the better flux to use

[nickBcap]

I can't find a stickie about this.
I used a acid based flux and learned that is why lol, the soldering iron tip corroded into the end of the soldering iron lol....any way...I even got the strongest acid based flux, gosh.
now I have tried a cheap chinese concoction in a little square plastic container which bubbles when heated ok and seemed to help but I still cant get a tiny piece of a capacitor lead out of a hole in a graphics card.
I think I remember I read on BadCaps that the metal tipped desoldering irons can tear the copper from the motherboard and they are not recommended but at this stage I am willing to try one and, to buy a pair of flush cutters and I looked at the atricle about flush cutters here in BadCaps, thank you.
Can anyone help about the choice of flux? ANd, does older solder need any special treatment to remove it, like from old capacitor holes?

[mariushm]

Re: the better flux to use

All fluxes are acids which "attack" the surface they're on and basically break up the metal oxide molecules, removing the oxygen from the molecules and leaving only the metal the solder can bind to. Depending on how active they are, they also corrode the underlying surface at certain degrees.

There's various types of flux, you're using the most acid ones which MUST be cleaned off the board because they're highly active and will continue to corrode the surface.

I'm not sure what you say about soldering iron tips and the flux - usually you shouldn't have a problem because after use, the normal behavior (or at least what I learned is proper) is to thermally shock the tip a bit by rubbing it against the wet yellow sponge to remove the oxidized solder and flux that may be on the tip, then apply a thin layer of solder to the tip to protect it from oxidation.
So the small time the tip is in contact with the flux on boards is probably too small to have any real effect on the soldering tips.

Personally, I use a no clean liquid flux I bought from a small specialized store here in my country, it's called TK83 and it's made by a Polish company:

http://www.termopasty.pl/pg_285_281_...lux_tk_83.html

For 4$ (50 ml bottle) it's actually quite good for my needs and it works great to ease in desoldering and soldering parts. I can't say it's better than others or worse, don't have a reference to compare it to.
All I can say is with the Hakko 936 station and a good thin diameter Multicore 63/37 with no clean flux in it, the soldering is super easy for me and everything turns out great.

The fluxes that are not "no-clean" you're really supposed to clean them from the boards after use. Some can be cleaned with water (it says on them if that's the case) but all can be cleaned with isopropyl alcohol (NOT regular sanitary alcohol). You might find it as rubbing alcohol for babies but those aren't usually good as they have perfume and other chemicals or they're low concentration/purity - you want at least 95% purity, preferably 97%+ .... I bought a 500ml bottle that's 99.7% pure for 2$ here, so they shouldn't be expensive.

As for removing solder from capacitor holes, sometimes it's simply very hard due to the holes being near very large ground traces which absorb the heat. Sometimes you just have to heat the whole area of the board hot air soldering gun before you even attempt to do anything.

The classic way to remove solder would be to apply a bit of flux over the holes, then to add a bit of leaded solder to the hole. This lowers the lead free solder's temperature and it will turn and stay liquid for a longer time.
Next, clean the soldering tip, get some solder wick... apply some flux on the solder on the hole and a bit of flux on the solder wick and put the solder wick between the solder on the hole and the solder tip.

You basically heat up the solder wick, which should absorb the solder you added over the hole along with the solder from the hole. The flux is there to help transfer the heat and remove the oxides on the wick.

Generally the same process is done to remove capacitors from the board. Flux on the pins soldered in the holes, add solder to the pins then as you have the solder gun tip on that solder keeping it liquid, carefully try to bend a bit the capacitor... and one of the pins should easily come out. Repeat the process with the other pin and you capacitor comes out. Now there's no guarantee the holes will be empty but you can just add a bit more solder above the hole and use the wires of another capacitor to simply try to push the wire through the hole from the side with the solder (if you do it as you would normally put a capacitor in, you may lift the pad around the hole)

I think your problem is actually a soldering tool that sucks - a good soldering tool with temperature control and 60-80w at least is needed for motherboards and video cards and more dense boards (with lots of layers and large ground planes).

I don't really have flush cutters - I just use a nail clipper. It's not ideal, because theoretically the "shock" when it closes can disturb or crack the solder that was just put there. I never had this happen to me, but I generally trim the leads on my parts in advance.

I guess you're in New Zealand based on previous posts - you should find solder wick there and no-clean flux pens on rs-online which will work for you.

Maybe it would help to post pictures or links to the soldering station/tool you have and the tips you have so we can give feedback.

[severach]

Re: the better flux to use

Stronger flux cuts thicker oxide faster. When wires are so bad that they would need acid flux I clean them shiny with a razor after which electronics rosin flux works fine.

With my tin lead solder I use Kester 186 liquid flux for removal and Radio Shack 64-022 rosin paste flux for insertion into cleared holes. Rosin paste flux is fine for both if you don't mind going slow. I clean all flux. Not cleaning is poor quality work whether you or an electronics assembly plant. All it takes is a cotton swab and alcohol, acetone, or brake clean.

I find solder wick to be the least useful tool for removing solder. It works good on single layer boards with lead solder. Add multi layer boards, heavy copper planes, vias, and lead free solder and wick is about as useful as a pea shooter in a war zone. The solder near the bottom of the hole is less attracted to the wick than it is to the copper where it's at so vias rarely clear more than 1/4 the way through. Hot air assist makes wick work but by the time the hole is clear to the bottom the trace is burned, and who has 3 hands to hold everything?

Metal desoldering tips do not destroy boards when used correctly and in good shape. As the flats wear to a sharp edges the heat transfer reduces. Then you need to push harder and angle it around. The sharp points dig into the board. When that is happening it's time to replace the tip. A desoldering tip will last a long time if used sparingly. Using it for soldering wears the tip out quickly. Solder with your iron on which the tips are cheap and last a long time.

A desoldering tool is overkill to remove a lead stub stuck in a hole. I use the butt end of a 0.8mm drill to clear holes chucked in a General Tools 92 Hand Vice so I don't poke holes in my hand. Note that the sharp drilling end must not be used and is hidden inside the hand vice. With a bit of flux on the board and a bit of solder on the iron apply and press and out the stub comes against the iron. Boards eating the heat with large planes will need some extra heat from a hot air gun. A light bulb would also work but is slow and clumsy.

Old solder can be reused. Add flux and it looks and works like new.

Cut leads before inserting. The work quality is better, there's no risk of shock to the joint, and cutting first allows you to flux the leads before insertion, crucial to make the vias solder properly. Find a wire cutter like Harbor Freight 98410 where the cut depth is almost exactly the width of a blade. It's easy to cock the capacitor against the blade and make even cuts at the perfect depth every time.

[ratdude747]

Re: the better flux to use

I find solder wick to be the least useful tool for removing solder. It works good on single layer boards with lead solder. Add multi layer boards, heavy copper planes, vias, and lead free solder and wick is about as useful as a pea shooter in a war zone. The solder near the bottom of the hole is less attracted to the wick than it is to the copper where it's at so vias rarely clear more than 1/4 the way through. Hot air assist makes wick work but by the time the hole is clear to the bottom the trace is burned, and who has 3 hands to hold everything?

I beg to differ.

I use braid on multilayer boards all the time. My iron is a Weller W60-P; its 60W and I usually do braid with my 800 degree medium-chisel (700 degree mini chisel for precision work). It takes practice, but if you are careful to add fresh solder right before you go to desolder and heat the joint for a second or two right before you actually use the braid, it can and often does work. Just be sure the braid is of quality, fluxed, and tightly braided (the cheap loose kind is indeed useless). The only time I have issues is with the largest ground planes, and in that case, I have a set of fine point picks that work very well for hole clearing that finish the job.

And as for leaving no-clean flux on the board, I personally don't see a problem with it from a functional point of view. I personally don't keep alcohol by my soldering gear (fire hazard?) and unless you are in a soldering contest (if they exist), it makes no difference. 90% of the time the side you soldered is going to be hidden by whatever the board is mounted to anyway, so I see it as a waste of time and materials.

I rarely, if ever, intentionally pre-cut my leads. That way I have enough sticking out that when I go to solder, I can bend the leads so the cap (or whatever) doesn't fall out. After I have soldered the lead, I then cut it. I have never had an issue with joint cracking; to me it doesn't even seem possible if the joints contain enough solder. Even if I did have cracking issues, after I've soldered everything in, I reflow the joints while I wiggle in the caps so I get them flush and perpendicular to the board, nullifying any chance of cracked joints.

[nickBcap]

Re: the better flux to use

Hi, I have not got through the first post fully yet, and I do see some useful tips in there to try out but I want to post pictures of the things I use to solder with first, and I aint got much. But I have restored some LCD monitors and power supplies by replacing capacitors. The 8800GT is the first graphics card I Have tried to repair and need to learn some techniques for removing stubborn capacitor leads. The type of solder I am using, it is the lowest cost and cools off to nice bright silver like shiney finish which makes me think I am an expert solderer; 0.8mm 60/40 Rosin Core Solder.
The things I am using.
The soldering iron is 30W temperature variable from 250C to 450C
http://img37.*************/img37/6728/250812056.jpg
http://img809.*************/img809/9489/250812057.jpg
http://img100.*************/img100/4337/250812058.jpg
I can clamp the small board to a larger board and use it anywhere I can find a space. If you look carefully you may see the 4 pins with shrink wrap around them so I can stand things like a graphics card or motherboard on edge to remove capcitor pins....agressively.... I have some cheap copper braid that worked great but I dont think I ever got a better result for removing solder from around a short length of capacitor pin in a board than with my first solder sucker which now needs unobtainable new heads that has the hole in it for the sucked solder.
I dont think I have been using it properly.
I was heating the solder in the capacitor lead holes until it melted then quickly getting the solder sucker tip onto the top of the soft solder and letting the sucker go lol. I was always afraid of the sucker tip rebounding back onto the board because it seemed I had to hold the sucker firmly onto the melted solder for the sucker to be effective.

[nickBcap]

Re: the better flux to use

I did think to use the advice about using the wick with flux on top and beneath it to help remove the stubborn piece of capacitor pin.
The idea of keeping on using the acid based flux I was using but cleaning the tip and the soldered parts with a sponge seems like a very good idea but I have not found a proper sponge yet. They seem to be a dense type of sponge < what type of sponge should I look for?
I am prepared to spend a little more now days to buy better equipment. Getting to the point where there is only a thin area of old solder and only a tiny piece of cap pin looks like an excellent way to begin before desoldering...but I loved the way my old solder sucker left only a speck of solder if any around the cap pins.

[nickBcap]

Re: the better flux to use

I went as far as looking up how to make plastic at home and making a mold for a solder sucker tip and just drilling it out to use in my original solder sucker. Did I tell you how much I liked it...but I am not sure how to harden home made plastic - if anyone can tell me, does adding glycerol help to harden plastic, but I dont fancy using chemicals.

[mariushm]

Re: the better flux to use

The soldering tool you use is not very good, especially when it comes to working with boards that have several layers or large traces and ground planes.

At 30 watts, it doesn't have the capability to recover fast... it may heat its tip to a decent temperature but the moment you apply the tip on a solder pad, the traces on the board or ground planes will absorb the heat and the soldering iron will need quite some time to raise the tip back to the proper temperature.

You say it's 250c to 450c which I doubt... keep in mind for proper soldering you're going to have to keep it in general to about 320c at minimum. These soldering irons are no very accurate so I wouldn't be surprised if it's much lower than that in reality. Oh, and these are not temperature controlled, the knob actually controls just how much power the heater element receives - there's no feedback from the tip as far as i can tell.

For example, the tip may be at 300c but there's oxides on the tip which make the heat transfer to be poor between the tip and the outside environment and also, when you touch the pads the heat may be pulled so fast the temperature could fall so much you won't be able to make the lead free solder liquid - lead free solder turns liquid at around 217c. If the soldering iron doesn't push more power to the heater to recover fast to the temperature you set, the soldering may not be right at the end.

If you plan on doing soldering more than just one or two fixes, you should invest into a soldering station which controls the tip temperature properly.
The cheapest are at around 60-80$... for example on Farnell's page for my country lists several under their own Tenma brand but they're actually Atten soldering stations:

http://ro.farnell.com/tenma/21-10115...-eu/dp/2062627
http://www.atten.eu/index.php/solder-rework.html

They're Ok and they're cheap, you can find them on eBay cheaper in New Zealand

Other Ok stations are the ones made by Aoyue... you can find lots of companies selling these under their own brands:

http://www.aoyue.com/en/Product.asp?...LE%20SOLDERING

In particular, the 936a and 937 I think they're Hakko 936 clones, so the Hakko tips should work on these and they're easy to find.

Search eBay for them and you'll find them easily.


-

I really don't like that flux you're using, seems overkill, to compensate for the soldering iron you use. You shouldn't need such flux for electronic components in general, unless they're VERY oxidized.

[nickBcap]

Re: the better flux to use

The soldering iron I am using is rated 200-450C and after reading the posts I bought a cheap 60W soldering iron to experiment with on the graphics card with the broken off capacitor pin.
The next thing I am going to have to do is get a 70W solder station, I found one on ebay for around US$80, and then look for a no clean flux. I have plenty of 100% isopropyl alcohol.
After reading the posts I thought I could keep on using the flux I have and just sponge off the tip when I am finished but I don not understand how the sponge is supposed to anything at all when the tip is hot enough to have anything cleaned off it. Wouldn't the hot tip just burn the sponge?

[mariushm]

Re: the better flux to use

The heat of the soldering tip causes a thin layer of oxidation on itself and the solder. This layer of oxide is formed very fast, the hotter the tip the faster it forms.

Any impurity on the tip acts as an isolator between the tip and the surface you want to be soldered. In this case, oxidized solder is an impurity, an isolator between your tip and the surface that needs to be soldered.

The sponge is supposed to be wet (you add water). By touching and rubbing the tip on the wet sponge, you "shock" that layer, you cause that layer to be removed. The cold sponge makes that layer break and remain on the sponge. So now you can add a fresh layer of solder that doesn't have time to oxidize and when you get the tip close to what you want to solder, the fresh unoxidized solder on your tip makes a close to perfect connection with the solder or metal (copper pad, wire of whatever piece) and the heat is transferred better.

The cheap 70w soldering iron may work, but again, it's not about the wattage but about how the iron actually works.

An iron without temperature control will just pump electricity to a heating element at a constant rate, so once the tip is let's say 300c, the heating element just maintains the temperature there. Once you touch the tip to a metal surface, the metal surface will "suck" the heat off the tip and cool the tip down.
So the surface not only sees a smaller temperature than 300c because with all your efforts the contact between parts won't be perfect, but the cold metal will pull heat from the tip and try to balance the temperature between the parts. Therefore the tip may go down in temperature very fast.

Now, as the soldering iron has no temperature, it just runs a heating element at same power constantly, it needs time to bring the tip to that 300c value, time which may be more than the maximum time you're supposed to keep parts under heat.

So these irons work well with simple boards that don't have a lot of metal surface to drain the heat from the tips and as long as you're patient to wait for the tip to get hot after you do one solder, they will work. But video cards and motherboards have 5-12 layers of pcb with layers of copper in them that drain a lot of heat from the tip, and that's why sometimes even regular 70w soldering irons don't do well.

Soldering stations with real temperature control can run the heating element to the max in an attempt to get the tip back to the set temperature and also allow you to set the tip to a much higher temp (like 400c) for example, which is useful when you know that the board will drain the heat from it fast.

I recommend watching these series of videos, they're very useful. The second series is a bit outdated but the advice is still valid

Dave Jones' eevblog Soldering Tutorial Part 1 (part 2 and 3 links in the video description)

http://www.youtube.com/watch?feature...&v=J5Sb21qbpEQ

Part 1 just goes into the tools one should use with detailed explanations about what's better to use. Part 2 is the meat where it does practical examples and explains about the heat and oxidation and domonstrates why flux is needed and so on.
Part 3 is optional, is mainly about soldering surface mounted parts.

Pace's Soldering Lessons ( a lot of parts, but the first 2 parts and part 7-8 are probably the most important and informative for you) :

http://www.youtube.com/watch?v=vIT4r...ature=g-user-c

Pace makes soldering equipment and they made video lessons for courses to teach engineers a few decades ago. I believe they explain everything very well, and even though the soldering irons they used were more basic, what they say still applies. We have soldering stations now which make the jobs much easier.

Lessons 1,2 go into how soldering irons work, how the flux works and so on. Still applies, with the only mention that they're pretty anal about cleaning the solder flux simply because they had very acid fluxes back then. Nowadays with no-clean fluxes, you don't have to clean the flux off.

They also have another whole series about how to repair circuits - in that one they go more into replacing pads, traces, how solder wick is used to remove solder and a lot of that stuff. Good stuff but optional for you.

Lesson 2 explains about tinning wires, why the sponge is needed and so on.
It then goes in lessons 3,4 into terminals and various connectors and how to solder wires to them in the following lessons, which you may want to skip if you're not interested

Lesson 6, 7 goes back to through hole soldering, soldering DIP chips and all that, which is good to watch and learn.

[Steve.B]

Re: the better flux to use

Dave Jones' eevblog Soldering Tutorial Part 1 (part 2 and 3 links in the video description)

http://www.youtube.com/watch?feature...&v=J5Sb21qbpEQ

This link should come with a warning telling you that Dave Jones's eev blogs can be highly addictive! Darn, i must have spent many hours watching his blogs. Great stuff!!

[nickBcap]

Re: the better flux to use

I like watching video tutorials and find I learn things from them, thank you I will definitely watch them, and rereading your guys posts is helping alot too. I figured, yes, the cheap higher powered soldering iron may be a challenge but am willing to try it for the few dollars, something like us$6 or 7, I could spare and when I can afford something more expensive with more power I think I will.