When to reflow a solder joint?

z-adamson

Addicted Member
Do you do this on all joints of a device to be restored or are there specific things to look for....such as a cold looking joint, cracked joint etc.

What about the joints in this pic? They have a blue tone to them indicating to me that they run warm/hot. Should they be resoldered or should I leave them? In the pic you can see that some look blue and others silver. The blue joints are for heatsink mounted transistors.

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Do you do this on all joints of a device to be restored or are there specific things to look for....such as a cold looking joint, cracked joint etc.

What about the joints in this pic? They have a blue tone to them indicating to me that they run warm/hot. Should they be resoldered or should I leave them? In the pic you can see that some look blue and others silver. The blue joints are for heatsink mounted transistors.
What you're seeing in the picture is solder Flux that was never cleaned off. Since the other connections do not have the flux, my guess is it has been worked on before. However, I have seen many production units where they do not clean off the flux.
Cold solder joints:
https://www.google.com/search?q=col...R-djbAhVQC6wKHd9-AosQ_AUIESgB&biw=360&bih=559
 
Thanks for the feedback.

I swear they look more blue-ish in person.

I will clean them up removing the flux then take another pic.
 
Pic....

What do you think.

I have done a scrubdown with alcohol.

Look at the two big joints in the middle. I cleaned the lower one, not the upper one. The lower one looks darker to me.
 

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Look fine to me as well, clean the flux off, and take another look - but otherwise leave them alone. :)
 
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Simple answer - reflow if it needs to be reflowed. I'd leave well enough alone as long as you don't have issues with dropout or intermittent connection.

Be interesting to know what component leads are bluing out on ya. Some things are designed to run hot - fusible resistors fer instance can cook pretty good in operation.
 
Practice and patience bring experience and that's best.
If things are working, they are working.
When hunting problems, that's when bad joints are a concern.

Reflowing joints is NOT a part of restoration.
Soldering causes stress to the traces and if your tools and skills are not excellent, you may be causing harm.

Bad joints typically have circle marks when the joint has gone.

But, a bad joint may not be visible, so when all else fails, reflowing may be the next trick to try to repair.
I think I finally sorted out a Yamaha here where 2-3 other problem possibilities were used (clean controls, clean relay points, clean in/out jacks. it would still drop a channel randomly. Reseating the jumpers would bring it back. I finally tore it all apart to check the jack mounts but they looked fine, BUT since I was there, I did a reflow. So far, so good.
 
Simple answer - reflow if it needs to be reflowed. I'd leave well enough alone as long as you don't have issues with dropout or intermittent connection.

Be interesting to know what component leads are bluing out on ya. Some things are designed to run hot - fusible resistors fer instance can cook pretty good in operation.
Voltage regulators, fuse resistors
 
Reflowing joints is NOT a part of restoration.
Soldering causes stress to the traces and if your tools and skills are not excellent, you may be causing harm.
But, a bad joint may not be visible, so when all else fails, reflowing may be the next trick to try to repair.
Basically the appreach I had taken up to this point.

But then I always read "I reflowed all the iffy looking joints" in other members documentation of their restoration which led me to try to do the same.
 
I cleaned the lower one, not the upper one. The lower one looks darker to me.

Of those two, the upper one looks the more suspect, as there appears to be a discontinuity in the solder fillet, around the lead. This may be where it moved slightly when cooling when first soldered, possibly related to the big pad it is connected to.

Heat stressed joints go grey, as larger crystals form, and the solder oxidizes.
 
But then I always read "I reflowed all the iffy looking joints" in other members documentation of their restoration which led me to try to do the same.
This sometimes gets translated into blanket reflowing as a standard restoration activity - which is ridiculous.

The joints either need reflowing or they don't - you can cause damage by unnecessarily reflowing joints, due to excessive heat. Reflowing alone will often not rectify a joint problem - only removing the old solder and addressing the reason for no-flow, with scraping/filing and/or adding extra flux to solve the issue if it exists.
 
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This one is very obvious

That's due to mechanical damage. And it looks like it will have no electrical consequence, since it appears to be mechanical support for whatever the three pin device is (ah: pot of some sort?). I'd re-solder their leads, as they look a bit grey around the lead. Even though it's unlikely to ever have got hot, the usual cause of dry joints (after initial faulty soldering).
 
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