next topic »

[on:]

Hello all,

I have just searched for 'soldering' and didn't find any threads that really answer the questions I have, and most of the stuff I find on Google is pretty much useless, so I hope it's ok to post a new thread about what must be a fairly well-covered topic...

Basically, I've just recently gotten really into Arduino (after having an UNO since November) and finally got round to buying a soldering iron. However, I haven't used one since my school days, which must be about 8 years ago now, and even then I didn't do a lot of soldering. Plus we were taught barely anything anyway, so I'm quite rusty.

I bought myself a Weller WTCP 51 station, which is a step up from what we used at school (though I'd imagine a long way from a professional iron). The iron and tip combo it comes with gives you about 370C (700F). I've used it to assemble two Proto Shields today, which is where the first of my problems come in.

Around the contact pads I've soldered the board (and on the pad and joint itself, actually) has some yellowish stuff on it (please see photo attached), at first I thought it was the board itself melting slightly or delaminating, but is it flux residue? And if so, is it bad having that much still stuck to the board, given that it's acidic? I'm using some RS own brand solder, it's Sn60 Pb40 0.75mm No Clean, probably with a rosin core (it doesn't say so on there but it's cheap and was branded as an 'essential', probably meaning not at all specialist and therefore just standard, common or garden solder).

Also, the tip of my iron was tinned when I got it (i.e. the last 5mm of the tip was silver whereas the rest was duller) but after a little bit of soldering (and loads of cleaning, I dabbed it on the sponge after basically every joint made because of the build up of brown/black stuff on it) the silver area is a lot smaller. Am I supposed to just keep applying solder to it to tin it (even though when I did that it just stuck to the bits that are already tinned and turned into a big drop of solder)? This is something I was never really taught. I have some tip tinner/cleaner so I just placed the tip of the iron on it, but now there are big yellow stains on the cleaner itself (which I imagine will end up back on the iron if I use it again), so I don't really know what's going on, I'm completely clueless about this stuff.

Finally, is 370C/700F a good temperature for soldering or would 310C/590F be more suitable? This iron's temperature is set by the tip you use, you see, there's no dials to adjust or anything, and tips come in 310/370/425/480C, but it came with a 370C tip. I guess the answer to my first question would answer this, though; I imagine if the yellow stuff is flux residue then the iron is fine, but if it's the board delaminating/melting then it's too hot!


Thanks for taking the time to read this, any help would be very much appreciated.

[Reply #1 on:]

Around the contact pads ... has some yellowish stuff on it ... but is it flux residue?

Most flux used in electronic solder is "no clean."  However, I personally prefer to always clean my boards with rubbing alcohol (or recently I bought some "Flux-Off" at Frys.

Am I supposed to just keep applying solder to it to tin it (even though when I did that it just stuck to the bits that are already tinned and turned into a big drop of solder)?

I searched Google for "tinning solder iron" and found quite a few guides.  My method is: every so often I put a ton of solder on the iron while twisting the iron around letting gravity pull the solder around the tip.  Then I let it sit for 20 or 30 seconds before cleaning the blob off.  Seems to work for me.  M.G. Chemicals makes a "Tip Tinning" solder paste you can dip the iron into.

Finally, is 370C/700F a good temperature for soldering or would 310C/590F be more suitable?

There are far more scientific ways to determine the ideal soldering temperature.  However, I stick to "use the least amount of heat I possibly can."

[Reply #2 on:]

Around the contact pads I've soldered the board (and on the pad and joint itself, actually) has some yellowish stuff on it (please see photo attached), at first I thought it was the board itself melting slightly or delaminating, but is it flux residue?

Yes, it is flux residue. Since you are using no-clean flux then you can just leave it there. You can remove it if you want with isopropyl alcohol (70% is OK, 99% is better, don't breathe it in) or with commercial (expensive) flux remover. It's usually not necessary to remove it unless you are concerned about appearance or long-term reliability. Flux will absorb moisture over time and sensitive electronic circuits will see an additional leakage path through the flux due to this moisture. But I doubt this will affect what you are doing.

Also, the tip of my iron was tinned when I got it (i.e. the last 5mm of the tip was silver whereas the rest was duller) but after a little bit of soldering (and loads of cleaning, I dabbed it on the sponge after basically every joint made because of the build up of brown/black stuff on it) the silver area is a lot smaller.

Don't use a sponge. Use brass shavings:

http://www.hakkousa.com/detail.asp?PID=2989&Page=1

While you're there browse through their great application notes on proper soldering temperatures, tip maintenance, etc.

http://www.hakkousa.com/doc_library.asp?DocType=Tech%20Note

The brass will keep your tip a lot cleaner without cooling it, thus allowing you to keep the tip on a lower temperature setting and preventing oxidation.

Am I supposed to just keep applying solder to it to tin it (even though when I did that it just stuck to the bits that are already tinned and turned into a big drop of solder)?

Yes, you must always keep solder on the tip. It is the first line of defense against tip oxidation.

Finally, is 370C/700F a good temperature for soldering or would 310C/590F be more suitable?

Turn the temperature down, increase the size of the tip if necessary. 590F should be doable (I usually use 650F but should probably turn it down) but 700F is definitely too hot. If your joints aren't heating up and solder is not flowing easily after 1-2 seconds, the tip is not big enough. You not only need temperature you need thermal mass to transfer that temperature to the joint. You absolutely positively definitely no-questions-asked need to get an assortment of tips of various sizes, then absolutely positively definitely CHANGE the tip to match the joint to be soldered. Plan your work, solder the small stuff first with a small tip, let the tip cool, change to a bigger tip, solder bigger stuff, etc.

And finally, I really doubt your soldering iron has enough thermal mass to delaminate your board.

--
The Gadget Shield: accelerometer, RGB LED, IR transmit/receive, speaker, microphone, light sensor, potentiometer, pushbuttons

[Reply #3 on:]

I searched Google for "tinning solder iron" and found quite a few guides.  My method is: every so often I put a ton of solder on the iron while twisting the iron around letting gravity pull the solder around the tip.  Then I let it sit for 20 or 30 seconds before cleaning the blob off.  Seems to work for me.

I did find a few videos, but they seemed to just be applying loads of solder to the tip and basically acted as if I was supposed to know what was going on already, so I thought I'd ask in case I was missing something! Thank you, I'll definitely give that a go.

There are far more scientific ways to determine the ideal soldering temperature.  However, I stick to "use the least amount of heat I possibly can."

Turn the temperature down, increase the size of the tip if necessary... I really doubt your soldering iron has enough thermal mass to delaminate your board.

So it sounds like I should get a bigger tip for the lower temperature (as the station doesn't have an adjustment knob, it's controlled by the type of tip used)? Sounds good to me. The tip I have is a 3mm chisel tip and has no trouble heating the board and component to be joined within a couple of seconds, so I presume by lowering the temperature but increasing the size means the temperature and thermal mass relationship will be about the same? Please bear in mind that I have no idea what I'm talking about,that's just an assumption.

The brass will keep your tip a lot cleaner without cooling it, thus allowing you to keep the tip on a lower temperature setting and preventing oxidation.

That's the first time I've heard anything like that and I've been looking up videos and tutorials all day! I wasn't sure if those things were just gimmicks, but I'll most likely pick one up; I'm guessing there's no harm in using the sponge until then, though?

Thank you both very much for the help, I really appreciate it!

[Reply #4 on:]

so I presume by lowering the temperature but increasing the size means the temperature and thermal mass relationship will be about the same?

Yes, they kinda trade off each other. The point is to heat the joint enough so that solder melts and forms a proper fillet. You can either do that by cranking the heat way up and using a joint with poor thermal conduction (low mass) or using a tip with high mass and turning the heat up just enough to do the job. The second is definitely preferred, will extend your tip life, and will stress your components and PCB pads less.

I'm guessing there's no harm in using the sponge until then, though?

There is, water causes rust and speeds oxidation, but I doubt you'll have much problems until your brass shavings arrive. Note that they're available in lots of places. I think this is the cheapest one I've seen so far:

http://www.elexp.com/sdr_3460.htm

--
The Rugged Motor Driver: two H-bridges, more power than an L298, fully protected

[Reply #5 on:]

Well that's kind of what I meant, I've just spent way too much money in a short space of time to really want to buy anything for another week or so, but I guess if I'm going to get one eventually I may as well do it now. I can't find anywhere near me that stocks tips for 310C, I guess this is the drawback of having a station without a heat setting. I'd feel much safer with the cooler tip, though, I remember frying a whole load of ICs, switches and PCBs and such in school... Better keep looking I guess.

I should point out that I'm not in the US, but I remember seeing the tip cleaners elsewhere, thanks though.

[Reply #6 on:]

Beware that lowering the soldering iron temperature can actually RAISE the temperature of the components you are soldering. If the soldering iron tip is on the cool side, it will take longer to get the junction heated sufficiently to flow the molten solder around it. That extra heating time allows more heat to flow through the leads into the component (and through the PC board). A nice hot iron (but not excessively hot) means that you can get "in and out" quickly.

Quoted in full, so you can read it again.

Our lab manager (who did soldering for NASA) recommends the wet sponge over the brass scouring pad.  If you insist on the brass scouring pad (I keep one for extreme occasions, and for removing lead fouling from my pistol barrels), buy it at the grocery store - it's much cheaper than the one with the Hakko logo on the package.

The sponge shouldn't be dripping - just damp.  If the sponge is burning, you need more water, or you're staying there too long.

The tip should be cleaned just before you make a solder joint, not after.  The idea is to leave excess solder on the tip to protect it.

Once your soldering session is complete, clean the tip, then melt a generous blob of solder onto the tip (I generally use as much as I can get to stay on the tip without dripping), gently return the iron to the stand to avoid drips, and power it off.

Use lead solder if you can get it.

-j

[Reply #7 on:]

Don't use a sponge. Use brass shavings:

Only use brass shavings on a non coated bit. It sounds like you have the magnetically controlled soldering bit. These are iron coated and any use of an abrasive cleaner (like the brass) will scratch the coating away and then the fine tip will corrode on the inside like a bad tooth. Likewise don't use tip saving solder (it has small amounts of copper in it), this will also attack iron coated tips.