2 layers PCB with through hole vias

Discussion in 'General Electronics Chat' started by adam555, Oct 7, 2014.

  1. adam555

    Thread Starter Active Member

    Aug 17, 2013
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    I need a 2 layers PCB for a new design prototype, and can't find anyone that would just print me one (75 x 100 mm) for a good price -the cheap ones will only print a minimum of 5, the ones that do are too expensive, or the P&P is too high- so I decided to try and do it myself. I made many before, but this will be my first 2 layers PCB.

    My main worry is that the design has a lot of through hole vias, and these are meant for components that can only be soldered from one side (e.g. 7 segments LED displays), so I'm not sure if the soldering will pick the pads on both layers without a barrel through each via. Therefore, any advice or help from anyone with experience making 2 layers PCBs will be appreciated.

    Thanks in advance.
     
  2. Papabravo

    Expert

    Feb 24, 2006
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    Vias are not supposed to be used for components. We always made vias with a diameter that was too small to accept a component lead. You'd be really surprised what an assembly tech will try to do if you let him. If there is no barrel, the the technique is to solder the component leads on both sides, solder won't flow on FR-4
     
  3. Lestraveled

    Well-Known Member

    May 19, 2014
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    ExpressPCB has free schematic capture and PCB layout software. They have a prototype special, 3 each, double sided boards, plated through holes, 2.5 by 3.8 inches for about $51 plus shipping.

    If you want to do it yourself, there is an excellent tutorial on making PCBs by Bill Marsden on this forum. I am sure someone will supply a link shortly. Also use the search feature. There are a lot of different ways to make PCBs at home.
     
  4. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    Here are some suggestions:
    https://oshpark.com/
    http://www.seeedstudio.com/service/index.php?r=pcb
    http://dirtypcbs.com/

    Since we don't know where you are, no one can calculate the effect of shipping. I have used Oshpark and have been very satisfied. It accepts Eagle files and allows you to view the results before ordering. Some of the others may do that as well.

    If you DIY, some people will use a small wire soldered on both sides to provide the plated via functionality. You may want to offset the vias a little from the pads needed for the component. I have also soldered the component on the top side, while it was lifted from the board. Then upon heating the leads from under the board, I have seated it properly and soldered the bottom. Obviously, that will be a bit more difficult with a 50-pin chip than with a 4-pin rectifier bridge.

    75 mm X 100 mm is quite a large board, in my experience. Can you use SMD to reduce the size and cost? Today, I rarely use TH components, except when that is the only viable option and/or for electrolytic capacitors.

    John
     
  5. adam555

    Thread Starter Active Member

    Aug 17, 2013
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    Thanks,

    Around $50 + P&P is also the cheapest I could find for just one board; but that's too expensive considering the use I'm going to give it. I found some that will do each for $25, but only if I order 5 boards.... By the way, I'm in Spain.

    The wire soldered on both sides sound good. I'll give it a try; unless anyone else posts an easier solution.

    It's already designed and I need it to be 75x100mm: first because it's a shield for the Arduino Mega; and because it has 20 x 7-seg digits, 2 rotary encoders, 4 buttons, which take a lot of physical space and need a lot of tracks.

    I never used surface mount components; I really prefer through hole because I can test the components that I will use in a bread board, and then pass them to a PCB.

    How do you test designs with surface mount components?
     
  6. NorthGuy

    Active Member

    Jun 28, 2014
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    I also used Oshpark many times. Exceptional quality and very cheap. The only bad thing is that you have to wait.
     
  7. adam555

    Thread Starter Active Member

    Aug 17, 2013
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    I thought about doing it this way, but these 7-segment displays (with 4 digits each) have a lot of pins, and on top look quite fragile -you know, Chinese cheap components-. So, I though I might end up making a mess.

    I don't really mind the wait; the price is the main issue in this case -even $25 sounds a bit expensive, though I know I'm probably being a bit unreasonable. That's why I'm opting for making it myself.
     
    Last edited: Oct 7, 2014
  8. Lestraveled

    Well-Known Member

    May 19, 2014
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    Some things to consider:
    - Based on your hands on skill level and that you have never made a PCB before, you will probably have to "shoot" it several times before you get a board that is good enough.
    - By the time you buy pre-sensitized double sided PCB stock, and etchant, you will be close to $25 just with these two items. Making an accurate double sided PCB using the cheaper laser printer method is really tough.
    - What kind of printer do you have access to?
    - What is the size of your smallest trace? On a home built board I never go less than .020 Inch.
     
  9. NorthGuy

    Active Member

    Jun 28, 2014
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    Don't forget to account for the cost of raw materials, chemicals, drill bits you break etc. etc. :)
     
  10. MrChips

    Moderator

    Oct 2, 2009
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    You can make your own double sided PCB with some careful planning to layout.

    (1) Wherever possible, make your solder connection on the bottom layer (solder side).

    (2) If you are going to solder on the top layer (component side) make certain you have access to the pad or trace for soldering. For seven-segment displays you may want to consider using wire-wrap sockets or single pin sockets that you can solder on the top side.

    (3) For vias, make sure you have access to the via from both sides. You can insert a short length of wire (that is what I save resistor and capacitor leads for) and solder from both sides.
     
  11. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    I may test a design on a breadboard with TH components. I then use new SMD's on the PCB. The failure rate for individual components is extremely low. I have never had an SMD version of a breadboard circuit not work because of a faulty component.

    John
     
  12. adam555

    Thread Starter Active Member

    Aug 17, 2013
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    No, I made many PCBs before; this is just my first with 2 layers.

    I already have all the tools needed -including the 2 layers PCB-. The only thing that I don't have is a laser printer or the means to do a photo print. I know both methods, and used them years ago; but at the moment I was just making boards by hand with a marker.

    I'm planning to print this circuit in a glossy photopaper down in my local cybercafe, and then transfer it to the board with an iron.

    Yes, it's probably a lot of work, and I might need more than one attempt; but it will require practically no extra cash.
     
  13. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    Just to add to MrChips' comment, I will sometimes use a carrier with bare machine pins, such as:
    upload_2014-10-7_18-11-53.png

    After soldering the pins, you pop the aluminum carried out and insert your IC. Other versions are made with plastic supports, like headers, that do not need to be removed. So-called machine pin contacts are very nice, but are not for repetitive insertion and removal of IC's.

    John
     
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  14. adam555

    Thread Starter Active Member

    Aug 17, 2013
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    One question...

    how do PCB manufacturers add the barrels? Can't it be done at home?
     
  15. Lestraveled

    Well-Known Member

    May 19, 2014
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    Very good, then ROCK ON.
     
  16. jpanhalt

    AAC Fanatic!

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    By barrels, do you mean the through-hole plating? If so, that process is described in many places. It is not beyond the home DIY'er with CNC drilling equipment, but most of us don't do it.

    John
     
  17. ISB123

    Well-Known Member

    May 21, 2014
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    Just use 1mm wire as via barrel. Manufacturers probably rivet the via's with some kind of CNC rivet gun .

    Example:
    [​IMG]
     
  18. adam555

    Thread Starter Active Member

    Aug 17, 2013
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    I think I can get similar pins from those rows of headers that connect on themselves. Might be worth giving it a try and using them as MrChips suggested.

    Thanks for the advice; I tried to keep all the soldering pins in just one side, but there are far to many tracks in the circuit. I was barely able to fit them all; even though I used half of the width I always do (reason why I can't use a marker this time).

    This is the board (most of the tracks are on the back):

    Arduino Mega Shield.jpg

    Thanks everyone for all the help...
     
  19. Lestraveled

    Well-Known Member

    May 19, 2014
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    Here is a very cool youtube video on do it your self through hole plating.

     
  20. MrChips

    Moderator

    Oct 2, 2009
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    Here are some examples of what I mean about careful planning to layout:

    [​IMG]

    Assuming that the white traces shown are on the top layer (component side), reroute the traces shown in red to the resistors.

    I have some more examples but first you need to confirm that the white traces are on the top layer.
     
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