Trace Routing Details Disco-Kraken -------------------------------------- Original Rev. 10-July-2024 Current Rev. 11-Feb-2025 This file holds the details about the trace routing on the DK bpard. This includes such things as: trace widths, vias used, differential trace design, differential vias, spacings trace to trace, diff trace to diff trace, and via to pin, i.e. the design rules. Traces to the various size bypass capacitors: --------------------------------------------- cap_ 0402 0.4 mm trace 0mm65 via 0.5 mm pad edge to via center spacing on axis 0603 0.6 mm trace 0mm65 via 0.5 mm pad edge to via center spacing on axis requires 0.19 mm of less pad to via design rule 0805 0.? mm trace 0mm65 via 0.? mm pad edge to via center spacing on axis 1206 0.8 mm trace 0mm79 via 0.6 mm pad edge to via center spacing to side Design Rules During Routing: ---------------------------- Disco: ------ Default Diff Pair HS Diff Analog ---------------------- ---------------------- ---------------------- Pin Via Trc Fill Pin Via Trc Fill Pin Via Trc Fill ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- Pin 1.00 0.50 1.00 Via 0.19 0.32 0.38 1.00 0.20 0.28 Trc 0.11 0.20 0.185 0.12 0.26 0.21 0.11 0.30 0.21 Fill 0.35 0.35 0.50 0.50 0.35 0.35 0.50 0.50 0.14 0.20 0.30 0.40 For Reference: Hub: ---- Default Diff Pair HS Quad SE ---------------------- ---------------------- ---------------------- Pin Via Trc Fill Pin Via Trc Fill Pin Via Trc Fill ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- Pin 1.00 0.50 1.00 Via 0.20 0.35 0.38 1.00 1.00 1.00 Trc 0.12 0.20 0.185 0.12 0.26 0.21 1.00 1.00 1.00 Fill 0.14 0.20 0.30 0.40 0.15 0.20 0.35 0.40 0.14 0.20 0.30 0.40 HTM: ---- Default Diff Pair HS Quad SE ---------------------- ---------------------- ---------------------- Pin Via Trc Fill Pin Via Trc Fill Pin Via Trc Fill ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- Pin 1.00 0.50 1.00 Via 0.20 0.35 0.38 1.00 1.00 1.00 Trc 0.12 0.20 0.185 0.12 0.26 0.21 1.00 1.00 1.00 Fill 0.35 0.35 0.50 0.50 0.35 0.35 0.50 0.50 0.14 0.20 0.30 0.40 Differential Pair Trace Length Matching: ---------------------------------------- After the Differential Pair has been routed and smoothed use our software to do a length comparision. If possible match the trace length by adjusting the routing. Where necessary add serpentines to match the shorter o the pair to the longer. The serpentines can be used in either HV or 45 deg trace segments. Place the serpentine close to where the trace length miss-match takes place. As the last step add a serpentine section to the shorter trace. We are using the following rules to make the serpentines: On a vertical or horizontal trace the serpentine is: A perpendicular step out of 0.2 mm for a length of 0.5 mm. Return to the normal trace path for 0.6 mm before stepping out again. Round the 4 corners of each step out with an arc of 24 segments/rotation and a radius of 0.10 mm. Each of these step outs will add 0.225 mm of trace length. On a 45 degree diagonal trace the serpentine is: A perpendicular step out of 0.2121 mm for a length of 0.4950 mm. 0.2121 mm is 3 grid dots diagonally with a grid of 0.05 mm. 0.4950 mm is 7 grid dots diagonally with a grid of 0.05 mm. Return to the normal trace path for 0.5657 mm before stepping out again, i.e. 8 grid dots diagonally with a grid of 0.05 mm. Round the 4 corners of each step out with an arc of 24 segments/rotation and a radius of 0.11 mm. Each of these step outs will add 0.265 mm of trace length. Add serpentine until the short trace comes within about 0.3 mm of the longer trace. Do not make the short trace longer than the originally longer trace. Stopping the serpentine about 0.3 mm short of a match allows for the possibility that the added electrical delay of the serpentine is greater than its added geometric length. Note that all of the high-speed differential signals need to have their corners rounded. This rounding was typically done with 24 segments/rotation for bend radius up to about 2 mm and then 48 segments/rotation for larger bend radius. There is the issue of either, having a common bend radius for the inner and outer trace, or having a common center point for the bend of the inner and outer traces. If anything it is probably best to let the separation between the two traces increase a little bit during the bend.