Soldering: Answering Beginners' Questions

written on Wednesday, October 21, 2015

Beginners suffer in the world of soldering; they spend endless hours during their first attempts creating a mess and then fixing it, only because of the absence of clear information and guidance. This article was written to simplify and explain some popular "one VS another" questions and provide some starting point for amateurs.

So, here we go!

"Basic Soldering Lesson" Videos From PACE

PACE is an established and reputable manufacturer of a high-end equipment for soldering. Back in the 1980 they produced a beautiful series of videos, which gives you almost - if not ALL - necessary information you need to start and progress with soldering and achieve good results. It also covers - although briefly - SMT component soldering.

It is highly recommended to watch all of them, but the first one: Basic Soldering Lesson 1 - "Solder & Flux" - is absolutely necessary. This video explains you all the magic and physics behind the soldering process, heat transfer, thermal capacity, tool wattage, etc.; and it is absolutely actual even today.

Also, there is nice series about desoldering, also from PACE and also very useful: I've learned some techniques and tricks from it.

In addition, here are some other videos worth watching, including one with really professional soldering:

The very first PACE video contains one very important message to beginners:

Good Soldering != Fancy Tools

Good tools - yes, fancy - no. Do not listen anybody telling you otherwise. Soldering stations, temperature control, RF stations, etc - all of these things are featured and praised by the Internet and real experts, but absence of them does not really prevent you from doing good soldering work, indistinguishable from the work done with station. Look at these shots:

cmoy1

cmoy2

mono

linear

All this joints have been done with a decent and properly chosen mains soldering irons, without any control except WPI (OK, Sijosae used a dimmer to reduce wattage of the beast):

Sijosae soldering iron and stand

  • Antex CS-18:

my soldering iron

I can only repeat what has already been stated in the video from PACE: there are so many factors influencing the temperature control, like tip thermal mass, connection between tip and heating element, lag of temperatures between tip and temperature sensing element, wattage, recovery speed, thermal mass of a surface and so on - that at the end what you really want is the tip being just hot enough and having reasonable storage of energy (wattage).

Sometimes, you can be mislead by temperature control indicators, like blinking LEDs, and I have not escaped this trap either: after I bought my first soldering iron - of course with temperature control, in order to follow a fashion, - I spent a lot of time wondering, why the iron with temperature set to 320 degrees and 1.6mm chisel tip does not really want to solder components to continuous bare non-fluxed copper strips of 2.2mm width. There were the following contributing factors:

  • LED was not blinking - in reality it doesn't actually mean the tip had reached the preset temperature
  • 2.2mm copper strip was just too wide for the 1.6mm tip
  • non-fluxed bare copper is somewhat problematic to solder without flux

All these things are not really related to temperature control, but still they have a great influence on your soldering job. At a certain level, with enough practice and certain skill, comes understanding and feeling for the whole process - just take your time to learn basics and progress with normal pace.

kiss

... with Mains Iron

It looks like I am advertising simple mains soldering irons, and indeed I am doing so :) Quality soldering iron from recognisable brand will cost you some money - although much less, then really good soldering station - and will be in service for years. For example, some of the Antex irons are well known to work for 20+ years with periodical tip replacement.

My personal rule of a thumb for soldering irons for electronics states: "try to stick with 15-20 watt irons with tip temperature below 400 degrees, somewhere in 350-390 range". In Europe you can find following irons satisfying these criteria:

  • Antex CS-18 - 18 watt, 390 degrees, it is a living classics of soldering irons; it's very light: 33 grams (without soldering I personally own and recommend one with silicon cable, and it is very light - on the home scales, the weight of my unit is 33 grams without cable on home scales!
  • JBC 14 ST (11w, but really good small iron) and 30 ST (25w, BUT 380 degrees)
  • ERSA MultiTip C15/Tip 260. Tips from ERSA are renowned for their longevity and quality.

    UPDATE: I personally own Ersa Tip 260 and the only real drawback is the heavy and rigid cable. Only 3 tips are available for this model: bevel, chisel/screwdriver and point - which are perfectly fine for a generic use.

In case you need to solder bigger and more massive stuff, there are more powerful models from the same manufacturers, with temperature of the tip above 400 degrees:

  • Antex XS 25 watt
  • ERSA MultiTip C25, MultiPro (20w/25w)

I own Antex XS 25 and find it too hot for normal electronics usage.

UPDATE: I actually managed to use it with a great success for soldering stripboards, where the Antex CS-18 tip was not able to quickly heat the "strips" of copper - need to check it, as tip showed some wear. Still, massive 2.3 mm screwdriver tip of XS 25 managed to do the work just perfectly - including the SMD work! Some practice is still necessary though to handle this hot beasty.

It comes handy when I need to re-solder/desolder bigger things, metallic parts and so on.

I omitted Weller (once in a while was German, now Cooper Tools USA) products as they are/were well-known for their soldering stations, not for their mains-powered irons (from my perspective); also, they are way too expensive - a factor definitively not contributing to their popularity.

One practical advantage of the fixed temperature mains soldering iron - personally for me - lays in the desoldering field. Desoldering wick/braid is a "heat thieve" and if the iron temperature is not high enough, you won't get the job done. The setting on my regulated iron was around 320 degrees - no idea how much was in the reality, I just trusted Goot and Antex - and I had to set it above 360 each time I wanted to desolder something from a stripboard using braid (thus plus two "heat thieves") fast enough. With the simple Antex CS-18 this hassle has been just forgotten.

It can be said with a certain amount of confidence, that any of the aforementioned units will have:

  • good heating element - otherwise they won't be in this list
  • good ergonomics

    From my point of view, it is almost the most important parameter of the iron, as there are plenty of offers with same performance, but very few of them has really good ergonomics and weight. This is, however, highly personal, but design of the proposed units has been polished for years and is quite often praised by the users across the world.

  • reasonable recovery time (how long does it take to heat the tip back after a contact with colder surface);

  • good choice of tips (Antex choice is a bit limited for CS and C-range, lacking chisel/screwdriver tips; XS-range is good; ERSA Tip 260/C-series is limited to only 3 bits, but they are rather universal: 2.6 screwdriver, point- and bevel-types);
  • replacement parts like heating element and tips are readily available and will not disappear suddenly; it is often possible to rebuild faulty unit even 10 years after initial purchase.

Personally, I like Antex irons for their heating element quality, design, weight, ergonomics (only models I mentioned earlier, as I tried both of them), and hook - special feature, which can be used for your index finger to improve control over soldering process. Unfortunately, Antex became a bit silly, and has recenlty stopped addings hooks to their irons anymore, so it should be asked/found/bought separately now.

In any case - aforementioned irons are worth getting and any of them is a good foundation for the quality soldering work.

heat

... properly and a little bit more to make sure, that a tip and a heating element are fully "loaded". This detail is frequently omitted by beginners - I was not an exclusion - while using classical irons, even regulated ones. While some manufacturers honestly specify "5 minutes" of heating time, others do not really care too much. Physical dimensions of the tip directly contribute to the heating time: bigger/thicker/heavier your tip is, more time is required to heat up the whole system properly.

I usually turn the iron on, prepare everything, go to get some water to wet a sponge, do some other small stuff - and voila, iron is hot and ready for soldering!

So, again, be patient and give it enough time to heat up - that's the key to success!

Power Recycling

Once I have encountered an instruction for some university electronics laboratory, which stated the following: "Tools like oscilloscope and soldering irons are not really intended to be switched on/off constantly: when you come in, you turn them on, when you end your session, you turn them off". Really, constant power recycling does not make any good to to your soldering iron due to constant heating/cooling (expansion/shrinking) process.

Do not worry about tip - if you keep it tinned and clean of flux/chemical residues, nothing will happen to it. During my 5-6 hour soldering sessions - not too frequently, but still - my Antex CS-18 is constantly "on" and nothing has happened to it yet, and I am still using the same tip!

Damp Sponge vs Brass Wool

Again, look at the PACE videos - for me it is clear, that the best practice is to use both. Follow the sequence "brass wool - damp sponge - soldering", and you will always be fine. If you want to use either of this things, take into account:

  • damp sponge is a better against chemical residues and smaller contamination, which is left after desoldering
  • brass wool is better against stronger and larger contamination, like accidentally melted plastic, also cleaning the whole tip body is possible

From my experience, after tip tinning and wiping it against damp sponge, it shines a little bit brighter, then after a brass wool ball :)

One precaution about damp sponges, which sounds rather reasonable (source)

Don't use cold water, or let the sponge get too wet. Doing so can cause the temperature to drop more than necessary, and can even cause thermal shock that damages the tip.

WARNING: do not use non-cellulose sponges from kitchen shop. Sponge you really want should be made out of 100% cell, and it should be hard and dense in a dry state; otherwise you are risking to kill the tip of your soldering iron!

UPDATE: currently I am trying to use exclusively brass wool with the Antex irons, and already one tip is damaged. Maybe I'm using it wrong, or brass wool ball is of a bad quality - let see. For the moment, I'm not really pleased with the results of my tests.

Leaded vs Lead-free Solder

Funny enough, the answer for amateurs and for high reliability the answer is the same: Leaded. Lead-free fluxes are more toxic, and it is FLUX - not a metal compound itself - which is posing the main danger to you while soldering. For for medical, military and aeronautic purposes, where the quality of soldering connections is critical, the leaded solder is obligatory: read more about whiskers. Also, lead-free solder has higher melting point (also it is a reason why different fluxes are used) and overall tip wetting process is much "slower", requiring longer heat application, thus increasing a risk to damage a component.

As a beginner, I made an error and started with lead-free and struggled a lot with it; managed at the end, but wasted a lot of time to produce solder joints of a reasonable quality. Today, leaded solder dominates my storage and I try and do work only with it.

There is a number of solder manufacturers, which are accepted as an industry standards: Kester, MG Chemicals, Multicore, Edsyn, Elsold and so on - stick to them. Compound wise, I would only use and recommend 63/37 (Sn/Pb) or 62/36/2 (Sn/Pb/Ag) solder nowadays, as it is better then 60/40 in every respect, as far as I am aware; only if you can not get one - use very traditional 60/40 solder.

Solder Wire Diameter

Obviously, thicker wire has more solder per unit of length - therefore, with a thinner wire you have finer control over the process (you spend solder wire per unit of length and per unit of time comparing to the solder with bigger diameter). Its diameter should be something between 0.4mm and 0.6mm. As a general rule, try to avoid extremes: do not use neither too small, as you probably do not want to feed 10 cm of wire per joint, nor too big for the opposite reasons (creation of a solder blob with 1 mm of solder).

Start with a small spool of 0.4mm/0.5mm/0.6mm solder wire and see, if it is OK or not, and then decide in what direction to move.

Flux It!

You can often see videos where soldering is done without any additional liquid flux. Quite a lot of such soldering is done to already pre-tinned surfaces, thus making the whole story a bit simpler; sometimes solder wire has plenty of "active" flux already in it. Overall, I would still add flux just to be sure and have best possible results. Good rosin flux - again, stick to normal proven brands, or even DIY (google the recipe) - it is what you need, nothing more. Residue can be removed with Isopropyl Alcohol; if they are solid - scratch them with something sharp and again Isopropyl Alcohol.

To simplify the flux application and make it more accurate, I would recommend to buy a syringe or a flux dispenser bottle with a set of needles - both variants from eBay; to prevent flux drying via needle, I insert a component lead into needle nose, and it works like this very well.

syringe

Also, fluxing the surface/connection prior to desoldering helps to keep the area nice and clear (an advice from one of the PACE videos :)).

flux-jam

Decrypt the Signs!

Today we have a great choice of solder wires and fluxes. The moment you see a solder spool or flux, you start to ask yourself a question: "What on earch all this numnbers mean?". Here is a picture and a "decryption" example for the solder I personally use.

solder-spool

  • Compound

    The actual alloy used for the solder; 63/37 preferred, 60/40 as a fallback solution

  • Wire Diameter

    It is what it says. Some manufactures (Kester, etc) often specify it in inch units, like .020: in this case, just multiply it by 2.5mm (0.020*25.4mm = .5080mm)

  • Flux Content

    C3 - type of the solder (might be producer dependent, worth to check), 3,5% - proportion of flux in the whole thing.

  • Flux Compound

    ROM0 means "Rosin Moderately Activated 0% halides". The naming convention is defined in J-STD-004 US standard. More reading: wiki and here. Usually, ROM0 or RMA is what you need for general electronics soldering tasks.

Sometimes manufacturers introduce their own abbreviations, thus additionally complicating our life - the only way to understand these magic number is to go to the producer's website and found proper documentation for it.

Instead of a conclusion

  • Watch videos from PACE
  • Get a decent soldering iron
  • Get stand, special sponge and brass wool ball
  • Get/make good flux and fine solder
  • Get solder sucker and solder wick to fix a mess
  • Try to solder some projects, like CMOY amplifiers, or something from Talking Electronics, and hone your skills from project to project
  • Try to make the solder joints ideal

And most important: Have Fun!

Mike.

Categories: electronics and soldering

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