Solding joint on component side

Discussion in 'General Electronics Chat' started by stoopkid, Oct 19, 2011.

  1. stoopkid

    Thread Starter Member

    Mar 3, 2011
    I'm working on a small circuit board and trying to conserve space. The board will have a component on top, and board to board pins on bottom. Instead of using up space on via's I was thinking I could just solder the component on bottom and on top where the traces will be. This shouldn't be a problem, practically, as the leads are very long and will be holding the component high off the board. I would have no problem getting the solder on that side. But I was wondering if this is considered bad practice for any reason.

  2. SgtWookie


    Jul 17, 2007
    If you omit a pad, even a via, you will likely lift the trace off the board when you attempt to solder the component on. Even if you manage to solder it without lifting the trace, it will be structurally weak, and the mechanical advantage due to the length of the lead will tend to pry the trace off the board.

    If you need to save space, use all SMT/SMDs and forgo using thru-hole components.
  3. stoopkid

    Thread Starter Member

    Mar 3, 2011
    It's a nixie tube and board-board pins so neither can be smd. Does it not help that I will have copper pads on both sides and solder on both sides? There's also 13 leads to distribute the weight.
  4. studiot

    AAC Fanatic!

    Nov 9, 2007
    There is nothing inherently wrong with your suggestion, indeed manufacturers have sometimes mounted some components on the track side of a pcb since they first came out.

    There are, however, issues to beware of.

    Firstly leads on the track side are at risk of coming into unwanted contact with another lead or a track.
    Short or no leaded components avoid this as SgtWookie says.

    Secondly in your picture, what would you solder the non trackside lead (the one soldered both sides) to ?

    This technique was not much employed in volume production because trackside components get in the way of hand or bath soldering and require a second operation, thus increasing unit costs.
  5. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    I don't even understand the question..and I work with circuit boards all day long. What do vias have to do with this?
    With plated through hole boards it doesn't matter which side you solder on. The solder will wick up into the through holes anyways. There is no point in soldering on both sides.. Maybe you are talking about a DIY PCB where you can't have through hole plating. If so you can't have vias anyways (well unless you use rivets,etc..)
  6. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    I don't see a problem or any concern with the overall concept, I do have a problem with the implementation.

    As drawn, the thru pin to plug into the other board has no annular ring on the bottom side. Thus when you insert this board you are making the topside PCB annular ring take all the insertion force, and it is possible you'll lift that pin and ring.

    The fix is to just put the annular ring on both sides of the board, and make it a plated hole. If you're not doing plated holes "make do" with just the double pads.

    And make those pads as large as can be to help distribute the force.
  7. stoopkid

    Thread Starter Member

    Mar 3, 2011
    There will be copper pads on both sides. I'm etching the board myself with double sided copper plating board. I've made double sided boards before without any issue but before I used copper wire for vias.

    Thanks, everyone.
  8. colinb

    Active Member

    Jun 15, 2011
    No, not a “bad practice” for prototype use. As other posters describe, you wouldn't want to do this for a production device, but then you would have plated through-holes so it wouldn't be needed. So go ahead and solder away! :)