Traditional PCB manufacturing processes typically employ mechanical drilling techniques to create through-holes physically on the surface of the board. However, as circuit precision requirements continue to increase, along with the demand for various complex hole patterns, traditional methods are starting to show some limitations. Hence, there is a need to utilize more advanced technology like laser drilling. Laser drilling uses a high-energy laser beam to precisely melt or vaporize material on the board’s surface, resulting in more accurate holes.
Necessity of Laser Drilling in PCB Manufacturing
Setting up a traditional PCB production line costs approximately $500,000, and to implement laser drilling, which requires advanced equipment, manufacturers are willing to incur higher costs. Why is this the case?
As you can see, electronic products are evolving towards becoming smaller, thinner, and faster, yet they are becoming more powerful. Take smartwatches as an example; they have shrunk in size but gained numerous functions, such as telling time, making calls, video conferencing, and internet browsing. To achieve this transformation, advanced microtechnology called high-density interconnects has emerged.
This is a novel microelectronics packaging technology that doesn’t rely on traditional PCB as its foundation. Instead, it involves designing and manufacturing from scratch to achieve high-density, complex circuits on a single PCB. This entails using multiple layers of insulating material and various advanced types of vias, like blind vias and buried vias, for necessary inter-layer connections.
Blind vias are holes that enter from the top surface of the board without traversing through it, while buried vias exist inside the board and do not penetrate the surface. In the realm of drilling techniques, laser drilling is considered the preferred choice for creating these tiny vias. In comparison to mechanical drilling, laser drilling offers smaller hole diameters, often as small as a few micrometers, resulting in reduced PCB real estate. Additionally, multi-layer PCB consist of inner layers for signal transmission like power and ground planes and outer layers for connecting various components and devices. When interconnections are needed between different outer layers, laser drilling technology allows penetrating only the outer layers without affecting the inner layers. This improves the Power Integrity and Signal Integrity of the circuit.
PCB Laser Drilling Process
Laser drilling utilizes laser beams to cut through or penetrate materials, employing beams with high energy density. When the light energy is focused, it can rapidly heat or vaporize the material, enabling cutting or penetration. Laser beams can be categorized into CO2 and UV lasers based on the beam frequency.
CO2 laser drilling is commonly employed for non-metallic materials. In this process, the laser beam is amplified by CO2 gas and then focused into a high-energy density beam using lenses. This intense energy beam is directed onto the substrate being processed, and the material absorbs the laser energy, causing it to sublime and create tiny holes or cutting paths.
UV laser drilling, on the other hand, are frequently used for delicate materials and involve photochemical or photolytic reactions. When UV laser light is directed at the material, the high-energy photons are absorbed, leading to the breaking of molecular chains within organic substances in the material, resulting in smaller fragments or particles.
The specific details of using lasers for PCB drilling are as follows:
- Heating: When the laser beam strikes the material surface, energy is transferred to the material’s electrons, generating heat through collisions.
- Melting: With sufficient intensity and exposure time, the surface begins to melt.
- Vaporization: As the material melts, it transitions from a solid to a liquid state and is ejected. When the ejected vapor reaches a certain temperature, it forms a plasma, where photons interact with free electrons, converting heat into ionizing vaporization energy.
- Evaporative Ejection: Liquid on the surface evaporates and drives the liquid to spray out of the hole.
- Fluid Ejection: As evaporative ejection continues, intense vapor pressure forms at the liquid’s surface, forcing the fluid to exit from one side of the laser channel, creating a via.
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