This board breaks out a USB Type-C plug to pairs of SMA connectors for each of the super speed pairs, a USB micro B connector for D+/-, and
It has been too long, but I finally got all the connectors on the board. There are pictures in the gallery. Stay tuned for testing performance.
SMA connectors are quite common for high speed interconnect in applications like this and you would think there would be plenty of app notes or examples to copy, but I was surprised how difficult it was to find a suitable reference to copy. I did find some information online to point me in the right direction. One issue I wanted to address was the fact that the pad for the signal pin is significantly wider than the trace width for a 50 Ohm trace. This article by Dr. Howard Johnson describes some techniques to deal with this ( http://www.sigcon.com/Pubs/edn/TaperedTransitions.htm ) I'm not going to go full tapered, but I did round the pad and cut away a little off the plane below to reduce the effect of the transition.
The lazy engineer in me has become a little too dependent on upverter and they have recently hosed me with their major system update that left several of my projects stranded, so I am finally making the long overdue effort to wean myself off and switch to KiCad.
One of the techniques I want to use is curved traces which should make the impedance more consistent, especially since I won't necessarily be able to hit it perfectly. I discovered that KiCad does not support curved traces, but fortunately Seth Hillbrand presented a technique to work around this at KiCon. It is a bit of a kludge and a little painful but usable for the number of corners I need. It sounds like real support for curved traces is coming to KiCad, so we shouldn't need to do this much longer.
The purpose of this project is to build a USB Type-C breakout board to facilitate the evaluation of boards designed to utilize the super speed differential pairs. This is intended to be a cost effective alternative to the commercial breakout boards. To keep this accessible to makers, I am designing this to be fabricated at OSHPARK to see what performance I can get with there standard 4 layer stackup. I'm designing the board to be as small as possible to keep the price down and the traces short. It should be a little easier to keep the traces short and matched now that vertical plugs are available ( https://www.digikey.com/product-detail/en/jae-electronics/DX07VN24WA2C1568/670-3103-ND/9695489 ) I don't have access to 3D field solvers, nor the time or patience to use them, so I will take be using my best engineering judgement, over-design a little and use every rule of thumb I can find.