First PCB Design. Any Errors?

Discussion in 'The Projects Forum' started by bubbagump0, Aug 12, 2007.

  1. bubbagump0

    Thread Starter Member

    Jul 10, 2007
    26
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    Well I just finished my first PCB design of a small 1W stereo amplifier. I really didnt have much of an idea of what I was doing, and it would be stupid to order boards that didnt work, so I was wondering if anyone could inform me of any errors, (Im sure there will be plenty) or tips to make my board better. The original schematic is on this page. My PCB picture will be attached. Please take a look. Thanks.
     
  2. GonzoEngineer

    New Member

    Jul 8, 2007
    46
    0
    Well.....first of all, the layout of the IC is wrong, unless you plan on mounting in on the other side! (Pin 1 does not match the silkscreen.)

    I also don't see pin 4 connected to anything.

    BACK TO THE DRAWING BOARD!
     
  3. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    You do need to redo the layout. The IC's pin 1 is the pin to the left of the notch. You have pin 5 to ground, instead of pin 4.

    I might also question why the board is double sided? the circuit can be done all on the bottom layer with some trace rerouting. That is always easier and cheaper to do, even if you need to use jumpers to go over a trace or two. Use thicker traces, too. For audio work, make them as thick as will fit. It may not look as tidy, but, at least for the outputs on pins 1 and 3, there will be a bit of current. Skinny traces may add a bit of resistance - never a good idea for audio.
     
  4. spar59

    Active Member

    Aug 4, 2007
    51
    0
    Another tip where space is available is to turn corners using 2 x 45 degree turns with a small bit of straight track between rather than a single 90 degree one, during etching the outside corner of a sharp turn can be eaten away slightly, hence this is even more appropriate if thin tracks are used.

    If you are intending this circuit as a production run hence the buying boards comment then fine. However if you are simply wanting a few boards and you have access to a laser printer or photocopier it may be worth considering using the diy press-n-peel transfer system, you could get quite a few of these boards on just one (approximately A4) sheet.

    Steve.
     
  5. bubbagump0

    Thread Starter Member

    Jul 10, 2007
    26
    0
    Thanks for the suggestions. After I work on the design more, I would really like to have just a couple of boards for testing. Spar59, can you tell me more about this press-n-peel system?
     
  6. spar59

    Active Member

    Aug 4, 2007
    51
    0
    No problem - the system is a sheet of plastic film with a matt coating on one side.

    You need to:-

    1) print your design via laser printer / copier onto the matt side of the sheet with the pattern as viewed from the TOP SIDE of the board.

    2) Put the matt side which has the track pattern on it in toner against a clean, bare, copper clad pcb board.

    3) Iron the pattern onto the board (a bit like t-shirt printing) - the toner sticks to the board.

    4) Let it cool and peel off the film - the toner is left stuck to the board.

    5) Touch up any gaps, if necessary, with a pcb pen (Steadtler permanent ink fibre pens designed for overhead projectors work well and have finer tips).

    6) Etch the board - the toner is etch resistant.

    7) Rinse it and clean off the toner.

    8) Drill the board - carbide drills are best but are rigid and hence brittle, standard HS steel drills don't last long on glass fibre boards.

    9) Solder your components.

    You can produce boards with quite fine track detail using this method - I've used it down to 0.01" tracks though where possible I use 0.02" or greater - there is definitely no problem getting a track between adjacent dil ic pads.

    Cheapest source of the film is probably EBay - just search for press n peel.

    After a bit of practice you will be able to get perfect boards even with complex track patterns - but make sure there are NO GREASY RESIDUES on the board or the toner will not stick (and neither will the touch up pen).

    Temperature is important, too cool the toner doesn't re-melt, too hot and the film (and hence the track layout) can be distorted, read the instructions supplied with the film.

    Steve.
     
  7. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    If you can make transparencies on a laser printer, then you can get positive resist coated pc board stock. I use the ones from www.circuitspecialists.com. They are reasonably inexpensive, and give good results down to trace widths of .008. The developer is only good for a few hours, but will do multiple boards in that time.
     
  8. spar59

    Active Member

    Aug 4, 2007
    51
    0
    I agree that the photo method proposed by beenthere is capable of better results than press n peel - the problem with the photo method is the need for a UV light source for exposing the boards - I've been trying to pick one up for a while but have been unable to find a reasonably priced one.

    Steve.
     
  9. nanovate

    Distinguished Member

    May 7, 2007
    665
    1
    Here is a link to a datasheet which has an example layout.

    http://www.st.com/stonline/books/pdf/docs/1464.pdf

    Samsung also has a datasheet but it doesn't contain as much info.

    If you are going to use 2-layers then you can dedicate one unbroken layer to the GND net.

    As was mentioned earlier your silkscreen does not follow the convention of having Pin 1 use a square pad. If you look on page 1 of the datasheet I linked to Pin 1 is on the upper left corner and the numbering goes counter-clockwise. Also the output, and supply pins are on side of the IC. These are typically the higher current carrying signals. Route them using thick traces (also mentioned earlier).

    Please post your revised layout when you complete it so some of the experts above can give you pointers to take it to the next level ;)

    John
     
  10. n9352527

    AAC Fanatic!

    Oct 14, 2005
    1,198
    4
    Or you could use inkjet photopaper. Not all papers are suitable, but I found an excellent one and it is also cheap, 99p for 15 A4 sheets. It peeled cleanly after ironing and produces clean, even, thick coating with my ML-6060 laser.

    I regularly make boards that have 10mils tracks with small leadless components, and the results are excellent.
     
  11. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    The sensitized pc boards list an 8 minute exposure to sunlight for acceptable results.
     
  12. geoff_p

    New Member

    Aug 14, 2007
    2
    1
    I use Kodak Film (don't know its proper name, 'cos a local computer shop gave it to me Free) and print onto its slightly-sticky side with an ordinary inkjet printer set to 'super fine'. Leave the print to dry for an hour, else the board sticks to it!
    I use Kingsten presensitized PCB at about 2$US for an 8" x 4" board, cut to size with my trusty, rusty hacksaw.
    For exposure I use a fluorescent tube for an insect-repeller/zapper, balanced in a cardboard box. With about 2" between the tube and my board, an exposure of four minutes does quite well.
    I use the D50 developer (it actually lasts a couple of weeks, with luck) applied from a perfume-type spray bottle.
    Rinse and etch.
    Good luck,
    Geoff
     
  13. cumesoftware

    Senior Member

    Apr 27, 2007
    1,330
    10
    I never saw a schematic of your circuit here. So, there is no way to tell if your PCB is wrong or not, since there is no circuit to compare with.
     
  14. John Luciani

    Active Member

    Apr 3, 2007
    477
    0
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