Issue link: https://iconnect007.uberflip.com/i/1527613
16 DESIGN007 MAGAZINE I OCTOBER 2024 But let's say each one of those consumes 100 milliamps—that's 800 milliamps of current, almost an amp of current just in the memory chips. at's not the processor, the GPU, or whatever type of device we're designing. You need to put a power supply on this board, and it will be on the same surface. We typically put all our ICs on one surface and our passives on the bottom side. If you're consuming 2 amps of current, or even 1 amp, and a single processor that will take another 200 milliamps of current, you'll hope for 1 total amp of current. e 1-ounce copper is 39 microns starting thickness, and aer processing, we'll say 30 microns total copper thickness. at's almost three times thicker than the 12 microns on the board right now. With 1 ounce of copper, 1 amp of cur- rent for a 10°C rise above ambient is about 10 mils of trace width. All of a sudden, you need about a 30-mil trace width to handle the cur- rent coming out of the power supply. If I'm doing a TSOP power supply linear regulator chip, not an SOIC, the pitch on those is only 20 mils. at means the width of my trace try- ing to come out of the output pin of my voltage regulator is wider than the pitch between the pins. You can see what's happening. LaRont: There's a balancing act going on. Right. You need to have this really thin cop- per for the digital to get out of these fine-pitch devices. But to meet the routing capabilities, there needs to be much, much thicker copper over by the power generation. How do we bal- ance that? ere are all kinds of tricks, like selective plating, thermal pads, and others, or we can accept higher temperature rise locally and then do some localized thermal controls. Again, we have to go through thermal management, ther- mal mitigation-related issues, compared to a standard board. Shaughnessy: If designers are looking into using partial HDI, where should they start? Start with the standards: IPC-2226 for the design side, which includes HDI and how to design microvias, and IPC-6016, which includes dielectrics and the manufacturing process. Modern EDA tools are set up to be able to do this successfully and right the first time, as long as the designer has the knowledge and the training. Partial HDI is not a big cost adder. But designers really need to work with their fabricator on this, because of the trade- offs with thin copper, and so on. As I say, the fabricator is your friend. Shaughnessy: We appreciate your time, Kris. anks, Andy. DESIGN007