ALL SOLDERING EQUIPMENT IS NOT CREATED EQUAL. HERE ARE SOME TIPS AND TRICKS
Get a few tips and tricks in part one of a two-part series
The other day I was having a conversation with The Shed editor Greg Vincent, and I realized that although we have been doing a variety of articles on electronics, we haven’t talked about the tools needed to do decent work.
Everyone knows that at some stage you need to blame your tools (after the other excuses have run out), and like most things you can pay a little money or a lot, and sometimes there is little difference in the result … or so it would seem.
The purpose of this article is not to separate you from your hard-earned cash, but to share a few tricks and provide some information so you can make an informed choice when buying equipment.
Stations and irons
Everyone knows that the best soldering iron is some large lump of material that you throw into the fire until it is red hot and then apply to the job and hope that some of the exploding material fuses the bits together.
That might work for simply joining two bits of metal together but it is not going to work for electronics.
Soldering electronics involves making not only mechanical bonds but also electrically conductive joints. The solder used has a particular temperature range and if it is too hot it will overheat the joint and make it porous, while if it is too cold it may stick to one or another part but not bond.
The basic soldering iron consists of a heater and a tip. The wattage is limited to 25– 40W to stop overheating the tip. It works well on small joints and relies on the thermal mass for larger joints.
As it takes time to warm up, it tends to get left on and there have been attempts to reduce the heating with inbuilt or aftermarket controllers, much like a light dimmer, which simply reduce the power applied and therefore the maximum heat.
Clever versions detect when the iron is in the stand and put full power back on when it lifted, but the thermal lag becomes a nuisance and often is bypassed.
Weller produced a version that controlled the temperature by using a magnet inside the tip. As the tip heated to the desired temperature, the magnetic force reduced and switched off the heater. As the tip cooled, it switched back on. The tips were expensive but lasted for many years if looked after.
Since then electronics has taken over and there are a range of stations with adjustable temperature control, either by using a setting or a knob.
Some models include active measuring of the tip temperature, although I have never really paid any attention when I’m soldering — it’s either hot enough or not.
I have never really paid any attention when I’m soldering — it’s either hot enough or not
The temperature control approach has allowed a much higher wattage iron to handle the wide range of solder joints we find on modern circuit boards.
As a consequence, the time to warm up has been reduced, along with the thermal mass problem with larger joints.
Rework stations often include a soldering iron, but if I were to purchase one separately I’d be looking very hard at this: http://nz.element14.com/tenma/ at980d- eu/ soldering- station- 80w220vac- eu/dp/2535192?rpsku=clone:25 3519201&isexcsku=true.
Proper solder joint
When introducing the subject of electronics, pupils are taught how to solder and how to recognize the difference between a good solder joint and one that may cause problems later.
The shape of Mount Fuji is an example of what a good solder joint should look like. When viewed in profile the mountain has a curve, or ‘fillet’, in the transition from horizontal to vertical on both sides (well, it does in the pictures).
The board (PCB pad) and component wire are heated equally and then solder is applied to complete the joint. This whole process takes less than five seconds.
Applying heat to a printed-circuit-board (PCB) pad for much longer is likely to lift the pad from the board (giving you another issue), so unless it is a very large joint, keep the heating time to a minimum.
The state of flux
One problem we see is that the iron is placed on the joint and solder is applied onto the upper surface of the tip, rather than at the junction of the pad and component. Solder for electronics contains a resin flux and the flux gets burnt off when incorrectly applied.
The smoke and visible fumes are indicators of this happening, along with dark flux residue on the board. By applying solder down at the intersection of the board and component, you’ll be able to see it melt and disperse. At this point remove the solder, then the iron.
Adafruit has a very good guide to soldering and problems: https://learn. adafruit.com/adafruit-guide- excellentsoldering.
Soldering takes practice and some people never seem to be able to master it, so don’t worry if you struggle … you’re not alone.
Poor solder joint
So now we have a good soldering iron, and we use the right technique, what can go wrong?
For proper bonding to occur, both surfaces need to be clean and shiny. If the components you are using have been sitting around, then the tin coating may have oxidized, which can cause problems.
You can ‘tin’ the component lead before inserting it, or sometimes the soldering process (flux) will clean it.
‘ Tinning’ is when you apply heat and solder to the component only and
the result is a light coating of solder. It may release the impurities (often darklooking reside), so sometimes a quick wipe is required to be sure it doesn’t get into the solder joint.
If the board is not shiny, then a pencil eraser works wonders to remove any oxidation.
You may have applied too much solder and the joint is covered, so you can’t be sure if it has bonded.
My first solution to this is to use gravity to remove the excess solder. I turn the board upside down and apply heat to the solder joint, then pull it down the component lead and away from the joint. The next solution is to desolder it. The guides always talk about finished solder joints being nice and shiny, and while that is true for lead-based solder, the move by manufacturers to lead-free solder results in a dull surface.
Surface-mount-technology (SMT) solder joints are far less obvious and the method, tools, and solder used to join the component to the board is different.
This is the process of removing solder, usually with the aim of separating the component from the PCB.
There are several methods and each has its place and cost for the tools required.
Here, we will talk about cheap, simple tools, and in a later article touch on desoldering stations.
I’ve heard people swear by desolder braid/wicks and I’ve heard people just swear.
‘Solder wick’ is a copper braid-like product that soaks up the solder. It is more suited to SMT but is useful to remove excess solder.
It comes in different sizes and there are some cheap products that cause more frustration and damage than they are worth.
The technique is to apply the soldering iron onto the wick and then onto the solder joint. The heat goes through and it pulls the solder away from the board.
The heat and force can lift solder traces so be careful about how long it is used in one spot. It is very useful for cleaning up holes, but then so is a solder pump.
Don’t be fooled — they come in different widths and the cheap stuff may not work as well. This soldering guide is rather good, and they use the braid/ wick to clean up a joint: https://www. sparkfun.com/tutorials/96.
The through-hole soldering guide is here: https://learn.sparkfun.com/ tutorials/ how-to- solder---through-holesoldering.
Soldering takes practice and some people never seem to be able to master it, so don’t worry if you struggle … you’re not alone
A ‘desolder pump’ is a tube with a spring inside that is released, causing a vacuum at the tip. The soldering iron and desolder pump are applied to the joint and once the solder is melted, the spring is released and the solder gets sucked up the tube.
It is a bit of an art but with some luck mixed with dexterity, you can easily suck all the solder from the joint. Again, excess heating of the pad can cause it to lift.
Desolder pumps work well on one or two joints, but can be a pain to use. To use them, you press down the plunger to compress the spring. Heat up the joint and bring the nozzle as close as you can, then press the release button.
As the plunger is released it sucks up the hot solder inside the pump. Obviously, the closer the nozzle is to the joint, the more effective it is.
The best model I have is a Phillipsbranded version that is slightly smaller than others and utilizes a smaller nozzle. This means you’re not fighting
I should have bought three or four at the time, because they don’t seem to be available anymore, so I’m looking after mine
the soldering iron for the same space and the suction velocity is higher.
I should have brought three or four at the time, because they don’t seem to be available anymore, so I’m looking after mine.
Buy and try
Something to watch for are desolder pumps models that have the nozzle inserted from the outside.
When you push the plunger down fully, it protrudes through the nozzle to clean out any solder lodged on the sides. With the external-insertion-type nozzle, they can be pushed out.
Models with softish nozzles can deform rather than clean out properly.
The only maintenance is to make sure the O-ring is clean and lubricated, and check that the nozzle is not damaged. Along with replacement tips, they should outlast your ability to keep soldering.
It’s rather hard to see all these things just from looking at a catalogue, so don’t be afraid to ask at your local suppliers or buy different types until you find the one you want.
If you have smaller hands, the length can also be very important as they are meant to be used with one hand. Element14 has a good range, with varying types and different prices; you can expect to pay from $5 to $70.
My suggestion is to buy one that screws together as I’ve seen the others fly apart.
I usually stretch the spring to apply suction more quickly; however some argue that Mr Newton’s third law of equal and opposite force means it makes contact with the heated pad and increases the damage.
Whatever version of solder pump you buy, make sure you grab a couple of extra tips for it.
Relative sizes of desolder pumps against AA batteries
Solder wick — 2.6mm width in a handy dispenser
There is too much solder, which could be masking a poor connection to the PCB pad
Here the solder has not adhered to the component lead either due to oxidation or use of the wrong technique
Using gravity to assist with the removal of excess solder
Correct iron and solder placement (photo is without heat to show placement)
Desolder pump placement while heating the solder joint
A solder joint where the solder has not adhered to the connector, resulting in issues later
Desolder pumps, with Phillips one on the left — note its smaller length
The internal components of a twist-lock-style desolder pump A metal plunger rod extends past the end to clean out solder from the nozzle
In the next issue of The Shed, we'll talk about desoldering stations like this one