Complete Beginner to Soldering about to try a Repair

dl324

Joined Mar 30, 2015
13,836
So would it be effective to move the iron away the same moment that you apply the solder?
No. If you're reflowing (remelting) solder,
  1. you melt the solder thoroughly
  2. insert the wire, let it get hot enough to form an alloy between the wire, solder, lead, and pad
  3. remove the iron
  4. let the solder cool without jostling it
If the wire hadn't already been tinned, you would either tin it or apply flux.

Solder joints with lead solder will be shiny. If you use 63/37, you're less likely to have cold joints. Lead free solder will give dull joints.


If you were soldering a new joint, you
  1. use the iron to heat the pad and lead/wire simultaneously
  2. apply solder to the pad/lead opposite from where the iron is positioned
  3. when enough solder has melted to form a good joint, move the solder wire away from the joint
  4. remove the iron
  5. let the solder cool without jostling it

Solder applied to the tip and/or flux applied to the joint can be used to facilitate heat transfer.

EDIT: All of these joints are bad. The burned insulation on the wires is indicative of a misplaced tip or too much heat...
clipimage.jpg
 
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Thread Starter

PokeyMongo

Joined Jul 25, 2020
8
So I was a little scared of turning the dial up past about 25%, which is about 275 degrees Celsius, because someone said I should use a low wattage pen and this one is 60w. I noticed that the old solder did not seem to melt, but the solder I was adding was melting pretty fast. What I ended up trying to do because of this was make the new solder glob onto the old one and jab the wire into the new glob as it cooled there. Could it be that the new solder doesn't like to flow well on unmelted solder?

I know those are some ugly joints, but I'm very proud of the fact that I got my radio working again. It's nice knowing I kept a piece of hardware out of a landfill and in operation.
 

jpanhalt

Joined Jan 18, 2008
11,088
Older solder may be lead-free with higher melting point. Also, heat conduction from the tip is facilitated by a little molten solder o the tip.

The idea of making a blob and then sticking the wire into it does not appeal to me, particularly if you are using a eutectic solder like 63/37. I would heat the wire and pad then add solder to both.
 

MrChips

Joined Oct 2, 2009
25,036
As I said, you need to practice first before attempting a repair.

Know your solder. The solder on the board could very well be lead-free solder. This would require a higher temperature. It also depends on the size of the copper surrounding the solder pad. A lot of copper creates a heat sink and again requires more heat to melt the solder.

The idea would have been to melt the existing solder and add fresh 63/37 solder. This would allow the solder to flow better. Then you would remove all the solder and create a new solder joint.

(If there is no thru hole where the wire was attached then the only reasonable technique is to first create a solder blob and then solder the wire to the blob.)

Live and learn.
 

Audioguru again

Joined Oct 21, 2019
4,117
Noobs put solder on the tip of the soldering iron then drip it from up high onto the solder joint.
Many cheap soldering irons use a light dimmer circuit with no sensing of the tip temperature. Then the tip is too hot or too cold.
 

djsfantasi

Joined Apr 11, 2010
8,075
So I was a little scared of turning the dial up past about 25%, which is about 275 degrees Celsius, because someone said I should use a low wattage pen and this one is 60w. I noticed that the old solder did not seem to melt, but the solder I was adding was melting pretty fast. What I ended up trying to do because of this was make the new solder glob onto the old one and jab the wire into the new glob as it cooled there. Could it be that the new solder doesn't like to flow well on unmelted solder?

I know those are some ugly joints, but I'm very proud of the fact that I got my radio working again. It's nice knowing I kept a piece of hardware out of a landfill and in operation.
Congratulations on getting your radio working. But the technique you used may end up breaking later.

When you stick the wire into the molten blob, the wire isn’t hot enough for the solder to make a strong connection. The wire is cold and the solder will crystallize before it has a chance to make a strong joint.

Personally, with solder on the PCB, I’d place the wire on top. Then, place the iron on top of the wire. The wire will heat up and melt the solder. Remove the soldering iron and keep the wire still. You can blow on the joint. When the solder hardens, you can take your hand off the wire.
 

jpanhalt

Joined Jan 18, 2008
11,088
FR4 and the cheaper paper versions have characteristic smells. Then, it is too late.

FR4 softens long before it burns. That is a greater problem because when it is soft, it is easier to pull a trace or plated hole from it. That will happen to you someday when you have a stubborn TH component and pull too hard.
 

djsfantasi

Joined Apr 11, 2010
8,075
At what point do I need to worry about burning a hole in the PCB?
Using good technique and properly prepared joints and iron, you needn’t worry about burning a hole in the PCB. Unless you’re trying to do something like jpanhalt suggested.

I’m a hobbyist. I use a 40W iron without any temperature control with through hole components. My joints are always like the tented example in the picture I posted. I’ve never burnt a hole in a PCB. I use a thin electronics solder and have desoldering braid on hand to clean up my joints.
 

MrChips

Joined Oct 2, 2009
25,036
You don't burn holes in your PCB. The PCB is made of material that will not burn at those temperatures.
What you are more likely to do is strip the copper foil and pads off the PCB. They are only glued on to the PCB.
Use too much heat, too much pressure, spend too long and you will strip off the copper.
 
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