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46 PCB007 MAGAZINE I NOVEMBER 2020 In addition, laser vias may be stacked or staggered relative to each other, and they may also be stacked or staggered relative to a bur- ied mechanical hole. Furthermore, laser vias, blind, and mechan- ically drilled through-holes can be placed in component pads (SMD pads), which requires special treatment. Filling Vias Laser vias can be copper-filled or filled with resin. If they just act as fan-out vias, they are simply covered with the solder mask used. When filled with resin, they can also be capped with copper, and then components can be mounted and soldered directly on them. Cop- per-filled laser vias is the latest method used, but both methods are still very relevant. PCB manufacturers operate with their own capability in terms of diameter, aspect ratio (AR), and pad diameter requirements on the various hole variants. The problems related to production are mostly the same with all manufacturers, but processes, equipment, technologies, etc., are the reason for PCB manufacturers to have a difference in capac- ity and capability. This is also reflected in the fact that some PCB manufacturers have specialized in prototypes and small, fast de- liveries, while others are specialists in high volumes. Considerations for Designers It is essential that designers become fa- miliar with the production processes so they can understand what is possible and not possible to produce. Some who were not aware previously operated with a through-hole diameter of 0.1 mm on 2-mm thick PCB. For- tunately, there are not many left, but some are still out there. For a PCB to be produced with a good result, it is important to provide the designer with this in- formation on capability and design rules. How- ever, the designer must also be obliged to obtain the necessary information before starting a lay- out. This is absolutely essential for a good result. As a designer, you must have access to the cur- rent IPC standards that the world's manufac- turers adhere to—typically, IPC-6012, IPC-6013, and IPC-A600. However, the designer must also clarify what is available in relation to the type of PCB that is to be realized. I have mentioned in previous columns how important this is, as the cost of redesign due to lack of knowledge about the rules that apply is not something you want to cover. Laser Vias Used in HDI PCBs HDI PCBs are an increasingly integral part of the PCB and electronics industry in gener- al. Electronic components are getting small- er and lighter but still require high perfor- mance. To meet this, you also need to pack more functionality in a smaller area with HDI PCBs. HDI PCBs have a higher circuit density per unit than conventional PCBs. They use a com- bination of buried and blind vias, as well as la- ser vias. Those that are ≤0.15 mm in diameter are also called microvias (mVias). Any Layer HDI, ELIC, and ALIVH High-density PCBs have a combination of different vias, as compared to others that only have laser vias and tend to be called any lay- er HDI. Other names are every layer intercon- nect (ELIC) HDI and any layer interstitial via hole (ALIVH). The maximum number of layers with this technology I have seen is 14 layers. Then, you have a finished PCB with stacked laser vias and a maximum thickness of around 1 mm. This anonymous stackup is one I have worked on, but I do not have permission to show this stackup, so Figure 1 and Table 1 show an equivalent of eight layers and is about 0.6-mm thick. The most common combination of vias in an HDI PCB is 1–3 sets of laser vias per side, in combination with mechanically drilled buried vias. Through-holes are for components that require this, as well as unplated holes. Via holes that go from top to bottom have been replaced with the combination of laser and buried holes already defined. This avoids a