Circuit Board Design Questions

Discussion in 'Homebrew and Kit Projects' started by WA2FTV, Jan 12, 2020 at 1:28 AM.

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  1. WA2FTV

    WA2FTV Ham Member QRZ Page

    Hello Everybody,

    If there is anybody that has done circuit board design (either professionally or as an amateur), I have a few questions regarding the design. This is my very first attempt at designing a circuit board assembly for a ham radio application.

    I am using one of the free shareware circuit board design SW to design a receive only switchable attenuater along with a Low Pass Filter, 50:75 ohms impedance transformer. I purchased a pre-amp that will be part of the system. It will be part of a Hula Loop antennas system.

    My questions are the following...

    1) What width is commonly used for the traces? The system default appears to be .010 inch. Does it need to be wider?

    2) Do my traces need to be at 45 degree intervals when changing direction verses 90 degree intervals?

    3) If I were to have components on both sides of the board (i.e. SMT devices), what size via feedthrough hole size would be appropriate?

    4) For THT (Through Hole Technology) parts, how much larger in diameter should the hole pad be compared to the lead diameter (Ex: 10% larger)?

    Thank You for your assistance.

    Best Regards and 73s,

    Cedric
    WA2FTV
     
  2. PY2RAF

    PY2RAF XML Subscriber QRZ Page

    Hello, @WA2FTV !

    Cédric; been where you are now. I do have a few articles to point and possibly help you :

    1. First, check this Michael Ossman Youtube presentation in https://hackaday.com/2016/03/23/michael-ossmann-makes-you-an-rf-design-hero/
    2. And then watch this one from Chris Gammell https://hackaday.com/2019/12/09/hackaday-superconference-an-analog-engineer-dives-into-rf/

    They do provide answers for almost all of your questions - and interesting insights, hints & tricks.

    A personal side note. I designed a few stuff (a IF panadapter board) prior to be exposed to this presentation (and yes, I found that I failed in a few best practices).
    Well, guess what? It does work great ¯\_(ツ)_/¯

    On the other hand, I'll be crafting in the future a new version with calculated microstrips etc and I'll compare how dramatical was the difference - if any.

    Anyways, hope it is of help!

    Best of luck; 73,

    - Rodrigo, PY2RAF.
     
  3. WN6U

    WN6U Subscriber QRZ Page

  4. G4COE

    G4COE Ham Member QRZ Page

    For through holes I always stick to 0.8mm, I reckon that's an 'happy medium' I bought a Proxxon Mini bench drill, for the purpose and does a stellar job.... I've still got the speed on the default setting, never ever altered the belt setting yet.... use drill with the shanks as they are far better than straight drills, and no shame in using re-sharpened bit's from PCB factories they are usually cheaper and do just as good a job.... even those down to 0.6mm.

    The only complaint I can think of with the Proxxon is they didn't put a light in the base of the drill, one of these day's. I'll visit the garden shop and get a..... roundtoit, have some white super bright SMD's LED's here should be easy enough to do.

    As for the tracks depend on what they do AND how you are going to get the design on the board, using toner transfer you don't want them too thin, I usually use 25th to 40th of an inch, for current carrying you'll need thicker tracks, unless you are prepared to tin the tracks with a coating of solder.... the tracking also depends on the density of the design too.

    Dave
     
  5. KI6J

    KI6J Ham Member QRZ Page

  6. AB9LZ

    AB9LZ Ham Member QRZ Page

    If it's a simple (and maybe not so simple) circuit, lay out the traces with a pencil, then cut them with a fine burr equipped moto tool and an aluminum straight edge. The same engraving burr will drill perfect fine gauge wire holes as well.

    This works especially well for smt stuff, and allows for easy on the spot corrections and additions.

    I used to use eagle cad and either did the laser toner sugar paper transfer and etch, or sent them out, but neither was really worth the time and expense for one offs. The one exception is if you are dealing with large, fine pitch smt's, like a DAC.

    73 m/3
     
  7. VK4HAT

    VK4HAT Ham Member QRZ Page

    1. The width of a trace is determined by the amount of current the trace has to carry and or the impedance required.

    2. Yes and No. Mostly no at HF which is very forgiving. Unless you are designing things in the microwave region where controlled impedance is a must, a lot of this good practice can be ignored. Electrons will not fall off the board at a 90 deg junction, but it might screw up your impedance control in critical circuits.

    3. Vias, it depends again on current carrying, whether the via is in a pad or not etc. Mostly for small signal stuff I stick with 0.4mm vias for everything and avoid using vias where I am carrying substantial current on the traces.

    4. Annular ring of a pad for through hole is mostly limited by the board manufacturer, they have a specs for how small it can be compared to the drilling, and also how much mechanical strength you need on the joint.


    Other than for trace widths, the rest of these will be fine if you accept the default sizes in your ecad of choice and use the default footprints for components. You can see in this board I designed some junctions where the traces meet at 90 deg, there are vias in pads as well, which is ok when hand soldering.

    [​IMG]
     
    Last edited: Jan 16, 2020 at 10:51 PM

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