Broken solder joint: an easy fix for printed circuit boards

And avoid paying for repairs or replacements

Picture the situation where something works just fine one minute, and then the next minute it doesn’t. Or maybe a situation where the item in question was working fine when you put it away and then the next time you go to use it, you get nothing? Sound familiar? Then you might have a broken solder joint on a printed circuit board (or PCB for short). 

Broken solder joints (don’t worry they don’t hurt…)

A cracked, fractured or broken solder joint is sometimes (erroneously) called a ‘cold’ or ‘dry’ joint (but both those terms relate to problems with soldered joints from the start). Calling it a ‘broken solder joint’ works for me, and is a better description for this very common electronic failure problem.

Especially electrical items which lead a hard life; for example, devices that create lots of heat, or ones that vibrate or even stuff you plug things into (and out off) repeatedly. All this heat, movement and action weakens the delicate solder joints holding all the gubbins onto the printed circuit board (PCB’s). Especially any joints that were not too good in the first place, most of our stuff is mass-produced by the lowest bidder don’t forget!

A broken solder joint is where the solder connecting the component pin or leg to the copper track on the circuit boards becomes damaged. Bad contact with the copper track of course means a poor connection (intermittent problems) or no contact at all (device stops working altogether).

Broken solder joints are often caused by…

1. Excess heat, where the pins/legs and the solder surrounding them expand and contract at different rates in use eventually causing cracking and erosion of the solder.
2. Fatigue, where the connection between the component pin/leg and the copper track cracks due to repeated movement or flexing.
3. Weakness in the joint from the start, due to poor soldering technique at the factory (too little solder or improper ‘wetting’ of the joint leading to poor connectivity between the component pin and the conductive track on the PCB).
4. NB: and finally, and most importantly; a failed component. i.e. if something is overheating to a dangerous level, it may melt the solder around the pin. In this case, the component must be replaced as re-soldering will only be a temporary fix and the overheating will either melt the solder again or could even cause a fire…

The likelihood of a soldered joint failing is increased by…

• Intermittent heating/cooling where expansion and contraction stresses connections, (power tools for example).
• Frequent and repeated moving of switches and other controls. Often the one used most creates very localised stress, (the max setting on the vacuum cleaner or cooker hood for example).
• Repeated pushing and pulling on plugs or cables physically flexes the joints between the component pins/legs and the circuit board (audio equipment for example).
• Devices that get very hot in use will eventually suffer from one too many heating/cooling cycles. Expansion and contraction stresses connections, (panel heaters for example).
• Machines that vibrate a lot because they use a big, fast motor. Vibration stresses the joints between the component pins/legs and the circuit board, (washing machines for example).
• Devices that move around a lot. Electronics don’t like being thrown around too much or being knocked about as they are a bit delicate really, (laptops for example).

Fortunately fixing most of these broken solder joints is simple. The hardest part is opening up the machine to expose the PCB affected. The range of machines and electronic devices is huge so I won’t go into detail about how to expose the electronics affected, but suffice to say, you’re going to need to undo any screws you can see and remove panels and/or parts that cover the PCB.

Once you can see the printed circuit board inside, go grab a (unless you have eyes like a peregrine falcon…) and look closely at the reverse side of the board (the side opposite the electronic wizardry). You’ll see hundreds of little shiny dots with pins sticking out of them.

A good solder joint looks nice and shiny whereas failing or ‘dry’ solder joint looks dull and crusty. You might even see a ring or crack around the pin or leg.

The fix…

The fix is to re-solder the broken solder joint with fresh solder. Provided the arcing or intermittent use hasn’t damaged any small electrical components, generally this fixes the problem. But first; the damaged joint has probably left the old solder in a dirty or even sooty condition due to arcing (sparks caused by a poor connection). Gently clean this away physically using a cotton bud or an old toothbrush. Dipping the bud/brush (and taking off the excess) into a light solvent (preferably isopropyl alcohol) works on more stubborn dirt (you can use water to dampen a cotton bud in a pinch, but make sure everything is bone dry before switching on again).

There are two important things to remember when trying to fix a broken solder joint. First, always use a proper   when soldering (and not one designed for copper plumbing pipework). This magical paste will chemically clean the joint making the solder ‘stick’ much better. In fact, soldering without flux is virtually impossible (trust me on this, I know!). Second; soldering irons get very hot so you need to work very quickly to avoid damaging the component.

How to solder a broken joint…

Get your soldering iron really hot, wipe some fresh solder onto the tip and wipe it off again by drawing the tip across a damp sponge (this cleans or ‘tins’ the tip). Once you’re ready, touch the hot tip to the component pin/copper on one side and touch the new solder to the other. Lift off the iron as soon as you see the solder melt (it runs and turns wet and shiny). It should only take a second or two…

Repeat on any broken solder joint which looks suspect. It’s very common to see several that are poor. Wipe away any excess flux that sits around the new joints once they’ve cooled down.

Having burnt our kitchen table in the past, I can recommend buying a proper holder for your . They look like a mounted spring and get one with a sponge on the base (check this one out at amazon… …). Wet the sponge before use and use it to clean excess solder off the soldering irons tip.

All done? Cool, now you can re-assemble the thing and tentatively switch it back on….. with a bit of luck you’ve fixed it and if not, well, it does happen. But remember it was broken, probably beyond economic repair before you started, so there was absolutely nothing to lose by trying this repair. Remember that and chalk it down to experience.

If you need more help on the soldering side, take a look at the links below and of course my quick video (you can turn your speakers off if you like, the music is a bit much!).

Click here to learn how to solder and here to learn how to solve some common soldering problems.

Stay well

Ian

Broken solder joint update:

Even after more than 30 years I still get surprised from time to time. The ‘star’ lamp fitting in the above video is one of a pair and lo and behold the second one started some erratic behaviour this week too, a mere two months after the first one! Amazingly consistent build quality on these very old lamps. Impressed? Little bit!

Here is a couple of close ups of the offending dry solder joints. The pins are clearly loose and the arcing has damaged the board. Sadly, the PCB looks a little too far gone to be safe this time, but I might give it a go and run it on a test rig for a while, keeping a close eye on it (to ensure it’s safe).

Another broken solder joint example… (11/09/2018 update)

This transformer turned up today.  It was running 4 35w low voltage 12v lamps and it just stopped working.

The casing was very easy to remove via some little slots either side of the case, (you can see the little cut out slots on the edges of the plastic case above). The PCB just lifted out and with my trusty I immediately spotted the broken solder around the pins on the choke. The choke is heavy and gets warm, making it an ideal candidate to cause the solder joint to deteriorate over ten years.

I cleaned up around the pins and re-soldered the pins. Wiped away the flux reside and bingo, no more broken solder joint. The transformer has been running a 4 lamp test rig all afternoon and shows only normal heat buildup. I’d say this is a good repair.

Many thanks go to Mr Bob Willis for his help and advice on repairing broken solder joints. Mr Willis is a leading specialist in electronics manufacturing and processes, with a list of qualifications, accolades, awards and testimonies a mile long. Check out Mr Willis’s videos on YouTube.

Hope this update helps, catch you later Ian