Need a "best" temperature or range for soldering on PC boards

Thread Starter

birckcmi

Joined Jan 1, 2018
149
I've run into problems soldering up some long-stored kits (10-20 years old) that may be due to my ineptitude, but could also be due to a bad choice of soldering iron temperature. The problems range from soldering simply doesn't work-no solder blob forms at the board surface, to that problem plus a big burned spot on the surface and a loose copper trace peeling off the board. Sometimes the metal spot around the hole in the surface disappears completely. Could it be due to the age of the board, or lower standards of manufacture? Could I need a hotter iron? The one I'm using goes only to 480˚F. Some authoritative sources say I should be working at 600˚; others, equally authoritative, claim I should work at 480˚ or lower. I also haven't been using flux. So is it me, or the circuit boards? Fortunately, I'm using the construction of these old kits to sort out my technique; if they work, great. If they don't, I salvage the parts and go on to the next kit.
 

MrChips

Joined Oct 2, 2009
23,524
For solder with lead you need 700˚F.
For non-leaded solder you need 800˚F.

You also need flux designed for electronics, not flux for plumbing.
 

dl324

Joined Mar 30, 2015
12,871
If you're getting board burns and lifted traces, it's you. 480F seems low to me. I use a 700F tip almost exclusively; my favorite irons only support 3 temperatures: 600F, 700F, and 800F.

Poor wetting could improper technique, temperature, or surface preparation. Pictures would help us determine what the reason(s) for poor joints might be.
 

BobaMosfet

Joined Jul 1, 2009
1,776
I've run into problems soldering up some long-stored kits (10-20 years old) that may be due to my ineptitude, but could also be due to a bad choice of soldering iron temperature. The problems range from soldering simply doesn't work-no solder blob forms at the board surface, to that problem plus a big burned spot on the surface and a loose copper trace peeling off the board. Sometimes the metal spot around the hole in the surface disappears completely. Could it be due to the age of the board, or lower standards of manufacture? Could I need a hotter iron? The one I'm using goes only to 480˚F. Some authoritative sources say I should be working at 600˚; others, equally authoritative, claim I should work at 480˚ or lower. I also haven't been using flux. So is it me, or the circuit boards? Fortunately, I'm using the construction of these old kits to sort out my technique; if they work, great. If they don't, I salvage the parts and go on to the next kit.
Make sure you know how to properly tin your iron and keep it clean during use without over-cleaning (lowers temp). You can pick up a spool of rosin-core solder just for cleaning/tinning your iron, and a small bottle of flux for the board.

I've found 700-800f works well. I also stay on a joint as little as possible. If you go past 3-5 seconds and it isn't done, get that iron off of it or you risk ruining the board, the via, and/or the component.

Figure out if the board has a ground-plane and that is wicking heat away faster than the iron can heat it, or non-clean/flux issue, or iron temp, or what.
 

Tonyr1084

Joined Sep 24, 2015
5,976
When it comes to soldering there are a whole mess of factors that affect solderability. First thing that stands out in my mind is the age of the boards. The copper has had a ton of time to oxidize, which is the first problem I would want to rectify. With plated through holes (PTH) the barrels can not be treated mechanically. The surfaces can be buffed clean using a very fine grit sand paper, one that almost removes nothing at all. My wife has (had, I now have it) a sponge for polishing her nails. It has three grits ranging from medium to very fine grit. When I have an old board that's the first thing I'll do - remove the oxidation manually. Under normal circumstances flux will do the job.

Then there's the age of the leads of components. They also oxidize. Again, flux and pre-tinning the leads will help.

Then there's the design of the board. Single layer, two layer (top and bottom), multi-layer (layers buried within the glass and resin of the PCB). With multi-layer boards inner layers can be large heatsinks. Ground plane and power plane will require a lot of heat. Often you may have to pre-heat the board in order to get solder to flow all the way through the board. I've been there PLENTY of times with defense contract solder work on PCB's

Then there's the solder iron. Temperature is important, but so is the ability to transfer that heat to the board. A dry tip (no solder) will hardly warm the joint. That's why it's common practice to tin the tip of the iron - to create a thermal bridge to the joint. Also important is tip condition. If it's caked with rosin it won't want to accept solder. The size of the tip for the job also affects solderability. A pin point solder tip will not solder a large joint as it does not have enough thermal mass. Mass can be increased by tinning, but it has limited usefulness. For a large joint you commonly need a large tip. Too large and you can lift pads and traces (the copper dot and lines).

Then there's the type of solder. And there are many different types. Solid core, rosin core, flux core, no-clean flux core to name many. 60/40 (tin/lead), 63/37, silver solder, high temp solder. There, again, it's important to know what you're working with.

Finally, there's dwell time. How long you apply heat to a joint. Too long and you can lift traces. Not long enough and you can get a cold solder joint. If you've successfully made a joint, while the solder is molten, if you move it while cooling you can get a "Disturbed" joint, one that looks like a cold solder joint.

To be sure, soldering takes practice. And I've seen some people who just don't understand solder and flowing solder. There are three states to most solders; solid, plastic and molten. The first and last are self explanatory. "Plastic" means the solder is not solid and not molten. If you fail to get it into the molten state it can not bond molecularly with the parts being joined.

To recap:
Dirty board
Heat sinking
Fluxes
Solder type
Solder tip
Solder temperature
Dwell time

And then there's the problem of failure to clean a board, leaving aggressive flux on the board can eat away the traces and you end up with a circuit that fails.

One point on heat and dwell time: Some components, look at the data sheet, it might tell you the safe amount of time and temperature you can apply to a component before it suffers internal damage. Heating a joint for too long a time can render a component dead before you even power it up.

Don't be afraid to learn to solder. Practice makes perfect. Get a bunch of cheap components and boards and just solder the hell out of it. You will develop a feel for when to apply more solder and when to stop.

THEN there's SMT (Surface Mount Technology) (components without leads that go through the board). I won't even begin to touch on that subject. It's not for the inexperienced for sure.
 

eetech00

Joined Jun 8, 2013
2,360
I've run into problems soldering up some long-stored kits (10-20 years old) that may be due to my ineptitude, but could also be due to a bad choice of soldering iron temperature. The problems range from soldering simply doesn't work-no solder blob forms at the board surface, to that problem plus a big burned spot on the surface and a loose copper trace peeling off the board. Sometimes the metal spot around the hole in the surface disappears completely. Could it be due to the age of the board, or lower standards of manufacture? Could I need a hotter iron? The one I'm using goes only to 480˚F. Some authoritative sources say I should be working at 600˚; others, equally authoritative, claim I should work at 480˚ or lower. I also haven't been using flux. So is it me, or the circuit boards? Fortunately, I'm using the construction of these old kits to sort out my technique; if they work, great. If they don't, I salvage the parts and go on to the next kit.
if your soldering components to a standard PCB, a 60W soldering iron is sufficient and forms excellent joints without lifting the circuit traces or pads. We used this type of soldering iron for PCB assembly in a company for years..
 
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Thread Starter

birckcmi

Joined Jan 1, 2018
149
if your soldering components to a standard PCB, a 40W soldering iron is sufficient and forms excellent joints without lifting the circuit traces or pads. We used this type of soldering iron for PCB assembly in a company for years..
Thank you for the info. What temperature were you setting the soldering iron at?
 

Thread Starter

birckcmi

Joined Jan 1, 2018
149
When it comes to soldering there are a whole mess of factors that affect solderability. First thing that stands out in my mind is the age of the boards. The copper has had a ton of time to oxidize, which is the first problem I would want to rectify. With plated through holes (PTH) the barrels can not be treated mechanically. The surfaces can be buffed clean using a very fine grit sand paper, one that almost removes nothing at all. My wife has (had, I now have it) a sponge for polishing her nails. It has three grits ranging from medium to very fine grit. When I have an old board that's the first thing I'll do - remove the oxidation manually. Under normal circumstances flux will do the job.

Then there's the age of the leads of components. They also oxidize. Again, flux and pre-tinning the leads will help.

Then there's the design of the board. Single layer, two layer (top and bottom), multi-layer (layers buried within the glass and resin of the PCB). With multi-layer boards inner layers can be large heatsinks. Ground plane and power plane will require a lot of heat. Often you may have to pre-heat the board in order to get solder to flow all the way through the board. I've been there PLENTY of times with defense contract solder work on PCB's

Then there's the solder iron. Temperature is important, but so is the ability to transfer that heat to the board. A dry tip (no solder) will hardly warm the joint. That's why it's common practice to tin the tip of the iron - to create a thermal bridge to the joint. Also important is tip condition. If it's caked with rosin it won't want to accept solder. The size of the tip for the job also affects solderability. A pin point solder tip will not solder a large joint as it does not have enough thermal mass. Mass can be increased by tinning, but it has limited usefulness. For a large joint you commonly need a large tip. Too large and you can lift pads and traces (the copper dot and lines).

Then there's the type of solder. And there are many different types. Solid core, rosin core, flux core, no-clean flux core to name many. 60/40 (tin/lead), 63/37, silver solder, high temp solder. There, again, it's important to know what you're working with.

Finally, there's dwell time. How long you apply heat to a joint. Too long and you can lift traces. Not long enough and you can get a cold solder joint. If you've successfully made a joint, while the solder is molten, if you move it while cooling you can get a "Disturbed" joint, one that looks like a cold solder joint.

To be sure, soldering takes practice. And I've seen some people who just don't understand solder and flowing solder. There are three states to most solders; solid, plastic and molten. The first and last are self explanatory. "Plastic" means the solder is not solid and not molten. If you fail to get it into the molten state it can not bond molecularly with the parts being joined.

To recap:
Dirty board
Heat sinking
Fluxes
Solder type
Solder tip
Solder temperature
Dwell time

And then there's the problem of failure to clean a board, leaving aggressive flux on the board can eat away the traces and you end up with a circuit that fails.

One point on heat and dwell time: Some components, look at the data sheet, it might tell you the safe amount of time and temperature you can apply to a component before it suffers internal damage. Heating a joint for too long a time can render a component dead before you even power it up.

Don't be afraid to learn to solder. Practice makes perfect. Get a bunch of cheap components and boards and just solder the hell out of it. You will develop a feel for when to apply more solder and when to stop.

THEN there's SMT (Surface Mount Technology) (components without leads that go through the board). I won't even begin to touch on that subject. It's not for the inexperienced for sure.
Thanks for all the information. Particularly the section about cleaning the board with fine abrasive. I have a collection of unused emery paper running from 1000 to 3000 grit, which should work. I had heard of performing that task on older boards, but without any details about why and with what.
 

crutschow

Joined Mar 14, 2008
27,209
I believe a somewhat hotter iron is better because it heats the spot you want to solder/desolder faster, so the heat doesn't spread so far.
But note that you need to apply the heat only as long as it takes to melt the solder on the board. Longer than that can lead to damage.

And always use added rosin (electronic) flux when soldering (even if you are using solder with flux), as this speeds the process and generates a better joint.
 

Tonyr1084

Joined Sep 24, 2015
5,976
One concern with higher local heat - thermal expansion. Another concern is with heat cycles, how many times you reheat a joint. Both can be detrimental to a PCB.
 

Thread Starter

birckcmi

Joined Jan 1, 2018
149
Make sure you know how to properly tin your iron and keep it clean during use without over-cleaning (lowers temp). You can pick up a spool of rosin-core solder just for cleaning/tinning your iron, and a small bottle of flux for the board.

I've found 700-800f works well. I also stay on a joint as little as possible. If you go past 3-5 seconds and it isn't done, get that iron off of it or you risk ruining the board, the via, and/or the component.

Figure out if the board has a ground-plane and that is wicking heat away faster than the iron can heat it, or non-clean/flux issue, or iron temp, or what.
OK. I'm dropping back to Beginner status and starting over, since I clearly don't know as much about soldering as I thought I did. I've stopped constructing any circuits for the time being and ordered a new iron that goes up to 800˚
I believe a somewhat hotter iron is better because it heats the spot you want to solder/desolder faster, so the heat doesn't spread so far.
But note that you need to apply the heat only as long as it takes to melt the solder on the board. Longer than that can lead to damage.

And always use added rosin (electronic) flux when soldering (even if you are using solder with flux), as this speeds the process and generates a better joint.
Thank you for your response. It seems to be agreed here that I have been using the wrong temperature. I've taken steps to remedy that, and remedy my non-use of flux and rosin. This is the stuff I need to know. Thanks again.
 

eetech00

Joined Jun 8, 2013
2,360
Thank you for the info. What temperature were you setting the soldering iron at?
First..a correction....its a 60W station.

The one I use is an old Weller 60W regulated soldering station. I've had it for over 25 years. :)
It doesn't have a temperature setting. It doesn't even have an on/off switch, but I still use it today and it still works perfectly!

Here a picture of one similar to mine:

1607457830402.png

Mine doesn't have the switch. :)
The trick to soldering components is having the correct soldering tip, knowing when the pad/lead is hot enough, and knowing when to remove the heat. This "know how" is gained only through experience. I use inspection glasses when I solder (a habit I've had since I was trained back in the day) and use a wet sponge to wipe the tip. The sponge is placed on a tray in the soldering station. Keep the soldering iron tip clean! When you apply the heat, you'll see the solder melt and become shiney and flow around the lead and into the pad. This is when you remove the heat. The joint should cool to a shiney finish. Don't blow on it to cool it! Let it cool on its own. If its a dull finish, its a high resistive cold solder joint (which is a BAD thing).

Generally speaking, you don't need a gazzillion watt soldering iron to do a good job of soldering components to a PCB.
 
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Ian0

Joined Aug 7, 2020
2,206
My solder supplier told me that the soldering iron should be 120 Celsius hotter than the melting point of the solder. So, 300 C for tin-lead, or 337 C for TSC (which is the only lead-free alloy worth using). If the blob of solder on your iron appears dull with a crust then it has oxidised because the iron is too hot.
If you are using the good old Weller TCP then it's type 7 bits for leaded and type 8 for lead-free; but I found the TCP bits lasted poorly on lead-free, turning black and being very difficult to tin.
 

dl324

Joined Mar 30, 2015
12,871
The one I use is an old Weller 60W regulated soldering station. I've had it for over 25 years.
I got my W-TCP in the late 70's and modified it to add a switch. It worked faithfully until a couple years ago when the heating element burned out. I was without my favorite iron for several months and decided that would never happen again. I bought a replacement heater, a W-TCP-L, and a WTCPN on eBay.

I bought the WTCPK military version 25-30 years ago for my Wife to use for stained glass. She didn't know where it was when mine died. So there's a 4th Weller around here somewhere...
 
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