PCB Technical - The difference between flexible PCB through-hole technology

This article is about the introduction of the difference between the through-hole technology of the flexible circuit board

The difference between flexible PCB through-hole technology

The difference between excimer laser and impingement carbon dioxide laser through hole on flexible circuit board:

Currently, the holes processed by excimer laser are the smallest. The excimer laser is ultraviolet light, which directly destroys the structure of the resin of the base layer, makes the resin molecules discrete, and generates very little heat. Therefore, the degree of heat damage to the periphery of 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 thickness-to-aperture ratio, the more difficult it is to wet copper plating. The problem of excimer laser technology drilling is that the decomposition of 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, which will produce bamboo-like residues.

The biggest difficulty of the excimer laser is that the drilling speed is slow and the processing cost is too high. Therefore, it is limited to the processing of high-precision and high-reliability micro-holes.

The impact carbon dioxide laser generally uses carbon dioxide gas as the laser source, which radiates infrared rays. It is different from the excimer laser which burns and decomposes resin molecules due to thermal effects. It belongs to thermal decomposition, and the shape of the processed hole is worse than that of the excimer laser. The aperture that can be processed is basically 70-100um, but the processing speed is significantly faster than the excimer laser speed, and the cost of drilling is much lower. Even so, the processing cost is much higher than the plasma etching method and the chemical etching method described below, especially when the number of holes per unit area is large.

Impact carbon dioxide laser should be noted that when processing blind holes, the laser can only be emitted to the surface of the copper foil, and there is no need to remove the organic matter on the surface. In order to clean the copper surface stably, 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 process, but considering the balance of the process and the proportion of equipment investment, it does not have an advantage, but the ribbon chip automatic welding The process (TAB, TapeAutomatedBonding) has a narrow width, and the use of tape-reel technology can increase the drilling speed. There have been practical examples in this regard.

The above is about the introduction of the difference between the through-hole technology of the flexible circuit board