Issue link: https://iconnect007.uberflip.com/i/1511130
24 DESIGN007 MAGAZINE I NOVEMBER 2023 rial, 10" x 4", with a full plane on the bottom layer of the right-hand half of the board. e 200-mil 1-ounce trace carrying 14 amps rises to about 75°C, consistent with what we would find in the IPC tables. e temperature lowers to about 49°C over the plane. But the smaller 120-mil-wide trace is the same temperature (at 14 amps) over the plane as the 200-mil-wide trace is without the plane. e presence of the plane drops the temperature by roughly 50% (a result that is very situation specific). Now, if your trace temperature specification is 75°C and you use the usual (IPC) method for determining trace size, you would design with a trace width of about 200 mils. But if you know there is a plane under the trace (or even just part of the trace), you can reduce the trace width (in this case by about 40%), open- ing up some additional board area for addi- tional routing. Vias Even a large trace carrying a high current oen only needs a single small via to connect to another trace segment. e specific exam- ple we simulated and experimented with was the comparison of a 27-mil trace carrying 4.75 amps and a 200-mil-wide trace carrying 8.55 amps, each using a single 10-mil diam- eter, one-ounce plated via 5 . e 27-mil-wide trace via rose to a temperature of 70° while the 200-mil-wide trace via only rose to a tem- perature of 48°C, even though it was carrying almost twice the current 5 . Figure 2 shows the result of another simu- lation 6 . is is of a 120 mm x 16 mm (4.7" x 0.65"), 1.55-mm (60-mil) thick board with a pair of 5-mm (200-mil) wide traces carrying 14 amps. e traces are connected with 10-mil 1-ounce plated vias. Conventional wisdom is that we should use as many vias as necessary Figure 2: Adding vias lowers temperature to a point.