Introduction to Soldering

You might be thinking,” tips, I don’t need no stinking tips!”  Ok, but there are many who could use some pointers on the basic tools and techniques, and who knows,  you might pick up an idea here.  My concern is that due to the miniaturization of components and the standardization of connectors, soldering of board mounted components is a bit of a lost art. This is not an exhaustive study, this is an introduction.The basic tool would be the soldering iron.  Not a soldering gun – most gun type solderers are:
(a) too heavy;
(b) too hot;
and,(c) too expensive.  The cost is really not a factor, just don’t fool yourself into thinking you would be better off if you spent the money. There are are some “gun shaped” irons that are acceptable(it’s just an ergonomics thing) – these can generally be determined by the shape of the tip – single straight tip is an iron.  Anything else is a standard gun (loop of wire for a tip).  Cold/cool type soldering devices like the Coleman(brand) are totally wrong also – they give off static electricity and are much to awkward for the work at hand. Get a decent soldering iron stand – a simple one with a heavy base and a coil of wire to hold the iron is perfect. Most will have a pocket at the front that holds a sponge( a folded cotton rag works just fine) – this is to be kept moist so you can wipe your tip clean of solder and other debris.  A slight rotating motion while pulling the iron toward you will do it. 25 watts – that’s all you need, max.  Some folks swear by 15-18 watt irons, but a beginner may be frustrated by the mechanics of melting solder AND pulling the iron away as soon as the work is done. .A simple soldering iron like this can be gotten from most hardware or electronics stores for less than $15(USA).  Be sure to buy one with extra tips available, and buy at least one extra – you may decide to shape one down for really tight work, or you will want at least want one spare.  Soldering tips don’t last forever – the contact with the heat, lead, flux and air will slowly  deteriorate the tip which is made of copper, even though it looks “shiny / silver” when you get it.  You will have to occasionally reshape the tip thru grinding or filing.  Then you will have to “tin” the tip(coat it with solder) first thing after shaping; otherwise, solder will not stick well to the tip and cause you great frustration.  And probably lead to you “cooking” a few good parts or circuits to death in the process.*A tip for keeping your soldering iron tip from getting “froze” into the body – put a little vegetable cooking oil on the threads of the tip.  The oil will cook on but stop the tip from getting froze in the threads.”Tinning the tip” – this is the process of coating a new or freshly shaped soldering tip with some solder so it “holds” solder better and doesn’t oxidize away quickly from the heat.  THe traditional method for tinning/re-tinning your tip is to file to shape desired, apply some flux, get hot and apply some solder to all filed surfaces(copper).  Instead, I will suggest you get a small tub of paste type tip cleaner.  Almost anywhere that sells soldering irons will sell this marvelous product in a small contain that can be stuck/glued to your soldering iron stand.  Basically it is a mixture of an acidic flux and some low temperature solder, some have an abrasive component.  You stick the hot tip in, give it a twist, pull it out and wipe on your wet rag/sponge – you are ready to rock!!Solder selection…this might be controversial.
I don’t suggest you buy standard rosin core solder, it is way too heavy for small components and the rosin flux makes a mess on a small circuit like a watch.  Buy  fine (.015″/.3mm)silver bearing solder – “angel hair”.  A few pennies more but it gives you just the right amount at a time for fine work, has a low melting temperature and flows nicely with no messy internal flux.  I alway recommend a solid core solder with a paste or liquid type flux, which I discuss some more below.MOVING ONWARD!Your first  task in many cases will be REMOVING solder.  Do not buy one of those fancy “desoldering irons” – most of them are too powerful and too clumsy for watch work – I have one that gets used occasionally, like when I am installing something like a sound system.  What you want to use is the time tested and very effective – desoldering braid.  Essentially, this is a braid of very clean, fine braided copper wire (looks like a thin, flat shoe-lace) that has a lot of surface area to suck up solder.  Usage is simple – lay the tip of the soldering braid against the joint, press your very  clean, heated ,soldering iron tip against the braid over the joint lightly for 2-4 seconds and lift the iron and your braid off.  The braid should have sucked the solder right off the joint.  If if didn’t remove the solder at all, you probably needed to go another second.  If you watch closely (myself, I wear a magnifying visor when soldering) you will see the solder creeping into the braid. After each use of the braid, snip it back  a few mm./1/8-1/4″ – fingernail clippers work fine as the copper is soft.  The braid is cheap and it is better to ALWAY use a fresh piece than roast good parts to death just because you didn’t want to waste a sliver of braid.Wow, this HAS gotten long!!  Well, I am going to desolder an old crystal and solder up a new quartz crystal, just to illustrate the action. But before I do that, I will talk about “heat sinks” – CRUCIAL!!  You cannot expect to successfully solder in new crystals which are housed substantially in plastic, despite the metal “can” exterior, or old crystals which have survived 30+ years, without protecting them from heat!!  You must put a “heat-sink”/clamp of some sort on the crystal’s lead/wire between the solder joint and the component to draw off heat before it gets to the crystal.  And don’t be opposed to blowing on the crystal for a few seconds after you lift your iron.  Learn to blow or your work will suck!! A “cold solder joint”(cooled too quickly) is hardly a concern when soldering such small components.Soldering.  Usually you will see/read soldering technique described this way, “you want to heat the joint and then apply the solder to the joint so it flows across and thru the joint.”  This is fine for heavy stuff like speaker wires, not for smaller, sensitive components.   You will want to use one of the following techniques :1. Apply a small amount of paste type solder flux to the cold connections – generally you need a dab that is less than 1/4 the size of a grain of uncooked rice. I personally use a wooden toothpick to rub on just enough that it just barely looks like something is there, and no more.  It melts and flows as soon as it gets warm, sort of like grease, so don’t overdo it.  If you purchase liquid flux, it will generally come with a small brush applicator or you can use a very small paint brush, like something used for painting models planes/cars.2.Melt a small amount of solder onto the iron tip so you have a small droplet, and then place the tip against the joint, pulling it off as soon as you see it flow/melt onto the joint.  One-ish seconds. OR3.Place the soldering iron tip against the joint at the same time you touch the tip of the solder to the point where the tip touches the joint. Pull the iron and the solder away as soon as you get some “flow”.  I would recommend against this technique for components that are small enough to fit in a watch…way too much heat exposure.Like all things, practice makes perfect – take an old, very dead module and go nuts on it.  Or tear open a slightly older radio and practice on the board. Finally, do not bend wires where they go into a crystal or any other electrical component – grab the wire with tweezers close to the body of the crystal and bend the wire that sticks beyond the tweezers.  It is best if you get the wires bent close to the right shape so no bending has to be done after you are done soldering.  If you have to push the crystal down or over, don’t hesitate to slip a piece of plastic, etc. between the wires or between the wires and the crystal “can” to prevent them from shorting out. Frequently people won’t realize they have pushed the wires together or shorted them out on the metal case of the crystal…. a highly effective way to NOT fix a watch. HEH!

Ok, you have a start.  In a future post I’ll talk about the times and techniques for using silver epoxy for making repairs instead of solder.  IT isn’t a replacement for solder, but sometimes it is just what you need.

Until next time,


A selection of soldering tools.

Soldering iron stand(left), solder(top), un-soldering braid

Typical soldering iron

Unsoldering braid in position against joint.

Wire-bending tool being used to support wire where it enters component.

Heat sink on crystal lead.

Soldering complete

Sucess – nice Frontier(brand) module.





About Retroleds

Ed Cantarella has been tinkering with electronics for about 47 years, and vintage digital
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