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16 DESIGN007 MAGAZINE I NOVEMBER 2024 Learning the Rules Shaughnessy: Kelly, where do designers begin learning rules of thumb? Dack: Typically, you learn a rule of thumb from other captive designers in your engineer- ing group. For instance, how many amps can a trace carry? e rule of thumb used to be that 10 mils can carry 1 amp. You can use that as an estimate, and then start dialing things in. It starts becoming critical for you to go into a calculator that has embedded formulas. Now our soware has embedded formulas, and it will actually tell you what the expected current carrying capacity of a trace is. We can say it's 1 amp for a 10-mil trace, but we must consider another critical factor: How thick is that cop- per? It's a function of the cross-section. LaRont: In general, a rule of thumb is usually correct 85% of the time. Is that about right for PCB design? Dack: Yes, it's a very conservative estimate. A rule of thumb gets you started, and new design- Physicists like to measure things, and they like those measure- ments to be as precise as possible. That means working at unfath- omably small scales, where distances are much smaller than even the diameters of subatomic particles. Researchers also want to measure time down to a precision of less than one second per tens of billions of years. The quest for these ultraprecise measurements in physics is part of a growing field called quantum metrology. Now, as reported in the journal Nature, a Caltech team led by Professor of Physics Manuel Endres has developed a new device that could lead to some of the most precise time measurements ever achieved. The method merges state-of-the-art atomic clocks with quantum computers. The device that allows these precise time measurements will help physicists better probe the laws of nature, such as Albert Ein- stein's general theory of relativity, and study some of the hardest problems in physics, such as the nature of dark matter. Detailed measurements of this sort are also needed to detect gravitational waves, ripples in space-time. In the future, the researchers hope to further reduce errors in the system to bring their clocks even closer to theoretical limits of preci- sion. (Source: Caltech) Merging Atomic Clocks with Quantum Computers ers need to understand that. They may hear a rule of thumb that says, "I must have a 0.040" diameter test point." Where does that informa- tion come from? They don't know. We need to point them to the IEEE spec that defines all that so they can start learning about it. Then an experienced designer can show them how they can go down to 0.035" diameter test points for a dense board. "How about a 0.035" square-shaped test point, which increases the overall area of the test point, which can be beneficial?" Shaughnessy: So, even in the best situation, a rule of thumb is just your starting point. Moyer: Right. As I mentioned earlier, it's a default position. Dack: Then you start dialing things in. LaRont: This has been great. Thanks so much, guys. Moyer: ank you. DESIGN007 Click here to access the desk reference guide: IPC Design Process Flow.