Soldering PCB

[Speedy Builder5Participant @speedybuilder5]

So what is going wrong. I have bought an electronics kit and the PCB has some surface mounted components already soldered to the board, and I have to solder in other components. The holes are through plated and pre-soldered, but I find it difficult to get my solder to flow with the pre-soldered holes. I have plenty of heat and using cored flux lead based solder.
Any ideas please as I don't want to overheat the components.
BobH

[Speedy Builder5Participant @speedybuilder5]

problems with solder flow

[Anonymous]

I solder mostly SM components these days, but I run an 80W iron at 360ºC for all components. Tin/lead solder should be easy peasy. I'd suspect the pre-soldered board; I wonder if lead free solder was used for the SM components? Do the joints look dull?

Andrew

Edited By Andrew Johnston on 16/11/2016 15:17:28

[Ian PParticipant @ianp]

Presumably your cored solder melts/flows easily when you test it against the hot tip?

If the PCB pads are pre-tinned and the component leads are not twenty years old and been stored in damp conditions, then the same solder and iron should have no difficulty with the PCB.

One thing is possible which I have experienced is that at some stage after the PCB tinning the board has acquired an almost invisible layer of resist. The resist is meant to be clear of the pads but the board might have been subject to a waft from a spray which is sometimes used to apply conformal coatings (which acts as resist as well).

Ian P

[DMBParticipant @dmb]

Andrew,

Re your post above regarding Tin/Lead and Lead-free. I get the impression that the 2 cannot be used together,am I correct?

John

[john carruthersParticipant @johncarruthers46255]

maybe give the pads a rub with a pencil rubber?

[DMBParticipant @dmb]

BobH,

The surfaces/contacts to be soldered, are they clean and grease-free? I have had some trouble in the past trying to soft-solder brass sheet and angle.

John

[MuzzerParticipant @muzzer]

It can be helpful to use a flux dispensing pen to help the solder to wet the pads. The bare pads are normally plated with nickel, silver or gold to prevent the copper becoming oxidised and difficult to solder. If the board has been badly handled, poorly made or left kicking around, the pads may be oxidised or contaminated. Flux helps with this.

You also need to be able to wet the tip of the soldering iron with the solder, otherwise it can be surprisingly difficult to get the solder to flow on the pads and the component leads. A tip cleaner is good for this.

Got any pictures?

[not done it yetParticipant @notdoneityet]

Start at the beginning. Are you a regular solderer or learning? Maybe tin the components first?

[john swift 1Participant @johnswift1]

any pictures of your solder joints available ?

provided the PCB tracks and component leads are free of any oxidisation and are not contaminated with the oils from your skin

any soldering iron equivelent to an Antex XS25 to a 50W Weller WTCP50 magnastat iron with a number "7" (700F) bit works with lead free or 60/40 solder

60/40 solder is the easiest to start with and should easily melt and flow as it comes into contact with the hot PCB track and component wires

John

[duncan webster 1Participant @duncanwebster1]

I've got one of these

**LINK**

which I use to clean the tracks on stripboard. Mine came from Maplins, but I can't find their listing

[Speedy Builder5Participant @speedybuilder5]

Thanks for all the replies:
Andrew – The SM component joints – bright and silvery.
Not done it yet – been soldering since 1952 when dad bought me a 25Watt "Henley Solon" with a 7/32" bit.
I am using an ANTEX 12Watt with a fine point as the 2mm diameter bit is too big. The component spacing is 2mm, so it would be too easy to short out adjacent pins.
The kit is brand new, I can get the component legs to wet, but very difficult to wet the plated holes.
Using cored solder to BS219.

I am suspecting that there is "resist" present on some of the pads and without special solvents hard to remove without damaging the pre soldered components already attached to the PCP. Consequently, I have to be careful not to overheat the pads or damage the components.

Incidentally, the kit is the DSO 062 Oscilloscope kit. It all looks good until you get to my bit!!

[MuzzerParticipant @muzzer]

Hmm. a 12W iron with a fine tip may struggle to get enough heat into the pads, especially if it's a double sided or multi layer board. I suspect that may be the core of the problem.

A good thermostatic iron with 50W or so available would be a good place to start. Something like a 65W Hakko 888 would be good value but possibly a bit OTT for occasional use.

[SillyOldDufferModerator @sillyoldduffer]

Posted by Speedy Builder5 on 16/11/2016 17:28:12:

…
Using cored solder to BS219.

…

I've had similar bother with BS219 85/15 solder. I bought a reel at a bargain price and should have read the label! Old fashioned 60/40 is a lot easier to use.

I think you may have a combination problem: small iron, high tin solder, and big pads. I like my 12W Antex but have 18W and 25W irons as well – some jobs just need the extra heat.

Dave

[Geoff TheasbyParticipant @geofftheasby]

Yes, I agree. Iron too small, I have used an Antex X25 for decades, with a quite large bit (I turn my own) possibly wrong solder (use 60/40 or Savbit) and 22 gauge cored solder, clean the solder pads with a fibreglass bristle brush (Brass can leave conductive remains) and 'tin' them first to make sure.

Geoff

Radio amateur of 48 years, quondam electronics technician

[Anonymous]

Posted by DMB on 16/11/2016 16:16:54:

Re your post above regarding Tin/Lead and Lead-free. I get the impression that the 2 cannot be used together,am I correct?

They can mix, although in my experience tin/lead solder can be difficult to get to flow well over joints that have previously been soldered with lead free.

The OP says that the pre-soldered joints look shiny, so quite possibly the board was soldered with tin/lead. I've had a look at the kit on the manufacturers website. It looks quite nice and simple, even the surface mount components are fairly large, and no fine pitch components. Sooooo, there should be no assembly problems.

I'd have to agree with previous posters; too small an iron. Many years ago I used a 15W Antex iron. That was fine for Veroboard but simply didn't cut it with PCBs. Especially those that are multilayer, which the one in the kit seems to be.

If the iron is at the right temperature, and has plenty of heat available then a good joint can be made in a couple of seconds. Note that heat and temperature are not the same thing.

Andrew

[Clive HartlandParticipant @clivehartland94829]

I also endorse the Fibre glass brush to clean before soldering, beware the residue of fibre as it is irritating like me!

make sure the iron is, 'Tinned' before use and frequently clean with one of those sponges slightly damp. Solder varies and you need to check how it goes on a sample first to get the nright heat/time of contact.

Clive

[Speedy Builder5Participant @speedybuilder5]

Sounds like it is time to make a smaller bit for the 24Watt ion then.

[Gordon WParticipant @gordonw]

I am quite good at soldering, but not good at electronic stuff. I've just been repairing a broken component on a board and had difficulty. Turned out to be the board, what looks like varnish over the board, once scratched off had no problems. Tin both parts, I'm using a 30w iron.

[Ian S CParticipant @iansc]

I got one of those fiber glass brushes last time I was in the UK, should have got half a dozen or so, it was 1984 when I was there.

All my electrical/electronic soldering is with an Antex X25, it struggles a bit at times, some times have to revert to dads old 65W Solon.

Ian S C

[SillyOldDufferModerator @sillyoldduffer]

Posted by Speedy Builder5 on 16/11/2016 21:40:15:

Sounds like it is time to make a smaller bit for the 24Watt ion then.

I'd buy one.

Soldering iron bits for electronics are more high-tech than you might imagine. There's an iron outer skin that improves bit life and solder transfer. (Not sure how it works but I guess molten solder wets the joint rather than the bit and flows off the iron.) There's also a relationship between the wattage of the iron, the size of the bit body and the size of the tip. You want the bit at the right temperature for the solder, with enough heat stored to complete the joint. Presumably this matters less if the iron is thermostatically controlled.

I'm relying on faulty memory here – are there any soldering iron experts out there?

Dave

[Gordon TarlingParticipant @gordontarling37126]

I've just about given up on non-temperature controlled irons now. For smaller stuff, I use a Weller solder station with a 45W iron – good for stuff from the tiniest up to 'medium sized' joints. For the larger stuff, I now use a Weller 100W temp controlled iron. Both irons work very well and much nicer to use than most non-controlled irons which usually get way too hot. I often find that adding a small amount of suitable extra flux to a joint will ease the soldering process, rather than relying totally on the cores in the solder wire.

[Martin WParticipant @martinw]

I gave up on non temperature controlled irons a long time ago now. Currently I have a relatively cheap soldering station, from CPC, that has a digital display of bit temperature (nominal) and the set temperature. The set temp can be selected using push buttons so that the tip temperature correct for the type of solder that is being used, typically 60/40 tin lead temp is 310C and tin/copper lead free is 370C. The iron itself is 48W so heats up very quickly and holds a stable temperature over a wide range of job sizes. The complete system only cost around £40 max which is cheaper than some stand alone irons.

Martin

[Steven VineParticipant @stevenvine79904]

+1 for the temperature controlled irons (an old 60w station from Maplins, around £40). I start off with a low heat setting, and if I find I am struggling, I keep turning up the heat, a little at a time until the job heats up and the solder flows. First priority, make sure the work is clean and uncoated

Steve

[Speedy Builder5Participant @speedybuilder5]

Glad to report that the 12Watt iron has done the job. Unfortunately I don't have glassf iber pens etc, and can't get a rubber into the spaces left between the surface mounted components, so had to scratch the pads with a scalpel. Initially, the oscilloscope didn't work, but there was one 'dry' joint which I found by using a magnifying glass, re-solderd and now it works. I just need to find out how to use a scope to see what is happening on my BBC Microbit computer / rev counter application. Thanks for the help, over and out.
BobH

[Author]

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