The difficulties of HDI PCB fabrication
2018-11-23 17:40Writer: qyadminReading:
The difficulties of HDI PCB fabrication lie in micro-via fabrication, via metallization and fine lines.
1. Micro-via fabrication
Micro-via fabrication has always been the core problem in HDI PCB manufacturing. There are two main drilling methods:
1). As for ordinary via drilling, mechanical drilling is always the best choice for its high efficiency and low cost. With the development of mechanical processing capacity, its application in micro-via has been on the way as well.
2). There are two types of laser drilling: photothermal ablation and photochemistry ablation. The former refers to the process during which the operated material is heated to be melted after absorbing laser with high energy and is evaporated off with via formed. The latter refers to the result caused by high-energy photons in UV zone and with laser length more than 400nm.
There are three types of laser systems applied for flex and rigid boards, namely Excimer laser, UV laser drilling, CO2 laser. Laser technology is not only applied in drilling, but in cut and formation as well. Even some manufacturers fabricate HDI by laser. Although laser drilling devices are costly, they have higher accuracy, stable craft and mature technology. The advantages of laser technology make it the most commonly used method in terms of blind/buried via manufacturing. Nowadays, among HDI micro-vias, 99% are obtained by laser drilling.
2. Via metallization
The biggest difficulty for via metallization is it is difficult for plating to reach uniform. As for the deep-hole plating technology for micro-via, besides the usage of plating solution with high dispersing power, via plating solution on plating devices should be upgraded in time that can be accomplished by either strong mechanical stirring or vibration, ultrasonic stirring, horizontal spraying. Also, the humidity of via wall must be increased before plating.
Besides the improvement of the craft, methods of via metallization for HDI see improvement as well with the main technologies: chemical plating additive technology, direct plating technology and so on.
3. Fine lines
The implementations of fine lines include traditional image transfer and laser direct imaging. Traditional image transfer has the same process with the ordinary chemical etching to form lines.
As for laser direct imaging, photographic film isn't needed while images are formed directly on photosensory membrane through lasers. UV wave light is used to operate so that liquid anti-corrosion solution is capable of meeting demands of high resolution and simple operation. Photographic film isn't needed so as to avoid bad influence caused by film defects and CAD/CAM can be connected to it directly so that manufacturing period is shortened to make it suitable for the production of limited quantities and multiple kinds.