QFP soldering trouble - is it the tip or the flux that's sh*t ?

[Dannyx]

Good day folks. As embarrassing as it may seem, despite not being what you'd call a complete amateur at soldering, it's dawned on me that lately that I haven't been able to do good quality jobs on SMD QFP packages and each time I'm faced with one, I get filled with anxiety like I'm about to deliver this big massive speech in front of a crowd or something. The problem I'm having is one I'm sure everybody who's ever done this had at some point: I start off OK, but about half way through soldering a side of the package, or sometimes even sooner, I'd make this big friggin' blob of solder which ruins my whole work. Trying to get rid of it is also a complete nightmare: the solder simply won't spread across the leads - it just keeps blobbing like mercury. Soldering wick doesn't seem to make a huge difference, in fact it seems to make it worse, as I sometimes bend the leads of the IC with it...so goddamn annoying. To add insult to injury, my workmate is able to solder these perfectly: even if he goes nuts and runs the tip back and forth over the leads repeatedly with complete disregard, he never seems to make a SINGLE blob of solder, whereas if I were to do that, it'd end up looking like the tab of a TO-220 package, instead of individual pins. Aside from being a matter of sheer skills, I know, me and him don't use the same soldering station: while they are virtually identical, his tip is conical and rather long and sharp, whereas mine is sharp also but pretty stubby and "fat"....go ahead and criticize me all you want, oh yee solder pros out there, but what's actually the cause of solder bridges ? The flux I'm using or the tip ? Another thing I noticed is that his tip is slightly more oxidized and gray in color and it doesn't seem like the solder actually sticks to it, which might explain why he's able to drag it like a maniac over even the smallest leads and not get any joints, whereas mine is shiny and silver from the solder I always coat it with, so what's going on here ? Should I NOT tin it for this purpose ? Seems I can't solder anything smaller than SOICs with it without running joints everywhere - maybe it's too fat :| I haven't taken his tip for a spin yet (sounds wrong, I know), but I WILL have a go on an old Samsung board which has plenty of those QFPs for me to ruin and see if it's just me that sucks or the tip.

[petehall347]

Re: QFP soldering trouble - is it the tip or the flux that's sh*t ?

too much solder i reckon ..watch all this especially from about half way through . https://www.youtube.com/watch?v=Ie8so5R_t70

[petehall347]

Re: QFP soldering trouble - is it the tip or the flux that's sh*t ?

here is a different way that might suit you .
https://www.youtube.com/watch?v=TJAByNlfkyE

[Dannyx]

Re: QFP soldering trouble - is it the tip or the flux that's sh*t ?

too much solder i reckon ..watch all this especially from about half way through . https://www.youtube.com/watch?v=Ie8so5R_t70

That's EXACTLY how my buddy's doing it and how his tip looks (albeit pointy instead of flat). Now if I try to do that, it'd turn into an immediate mess of solder blobs, it's really unnerving....starting to think the temperature is also key, judging by how the solder in the video melts: my mate keeps his soldering station on the maximum possible setting ALL THE TIME (the dial is turned all the way to the max), regardless of what he's soldering. He claims that it's never putting out enough heat and the markings on the dial don't actually match the temperature of the tip anyway...I, however, oppose to this and we often get into heated debates over it, since I believe it ruins the soldering tips and can damage components, so I keep mine at about 400C at most...haven't tried going silly with it to see if it changes anything. The soldering wick I have is mostly useless, because it doesn't really suck any solder, though I'm aware it's because it's cheap crap from radioshack so I'm not expecting much of it anyhow...tools DO make a difference in this field.

[petehall347]

Re: QFP soldering trouble - is it the tip or the flux that's sh*t ?

i seem to manage fine with a 2.3mm conical bevel tip and 25 watt iron with no controls .
i just got a 1mm conical bevel tip that i tried today with a couple of 0805 resistors and it was a breeze .much better than the 2.3mm tip . i have to try it on chips yet to see how it goes .
i rarely bother with extra flux as its in the solder .

[Dannyx]

Re: QFP soldering trouble - is it the tip or the flux that's sh*t ?

i seem to manage fine with a 2.3mm conical bevel tip and 25 watt iron with no controls .
i just got a 1mm conical bevel tip that i tried today with a couple of 0805 resistors and it was a breeze .much better than the 2.3mm tip . i have to try it on chips yet to see how it goes .
i rarely bother with extra flux as its in the solder .

Did you tin that tip ? I'm mostly interested if solder seems to want to to stick to it or not...seems that's the actual issue I'm facing: I may have done TOO good a job at tinning mine.

[petehall347]

Re: QFP soldering trouble - is it the tip or the flux that's sh*t ?

yes i tin the tip frequently .
if you switch from lead free to leaded or other way round you should really add solder to tip and wipe off . repeat this 7 times ... well this is what i heard . sort of makes sense a couple of times but 7 is over the top in my opinion .
a clean tip is a happy tip .
yes the solder sticks and leaves it nice and shiny ..60/40 leaded is what i use .. 0.7mm .. i did have 0.5 but a reel of this is cheaper .
MBO 0.7mm Wire Lead Solder, +183 → +190°C Melting Point, 40% Lead, 60% Tin,

[keeney123]

Re: QFP soldering trouble - is it the tip or the flux that's sh*t ?

Your tip is fat and his is conical. What may be the problem is his heat is directed to a small area allowing the iron to recover before it goes to the next pin. Your iron is being directed to a larger area and the wattage may not be large enough to recover as quickly for such and area. A blob indicated the tip is to cold and is not melting the solder. As long as you are using flux and you start out with a clean tip you should have no trouble soldering. The only other thing is the iron needs to be hot enough to melt the solder.

[mmartell]

Re: QFP soldering trouble - is it the tip or the flux that's sh*t ?

Turn that damn iron up! You should be able to pull any blob along the pins with a little flux and failing that any wick will pull the rest - even Radio Shack stuff.

Turn up the heat then come back and tell me i was wrong

[jondoe]

Re: QFP soldering trouble - is it the tip or the flux that's sh*t ?

If you iron has poor thermal inertia you often need to heat it up a little higher to get through a job, if its variable of course.

[keeney123]

Re: QFP soldering trouble - is it the tip or the flux that's sh*t ?

Only problem with turning the iron up is you can damage the components. This would be when you first touch the pins the iron will be hotter than what the circuit can stand. Turning the iron up may get you through the whole chip, but may cause damage. Best to use the correct wattage iron with recovery or down size the tip.

[jondoe]

Re: QFP soldering trouble - is it the tip or the flux that's sh*t ?

Certainly. I have a cheap Chinese solder station and I suspect the temp at the tip is much lower that indicated!

[Longbow]

Re: QFP soldering trouble - is it the tip or the flux that's sh*t ?

Sorry, we're all missing one important element. Soldering is magic, anyway, so don't feel bad. I would say as far as tips, you should have some new ones handy at all times and replace them once they look ragged or won't tin.

Even newer tips that will tin and flow solder on the tip don't guarantee you will produce good joints. The main thing is to match your tip size with the work you are doing. Soldering tiny pins of an IC can be done with a fine tip, but that tip won't de-solder a power transistor.

A good 50% of making a good joint is using the right flux. Not just any flux core solder will work. If your joints are consistently failing to flow, you are either using too little heat or the wrong flux or both. Clean, enough heat, correct flux. Goes for brazing also.

Important point. Lead solder, or lead free? 2 different techniques are required, and definitely 2 different fluxes. Personally I would never use lead free solder on anything - let the production houses deal with those headaches.

A point about desoldereing braid. These braids are supposed to come with embedded flux. Don't count on it working. Keep a bottle of liquid flux handy and spread a little on the braid. Then you will find that any blobs will immediately be sucked onto the braid. Sure you will have to clean up after yourself with alcohol or tri-chlor. Use small braid for tiny joints and heavy tips and thicker braid for big joints. Practice.

[Dannyx]

Re: QFP soldering trouble - is it the tip or the flux that's sh*t ?

Sorry, we're all missing one important element. Soldering is magic, anyway, so don't feel bad. I would say as far as tips, you should have some new ones handy at all times and replace them once they look ragged or won't tin.

Even newer tips that will tin and flow solder on the tip don't guarantee you will produce good joints. The main thing is to match your tip size with the work you are doing. Soldering tiny pins of an IC can be done with a fine tip, but that tip won't de-solder a power transistor.

A good 50% of making a good joint is using the right flux. Not just any flux core solder will work. If your joints are consistently failing to flow, you are either using too little heat or the wrong flux or both. Clean, enough heat, correct flux. Goes for brazing also.

Important point. Lead solder, or lead free? 2 different techniques are required, and definitely 2 different fluxes. Personally I would never use lead free solder on anything - let the production houses deal with those headaches.

A point about desoldereing braid. These braids are supposed to come with embedded flux. Don't count on it working. Keep a bottle of liquid flux handy and spread a little on the braid. Then you will find that any blobs will immediately be sucked onto the braid. Sure you will have to clean up after yourself with alcohol or tri-chlor. Use small braid for tiny joints and heavy tips and thicker braid for big joints. Practice.

Great points there. Long ago, I also thought of having two separate irons for different jobs, each with its own tip ready to go. Easy to do on my soldering station, since in addition to the hot air dildo-thingy it has separate inputs for 2 different handpieces, each with its own temperature control of course - I'm asking too much of a single tip after all. There isn't an universal shape and size that can do EVERYTHING from TO-220 tabs to SMDs, is it ? One thing I've used for a while before giving up on it is the sort of stuff that looks exactly like amber or hardened raisin and you'd dip your tip in this stuf before wiping it on the copper sponge and it would get rid off all the gunk and make the tip nice and shiny. It has a very funny name in my language, I won't mention it here, but I called it "non-stick" because it seemed that when I dipped my tip in it prior to soldering something, the solder wouldn't adhere to the tip which seemed to cause bridges, but instead to the pins/pads I was trying to solder, which is what I wanted. The reason I stopped using it is because I felt like it "ate" away at my tips after a while and they would end up looking sort of like a horseshoe: dented in the middle and with two prongs on either side....horrible. And of course, at the end of the day, although tools do make a difference, it all comes down to practice, practice, practice....

[llonen]

Re: QFP soldering trouble - is it the tip or the flux that's sh*t ?

As previously mentioned a good liquid flux, clean tip regularly, and some of the best results I get are with a std conical / hoof tip. The pace and weller soldering stations I use allow you to change tips on the fly but then I paid a lot of money for the and they were second hand.