How hot should the solodering iron tip be?

[Henry89789]

In the thread about bridged joints  the issue of the temperture of the  tip for soldering was raised. I read about too much heat damaging the board or components so I have been careful about how hot to allow the tip to get. In order to better control this I bought a digital soldering iron which allows you to exactly dial in the temperature. I have been soldering and unsoldering at 700 degrees. At what temperture should one unsolder?   solder? Thanks for your replies to my novice questions.

[R.G.]

I apologize for how circular this is going to sound, but the correct answer is "Hot enough to make the solder flow very freely."

The reason I can't quote a specific temperature is that (1) different solder compositions melt at different temperatures (2) only the solder actually in contact with the tip is at the same temperature as the tip, (3) there is a time-distance heat flow effect where it takes time for the heat to raise the temperature as you get further from the tip and (4) the tip temperature drops when it transfers heat to the joint - yes, even if it's temperature controlled.

For some perspective, a lot of industrial soldering with tin-lead alloys is done with propane torches, which have a flame temperature of a few thousand degrees.

If your solder is not flowing very fluidly, like water soaking into a bit of cloth, your soldering iron is not hot enough, no matter what the degrees display says.

Here's another thing to think about. The electronic control on the soldering station cannot control tip temperature fast enough. Ever. What it does is adjust the average amount of heat going into the tip to bring it up to the set point temperature, then quit. This takes some time. When you touch the tip to a joint, *instantly* heat flows out of the tip bringing the tip temperature down, and the soldering controller has to play catch up.

You want the tip hot enough that solder flows within 1-2 seconds of the tip being in contact with the joint. If that's not true,
1. make sure the tip is clean and mirror-shiny with a thin layer of molten solder
2. make sure the joint to be soldered is clean
3. turn it up till solder melts within 2 seconds ("one-thousand-one, one thousand-two") for joints where you're soldering one lead in a PCB or vero board hole.
4. turn it down if you notice excessive smoke, burning of the board, lifting copper, or excessive gray oxidation on the tip.
5. put a piece of black tape over that temperature display till you get the above right, then take the tape off and look at what it says.

There are other joints which need a different approach, but this is a good one for PCB soldering.

[runmikeyrun]

Hot enough to burn your leg when you drop the iron!

[defaced]

1. make sure the tip is clean and mirror-shiny with a thin layer of molten solder

This is much more important than it seems at first.  If there is not molten solder on the tip, you are relying on the 1 to 2 points the tip is touching on the joint to transfer heat instead of the surface molten solder will conform to to transfer heat.  More surface area = faster heat transfer = higher allowable tip temperature = faster working time = cooler components.  Heat takes time to flow because of a part's heat capacity.  The less time you're in contact with the joint, the less time you allow for the part to heat up. 

[darron]

what type of solder are you using? it makes a big difference


on mine, for the lead free solder i use, i set just above 350 celsius. definitely less than 400 unless you want to solder onto the back of a pot or something and need a lot of heat very fast.


get metric people!

[Taylor]

Using leaded solder, I personally have found that about 324 degrees celsius is the perfect compromise - makes really nice, clean joints very quickly, but low enough that tip life is not compromised too much. This is on digital Hakko or Aoyue stations.

324 because the digital display only selects even numbers.  I'm not just being a weirdo with an arbitrary number.

[Henry89789]

I have been using 60/40 rosin core solder from radio shack.  Thanks for replies.

[R.G.]

I reiterate my advice: put opaque tape over the temperature display, turn it up till you get good joints, then remove the tape and say "OK! Now I know!". 

[wavley]

I reiterate my advice: put opaque tape over the temperature display, turn it up till you get good joints, then remove the tape and say "OK! Now I know!". 

A big +1 on that good buddy, there are way to many variables to make numbers relevant.

[Perrow]

I reiterate my advice: put opaque tape over the temperature display, turn it up till you get good joints, then remove the tape and say "OK! Now I know!". 

If R.G. writes something twice on the same page consider it extra valuable information and do seriously consider following the advice. I've haven't had any major problems soldering, but will try this exercise and see where it gets me.

[Taylor]

My comment was not contrary to RG, BTW; rather, I find that type of explanation to be very useful, but at the same time, for a noob, a starting place is good IMO. He can later tweak it per RG's suggestions, but when we stuff advice so full of caveats that he's sitting there with his iron at 5 degrees, then 7 degrees... I think we can give slightly more directed guidance than that.

[waltk]

I like 63/37 solder.  Don't know that I've ever seen it Radio Shack, so you would probably have to get it somewhere else.  The difference (vs. 60/40) is that it's eutectic.  That means it goes straight from liquid to solid as it cools - without a slushy in-between phase.  This is an advantage because there's less opportunity to nudge your work and wreck the joint before it's solid.

[Paul Marossy]

324 because the digital display only selects even numbers.  I'm not just being a weirdo with an arbitrary number.

Are you sure about that?! You sound kind of defensive with that statement. 

[deadastronaut]

slightly OT: but i'm gettig a new solder station..and...

what is the best advice for a brand new tip...treatment wise?...heat up n put a blob on the tip, dab it on sponge , then use...

i just don't want to mess up a new tip...ive never had a new one...always old jobbies...

cheers.

[R.G.]

My comment was not contrary to RG, BTW; rather, I find that type of explanation to be very useful, but at the same time, for a noob, a starting place is good IMO.

I certainly didn't take it for contrary.  I was (but only mildly) exaggerating to make a point. I've run into a similar situation with pedals that I call "listening with your eyes".

People sometimes thing that the knobs shouldn't have to be turned all the way up, or ought to be about middle, or shouldn't have to be all the way down, regardless of the fact that the knob range is - or should be - limited to a useful range and that no position is any more valid or better or possibly damaging or "too much" than any other. We've actually had people write us saying words to the effect that this or that sounds great when set like this, but one of the knobs has to be all the way up and they don't think they should have to turn it all the way up to get that sound. 

The idea that where you see the indicator line on a knob, or numbers on a display pointing makes a bigger difference than getting done what needs done has always struck me as odd. But people vary. Some of them won't turn it above the recommended X, and others will use anything *except* the recommended X, whatever X is. Yes, a starting point is useful for a beginner, but they have to get to where they do it right, develop the experience and feel for it. Like Obi-Wan putting the helmet on Luke and making him use the Force instead of looking at the drone.

And I'm always having problems with beginners using too cold an iron. 

[Taylor]

People sometimes thing that the knobs shouldn't have to be turned all the way up, or ought to be about middle, or shouldn't have to be all the way down, regardless of the fact that the knob range is - or should be - limited to a useful range and that no position is any more valid or better or possibly damaging or "too much" than any other. We've actually had people write us saying words to the effect that this or that sounds great when set like this, but one of the knobs has to be all the way up and they don't think they should have to turn it all the way up to get that sound. 

Yes, I have the same exact customer support stuff all the time. It's really baffling. I've even seen people who will sell a particular pedal because of that - they can get the perfect sound with a particular knob combo, but they want it to be perfect with all the knobs flat.  Humans are weird sometimes. I have a feeling alpacas would not complain about that if they used pedals.

[R.G.]

I have a feeling alpacas would not complain about that if they used pedals.

Yeah - but alpacas spit at you. 

[waltk]

slightly OT: but i'm gettig a new solder station..and...

what is the best advice for a brand new tip...treatment wise?...heat up n put a blob on the tip, dab it on sponge , then use...

I got a new station a little over a year ago.  I was burning through a lot of tips on my old iron, so I wanted to see if taking care of the new one would work better.

I drag it across the sponge every time before going to the PCB.  If it looks dry at all, I add a little extra tinning.  So I might have 6 or 8 joints to solder at once, then put it back in the holder.
When I turn it off, I always make sure the tip is covered with solder.

Just a couple months ago, I noticed that there was some kind of plaque or oxidation on part of tip that the sponge would not remove, and the solder would not wet.
So I stabbed it into my little tin of "Tip Cleaner / Tinner", and now it looks/works good as new... for now.  I don't know how long the tip will last, but I'm pretty happy with the 1+ year for the first tip. (And I got bunch of spares with the station)

With my old iron, having to resort to the tip cleaner was a sign of impending doom.  Seems like every time I used it, it was only a matter of time before large cavities were rotted into the tip and it was dead.  I don't know whether the tip cleaner hastened the tip failure (because it's harsh), or it helped prolong the life of the tip that was doomed anyway.

So I guess I've put this in melodramatic terms, but it's really nice to have a soldering station that helps rather than hinders the building process.
Good luck with yours, Rob.

About setting the temperature... I know what good temperature is when I have it, and it doesn't bother me too much that I have to krank the thing up as high as it will go.

[Henry89789]

I appreciate all the thought you all put into these replies. 324 and 350 degrees celsius is colder than the  700 degrees fahrenheit I have been working at. Maybe it is the solder. The package of the Radio shack solder does not say whether it is lead free. Small bear has 63/37 but their description says "tin/lead".

I was hesitant to  try R.G.'s method on an actual project but I found some old PCBs from some worthless electronics with caps, resistors and diodes that I am going to experiment with. I am going to use the opaque tape over the temp display and start at 324 degrees celsius (615.2 degrees fahrenheit) and raise the temperature until I find the temp at which the solder flows properly within two seconds. I am even going to see how long it takes to damage  the PCB at each temp.

You all want to recommend some specific brands of solder?

[waltk]

The package of the Radio shack solder does not say whether it is lead free. Small bear has 63/37 but their description says "tin/lead".

If it doesn't say "lead free", it's probably not.  If it says "60/40", that means its 60% lead and 40% tin.  Likewise for "63/37" - 63% lead 37% tin.  Whether to seek out and use lead-free solder is a whole 'nother discussion.  I personally like and trust leaded solder.

You all want to recommend some specific brands of solder?

Kester is well-known long-established quality brand, but any other brand of 63/37 with rosin core would be fine.