Laser drilling represents an advanced technology for creating tiny and precise holes on a PCB. It relies on precise control of a laser beam, eliminating the need for mechanical contact with the material, thereby avoiding the instability issues associated with mechanical drilling. Currently, three primary PCB laser drilling technologies are gaining significant attention in applications: CO2 laser drilling, fiber laser drilling, and UV laser drilling. In this article, we will provide a detailed overview of these three technologies and compare them to help you better understand their applications and distinctions.
CO2 Laser Drilling
CO2 laser operates with a wavelength in the vicinity of 10.6 micrometers, falling within the high-energy infrared spectrum. During drilling, the laser irradiates the substrate with high energy. These materials absorb the infrared light and convert it into thermal energy, resulting in a rapid localized temperature increase that causes vaporization, thereby creating holes. It’s important to note that not all materials are suitable for this drilling method. Only materials with the capability to absorb infrared light can be effectively processed, as depicted below.
From the diagram, we can observe that whether it’s resin, fiberboard, or copper foil, their absorption rates for CO2 laser are significantly lower compared to UV laser. As shown in the graph, the copper foil material exhibits an absorption rate for CO2 laser even below 10%. This implies that without further treatment, it’s challenging to penetrate copper foil and create holes using CO2 laser. To overcome this issue, we employ a surface treatment technique known as browning or blackening.
Browning or blackening is a surface treatment method that creates tiny recesses or textures on the surface of copper foil through chemical or physical means, making the copper foil surface rough. This results in light being reflected and scattered on the surface instead of being completely reflected, thereby increasing the absorption rate of copper foil for CO2 laser. This allows the laser to interact more effectively with the copper foil and deliver energy.
UV Laser Drilling
UV laser drilling is a actinic cracking process based on ultraviolet light. It utilizes the high photon energy characteristic of the ultraviolet spectrum to break the chemical bonds in long-chain polymer organic materials. This results in the rapid removal of material, leading to the creation of holes as numerous fragments increase in volume and are removed under external suction forces. This reaction is a “cold work” process that doesn’t involve melting, so there are no carbonized residues left on the hole walls. As a result, there’s no need for material pre-treatment, and different residues are absent.
Currently, various UV laser drilling machines are available in the market, capable of producing microvias with a minimum diameter as small as 25 micrometers. This technology is particularly beneficial in fields like semiconductor manufacturing, where it can efficiently and precisely process tiny holes, meeting the requirements of modern electronic components.
Fiber Laser Drilling
Fiber laser drilling is a drilling method that combines fiber optic technology with laser technology. What sets this method apart is its ability to adjust the operating wavelength according to specific requirements, catering to a wide range of diverse application needs.
In the absorption rate chart of materials with respect to lasers, we can observe that both ultraviolet and infrared light have their limitations. Ultraviolet light, due to its higher energy, can sometimes lead to material breakdown. In contrast, the energy of infrared light might not be sufficient to effectively process certain materials. This is where fiber laser drilling technology comes into play. This technology typically employs a YAG head to remove the copper layer and utilizes a CO2 head to remove the substrate. This dual-headed approach is capable of handling more complex drilling tasks, ensuring the optimal quality of the holes.
CO2 vs. UV vs. Fiber
| Attributes | CO2 | UV | Fiber |
|---|---|---|---|
| Top Brands | Lumonics | ESI | Eecellon |
| Aperture | 4~8mil | Below 3mil | 4~6mil |
| Speed | Ten times that of YAG | Slow | About 6,000 holes per minute |
| Limit | Some materials cannot be processed | Too high energy leads to breakdown | Combining the two is difficult and complex |
| Principle | Photothermal Ablation | Actinic Cracking | First YAG then CO2 |
| Quality | Dirt Residue | Neat and tidy | Dirt Residue |
| Processing Range | Blind via | All | All |
| Cost | Low | High | Middle |
| Process | Layered processing | One-time processing | Two processes |
| Cooling | Yes | No | No |
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