soldering (dry joint) 2

[dogbural]

Hi,

Is it a common observation that when the electrical parts are soldered but their quality is bad, it could still work at the beginning but eventually it will intermittently be failed?

If the parts were soldered very well, does it still get failed due to transportation vibration or temperature (environment) ?
Or they just failed because their soldering was poor?

 

[3DDave]

I have more seen a problem where the circuit board is very flexible relative to the components and the difference in flexibility causes a fatigue crack in the solder, though other components can fail for internally, such as solid state/chip capacitors and resistors. It can be vibration, but it can also be due to thermally induced loads when the component heats and expands and then cools and contracts.

This leaves cracks that can be nearly invisible without high magnification and will generate intermittent problems. Some will simply go over the entire board with a soldering air station tool and reheat/reflow all the solder on the board. This won't help components that have fractured, but it will repair the solder related ones.

Another cause of intermittents related to solder is low-lead solder tends more to making "tin whiskers," where tin atoms are forcibly ejected from the solder in an extremely thin crystal that can reach significant lengths and short or cause high-resistance connections unexpectedly. It's not hugely common, but it is really annoying.

 

[waross]

At one time, almost all joints were soldered.
In the 40's all of the splices in a house were soldered.
Into the 50's compression connections were introduced.
If the solder joints were well made, they never failed.
The early compression joints had a tendency to fail far more often then the soldered joints.
Per code, the wires had to be securely twisted together before soldering.
While the solder did prevent the wire from becoming untwisted, the main advantage was that the solder prevented corrosion of the wires.
When lugs were soldered onto wires, the quality of the solder application could be bad, eventually leading to failure.
One type of failure was the cold solder joint.
This may have been more common in electronics than in power wiring.


Early electricians used plumbers solder pots to melt the solder.
All the joints in a house would be arranged pointing downward, flux would be applied to all joints and then a "Dip Cup" would be used to apply molten solder to each splice.

I only saw one dip cup, I never used one. They are so old that I can't find a picture on the internet. If I find a picture in an old text book, I'll scan and post it.
When I was in school, I worked for one of the last electricians who still soldered all the connections in a house. We had progressed past the dip cup and used a propane torch.
I was too young to drive, I rode my bicycle to work.
I'll let the electronics guys share their experience with solder.

 

[Gr8blu]

@dogbural
Your original post is a bit unclear. You stated " ... when electrical parts are soldered but their quality is bad ... ". Does this mean the application of the SOLDER is incorrect or bad, or that the PART being soldered was bad?

A poor joint is a poor joint. Doesn't matter how it's made. Eventually, the thing will fail. Some things might appear as intermittent failures (affected by transient stresses such as heat/cool cycles, vibration during transit or in regular operation, by physical positioning/motion, etc.).

A bad part is a bad part. It will ALWAYS fail - but the conditions required for the failure might be intermittent (thinkhow often use use your air bags in your car for example). The reason for the failure might be something internal (i.e. a connection) that changes condition or was simply wrong to begin with. Might be a bad fit with the surrounding assembly.