# Solder won't flow right ...



## pcb rookie (Feb 11, 2022)

Practice builds confidence. I did more soldering lately and got better at it overtime. I did some pretty clean PCBs lately. Most days the solder just flows through easy peasy. Every now and them, I hit a project that the solder just won't flow right. Today was one of them. The solder would stick to the lead instead of flowing though/on the contact eyelet or just bunch up. I stopped, cleaned and tined my tip. Cleaned up the PCB with IPA. Tried again, same. Applied some flux paste (usually don't). It got better but barely. Flowed perfect in the end when I got to transistors and trim pots ... 

Any one as leads on what's the cause when solder just won't flow? 

When do you do or adjust when that happens? 

FYI - I use 60/40 Aims .032 diameter solder @ 400 degrees average. I tin my tip between every 2-3 solder and keep in clean.


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## vigilante398 (Feb 11, 2022)

I'm assuming that's 400 C, not 400 F? Does your solder have flux, like rosin core? Good flux can make a world of difference. 

As for why some parts may flow easier than others, it comes down to how much copper is connected to the pad. Something like a ground plane will make it more difficult, as you heat the pad the copper surrounding the pad wants to heat up as well, so you need to heat it up long enough that the pad is hot enough for the solder to flow. Copper is a great conductor of heat, so it's an uphill battle sometimes, but the right amount of heat is critical to make it work.


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## spi (Feb 11, 2022)

I always find that electrolytic caps are the most stubborn.  I assume they must suck up the heat.


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## BuddytheReow (Feb 11, 2022)

I too have some solder that doesn't flow very well. The workaround for me was to have a hot iron (400C+). It also helps to have a good iron tip. I like the fine tipped ones since I can heat up the lead and the pad simultaneously. It only takes a few seconds or sometimes instant! I then feed the solder where all 3 meet. Once I see the solder "fall" into the pad I know I'm good. This process isn't fool proof and sometimes I need to suck it out and start again.


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## dlazzarini (Feb 11, 2022)

What vigilante398 said


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## pcb rookie (Feb 11, 2022)

vigilante398 said:


> as





spi said:


> I always find that electrolytic caps are the most stubborn.  I assume they must suck up the heat.


That was on of the component that was more challenging in this case so that may be a factor.


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## pcb rookie (Feb 11, 2022)

From 


vigilante398 said:


> I'm assuming that's 400 C, not 400 F? Does your solder have flux, like rosin core? Good flux can make a world of difference.
> 
> As for why some parts may flow easier than others, it comes down to how much copper is connected to the pad. Something like a ground plane will make it more difficult, as you heat the pad the copper surrounding the pad wants to heat up as well, so you need to heat it up long enough that the pad is hot enough for the solder to flow. Copper is a great conductor of heat, so it's an uphill battle sometimes, but the right amount of heat is critical to make it work.





BuddytheReow said:


> I too have some solder that doesn't flow very well. The workaround for me was to have a hot iron (400C+). It also helps to have a good iron tip. I like the fine tipped ones since I can heat up the lead and the pad simultaneously. It only takes a few seconds or sometimes instant! I then feed the solder where all 3 meet. Once I see the solder "fall" into the pad I know I'm good. This process isn't fool proof and sometimes I need to suck it out and start again.


The solder as rosin core but I still added some additional flux when I noticed It wasn't flowing as usual. So being a combination of things, I went back this PCB with the solder sucker and redid a few solder to my taste. My soldering station temperature was dropped to 390C so I cranked it back to 400C and it worked better. I also changed the iron contact orientation to a be more vertical (may have more contact with the small eyelet). As BuddytheReow recommended I payed attention to hit the spot where the contact eyelet meets iron and the component. It flowed better.

After cleaning the PCB and inspecting again, it looks better. In truth it was probably fine but as is but as some of you, I get obsessive trying to hit it right! 

Anyone else as recommendations, feel free to jump in!


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## Stickman393 (Feb 11, 2022)

It can be helpful to obtain a variety of soldering iron tips for different applications.

Personally, I'm a fan of chisel tips, as they allow me to manuver the tip in such a way that I can increase or decrease the amount of surface area in contact between the iron tip and the PCB.

Heat transfer increases as the difference in temperatures between surfaces increases.  In conduction, the surface area in contact between the two surfaces matters a great deal to the rate of heat transfer.  Increase the surface area of your soldering iron tip, and you may find those stubborn joints become much easier.


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## pcb rookie (Feb 11, 2022)

Stickman393 said:


> It can be helpful to obtain a variety of soldering iron tips for different applications.
> 
> Personally, I'm a fan of chisel tips, as they allow me to manuver the tip in such a way that I can increase or decrease the amount of surface area in contact between the iron tip and the PCB.
> 
> Heat transfer increases as the difference in temperatures between surfaces increases.  In conduction, the surface area in contact between the two surfaces matters a great deal to the rate of heat transfer.  Increase the surface area of your soldering iron tip, and you may find those stubborn joints become much easier.


I believe I use the 1/32 size but I'll order a chisel tip and try it out. Thanks for the tip!


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## spi (Feb 11, 2022)

chisel tip +1


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## giovanni (Feb 11, 2022)

Since you are saying that flowing got better over time, I wonder if your iron needed time to get to the right temperature? Do you use a water sponge to clean the tip? I read that that might lower the iron temperature. I switched to a brass sponge for that reason.


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## Stickman393 (Feb 11, 2022)

^oh, it absolutely does.  A good iron will use a thermistor in the tip element that will sense that reduction in temperature and crank up the current going through the heater element to compensate.

Water is a great heat sink...it has a latent heat of vaporization of 970btus per pound.  It'll carry the heat away from your tip real quick.

BUT...that should be a transient dip in temperature.  The iron should recover relatively quickly.


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## andare (Feb 12, 2022)

I use a small flat tip. It's thin enough to negotiate those thick resistor leg forests but I can lay it flat against the pad and lead. Then I come in with the solder from the opposite side.

If everything is correct, the solder will naturally flood the pad. Otherwise it won't but it also won't ball up on the iron's tip.

I stay around 375 C and clean the tip on a wet sponge every couple of joints. The brass afro doesn't work as well for me.


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## pcb rookie (Feb 12, 2022)

giovanni said:


> Since you are saying that flowing got better over time, I wonder if your iron needed time to get to the right temperature? Do you use a water sponge to clean the tip? I read that that might lower the iron temperature. I switched to a brass sponge for that reason.





Stickman393 said:


> ^oh, it absolutely does.  A good iron will use a thermistor in the tip element that will sense that reduction in temperature and crank up the current going through the heater element to compensate.
> 
> Water is a great heat sink...it has a latent heat of vaporization of 970btus per pound.  It'll carry the heat away from your tip real quick.
> 
> BUT...that should be a transient dip in temperature.  The iron should recover relatively quickly.





andare said:


> I use a small flat tip. It's thin enough to negotiate those thick resistor leg forests but I can lay it flat against the pad and lead. Then I come in with the solder from the opposite side.
> 
> If everything is correct, the solder will naturally flood the pad. Otherwise it won't but it also won't ball up on the iron's tip.
> 
> I stay around 375 C and clean the tip on a wet sponge every couple of joints. The brass afro doesn't work as well for me.


I use both brass and sponge to clean my tip depending on the look of it. My soldering station temperature gets the iron back to set temperature pretty quick. Most of the time in flows as expected but once in a while on some projects or components, solder just does not wish to cooperate. 

In this case I think I have, by accident, moved temperature to 390C instead of my usual 400C ... and probably combined with some of the above. 

I still intend to use all the recommendations above including experimenting with a larger iron tip. I have both unused chisel and a conic beefed-up tips waiting for me to put them to test! 

Cheers!


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## andare (Feb 12, 2022)

pcb rookie said:


> I use both brass and sponge to clean my tip depending on the look of it. My soldering station temperature gets the iron back to set temperature pretty quick. Most of the time in flows as expected but once in a while on some projects or components, solder just does not wish to cooperate.
> 
> In this case I think I have, by accident, moved temperature to 390C instead of my usual 400C ... and probably combined with some of the above.
> 
> ...


Let us know how it goes!


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## pcb rookie (Feb 12, 2022)

andare said:


> Let us know how it goes!


I will … I plan to begin a project next week! Possibly a Big Muff ….


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## Stickman393 (Feb 12, 2022)

pcb rookie said:


> I will … I plan to begin a project next week! Possibly a Big Muff ….


For sure!

Don't worry about cranking up your heat every now and then too.  The temperature of your iron doesn't matter as much as the absolute quantity of heat transferred over time.

To illustrate what I mean...it's important to know two terms...I'm gonna use the imperial system cause that's what I know...

Specific heat: the amount of BTUs required to raise the temperature of one pound of a specific substance 1 degree Fahrenheit. (Water is the baseline; 1 btu will increase temperature of 1 pound of water 1 degree Fahrenheit)

Latent (or "hidden") heat: the amount of BTUs required to cause a state change (solid to liquid, liquid to vapor) of one pound of a specific substance (Using the same example as before: water has a latent heat of vaporization of 970 BTUs, which means that it takes 970 BTUs to cause a pound of liquid water at it's boiling point of 212⁰F to boil into a vapor).

So...the same concept applies to solder.  60/40 solder has a specific heat of about 0.04 BTU/lb, where as it's latent heat of fusion is about 15.9BTU/lb.

In a normal soldering process, the goal is to elevate the temperature of the solid solder to it's melting point, add enough heat to cause that change of state from solid to liquid, and then slightly superheat the liquid solder beyond it's melting point in order to give yourself time to allow the solder to flow and make a good joint. 

So, just by seeing the difference in 60/40's specific heat and latent heat of fusion (0.04/lb and 15.9btu/lb, respectively) it's easy to see that the actual melting of the solder is where your iron is doing the majority of the work.

If you find that you're having trouble getting the solder to remain molten, the solder is losing heat faster than your iron is able to deliver heat to the joint.

Yup...the name of the game here is heat transfer.  Knowing that conduction between two materials is a game of surface area and delta temperature, there are two ways in which one can improve heat transfer: increase the temperature delta, or increase the surface area in contact.

Once the solder is molten and you can dip the circumference of your solder tip into the solder blob, the style of tip matters a little less, as the entire circumference is involved in the heat transfer process.

But...getting that process started is the trick.  That's why I like using chisel tips, because they have a nice flat edge to em that you can use against the wire lead/PCB.

Happy soldering!


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## pcb rookie (Feb 13, 2022)

Stickman393 said:


> For sure!
> 
> Don't worry about cranking up your heat every now and then too.  The temperature of your iron doesn't matter as much as the absolute quantity of heat transferred over time.
> 
> ...


Very well explained! Thanks for taking time to elaborate. Understanding that, I won't hesitate to adjust the heat as I go when solder won't flow ... combined with the chisel tip.


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## bowanderror (Feb 13, 2022)

I used to have similar problems with 60/40 solder, but have switched over to 63/37 eutectic and it's SOOO much easier! I prefer 0.031" Kester 44 Sn63Pb37 with 3.3% flux content (part number 24-6337-0027).

Most solder alloys melt and solidify across a temperature range, which for 60/40 is 361-376F. Eutectic solders take advantage of a unique property of the 63%:37 Tin:Lead ratio, where the alloy melts & freezes at the same single temperature, ~360F/183C:




This means the solder doesn't go through that "slushy" phase where it is only partially melted, and usually doesn't require temperature adjustment for larger pads.


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## Stickman393 (Feb 13, 2022)

^great point there.  I didn't realize that the 60/40 isn't eutectic...using an eutectic solder made a huge difference for me, personally.

I'm a SN100C man myself...not a big Pb fan.  Concerns and such.  It's a bit more of a pain to desolder, and melts at a higher temp, but it's eutectic and flows very well.  Much better than the sn-ag-cu stuff that I was using before.


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## pcb rookie (Feb 11, 2022)

Practice builds confidence. I did more soldering lately and got better at it overtime. I did some pretty clean PCBs lately. Most days the solder just flows through easy peasy. Every now and them, I hit a project that the solder just won't flow right. Today was one of them. The solder would stick to the lead instead of flowing though/on the contact eyelet or just bunch up. I stopped, cleaned and tined my tip. Cleaned up the PCB with IPA. Tried again, same. Applied some flux paste (usually don't). It got better but barely. Flowed perfect in the end when I got to transistors and trim pots ... 

Any one as leads on what's the cause when solder just won't flow? 

When do you do or adjust when that happens? 

FYI - I use 60/40 Aims .032 diameter solder @ 400 degrees average. I tin my tip between every 2-3 solder and keep in clean.


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## bowanderror (Feb 13, 2022)

Stickman393 said:


> ^great point there.  I didn't realize that the 60/40 isn't eutectic...using an eutectic solder made a huge difference for me, personally.
> 
> I'm a SN100C man myself...not a big Pb fan.  Concerns and such.  It's a bit more of a pain to desolder, and melts at a higher temp, but it's eutectic and flows very well.  Much better than the sn-ag-cu stuff that I was using before.


I use lead-based solder at home for simplicity, but we use 99C or K100LD (Kester's proprietary version) at work and it's decent enough.

Coming from lead-based, I'm never that impressed by the finish on my lead-free joints. Any tips on working with high-Sn content alloys?


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## Stickman393 (Feb 13, 2022)

I can typically just flow and go with my roll of AIM SN100C.

Buttt...sometimes I do find that, especially when working with a large ground plane, hitting the board with my little mini heat gun can help a bit.  Keeps the heat at your joint from migrating as quickly as it would on a room temp board.

Also...I'm working with a HAKKO FX-100 induction iron with the 450⁰C tips for general use...though sometimes I'll swap in the 400⁰C tips.  High heat, get in, get out.

The joints don't look as shiny as leaded solder, but they look pretty good.


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## bowanderror (Feb 13, 2022)

Stickman393 said:


> I can typically just flow and go with my roll of AIM SN100C.
> 
> Buttt...sometimes I do find that, especially when working with a large ground plane, hitting the board with my little mini heat gun can help a bit.  Keeps the heat at your joint from migrating as quickly as it would on a room temp board.
> 
> ...


Good to know about the ground planes. I think I'm just used to any joints that have a hint of haze or texture being sub-par with leaded solder. 

Our shop recently upgraded from 1990s Metcal induction stations to modern Hakko FX-951 resistive ones and it's been a big improvement. We don't do much PCB work, so the constant swapping of tips (and keeping the right selection in stock) was becoming an issue. I would have loved to try a newer induction system, but these seem to do the trick. How did I ever survive without cradle sleep?


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## pcb rookie (Feb 14, 2022)

bowanderror said:


> I used to have similar problems with 60/40 solder, but have switched over to 63/37 eutectic and it's SOOO much easier! I prefer 0.031" Kester 44 Sn63Pb37 with 3.3% flux content (part number 24-6337-0027).
> 
> Most solder alloys melt and solidify across a temperature range, which for 60/40 is 361-376F. Eutectic solders take advantage of a unique property of the 63%:37 Tin:Lead ratio, where the alloy melts & freezes at the same single temperature, ~360F/183C:
> 
> ...


I'll order Tester 44 (p/n 24-6337-0027) on my next order. What the average temp you set your iron at?


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## pcb rookie (Feb 19, 2022)

- Reporting back -

The chisel tip is a game changer for me. It flows much better. I had read about it a few times but stuck to the 1/32 tip that came with my iron station. There is no going back now! 

Also, I noticed that by using a filter fan to capture the solder fumes, my iron temp was dropping in front of the PCB. So slightly but still 2-3 degrees so I cranked up the temp just to get it to desired temp. It's probably pulling some of the heat that should be transferred to the contact eyelet/component. I'll crank it even more if I notice it effects the solder flow but the chisel point seams to be doing it right now. 

Thank you all for sharing your experience!


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## giovanni (Feb 19, 2022)

Are you using a generic fan or a filter for solder fumes?


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## pcb rookie (Feb 19, 2022)

giovanni said:


> Are you using a generic fan or a filter for solder fumes?


I use the Kotto fan. It has a fume filter. I don't know if it's a good model but it seems to be working (I hope so!) 

I also have a bathroom ceiling fan that I turn on.


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## vigilante398 (Mar 15, 2022)

I need to bump this thread. So I decided to try out some Kester with water-soluble flux. It's fine, flows great, and the dried flux turns milky white instead of yellowish brown, so it doesn't look as bad when I don't clean it (because I never clean it).

Well I finished my February batch of builds a couple weeks ago and I had an unusually high number come back for repair due to weird noise issues. I didn't connect the dots until a friend of mine pointed me to an article about how some fluxes are "leaky insulators," meaning conductive but just barely. Well guess what? February was the first month I used the new solder on, and I just thoroughly cleaned all the flux off a board that was oscillating and now it's fine. So I'm thinking my messy rosin flux wasn't conductive, but this new water-soluble flux is, so I either need to switch back or I need to clean all my boards.

Now you know.


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## grabo99 (Mar 16, 2022)

pcb rookie said:


> I use the Kotto fan. It has a fume filter. I don't know if it's a good model but it seems to be working (I hope so!)
> 
> I also have a bathroom ceiling fan that I turn on.



I also own this fan I like it so far, been using it since June


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## Barry (Mar 16, 2022)

grabo99 said:


> I also own this fan I like it so far, been using it since June


Ditto


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## pcb rookie (Mar 16, 2022)

Barry said:


> Ditto


The kotto fan came with a replacement filter. How often should it be replaced?


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## Barry (Mar 16, 2022)

pcb rookie said:


> The kotto fan came with a replacement filter. How often should it be replaced?


Don't know, haven't felt the need to yet, I assume it's impregnated with activated charcoal


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## vigilante398 (Mar 17, 2022)

pcb rookie said:


> The kotto fan came with a replacement filter. How often should it be replaced?


Depends how often and how heavy you use it. I would say use it until there is a noticeable drop in airflow. With hobbyist use I would expect it to easily last 10 years or more.


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## fig (Mar 17, 2022)

Barry said:


> Don't know, haven't felt the need to yet, I assume it's impregnated with activated charcoal


You mean like Tareyton cigarettes used to have? Remember, Tareyton smokers would rather _fight_ than switch!


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## Barry (Mar 17, 2022)

fig said:


> You mean like Tareyton cigarettes used to have? Remember, Tareyton smokers would rather _fight_ than switch!


Yes, they all had a black eye in their ads


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## pcb rookie (Mar 17, 2022)

fig said:


> You mean like Tareyton cigarettes used to have? Remember, Tareyton smokers would rather _fight_ than switch!





Barry said:


> Yes, they all had a black eye in their ads


Black eye is while soldering would be concerning but I just hope that soldering with the charcoal filter fan is less damaging than smoking! Maybe I should go the Tareyton way and double up my charcoal filter after all ....


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## Barry (Mar 17, 2022)

I bought about 10 extra filters with mine, no Idea what the recommended cycle is, I'll change it when it starts looking nasty


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## andare (Mar 18, 2022)

grabo99 said:


> I also own this fan I like it so far, been using it since June


How close do you have to be for it to suck in the fumes? My extractor works well within 15-20cm only. More than that and the fumes just rise to the ceiling. It is hard to work with that thing so close.


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## grabo99 (Mar 18, 2022)

andare said:


> How close do you have to be for it to suck in the fumes? My extractor works well within 15-20cm only. More than that and the fumes just rise to the ceiling. It is hard to work with that thing so close.



I'd estimate around 30cm? I don't have a magnifying glass so I work close (with safety goggles). I don't have any solder/rosin smell that lingers around. With my bright light pointed at everything, I can even see the "smoke" heading into the fan. I'm not an expert though.


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## djmiyta (Mar 18, 2022)

Stickman393 said:


> For sure!
> 
> Don't worry about cranking up your heat every now and then too.  The temperature of your iron doesn't matter as much as the absolute quantity of heat transferred over time.
> 
> ...


How do you know these things? are you a plumber? or someone in a trade that involves knowing stats like that? I'm not doubting you at all ,  just like always I'm just curious. I'm a plumber been one for like 30 years and what you say reminds of apprentice classes I took it's just that technical stuff that usually doesn't find a way to be useful sometimes does and was just wondering. FYI my plumbing skills have not furthered my effects building my effects building has furthered my plumbing though kinda funny that way going through school for one thing and.......... well enjoying another. Is what it is.  Stickman please dont take  what I say as a doubt or a dig at what you post it's all good no matter what. I'm just as  always curious (yes I know what happened to the cat)


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## pcb rookie (Feb 11, 2022)

Practice builds confidence. I did more soldering lately and got better at it overtime. I did some pretty clean PCBs lately. Most days the solder just flows through easy peasy. Every now and them, I hit a project that the solder just won't flow right. Today was one of them. The solder would stick to the lead instead of flowing though/on the contact eyelet or just bunch up. I stopped, cleaned and tined my tip. Cleaned up the PCB with IPA. Tried again, same. Applied some flux paste (usually don't). It got better but barely. Flowed perfect in the end when I got to transistors and trim pots ... 

Any one as leads on what's the cause when solder just won't flow? 

When do you do or adjust when that happens? 

FYI - I use 60/40 Aims .032 diameter solder @ 400 degrees average. I tin my tip between every 2-3 solder and keep in clean.


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## djmiyta (Mar 18, 2022)

Stickman393 said:


> ^great point there.  I didn't realize that the 60/40 isn't eutectic...using an eutectic solder made a huge difference for me, personally.
> 
> I'm a SN100C man myself...not a big Pb fan.  Concerns and such.  It's a bit more of a pain to desolder, and melts at a higher temp, but it's eutectic and flows very well.  Much better than the sn-ag-cu stuff that I was using before.


eutectic? holy shit on toast!  I had to look that word up. Never heard that word ........... EVER! love  expanding my vocabulary


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## bowanderror (Mar 18, 2022)

djmiyta said:


> eutectic? holy shit on toast!  I had to look that word up. Never heard that word ........... EVER! love  expanding my vocabulary


I'm always interested to find words that are (mostly) unique to one particular field. Here is another fun one for you: Disproportionation

Ever watch the small bubbles in the head of a beer combine into ever larger and larger bubbles? That's disproportionation. The science of beer foam is pretty fascinating in and of itself.


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## djmiyta (Mar 19, 2022)

Ever watch the small bubbles in the head of a beer combine into ever larger and larger bubbles? That's disproportionation. The science of beer foam is pretty fascinating in and of itself.

All I read was beer


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