does solder break down over time?

[pucho812]

had a vintage eqp1a on the bench today. the issue was unit would not boost or cut at the 100 cps setting, opened it up expecting to  have to take apart one of the square cans in the back and deal with those capacitors. Anyway as I opened the unit I found a wire that obviously  broke off on the selector switch. Now the unit came from a studio where it was babied, never left the rack and all the pots and switches are perfectly tight to the face plate.

so More out of a curiosity but does any body have a rough idea how long solder will hold/work?

 

[shabtek]

was probably nicked when the thing was built... on a molecular level lead-tin is pretty stable.

 

[mjk]

Did the wire break or did the solder joint fail?

If the joint failed, it may have been cold from the factory.

If the wire, it could have been nicked or failed in the usual way due to the stiffness of the insulation and the solder wicking up the wire a bit, making the joint inflexible.

The oldest solder joints I've seen are maybe 70 years old from 1940s gear and are still shiny and good.

However, acoustic vibration can result in considerable stress over time, and in the case of a poor mechanical connection of the wire to the terminal may degrade solder joints (in my experience).

 

[pucho812]

well up until recently the unit was functioning flawlessly. so possible acoustic vibrations caused it to break? I did strip the wire a bit more to make a good connection but I could have reconnected without stripping it. the unit is an original eqp1a. I was dreading worse things like have to go into the sqaure can and replace  a cap , nothing beats  have to go through all that glue just to get a cap out and a new one in.

 

[JohnRoberts]

Solder integrity will degrade from elevated temperature. Visually the joint will become dull looking.

JR

 

[PRR]

Old stained-glass window caming. Old pewter tableware.

Tin/Lead alloys are very stable. (Old stain-glass sags because lead flows under high stress- your wire is not that heavy.)

That joint was bad from the factory. It happens. Barely-working soldering happens a LOT. You don't get 99.99% good solder joints until 1960s NASA and Computer work, and that level of care was uncommon in  the audio industry.

 

[pucho812]

so luck of the draw it lasted this long...

 

[JohnRoberts]

Besides losing strength due to overheating, solder connection can fail from repeated mechanical stress. Best design practice is not to rely upon solder connections for mechanical attachment of massive parts that receive lots of mechanical stress like connectors. If you look at most multi lead connectors that solder directly to PCBs there will also be a screw boss, or other mechanical attachment used to stress relieve the solder connections.

It is not impossible that your solder connection degraded due to vibration, but close inspection usually shows that the wire will fail before the solder in most such connections. Of course hand soldered connections are less consistent than machine soldering so YMMV.

Back in the day mil-spec soldering required that wire leads actually make a robust mechanical attachment, before it was even soldered. Even without the solder present the wire would stay attached.  As you can imagine, the solder strength could degrade significantly before such a connection would fail. 

JR

 

[pucho812]

Besides losing strength due to overheating, solder connection can fail from repeated mechanical stress. Best design practice is not to rely upon solder connections for mechanical attachment of massive parts that receive lots of mechanical stress like connectors. If you look at most multi lead connectors that solder directly to PCBs there will also be a screw boss, or other mechanical attachment used to stress relieve the solder connections.

It is not impossible that your solder connection degraded due to vibration, but close inspection usually shows that the wire will fail before the solder in most such connections. Of course hand soldered connections are less consistent than machine soldering so YMMV.

Back in the day mil-spec soldering required that wire leads actually make a robust mechanical attachment, before it was even soldered. Even without the solder present the wire would stay attached.  As you can imagine, the solder strength could degrade significantly before such a connection would fail. 

JR

interesting.

 

[Rob Flinn]

was probably nicked when the thing was built... on a molecular level lead-tin is pretty stable.

You do get a thing called cold flow with solder.  This happens when the solder connection is under pressure, it does change on a molecular level & the solder softens.  You can see this is you "tin" some stranded flex & then pinch it tightly in some pliers a few times, & it kind of turns to powder.  This is why I NEVER solder cover or "tin" wires that are going to be secured by a screw terminal where there is pressure, because the solder moves over time and gives you a loose connection.  The example that springs to mind is something like a Speakon connector, where you have multi strand wire & people like to tin the bare strands so that they are held together neatly, but this in fact could cause the connection to deteriorate in the future.

 

[JohnRoberts]

Speaking of cold flow I think even window glass can flow over time,,, reportedly very very very old windows are thicker at the bottom than top.

Yup, solder works well for it's intended purpose, but we need to keep in mind that soldering is not welding, so it is more like a firm  glue than a metal melting into metal connection.

is this TMI yet?

JR

 

[radardoug]

As mentioned previously, heated solder can discolor, and also in areas such as the deflection circuitry of TV sets, it is not uncommon to get dry joints where the solder has migrated.
In a lot of MCI gear there were bad problems with the molex connectors, where the solder migrated away from the pin causing dry joints. I've had the same problem in Neve 1084 modules.

 

[lassoharp]

I'm partial to the nicked wire theory.  I certainly nicked several in my own build and had to replace a few weeks later - didn't take much.

Another good possibility is that the wire was literally severed from tension/torsion by the switch connector.  Most of those old wafer connectors are thin square and relatively sharp (cut my fingers on a few.)  If the feeding harness was looped then that's a whole bundle (with heavy jacket waxed cloth) adding tension in one direction.  If there was a small bit of exposed wire where the solder didn't flow in contact with the edge of the switch connector I can see it getting sawed in two over time from the pressure, especially if stranded wire.


Most of the  point to point stuff I've desoldered from the late 40's to 60's has been pretty solid.  I'm basing this on how difficult it was to remove the old solder.  For comparison, I was just doing some work on a tape recorder from the late 60s and it barely took a second or two for the solder to melt and the wires just fell off.  Maybe difference in rosins or flux content? 

 

[erjos]

In moving parts its normal that generally, soldering fails after a period of time. You can easily observe this by naked eyes, in form of small cracks in the soldered pads.Generally near Pots and switches. It is so usual, that i have to resolder in a regular basis the channel strips in a Yamaha PM4000. I resolder pan pots, eq in,out buttons, etc. And notice, those are factory soldered, nothing hand made. In some ocasions, some non working equipment with different issues, was fixed bu just resoldering all joints near the problematic areas.

 

[nielsk]

Don't forget sympathetic vibration. I have had to do many repairs of things that have vibrated loose or completely apart in studios that regularly monitor bass heavy material at high volume.

 

[lassoharp]

With pots, switches, and I/O connectors on PC boards I think it's often more mechanical stress that creates problems.  For bad cases like the newer plastic XLRs the PC board pins wind up taking the brunt of the mechanical stress.  The best soldering is eventually overcome by that.  I'd call the newer plastic XLRs more a design problem than soldering issue.

 

[JohnRoberts]

With pots, switches, and I/O connectors on PC boards I think it's often more mechanical stress that creates problems.  For bad cases like the newer plastic XLRs the PC board pins wind up taking the brunt of the mechanical stress.  The best soldering is eventually overcome by that.  I'd call the newer plastic XLRs more a design problem than soldering issue.

I am probably repeating myself by now, but good quality "plastic" (I assume you mean housing or panel attachment), XLRs will typically include a dedicated mechanical stress relief attachment to the PCB in addition to the connecter terminals. Some are snap or press-in to save the labor of fastening with a screw, but serve the same function.

I recall when it first became popular practice (in value mixers) to no longer secure mixer pots to the front panel with threaded bushings ( a lot of labor for large mixers). There was a bit of a learning curve to get these reliable, but that was decades ago and they generally work pretty well after this was sorted out. Simultaneous with this cheaping down of manufacturing processes, marketplace expectations about product life and repairability have similarly relaxed... It is easier to justify trashing a mixer you can replace for a few hundred dollars, than a few thousand.

None of this sound's like the OP's question.

JR

 

[user 37518]

Speaking of cold flow I think even window glass can flow over time,,, reportedly very very very old windows are thicker at the bottom than top.

This is true, a chemist once explained to me that glass is in fact a liquid, not a solid, the solid state of glass is ( i believe) crystal, so yes on very old glasses, windows become thicker at the bottom.