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How to solder

post #1 of 13
Thread Starter 

Since there isn't a thread on this, I decided to create one that I could point to...


People think, 'Soldering. How difficult can that be?'


The answer is, 'As difficult as you want to make it...'


The fact is, there's a wrong way to solder, and that's the way most people instinctively try first.


You DON'T melt solder onto the soldering iron and try to get it to stick to the items you're trying to solder. This is GUARANTEED not to work. Why? Because the flux core of the solder will no longer be effective by the time you get the solder to the surface you are trying to solder.


You need a soldering iron and rosin-cored solder.


When you get the soldering iron, you turn it on for the first time, that's when you melt solder onto it. You turn it round and round and push the solder onto it and make sure that every part of the tip has a thin shiny coat of solder. This is called tinning. Ignore any drips that form and fall off. Then you wipe it on the wet sponge (you did wet the sponge?) on the solder station, or wipe it on a damp rag. Be careful if you use a rag, steam will form and if the rag is not thick enough (folded) you will get burnt. Wipe off all the drips of solder and any flux.


Everything you're trying to solder together must be clean. This means shiny clean. If it's copper, like perfboard, you need to polish it with emery paper (sandpaper) unless it is brand new. Boards may be tinned. They will remain solderable for quite some time and it is usually easy to break up any oxide film that appears on them. Components are treated to stay solderable for a while, but even they will not stay good for soldering for ever. A layer of oxide forms with exposure to air. YOU CANNOT SOLDER THROUGH IT. You may have to clean them with emery paper too. With resistors you fold the paper round the lead, hold it tight and pull it off the lead. Do this a couple of times to make sure the metal is exposed. Otherwise you can scrape the leads with a scalpel or craft knife blade. If you are unsure whether the part is clean you can check by pre-tinning it. Heat the LEAD with the iron, push the solder onto it, and check that the solder forms a thin film on it, just like the tip of the iron.


When you have inserted a component into the board, you push the tip of the soldering iron into contact with the lead AND the copper on the board. The tip must be tinned, but not dripping with solder. After a couple of seconds you push the solder (wire) into contact with the LEAD and the COPPER on the board. If you can get it to touch the tip simultaneously, so much the better. Make sure the solder flows onto the copper pad and the lead. If it forms a ball or puddle the joint is not wetted. The solder must wet the joint for it to be effective. You can see the instant when the solder collapses and goes from sitting on the surface to actually wetting the joint. You MUST be able to see that the solder slopes onto the parts and board gently and does not sit up like raindrops on a dry window. It should look like a little volcano with the lead sticking up out through the peak.


Remove the solder from the joint, remove the iron from the joint without disturbing the parts, blow gently on it if you like to cool it. Wait until you see that it has set or you will have to reapply the iron, because a joint that has been disturbed in the process of setting may fail.


Job done. Move on to the next joint.




Although many people swear by it, supplementary flux is unnecessary for the very large majority of jobs, and depending on it only encourages a poor technique.

Edited by wakibaki - 4/9/13 at 12:57pm
post #2 of 13

I have used the liquid flux with good success UN-soldering stuff... you know that one joint that just will not come out with the braid...

post #3 of 13

Is solder with silver in it worth it? What would a good solder be like?

post #4 of 13
Thread Starter 
Originally Posted by vixr View Post

I have used the liquid flux with good success UN-soldering stuff... you know that one joint that just will not come out with the braid...


Yes, unsoldering stuff can be problematic. I don't mean to try to discourage people from trying flux, but I just want to make it clear that for most purposes, a good soldering technique will get you through, and this is what a beginner should focus on. I have flux (jelly), but it's in the fridge. I mix it with solder paste for application with a syringe. I'd rather people thought 'I need to change what I'm doing' rather than 'I need some flux'


I know the problem you're talking about. I usually deal with it by adding more solder and using a good solder sucker. 


I use a toaster oven for soldering multiple surface mount parts simultaneously. I might write a few more posts dealing with that subject.



post #5 of 13
Thread Starter 
Originally Posted by HolyCheese View Post

Is solder with silver in it worth it? What would a good solder be like?


I use Ersin 366 Multicore Savbit Type 1, 18 SWG. I have about half left of a 7 pound reel. Savbit has a small quantity of copper added to the tin/lead alloy to prevent erosion of copper tracks, leads and soldering iron tips. It's an excellent all-purpose solder. Ersin 362 is a mil-spec (UK MOD) type rosin-core halide activated flux. Joints have a very good lifetime. Ersin 366 is intended for use with slightly more difficult surfaces, but without a marked reduction in lifetime.


A smaller gauge is useful for fine work, but I don't need it.


I've used a variety of solders in industry, including more than one kind of lead-free. For domestic use I don't recommend lead-free. Savbit is about the easiest to use for hand soldering and IMO you're not at risk from the lead.


I use silver solder for soldering piano wire for model airplane undercarriages. It's stronger than lead-based solder. I don't use it for electronic applications and I recommend that beginners use the solders that are the easiest with which to get a good result with high durability, tin/lead 60/40 or 63/37(eutectic) or preferably Savbit. All 3 are low-temperature with a narrow freezing range. Savbit has been demonstrated to increase the strength and reliability of soldered joints very considerably.



post #6 of 13

Thank you, I'll try to get my hands on some of that savbit you are talking about. 

post #7 of 13
I had noticed that some custom cable companies like DHC offer their own liquid flux.

I plan on focusing more on my techniques, but was curious if there is really any difference between their 'special' liquid flux vs others, like the stuff on ebay. Usually I call BS, but I thought I'd get an outside opinion.
post #8 of 13
Originally Posted by HolyCheese View Post

Is solder with silver in it worth it? What would a good solder be like?

Just to reply about the silver in the solder...


The silver is there to prevent erosion of SMD parts.

Other than that, follow wakibaki's advice

post #9 of 13

wow,  there is no source for this stuff in the USA that i can find - Newark will bring it in from Farnell UK, for an additional $20 for the order, on top of normal shipping charges!  anyone have better luck than me finding it - and is it really better than Cardas or Johnson?

post #10 of 13

Kester has always been the preferred brand in electronics shops I've worked at. Available at digikey, mouser, etc. I'm pretty partial to the no-clean stuff myself...(series 275 IIRC?)


EDIT: 245, and 63/37 - you're gonna pay a hefty premium for any silver bearing solders...just stay away from the RoHS lead-free garbage

Edited by realpsyence - 4/10/13 at 10:59am
post #11 of 13
Thread Starter 
Originally Posted by Avro_Arrow View Post

Just to reply about the silver in the solder...


The silver is there to prevent erosion of SMD parts.

Other than that, follow wakibaki's advice


This is true, but TI, for example, do not use silver in their SMT plating, it is nickle/palladium/gold. Silver-free solder will wet and bond with all SMT parts, erosion is really only of consequence in long term manufacturing reliability, and it is beyond reasonable expectation that a range of solders, each suited to the particular parts being soldered, should be in every amateurs toolbox.


Solder is just another area where unscrupulous merchandisers seek to take advantage of audiophiles and other amateur electronics enthusiasts. The question is more, does Cardas offer any significant advantage over the conventional solders which were approved for military applications for years prior to the introduction of lead-free? 


I don't want to get into an argument about the value or otherwise of exotic (and overpriced IMO) solder types, but simply offer a beginner some advice about how to work effectively and without unnecessary cost to build things that work first time.


It's a mistake, IMO, to focus too much on the type of solder, other than to choose one which is easy to use and which produces durable joints with the large majority of parts in common use, although the differences in durability we are discussing are not large.


Here is a sample of 63/37 (eutectic) resin activated cored solders from Kester.http://www.digikey.com/scripts/dksearch/dksus.dll?FV=fff40014%2Cfff80076&k=solder&vendor=0&mnonly=0&newproducts=0&ptm=0&fid=0&quantity=0&PV-1=117&PV1303=1&PV183=6255&PV1433=3&PV174=1


63/37 is still, AFAIK, used by NASA.


I can't find an equivalent to Savbit on sale in the US. I use it now because I bought a large quantity a long time ago. You will find the above 63/37 has the lowest melting point and narrowest freezing range (zero) with an incorporated activated flux (RA). This is the baseline for ease of use. You won't find a solder that is easier to use than this. 60/40 solder comes close, it melts slightly higher, it has a narrow range of temperatures where it is semiliquid, and it is made available because it is cheaper than 63/37, purely because of the cost of the metals. Both are also available with RMA (resin mildly activated) flux, which is slightly less aggressive and not quite as successful in dealing with mildly oxidised surfaces.


Soldering can be a complex subject in a modern manufacturing environment. Products are produced in the millions sometimes, and a small percentage of failures can become significant. Since products are no longer hand-assembled, but wave soldered, or IR reflowed, issues such as temperature profiling (boards are pre-heated to allow components to be soldered without cracking) have been the subject of considerable study, but it must be remembered that for decades prior to the development of these techniques, products were hand-built on an assembly line, often wired point-to-point and soldered mostly by large numbers of women.



post #12 of 13

Are any potential chances of damaging headphone driver or degrading sound quality if soldering is not done well but it still works? if we do not have distortion is it means that soldering is well done?


I struggled to solder wires and wires on driver, I managed something... it works I can't hear distortion, is that enough to say that everything OK ?



post #13 of 13
Thread Starter 

I would think the possibility of damaging a headphone driver due to a poor solder joint is nonexistent, but an intermittent contact can certainly result in degraded SQ or crackling or complete dropouts of the sound.


Soldering the wires is a problem in some cases.


You should always try to 'tin' the wires before making the joint.


There are 2 principal causes of problems.


1) The fine wires are coated with enamel, oxide or other substance making it difficult to tin them.


2) The wires are not wire at all, but cotton or other fibre stranding with copper deposited on them.


Copper coated cotton is sometimes used for making headphone cables. It is used because of its lightness and flexibility, not much current is carried in some cases. It was common to find it used for the old high-impedance crystal earphones that used to come with transistor radios. Manufacturers don't have the soldering problem in that case, because the connection is crimped. The bared end is passed into a metal fitment on the driver or plug which is crushed onto the 'wire' to form a reliable and robust (to a degree) contact


I recommend that if you find it necessary to repair the coated-cotton type of cable, that you should replace the cable in its entirety if at all possible.


Cables with coated wires and even coated-cotton types are sometimes solderable by passing the end through a blob of molten solder, while 'growing' the blob by adding fresh solder to it (to make sure that the flux is active). You can see when tinning takes place, although it may be patchy. You just have to make the best job of it that you can. Sometimes applying a naked flame from a lighter briefly can help.


There is a technique for soldering in these circumstances. Not everybody has a 'third hand' or miniature vice handy. What you do in this situation is to take the solder and wind a few turns round your fingers to form a steady base on which to set it. Pull a length up into a curved shape so that the solder looks like a coiled snake with its neck and head raised, like a cobra ready to strike. Now you can hold the soldering iron in one hand and the wire in the other, bring the wire into contact with the hot tip, and bring both into contact with the end of the solder. In this case it is easy to get the wire end to contact a freshly melted blob of solder. 






Edited by wakibaki - 4/16/13 at 2:10pm
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