How do you test for cold solder joints? Is there a tool for it? Can it be done with a multimeter?

 

They will probabely measure just fine... That's the trickky part...

The only way to detect them is by watching thze solders carefully. Bad solders usually have a little, hardly visible, circle around the soldered pin where the solder is cracked...

Just resoldering all the joints your not sure about is, off course, the best way..

 

I'm sure that equipment like the "Huntron Tracker" component waveform generator ( www.huntron.com ) could probably show anomolies at higher frequencies, but it would require getting used to what to look for in the trace on the screen.

Usually a cold solder joint will give itself away in appearance by being "dull" or crystaline looking. Close examination often reveals small cracks, or lack of a smooth flowing " fillet" where the metals have combined and produced a sound joint.

Bottom line... you just get good at recognizing them through experience.

 

Very true!, I hunt for them on a daily basis :lol:

I've found one in a Grundig TV today, actually on a wire link connecting the drive to the base to the line output transistor - which is fairly uncommon.

All the previous suggestions are sound, a good tool though is a magnifying glass, often you can see a faint ring around the joint under a little extra magnification. Measuring them is next to useless - it's easier (and faster) to resolder a joint than measure it, and it's probably going to read OK anyway.

Common places for them are on components with thick leads, or mounted on heatsinks - PSU regulators (like 7805's) are a very common place. Often it's fairly obvious that the dry joint has been caused by mechanical stress (and poor soldering in the first place, flow soldering isn't as good as a competently hand soldered joint).

Anyway, essential tools:

Soldering iron
Magnifying glass
Screwdriver (for tapping the board with it's handle)
Freezer spray (often cooling and heating the board can help find the fault)
Hair dryer (see above)

__________________
PIC programmer software, and PIC Tutorials at:
http://www.winpicprog.co.uk

 

I like to give suspect components a wiggle with a finger while watching for the lead to move on the solder side of the board.

 

how bad is it to leave a joint cold that you know is cold? what could happen?

 

If you know its bad, don't leave it ....

Leaving it bad will likely introduce all kinds of erratic behaviour as the joint expands and contracts with temperature changes, causing open circuits. You may not damage anything, but it is an uneeded fault that you don't want to have to deal with.

Repair it now, before you cause other issues!

( in the repair trade, there is a certain satisfaction you get when you find a cold joint, since it often results in an easy fix, or atleast removes an agravating random symptom )

 

well u know that the main reason for a soldering is providing good electrical contact. while a cold joint isnt a good joint at all. there could be a number of consequences. the joint could break at sometimes and re-join at some times. that might damage the whole circuit. so whenever u see a cold joint dont just leave it there. get a soldering iron, apply heat to the solder and the pin and let the solder flow and catch the pin.

in my experience ive mostly seen cold joints on pins that are bigger than the normal. like the fats pins of the three terminal regulators and the pins on the connectors with the screws on top of them (i dont know what their name is). when dealing with such cases u have to give a little extra heat to the pin. the more heated the pin, the more the solder will flow towards it. u have to heat both the pin and the copper track. or else the solder wont flow from the iron because the iron will have more heat. so u have to heat it so that the solder flows to the pin.

for more info on soldering see the "EPE Basic Soldering Guide" http://www.epemag.wimborne.co.uk/solderfaq.htm and dont forget to see the "Desoldering Photo Gallery & Black Museum of Bad Soldering"

i hope that helps

 

well I went over and had a looksee at the kit I was working on and it seems as if nearly all the joints I made were cold!! This is unsettling. I am beginning to think that perhaps my soldering technique is bad. Maybe if I explain how I solder, someone can help me out.




I string the lead through the hole and then bend it to one side and then heat the side that has the metal ring and the lead closest together (b). I then apply the solder to the other side. (a) It melts slowly, and then I pull back and heat a small bit up from the joint and add more solder until the entire joint is filled. I have noticed however, that I am continually needing to sand down my iron and retin it. Also, there is very rarely smoke coming up when I connect joints.

And fixing cold joints just means applying heat to the cold joint until it turns to liquid. Or does it mean removing the old solder entirely and resoldering?

 

do you use solder with flux in it ?

 

Yes, I do. It also seems that after I apply solder to the opposite side, It is impossible not to get solder on the tip of the iron. Is that just me? Also is that ok? If I apply a good connection and the solder covers the joint on one side, but I get the tip dirty as well?

 

You should have solder on the iron, it helps the heat to flow into the joint, wipe excess off on a damp sponge - or 'flick' it off (but not anywhere that matters!).

You shouldn't be sanding soldering iron tips, any I've used in the last 30 years or so have been iron coated - sanding will ruin the tip. A simple damp sponge is all that's required (or a jeans trouser leg!) - I must admit the sponges in my soldering iron stands at work (and at home) rarely see any water :lol:

__________________
PIC programmer software, and PIC Tutorials at:
http://www.winpicprog.co.uk

 

Just make sure you're not in it when wiping your soldering iron...

 

I always am! - it works best with jeans as the material is nice and thick!, don't try it with nylon trousers :P

__________________
PIC programmer software, and PIC Tutorials at:
http://www.winpicprog.co.uk

 

So, how do you fix a cold joint?