3
\$\begingroup\$

I like the idea of making very compact circuits. However, it worries me that the connections will be too close of each other, increasing the likelihood of shorts or melting nearby solder by accident.

enter image description here

enter image description here

Is this a real concern? Should circuit connections be more separate?

\$\endgroup\$
7
  • 1
    \$\begingroup\$ That is more than ample spacing! Check as you work, and if a short does occur, resolder. If you're worried about subsequent issues, such as a metal filing falling onto the board and shorting things, spray both sides with clear acrylic, or pot the circuit. \$\endgroup\$ Commented May 24 at 1:22
  • 1
    \$\begingroup\$ Visual inspection (use a magnifier) and/or ohmmeter. \$\endgroup\$ Commented May 24 at 2:51
  • 1
    \$\begingroup\$ This is not your new idea. The spacing you have on a through hole solder board is more than adequate spacing. This idea has existed for decades. \$\endgroup\$
    – Amit M
    Commented May 24 at 2:53
  • 1
    \$\begingroup\$ Another advice for "perf board" work like this is to buy the ones with through-plated holes. You hold the iron against the leg and plating on the solder side like usual, but you'll be able to observe if the join is good by observing the wetting on the top side. A correctly done through hole joint will not just cover the bottom of a through-plated hole, but also the top, forming a conical shape against the leg on both sides. \$\endgroup\$
    – Lundin
    Commented May 24 at 6:25
  • 1
    \$\begingroup\$ @wyc Yes but also "through-plated", as in the hole is covered with plating on the inside like a PCB via. \$\endgroup\$
    – Lundin
    Commented May 24 at 6:55

3 Answers 3

7
\$\begingroup\$

The spacing is fine. As @vir says you have a bunch of joints where the solder did not 'wet' the wire properly. This can be caused by old corroded wires or by weak flux, and can cause intermittent faults. Use fresh parts, fresh wire and good quality solder. If necessary, additional electronic grade liquid flux from a reputable supplier.

I've circled a few of the worst ones, but more don't look great.

enter image description here Although relatively rare, in some cases an open joint can cause other parts to be destroyed (for example, the centre pin of an LM7805, if open, could cause every part connected to the 5V supply to see overvoltage).

Here are some common solder joint faults in a good tutorial from Adafruit.

enter image description here

What I call a "cold joint" is one where the parts moved during the solidification process. They call it a 'disturbed joint'. That can be prevented by having the parts not move while the solder is solidifying, obviously, but also by using a solder such as Sn63Pb37 that is eutectic so it solidifies sharply at a single temperature rather than going through a range of temperatures where it is semi-solid. This kind of joint is very weak and has a gray granular/crystalline appearance and can easily be intermittent or break later.

What they call a 'cold joint' is just where the solder didn't melt fully. For a good joint the solder has to melt, has to 'wet' the objects being soldered, and it has to solidify without being moved. SnPb solder has a bright shiny appearance when this happens. Lead-free solders joints, even good ones, don't tend to be as nice and shiny.

\$\endgroup\$
5
  • \$\begingroup\$ Thanks for the detailed feedback. I was actually applying heat directly on the solder a few times because applying the heat on the wire wasn't melting the solder wire on the other side. I was using 20W. I think I have to use a higher wattage? \$\endgroup\$
    – wyc
    Commented May 24 at 5:00
  • 1
    \$\begingroup\$ @wyc Pretty much all the joints at the bottom look like cold joints to me. Some have wetted against the board but nearly none against the wire/component legs. I think this might not just be wrong temperature or oxidation but also technique. When doing things like this it is important that the loose wire is fixed against the board, at least temporarily. This can be done by making 2 bad joints on purpose just to hold it, then revisit them. Or otherwise by using tape etc. Holding it with flat nose pliers works too but requires a bit of skill since the pliers tend to absorb heat. \$\endgroup\$
    – Lundin
    Commented May 24 at 6:22
  • 1
    \$\begingroup\$ @wyc It still looks a bit fishy, particularly the left-most one. If done proper then the solder will flow out along the wire (cut off component leg?) which in turn suggests that the wire wasn't heated enough. It shouldn't look like the wire is "passing through" the joint but rather as if it has melted together with it. You could try to pre-apply a bit of solder to the wire to ease the wetting. Also, just to solder a wire onto the plated holes, you shouldn't need this much solder. \$\endgroup\$
    – Lundin
    Commented May 24 at 13:02
  • 1
    \$\begingroup\$ @wyc Particularly, it is important to realize that solder isn't just some "hot glue" that you heat up, melt and leave to cool in order to hold two surfaces together mechanically. In order to get a good electrical connection, as well as preventing oxidation longterm, the solder needs to wet across both surfaces. For the ideal solder joint, the iron tip should never even be touching the solder - often hard to do in practice, but that's what you should strive for. \$\endgroup\$
    – Lundin
    Commented May 24 at 13:05
  • \$\begingroup\$ @Lundin Thanks for the feedback. I'll practice some more. \$\endgroup\$
    – wyc
    Commented May 24 at 15:52
2
\$\begingroup\$

The pads are appropriately spaced on the board. As long as you don't have giant blobs of solder on them, the spacing would be adequate for low voltage designs. Beware of bridges and small splatters that can cause shorts. It also looks like you have a lot of cold joints in your circuit.

\$\endgroup\$
5
  • \$\begingroup\$ Thanks for the reply. How do I fix the cold joints? \$\endgroup\$
    – wyc
    Commented May 24 at 2:46
  • 1
    \$\begingroup\$ @wyc The best way to fix existing cold joints is to apply external flux. Either buy the kind kept in a bottle and applied with a brush, or buy a flux pen (looks like a marker pen but applies flux). Then reheat the joint by touching it directly with the iron tip, make sure that both metal surfaces are heated at once. \$\endgroup\$
    – Lundin
    Commented May 24 at 6:34
  • \$\begingroup\$ @Lundin How about now? I used additional flux like you suggested: ibb.co/NttBSKC \$\endgroup\$
    – wyc
    Commented May 24 at 13:02
  • 1
    \$\begingroup\$ That's much better, and the joints are acceptable but you can tell that it's not optimal. Fresh parts will wet very easily- the solder just runs up the wire almost instantly. \$\endgroup\$ Commented May 24 at 13:08
  • 1
    \$\begingroup\$ @wyc I posted a reply to your comment below the other question. And this photo has too poor focus really. Like Spehro said in their updated answer, good SnPb (60/40) leaded solder joints looks all shiny and pretty like polished silver when done correctly. Good RoHs solder Sn99/something looks shiny but grainy when done correctly. A joint which is a dull grey one is almost always a cold joint. \$\endgroup\$
    – Lundin
    Commented May 24 at 13:09
1
\$\begingroup\$

Your spacing is good as long as you don't have solder bridges or large blobs of solder. Those cause short circuits and break the circuit. You might want to not move the component until the solder solidifies. Or use less solder.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.