dull coulored solder joints

[e44-72]

Hello

When I have a component lead poking through a hole on a pcb, I first tin my iron and clean it well, I heat the joint the opposite side to where I then feed my solder. I take the iron away and often there is a shiny joint.
However if I thin a wire and melt some solder on a board track then reheat and put the tinned wire in the heated solder, i find when i remove it and keep it still the joint still turns dull and grey coloured even after applying heat for a long time.
Is this a cold and bad joint or is this ok

Thank you for any replies

 

[Boncuk]

Hi,

the longer you apply heat to any electronic part the more you fry it than soldering it.

Using a magnifying glass you'll see the solder spot filled with little craters which make the joint look dull.
A solder joint like that is a self destruction joint which will loose electrical connection sooner or later.

Apply heat evenly to the part wire and the solder pad just for the time it takes for the soldering tin to flow around the part.

Boncuk

 

[KJ6EAD]

In the situation you describe, you've cooked the flux out of the joint before completing it.

This is my favorite basic soldering video, "How and why to solder correctly".

https://www.youtube.com/watch?v=I_NU2ruzyc4

 

[DerStrom8]

I agree with KJ6EAD. I think you're burning off all the flux during the tinning, so the joint oxidizes when you re-heat it. I would suggest only tinning the wire, putting it through the hole in the PCB, then add fresh solder to the pcb to join the wire to it. Do not tin both the wire AND the PCB.

 

[KJ6EAD]

If you're soldering the wire flat on the surface of the copper instead of through a hole, you should be prepared to complete the joint quickly by having the wire fixed in position by a tool or apply additional flux.

 

[KeepItSimpleStupid]

Lead free solder has a habit of making dull looking joints.

 

[e44-72]

Thank you for your replies

for ages I have tinned to pieces of metal with no additional flux and found the joints go grey and dull when the solder is reheated and no more solder is added. In that case can I ask for your opinion if you were to solder onto a solder lug/tag on say a panel mount switch, would you put the wire through then solder or melt solder on both tag and wire seperately and just reheat. Is reheating old solder without fresh solder being applied always asking for cold joints or this ok to do on solder lugs/tags.

Thank you for your replies and any more and the solder video was really helpful, thanks to KJ6EAD

 

[DerStrom8]

In that case can I ask for your opinion if you were to solder onto a solder lug/tag on say a panel mount switch, would you put the wire through then solder or melt solder on both tag and wire seperately and just reheat.

As I mentioned before, I would only tin the wire, then put it through the hole in the board or switch contact, then add fresh solder to finish it off. That way you reheat the solder on the tinned wire, but you're also adding fresh solder/flux to keep the joint clean.

 

[e44-72]

Thank you derstom8 for your advise its helped me see my errors, soldering should get better now. I also just wanted to ask even when the joint is dull in colour it often still feels strong and has electrical continuity so is it really a problem.

 

[DerStrom8]

Thank you derstom8 for your advise its helped me see my errors, soldering should get better now. I also just wanted to ask even when the joint is dull in colour it often still feels strong and has electrical continuity so is it really a problem.

A cold solder joint is generally easier to break or to fracture, which could make the connection intermittent. If you have a cold joint, it is best to use a desoldering tool (a pump or bulb) to remove the solder and to redo the joint. That would be the best thing to do at this point.

 

[e44-72]

Thanks again, good advise from all

 

[KeepItSimpleStupid]

I can go back to the way my father taught me plumbing. He would clean and tin each part of the fitting/tubeing, insert and then add solder.

When I was taught later by a machinist, the tinning was unnecessary. Cleaning, fluxing and cleaning after the joint is made is important. The rest is pretty much thermodynamics. Heating the more massive fitting first and letting the solder wick into the joint.

A good plumber can use MAPP gas without issues. He can make the joints much faster.

Later, a friend had a small plumbing project which involved a few water heaters. I taught him how to solder and I did only the critical joints or the ones that would be a real pain if they leaked.

He later completed a 40 fitting project and none leaked.

In the case of electronic soldering of lugs, you HAVE to make a mechanical contact first. Solder, basically without touching the solder to the iron and clean the flux off the joint after it is made. You do need adequate heat for a lug, so a temperature controlled iron helps. I would use my butane iron for this application.

"tinning" the tip and wiping with a damp rag is essential to get good thermal contact. DO NOT file the tip.

 

[KJ6EAD]

If you were to solder onto a solder lug/tag on say a panel mount switch, would you put the wire through then solder or melt solder on both tag and wire seperately and just reheat? Is reheating old solder without fresh solder being applied always asking for cold joints or this ok to do on solder lugs/tags?

In this video, the correct method is shown but for most field repairs, as long as the terminal is clean and the solder wets well, tinning just the wire should be sufficient. In a production setting, wire and terminals are often tinned by fluxing and dipping in a solder pot.

https://m.youtube.com/watch?desktop...wswU&v=Ql6Vkw5wswU&gl=US#/watch?v=Ql6Vkw5wswU

This shows more wire tinning using a heat sink to prevent wicking under the insulation and insulation melting/retracting. On stranded wires with minimal twist, twist the end a little tighter before tinning to prevent the strands from splaying.

https://m.youtube.com/#/watch?v=xpiyB7ZM3vg