laser-aspect-ratios-and-drill-sizing

https://www.protoexpress.com/blog/how-does-laser-drilling-work-pcbs/