Sol­der­ing tips

ALL SOL­DER­ING EQUIP­MENT IS NOT CRE­ATED EQUAL. HERE ARE SOME TIPS AND TRICKS

The Shed - - Contents - By Mark Beck­ett Photograph­s: Mark Beck­ett

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.

Tem­per­a­ture-con­trolled irons

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.

Sol­der so­lu­tions

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.

Desol­der­ing

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.

Desol­der braid/wick

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

Desol­der pump

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

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