"Flush" through-hole soldering technique?

[Syzygies]

I need to make a MINT board as thin as possible, on the resistor/IC/diode side (plan). I'm struck by the constrast in how little solder one uses in refined surface mount technique, compared to the tiny solder mountain ranges one sees on the solder side of through-hole boards. I have a good iron and reasonable technique.

My plan is to glue each 1/8 watt resistor in place (working carefully, no backing out), snip the leads flush with the underside of the board, then solder carefully as if surface mount, filling each hole around each lead without making a mound of solder. The glue is both scaffolding, and added strain relief for the components.

Do the solvents in some glues compromise resistors and diodes? Is there a better way to achieve the same result? I'd rather get it right the first time than attempt sanding afterwards.

 

[gsferrari]

This will take a LOT of effort and it will be quite frustrating. I cant see how the results will justify the effort in this case. Lot more chance of a cold solder joint this way.

Why dont you just draw up a new schematic that uses SMD components and pack it all into a tiny area? I am sure this is doable...

 

[PeterR]

Yes, if space becomes so critical that the thickness of proper solder joints starts to bother you, go SMD. Look at this and stop worrying about a mil more or less with through hole components...

 

[tangent]

I agree about SMD, but another way you can go is to solder it up normally, and then file or Dremel down the 'mountain peaks' after it's tested. I'd leave a good 20 mils of bumpiness on the solder side, just for mechanical strength.

 

[Syzygies]

I'm completely there on surface mount design, it's in my plans. However, working through the available boards first, e.g. what Tangent sells, is a great way to get one's bearings and understand the circuits, before venturing off into one's own designs. One way to learn to paint is to copy great paintings.

I don't see what I'm trying to do as an absurd squeeze. So far for me, everything I've tried that looks rather tight in a drawing turns out to slide freely in practice. All one ever needs is a fraction of a mm of clearance.

Anyhow, the pads on both sides of the MINT look identical, and my 1/8 watt resistors will give me plenty of room. Any reason I shouldn't just solder generously on top?

 

[Ozymand]

As I don't own a MINT nor have a PCB handy, and assuming the hole is plated (not just the pads on the top and the bottom), then it may suffice. However if the hole is bare it may cause connection problems if the signal/power/ground trace is on the bottom of the pcb and there is no solder there to make a good connection.

 

[Syzygies]

Quote:

Originally Posted by Ozymand assuming the hole is plated (not just the pads on the top and the bottom), then it may suffice.

They sure look plated, Tangent can answer for sure. I get 0 ohms resistance, to the nearest 0.1 ohms, measuring pairs of pads.

I'm hoping that the solder will wick beautifully through the hole, then if I need to sand as Tangent proposes I'll have a stronger construction. (Though he was counting on solder wicking the other way. 6 of one, half dozen...)

 

[Ozymand]

If it's plated all the way through, then you could do that. Apply the iron to the bottom of the PCB, apply solder to the component side of the PCB. Solder will wick to the source of the heat, creating a solid junction (and hopefully the resulting solder will be of very little height on the bottom of the PCB).

Good luck!

 

[tangent]

Quote:

Any reason I shouldn't just solder generously on top?

It's just harder to do, and harder to clean. But if you're up for it, go to it.

Quote:

They sure look plated

Yes, PTH on all my boards.

Quote:

I'm hoping that the solder will wick beautifully through the hole

If the resistor leads are thin enough, then it will wick nicely. I find that with thicker leads, you have to hold the iron on longer to get good wicking.

 

[n_maher]

I've actually found that if I solder each joint twice (giving appropriate time for things to cool) that often I get solder bleeding through the hole. I generally do this so that I know I've got a good connection and so I'm hopefully assured of no cold joints. Also, it lets you feel pretty good about trimming the bottom side nice and short.

That's my story,

Nate

 

[Edwood]

Buy yourself a really nice pair of flush cutters.


-Ed

 

[__redruM]

This seems like a good way to get the cut boards closer after the cut, but it won't look pretty. Also it won't work for the cap side, so you'll still have solder mounds between the boards.

You could try cutting the cap leads flush with the boards and soldering the leads to the through holes.

Good luck, let us know if you save a usefull amount of space.