Cold Solder Joint


When we had our first child, we had an audio monitor that consisted of 2 pieces: a microphone with a wireless transmitter and a speaker with a wireless receiver. Thus we could hear the baby from afar.

 

Times have changed. Now the hospital uses disposable diapers rather than cloth. Infant monitors have improved.

 

We have a Safety 1st video monitor which consists of a little TV set wireless receiver and a little TV camera. It’s quite useful.

 

However, the power supply for the camera seemed to be flaky. Every once in a while, the system failed. We’d just see static on the TV monitor. Upon further inspection, the camera’s green LCD would be off, indicating lack of power.

The power jack plugs into a simple hole which has a rod for one contact and a metallic contact for the other. It looked as if the metallic contact wasn’t making contact with the plug, so I bent the contact a little. Sure enough, it worked, so we’d be in business again.

 

However, the intermittent failures continued to occur. I’d have to dismount the camera, get out the toolbox, rebend the contact, and we’d be ok for a while. This got frustrating. It dawned on me from past experience that maybe the problem wasn’t the metallic contact, but could have been a cold solder joint.

 

Many years ago, I installed a remote keyless entry system to my 1990 Camry. I bought a kit from a mail order firm and it worked fine for many years. However, it had a cold solder joint. Diagnosing it was not simple, as there were many integrated circuits. Luckily, I had made myself a Heathkit (remember those?) oscilloscope with which I could trace circuit signals. Once identified, the fix was easy. Just whip out my soldering iron and re-heat the joint.

 

I did just that for the power contact on the TV camera, and it’s since worked like a charm!

 

I wonder how many consumer electronic devices have failed due to such a simple problem?

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Comments (7)

  1. kevin gaw says:

    Do these cold solder joints heat up by themselves (with current) and melt the solder that is present? Is this a known phenomenon?

  2. Colin Lipworth says:

    Cold solder joints do not heat up to melt the solder. This would make them self-repairing. They become insulating and no current flows. A

    I recently had a TV set repaired. The technician showed me how the set had developed several cold joints over the years. He said that this was due to heat because I switched the set off using the remote and not the switch on the TV. This keeps power to the electronics and only switches off power to the tube. Certain parts of the circuitry such as the power board and the vertical deflection board run hotter than others and become prone to cold joints over time.

    This surprised me. I had always known that solder joints could be cold if they were improperly soldered e.g. if the iron was not hot enough, but I did not know that a joint that was once properly soldered could dry out over time.

  3. John says:

    Failed solder joints are a *very* common problem in electronics, and as well are hard to diagnose when the fault is intermittant.  Someone once said "the probability of a component is proportional to the number of pins that it has" (ie the bigger the chip, the more reliable it is). Any component that gets hot is more likely to fail, then you have ‘dry joints’.  Those 3 are what most electronic devices fail from.  Hot components, dry joints and chip failures.  Probably in that order, but don’t quote me on that.  For further reading on reliability of electronics equipment, download http://www.weibull.com/mil_std/mil_hdbk_217f.pdf (note: 15MB file).

  4. Charles says:

    Joints also can fail when there are repeated temperature cycles to the electronic board. The board and its electronic components heat and expand to differing amounts, based on thermal expansion properties (CTE). This is made worse by what Mr. Lipworth wrote about how some components are hotter than others. Over time, the repeated thermal cycles cause creep strain on the solder joints, and some can break or separate.  Most likely, the cold solder joint of this author’s webpage story was simply because the manufacturer had a poor quality of solder applicatoin (solder reflow). It was marginal, so we can assume that it passed quality inspection, but failed once some small physical forces were applied. A more reliable product would have been devised whereby the the user’s stress applied power connector didn’t get absorbed by the solder joints. They should have relieved that stress into the body of the transmitter.