Solder won't flow right ...

[pcb rookie]

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.

 

[bowanderror]

^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?

 

[Stickman393]

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.

 

[bowanderror]

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.

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?

 

[pcb rookie]

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:

View attachment 23035
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.

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

 

[pcb rookie]

- 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!

 

[giovanni]

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

 

[pcb rookie]

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.

 

[vigilante398]

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.

 

[grabo99]

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

 

[Barry]

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

Ditto

 

[pcb rookie]

Ditto

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

 

[Barry]

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

 

[vigilante398]

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.

 

[fig]

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!

 

[Barry]

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

 

[pcb rookie]

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

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 ....

 

[Barry]

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

 

[andare]

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.

 

[grabo99]

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.

 

[djmiyta]

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.
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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

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)