The difference between the excimer laser and the impact carbon dioxide laser through-hole of the flexible circuit board:
At present, the holes processed by excimer laser are the smallest. The excimer laser is ultraviolet light, which directly destroys the structure of the resin in the base layer, disperses the resin molecules, and generates very little heat, so the degree of heat damage around the hole can be limited to a minimum, and the hole wall is smooth and vertical. If the laser beam can be further reduced, holes with a diameter of 10-20um can be processed. Of course, the larger the plate thickness-to-aperture ratio, the more difficult it is to wet copper plating. The problem with excimer laser drilling is that the decomposition of the polymer will cause carbon black to adhere to the hole wall, so some means must be taken to clean the surface before electroplating to remove the carbon black. However, when laser processing blind holes, the uniformity of the laser also has certain problems, resulting in bamboo-like residues.
The biggest difficulty of excimer laser is that the drilling speed is slow and the processing cost is too high. Therefore, it is limited to the processing of small holes with high precision and high reliability.
The impact carbon dioxide laser generally uses carbon dioxide gas as the laser source, and radiates infrared rays. Unlike excimer lasers, which burn and decompose resin molecules due to thermal effects, it belongs to thermal decomposition, and the shape of the processed holes is worse than that of excimer lasers. The hole diameter that can be processed is basically 70-100um, but the processing speed is obviously much faster than that of excimer laser, and the cost of drilling is also much lower. Even so, the processing cost is still much higher than the plasma etching method and chemical etching method described below, especially when the number of holes per unit area is large.
The impact carbon dioxide laser should pay attention to when processing blind holes, the laser can only be emitted to the surface of the copper foil, and the organic matter on the surface does not need to be removed at all. In order to stably clean the copper surface, chemical etching or plasma etching should be used as a post-treatment. Considering the possibility of technology, the laser drilling process is basically not difficult to use in the tape and tape process, but considering the balance of the process and the proportion of equipment investment, it is not dominant, but the tape chip automatic welding The width of the process (TAB, TapeAutomated Bonding) is narrow, and the tape-and-reel process can increase the drilling speed, and there have been practical examples in this regard.
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