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Testing solder joints

post #1 of 32
Thread Starter 
I'm starting to build a SOHA II and the instructions on cavalliaudio.com says to visually inspect every joint for bidges or cold joints. I understand what a bridge is, but how do you tell if you have a cold joint?

Also, Tomb, on a thread about mistakes building B22s, mentioned he tests every solder joint. I think I know how to test solder joints for things like resistors, diodes, etc, just test continuity though the joints. Is this correct? And how do you test joints for caps
post #2 of 32
A good joint is smooth and shiny a cold joint will probably look dull and bumpy, also it will wiggle under force.

xx
post #3 of 32
I don't know about testing every joint, but if you put meter leads on the part and the trace (or the parts that the solder is supposed to connect) you should measure something like 0.01 ohms or less.

There are some cases where this won't work.

1. There may be other paths through the circuit. I'm never sure if it matters or not. The electrical contact would be correct according to the schematic, even with a cold joint. Maybe it's a problem in grounding circuits where you don't have the straight path you wanted. It's very hard to distinguish a direct path to ground vs. a roundabout path. One may be 0.002 ohms, the other 0.005 ohms. Is your meter and your brain gonna pick that up? Doubtful.
2. You also want to visually inspect them because a cold joint is basically a loose connection. It might measure perfect but then it moves and becomes open.
3. That other path may be coupled, like through a capacitor. The only thing on your side here is that there's a resistive load of 0, so you shouldn't see the capacitor at all. If life were only as simple as a textbook.
post #4 of 32
Quote:
Originally Posted by Mayzei View Post
A good joint is smooth and shiny a cold joint will probably look dull and bumpy, also it will wiggle under force.

xx
This. It will look grainy and bumpy and might move.

When working a PCB, I solder the leads in, clip the leads, then spend a second to reflow the joint. That's how you get smooth pads after clipping leads and the reflow pretty much guarantees against a cold joint.
post #5 of 32
Just give each component a light tug or wiggle as suggested by Mayzei. If it doesn't feel like it's kinda-loose-but-still-in-place it should be fine.

You can also try giving the whole board a good shake, nothing should rattle (or God forbid, fly off the board LOL) at all unless the nuts on your pots and jacks aren't tightened.
post #6 of 32
Hmm ... I don't remember the specific comment, but I definitely test every joint on the PCM chip when building a BantamDAC. As for other stuff, I think these guys have given some pretty good comments.

One thing that helps is to be sure that you're wicking properly. I didn't do that enough in my early days. Now, however, I go over every solder joint on both sides, making sure there's a good shiny solder blob on both sides of the board. As you say, that's difficult to do with a radial cap, but Erik's suggestion is a good one. I also make sure there's plenty of solder pushed into the joint and that heat is applied for several seconds after the solder blob has already melted - just to ensure you get good coverage into the plated hole and some wicking.
post #7 of 32
I set my DMM to a continuity beep, after soldering I check visually under a magnifying glass. I take I continuity check from the excess lead to another part of the trace on the pcb. I then take another measurement from the solder joint, once the excess lead is cut. I then turn over the board, and take another measurement from the lead of the component that I’ve just soldered (not the pcb pad) to another part of the board trace for continuity. The last part doesn’t work for large capacitors etc, but it’s good for resistors and components with exposed leads.
post #8 of 32
SiBurning mentioned some very good points. The tricky thing about cold solder joints and testing them is that testing for resistance and continuity checks with a multimeter aren't fool proof. The problem with cold solder joints is that in one position the joint will test ok, but if the board is flexed just right, you can get a no go. As the temperature of the circuit/board/joint increases or decreases can affect the results as well.

Like everyone has already mentioned usually the dull appearance is a good indicator. Desolder any suspicious joints, make sure that every thing, ie solder iron, flux, solder, board are free of contaminants. Shock your iron with a wet sponge before tinning with solder, then use enough flux to create the heat bridge, use the heat bridge from the iron/solder/flux to allow the lead, wire or trace to heat the solder (not the iron/tip) so that it flows/seaps. The iron temp being the right temp is a factor as well, too hot/cold not good.

We used to have boards with intermittent problems, and desoldering the whole board, and reflowing would do the trick, again, just reapplying heat doesn't always work, the best practice is to desolder and apply fresh solder. IMHO
post #9 of 32
Eutectic solder of course, the 40/60 does not cut it. I always got at least a couple of cold joints here and there with this stuff. But since the switch I haven’t had any.
post #10 of 32
Quote:
Originally Posted by johnwmclean View Post
Eutectic solder of course, the 40/60 does not cut it. I always got at least a couple of cold joints here and there with this stuff. But since the switch I haven’t had any.
I just got some of the eutectic, going to be trying that out real soon. I've heard it flows real nice, and low melting point.

I don't care for the 40/60 either, always had better luck with 60/40 and expect to be using the eutectic from now on.
post #11 of 32
I’ve been using cardas exclusively for my b22 and two s22’s, all boards are finished - no cold joints on anything. Although Cardas is a dull finish, it flows wonderfully at low temp, and goes to a solid state within a flash. Also it’s feels tough and super strong, great for wiring work. The only downside as I’ve said is it’s appearance... dull
post #12 of 32
Quote:
Originally Posted by johnwmclean View Post
I’ve been using cardas exclusively for my b22 and two s22’s, all boards are finished - no cold joints on anything. Although Cardas is a dull finish, it flows wonderfully at low temp, and goes to a solid state within a flash. Also it’s feels tough and super strong, great for wiring work. The only downside as I’ve said is it’s appearance... dull

Wow, I'm glad you told me that - I would have been going crazy trying to figure out why I wasn't getting the "bling-bling"

That will take some getting used to but like my Grandma always said "Beauty is usually only skin deep", but I still think ugly can be to the bone.
post #13 of 32
Also forgot to mention, Cardas leaves hardly any flux residue. I’ve often finished a board and though should I clean this, because dang it already looks pristine.
Upside to looking dull
post #14 of 32
Leave the heat on the joint for an extra second or 2 after applying the solder, you shouldn't ever have a cold joint if you do that. And use flux and reflow it if anything looks a bit sus if you happen to overwork a joint and burnt all the flux out
post #15 of 32
Thread Starter 
With a couple of the resistors I've soldered so far on my SOHA II, the solder has flowed though the hole to the front side of the board. I assume this is OK as long as it doesn't cause a bridge. Fortunately, the first time it happened, I stopped applying solder before it formed a bridge, but there is a big ball of solder on the front of the board. Almost as big around as the resistor.
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