PCB007 Magazine

PCB007-Mar2024

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MARCH 2024 I PCB007 MAGAZINE 79 negative environmental impact. Halogen-free materials took off in the late 1990s and early 2000s, driven by cellphone manufacturers. Nokia was a main driver, and that was purely to prevent halogen material absorption by Nokia mobile phone users. Halogens were also in plastics in other parts of the mobile phone, so Nokia was concerned about this issue for their customers. Requiring halogen-free material was still a market-driven decision. But even with regular materials, it is well known that 1.6 mm is a standard PCB thick- ness, but do you need 1.6 millimeters? Could it be 1.2 or one or even 0.8 mm? There are those who say that we use 1.6 mm for historical purposes and it is no longer nec- essary. Exactly. By making it 0.8 mm instead of 1.6, you get a product that is half the weight. What's not to like about that? It costs half the money to transport it halfway around the globe. Trans- portation is significantly more expensive today compared with just a few years ago, so there's money to be saved for our clients at many steps along the way. It will also have a positive impact on the environment. It would be positive for the supply chain as well, because when you can make boards with half the substrate, that means, at least theoretically, that there will be more material capacity to do more boards. Another small example is when you look at the balance between design values and PCB func- tionality and performance: A standard 1.6 mm PCB with a 0.20 mm through-via will reduce the number of panels you can stack at drilling. You can have only one or two panels per stack, or you will have out-bending at the exit hole. If we could increase the via size to 0.25, 0.30, or 0.35 mm, you can increase the number of pan- els in your stack. You will save time and energy and the material used to create these holes. Oen, we see boards designed with 0.20 mm holes that could just as well have been made with 0.25 or 0.30 mm vias. is brings up another important point: As your BGA pitch starts to go below 0.8 mm, and you begin to apply laser-drilled microvias and buried vias to your design around the BGAs, but the rest of the board doesn't have the same kind of complexity, the default is to design the non-BGA board areas with through-holes. But there's absolutely no reason to use so much through-hole drilling when you have intro- duced laser-drilled microvias and buried vias. You can make the connections through them. What will you achieve by that? You will get less signal disturbance because every through-hole you have in a PCB acts as a kind of antenna, sending a signal out. If you can avoid going all the way through the board, but rather only go down to layer two or layer three, the signal disturbance stops there. e number of laser drilling steps and lamination cycles required depends upon the BGA size and pitch. When needed for, say, pitch 0.4 mm and below, stacked laser drilling steps can interconnect through all layers, which is what we call every- layer interconnect PCBs (ELICs). Erik Pedersen

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