manufcaturing PCB...double vs single sided

Discussion in 'General Electronics Chat' started by Gibson486, Feb 28, 2013.

  1. Gibson486

    Thread Starter Member

    Jul 20, 2012
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    When making a PCB, is there an issue making things too compact together? I'd prefer spacing it out and going the double sided route. Yes, it would cost more, but it seems that compacting everything together so you can just use one side would be a mess when it comes to debug.... Also, the PCB guy says that since I have through hole devices, going double sided is not a good idea....thoughts?
     
  2. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    Its more about cost than anything else.
    As for the "with through hole, going double sided is not a good idea"
    I have no idea what he is talking about there. I can't see why it would be a bad idea at all. I do through hole and double sided PCB's all day long.

    But heck you have a "pcb guy" whatever that means.. Are you afraid to ask more specific questions to him versus some "random" internet suggestions.
    A simple "Why do you believe it is not a good idea?" would have solved that..more than likely.

    Having said that.. I "rarely" see single sided PCB's anymore.. If I do its a "cheap" Chinese toy or something.
     
  3. MrChips

    Moderator

    Oct 2, 2009
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    There are no hard and fast rules and the choice of single sided vs double sided PCB will depend on specific application.

    Let's begin with basics. If you are laying out a relatively simple circuit operating under say 1MHz with no special requirements with keeping the noise level low, try single sided. If you are using through hole components such as resistors and capacitors then adding a few extra wire jumpers on the component side is not a terribly bad thing.

    You want to start considering double sided layout (or even multilayer) when the layout becomes so complicated that you just cannot resolve getting all the traces on one layer even with a few jumpers. This is practically the case for a PCB with microprocessor chips with large number of pins.

    The next reason for going to double sided layout is when operating at higher frequencies, say above 10MHz, when you have mixed signal components, analog and digital, or when low noise analog signal is critical. In such cases, you want to create solid ground planes which will go a long way in reducing noise pick-up and cross-talk.

    Lastly, using SMD components make it even more difficult to do a layout on single sided. You don't have the luxury of being able to run traces in between pins or under components.
     
  4. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    "Double sided" has two meanings: first (which I think the previous posters used) is one layer of metal. The other meaning is parts on both sides, and I believe this is what your PCB guy is talking about.

    For thru hole, single sided is usually demanded, especially if you wave solder the entire board in one step (after placing all the parts).

    For all SMD parts double sided is simple: screen solder paste one side, place parts, reflow, repeat for the other side.

    If you mix parts or have thru hole parts on one side you are insuring that parts must be hand soldered. That's time (=$$$).

    For a low quantity build, that may be OK. For a huge production run we're talking major PITA.

    Pick your PCB guy's brain, ask if he has examples for you to see. I think he knows what he's talking about.
     
  5. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    That is the big difference between double sided PCB (copper traces on both sides) and double sided load (components on both sides).
     
  6. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    5+ years ago sure.. Now not an issue.

    #1- There are selective soldering machines which have a small/bullet point wave to do point to point soldering. We have one and actually I do not recommend it anymore because #2 is a much better solution (I wasn't involved in the purchase sadly or I would have stopped it). While selective soldering is much more precise and as its machine based the quality/reliability should be much higher than hand soldering the amount of maintenance required on the machines lend it to mostly middle volume and up where the machine is full for 40+ hrs a week. They require at least 2-4 hours per week of cleaning/maintenance/downtime.

    #2- Very few people know that through hole parts can be soldered using conventional reflow techniques at the same time as SMT parts. Its referred to as "pin in paste" or "PTH reflow" or "THR" methods. If attempting to move away from hand soldering/increase production without having to add more manual labor this is the ONLY method I would recommend for through hole parts and mixed (TH/SMT) boards now.
     
  7. JMac3108

    Active Member

    Aug 16, 2010
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    Its a non-issue anymore to mix thru and SMD parts on a board. Its done routinely on designs at every company I've worked at with no issue from the PCA assy house at all. No hand-soldering is done.
     
  8. Duane P Wetick

    Active Member

    Apr 23, 2009
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    SMD's only need single side pcbs, but when adding terminal blocks, you definitely want plated-thru holes (double sided) pcbs; (avoids many intermittent problems).
    Many dense pcbs are 5-sided (or more) and 10-15 components/ sq. in. of real estate are common.

    Cheers, DPW [Everything has limitations...and I hate limitations].
     
  9. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    5-sided? As in a part of a cube?
    PCBs are amost universally 2, 4, 6, 8.. sided, you would pay an arm and a leg if you wanted a pcb with odd number of layers.
     
  10. #12

    Expert

    Nov 30, 2010
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    Too compact? Only with high power. I built a very nice 150 watt battery charger in 77 cubic inches. Had to add a fan to keep it from baking.
     
  11. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    Tell my ex boss. They wanted everything crammed together using smallest SM components to show how small it was ... making it useless for evaluation. We ended up making two different PCB, one for a "demo" and one for "eval".

    As for:

    ask him if he ever heard of plated through holes.
     
  12. Gibson486

    Thread Starter Member

    Jul 20, 2012
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    OK, I am not sure I really want to believe the PCB guy anymore. It looks like trying to make single sided PCBs may have been a thing of the past, because i asked various vendors and they said going double sided with mixed components is not an issue at all and is only a slight increase in cost.

    Also, we got our first rev of our broad design for fab. The first one one every vendor said was unbuildable. When I finally found one vendor willing to build it, he wanted 12 grand per board (that is fab only).

    We got him top redesign it....now assembly is saying that this is one of the more difficult boards to assemble.

    FML!
     
  13. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    What kind of board is it? I would expect such price for a one-off board the size of ATX motherboard with 12 layers, buried vias and other complicated features.
     
  14. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    ?? Even that wouldn't even come close to 12 grand (assuming 12 grand means $12,000 USD and not 12,000 pesos or something)..

    Gibson.. what exactly is so special about this board and whats so difficult with the assembly? Me thinks your "PCB guy" has NO idea what he is doing.
     
  15. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    I can get it done for 10.
     
    #12 likes this.
  16. copper dog

    New Member

    Apr 15, 2013
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    Double sided mixed (through hole and SMD) are not difficult to do in house. Sounds like they don't really want to take on the job and are pricing it that way. How big is this thing anyway?

    Below is an example of a combined board done in my basement lab using photo sensitive copper board a light box and heated etching tank. THere is only one through hole 'component' a diode but the wiring, LAN jack and vias are through hole. (The photo quality isn't great. I was using my phone.)

    After etching.jpg

    You can see by the penny that its not a large board and yes that's a Canadian penny.

    DTI 3.1 Bottom Detail.jpg

    Bottom of the board. All vias were done using saved component leads.

    DTI 3.1 Completed.jpg

    The entire device is roughly the size of a 9 V battery. It could be smaller but I needed the battery space anyway. This is about as small as I can hand solder. Much more compact would require reflow techniques. You can do a lot in house. If this is a prototype you're after can you do it yourself?
     
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