Circuit board soldering tips please

[AnthonyL]

I have 9 capacitors to replace and have very little experience with soldering on circuit boards. Tips for removing and replacing welcomed.

[newshound]

Cutting the legs off to remove the can makes removal much easier. Suction tool or wick makes removal of surplus solder easier. Biggest risk is probably overheating and delaminating the copper. Try to get everything clean before re-soldering (may be worth abrading the new capacitor legs lightly). You need to be fast when re-soldering.

Otherwise it is practice practice practice.

Play around removing stuff and soldering in replacement copper wire on a totally dead circuit board of similar scale?

[newshound]

Modern temperature controlled iron with fine tip helps too, not expensive on eBay.

[Tim Watts]

On Thursday 25 July 2013 11:13 AnthonyL wrote in uk.d-i-y:

1) If you can clamp the board (gently, wtach the tracks!) you can often heat one lead whilst using afinger to put sideways pressure on the cap. The lead will slip out - not all the way in one go.

Repeat on the other lead, rocking the cap the other way.

repeat on the first and second lead until it is free (pulling the body when it's down to being held on by one lead only).

The holes may still contain solder making insertion of the new component impossible so combine or replace with one of the two following techniques:

2) Use solder braid to suck the solder off

3) Use a solder sucker gun:

2 and 3 sometimes do not quite remove the last little bit requiring a bit of technique (1).

YMMV.

Avoid overheating the tracks - they can become detached. 1 second heat application at a time. Few seconds rest between heatings.

[Road_Hog]

Make sure the iron is hot (i.e. reached optimum temp), that you are using the right sized iron for the job (you don't want to be using some old industrial iron on electronic components) and tip. You can be quite rough with the old ones and just heat each side individually and withdraw the leg or if you're quick, heat both sides and yank it out.

If they're electrolytic capacitors, make sure you make a note of the polarity (there will be a negative sign running down one side), Slightly widen the legs to a tiny bit bigger than the holes, that way you'll have the legs applying pressure against the holes and when you flip the board over to solder, the capacitor want drop back out.

Make sure you have put solder on the iron tip and apply solder and iron together and try and do it quickly, if you've done it right, you'll have a nice shiny solder joint. A steady hand always helps, but unfortunately not everyone has one of those.

[John Rumm]

[Harry Bloomfield]

It happens that Tim Watts formulated :

Sharp pointed, wooden cocktail sticks are useful to reform the hole inthe PCB. Just push the point through the hot solder, the wood will not draw the heat out, giving you time to to get it all the way through the hole. Leave it in until the solder resets.

Another technique i use on more robust PCB's, is to melt the solder, then give the PCB a sharp tap on a hard surface. The weight of the molten solder will carry it away from the PCB.

[fred]

In article , AnthonyL writes

In addition to all other good points.

9 caps sounds like power caps on a motherboard so extra advice required.

On a well designed PCB, connections to power planes (large areas of copper either on the surface or buried internally) are made by 'thermal reliefs', small circular cutouts in the copper plane with 4 very short radial tracks on the compass points to bridge the gap and connect the pad to the power plane.

These reliefs allow the pads to reach soldering temperature quickly so a good joint can be made. If these reliefs are not present then heat is conducted away from the pad meaning that it may not solder properly or more importantly for you may be difficult or impossible to desolder cleanly.

For reasons partly technical and partly arrogance I'm sure, mobo designers ignore rules of thermal reliefs and just flood the planes with copper making a huge heatsink and making holes very difficult to desolder.

First of all you are going to need a powerful iron with a big tip, power to get heat in quickly and a big tip to transfer the heat effectively. I have variously used 45W temperature controlled and a 60W temperature controlled iron for this, the latter just because I have it. Anything less than 25W will struggle and 25W may be borderline.

In contrast with some, I do not clip off the cap, I cut the device leads on the solder side very short then add plenty of solder to each pad then apply heat to the solder side one pad at a time, leave heat on for plenty of time (not long enough and you may not melt the top side solder and pull the pad) then pull/tilt the device in a direction that will result in a pull on the pin (not too hard). After pulling the pin part way, switch to the other pad and pin, repeating until the device is removed.

If you are lucky you will have a hole with only a little solder in so less to clean out. Due to the high thermal mass of these pads/plane it can be difficult to use conventional solder sucker / solder braid techniques to clean the hole. An alternative is to take a hot wire (heated by soldering iron or blowlamp - away from the job!) and use it to try and clear solder from the hole by keeping it moving in the part cleared hole.

Resoldering is no bother, just leave the heat on a little longer than you might think as the high thermal mass of the joint slows the flowing.

Extra flux never hurts either (desoldering or resoldering), it makes everything flow more easily.

Note: this is not the way to work on anything other than power plane connections without thermal reliefs, carried out on any other connection and you will quickly wreck the board.

[Bob Eager]

If it's through hole plated, be especially careful!

[AnthonyL]

Thank you all for your help and for a reminder for the diy faq.

No it's not a motherboard, but a power supply.

I think I will have a fair bit of room to work around but I'm more mechanical than electrical/electronic so although I've got all the bits I haven't done and circuit board soldering since I made my own

3-way speaker cross-over circuit around 40yrs ago.

I have successfully done quite a lot of RS232 connections though, but not much to damage there other than unwanted molten plastic.

[fred]

Piece of piss then :-)

Different techniques, single sided glass fibre board by the looks, no power planes.

I'd still pull the components in the manner I described, albeit using less heat to avoid lifting pads. Go very easy, there is solder only on the solder side (no plated through holes) so you can pull the second you see it melt.

Pretty much any old iron will do but 25W & up better.

You can use solder braid (gently) to clean up, a solder sucker or use the melt & tap method that someone mentioned if you have neither of those. Beware that the inexperienced can damage pads when using a solder sucker and the recoil from the spring doinks the nozzle onto the heat loosened pad.

The cap polarity marks on the board don't look that clear, I'd be tempted to go round with a marker dotting the board near the polarity stripe (negative btw).

I'm sure you'll be fine, just whip the board out and you can work on it where you want. That said, I can't see any bulges on the caps which would be normal for failed ones.

Just keep the soldering time down, flow, hold for 1/2 second then off.

[1] might be resin bonded paper but the technique is similar, they're just a bit more fragile, both physically and pad bonding strength wise.

[whisky-dave]

Just wondered why you're replacing them, usually it's because they have blown, which is a common problem but from the picture they don;t look blown or damaged, well not as bad as those I have seen. Where the tops are raised.

So maybe something else could be wrong.

[John Rumm]

Yup, second that...

While bulges normally indicate knackered, no bulges does not guarantee not knackered. When my PVR started doing daft things, I checked the voltage rails and they were all drifting out of spec. Yet all the caps looked fine. However they tested at often less than half their marked value as well as leaky / high ESR.

Yup. All I would add is before the joint, wipe the tip clean (damp sponge or pad of kitchen roll), apply a *small* amount of solder to the tip of the iron to tin it, and provide a film of solder to aid heat transfer. Apply the iron to the job - both the wire and the pad. Wait a second or so, and then flow solder wire into the job (not the bit of the iron). When suitably coated and flowed, withdraw the solder, then the iron. Leave to cool.

[alan]

DO NOT use lead free solder!

Before removing the capacitors resolder the joints with a tin/lead solder with a integral flux. This re-fluxes the joints.

If the capacitors are in a power supply and the printed board tracks are thick you can walk the capacitor out. Heat up the solder on one leg and when its melted for the capacitor side of the board pull on that side of the capacitor (lever it up a bit). The leg will move slightly. Now do the same on the other leg. Repeat until the capacitor comes out.

[alan]

It looks like a Topfield 5810 PSU. Its a single sided board with thick, robust tracks.

The pull out (walking out) method of removal works well.

Just make sure that you remove the mains plug before opening up the box and/or removing the power supply. There is 300V+ on one of the heat sinks in the power supply when mains is being supplied (both in standby and normal operation).

Circuit diagram and location of capacitors can be found at the bottom of the page at

see also

[alan]

95%+ of the hardware faults on this box are due capacitors in the PSU failing after 2 to 4 years. In most cases fixing the PSU restores the correct operation of hard discs and tuners etc. From the experience gained from the many hundreds of PSU repairs documented in the toppy.org.uk forums it is now recommended that up to 13 capacitors are changed (depending on model).

If the OP had multimeter it is easy to check to see if the PSU voltages are out of tolerance.

[jkn]

As someone beat me to saying, that looks like a Topfield PSU.

They are 'easy' to replace, much easier than on a PC Motherboard. But are you sure the PSU is faulty?

When mine failed the measured voltages were well down and the caps showed noticable doming, which doesn't appear to be the case with yours.

J^n

[Road_Hog]

They're are as clear as day, a big bloody black mark on the neg side. Besides, do one at a time and you should be able to remember which is which.

Note to the OP, as mentioned in my previous post, they are electrolytics and have to go in the right way around.

[Dave Plowman (News)]

It also worthwhile re-soldering with leaded multicore before attempting removal. The new solder will flow more easily when you come to remove the component.

With ICs I'll generally cut them off first, but large capacitors usually have chunky tracks to them so come out ok.

[AnthonyL]

This unit has was factory supplied with a suspect set of capacitors and the advice to avoid trashing the whole thing is to replace these before any problems arise. Purely precautionary.