Please comment on my lousy PCB layout (Eagle) - Page 1
Forum section: electronics / beginners

author: pstkk
author_rank: Newbie
timestamp: December 14, 2015, 02:53:19 am
content: Warning: I'm a complete beginner...Anyway, attached to this post are two images, a schematic and a board layout done in Eagle. This is my fist time using Eagle, so what I hope for is any kind of feedback to help me improve on the design. The schematic was provided by the company making the central IC, so it should be fine. But, since I did the PCB layout, it's likely to be full of bad routing and mistakes. Please comment on anything you would have done different.The board is for a PowerLine Communication modem (PLC modem). The IC is a Sig60 from Yamar. More info here:http://yamar.com/product/sig60/. The Sig60 chip injects a serial signal into a 48V DC powerline connected to JP2. HDI and HDO are RX and TX.This board is an early test to familiarize myself with the design process and to see if I can actually make a working prototype. If it works out, the the next step will be to design a similar board, only a lot smaller, no wider than 0.6 inch / 1.5 cm. The production version is to be fitted into thermal ice drills. These drills are designed to melt deep down in glaciers. The reason for implementing a PLC modem, is to reduce volume, weight and price of the surface cable.

author: pstkk
author_rank: Newbie
timestamp: December 14, 2015, 03:35:08 am
content: Quote from: blueskull on December 14, 2015, 03:11:45 amThank you so much blueskull! This was exactly the kind of feedback I had hoped for. I'm already working on a better layout.

author: matseng
author_rank: Frequent Contributor
timestamp: December 14, 2015, 03:43:42 am
content: Quote from: blueskull on December 14, 2015, 03:11:45 amIsn't both the myth (which might have been relevant one upon a time, but not with todays manufacturing techniques) about acid traps at sharp corners as well as 90-degrees-is-bad-for-your-signals (as long as you're not having rise times in the range of like 100ps) severely debunked by now?I agree that 45's looks better - but does it *really* matter for the average hobbyist-grade digital electronics project?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: December 14, 2015, 03:51:39 am
content: I don't know about manufacturing.For very high speed signals, a 90 degree corner does leave an impedance discontinuity; for that, the outside corner should be mitered back, pretty severely. But this is only relevant at high precision >1GHz say, which includes 10GHz+ RF circuits, and very fast digital signals (usually some kind of LVDS).Board layout is a technical art. While you can very easily make a board that's sufficiently well connected for operation, that leaves a lot of free variables undefined. Do you route a trace out and down, or diagonal, or a little bit here and there? Straight lines top and bottom, or meandering routes? Traces bunched together, or spread apart? Ground pour or ground plane (or both, or neither)? The final decisions made on these matters are what encompasses the art form of board layout. Since these variables are entirely under your control, why leave them in an unpleasing state?Tim

author: v8dave
author_rank: Regular Contributor
timestamp: December 14, 2015, 04:02:50 am
content: As well as the above recommendations, increase the width of your power traces. This is stated in the datasheet for the device. Drop down the size only when you are close to the IC.Change the size of the via's on your signal lines and power lines. For power rails I use a larger diameter VIA and for signals I use a smaller diameter one. Makes it easier to route everything tighter

author: pstkk
author_rank: Newbie
timestamp: December 14, 2015, 09:38:00 am
content: Thank you for all the feedback.Attached is a new layout. I have tried to follow your recommendations as much as possible. It looks better for sure. The only part I don't like is around R3 but I guess it's OK.I will do smaller via's and thinner signal lines for the next version, where I'll also try and make more use of the bottom layer. For now I think this version is OK as a prototype so I'm going to order a pair to see if they'll catch fire.Once again, thanks you for the fast and useful advise.

author: Dave
author_rank: Super Contributor
timestamp: December 14, 2015, 10:23:33 am
content: The current loop for C21 is still HUGE. Try flipping it to the other side of the track and have the ground connected directly to the IC pin.