Author Topic: Soldering PCBs  (Read 729 times)

Offline SamT

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Soldering PCBs
« on: November 03, 2018, 10:12:26 pm »

Bit of a general question.

need to replace a charging point on a mobile phone. It looks do-able, but very intricate.

see -

Going to give it a shot as the phone is a bit buggered without it.

Done a fair bit of soldering, but not really at the micro level.

My main questions are a - which solder and b - which flux.

my pot of flux is like a grease, yet all the vidoes show a liquid being applied via a fine needle bottle thing.  Just want to be sure I buy the right stuff.

And whats the deal with solder, I assume now its all lead free etc.  ( I have various bits in the garage, but god knows where it came from/what it is.

Cheers in advance for any advise.  :thumbsup:

Offline Fulk

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Re: Soldering PCBs
« Reply #1 on: November 03, 2018, 11:27:15 pm »
Sorry SamT, you just don't get the way the World works these days. You don't mend things, you just chuck 'em in  the bin and f*** up the poor old planet even more.

Offline Dave Tyson

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Re: Soldering PCBs
« Reply #2 on: November 04, 2018, 12:08:36 am »
I would use 60/40 solder rather than lead free - you can still buy it and it melts and flows easier as well as not being prone to 'whiskering'.

With regard to flux, use fluxite or similar - don't use acid fluxes or pastes designed for plumbing.  When you have finished soldering, cotton wool soaked in meths will remove any traces of flux. If you tin the contact area and socket connections carefully then you may find you can just press the soldering iron on each contact to melt the solder so it flows. A bit of practise with a fine tipped soldering iron is recommended.

It is also possible to use solder paste rather than thin solder wire - apply to the contacts and then put the socket on top and apply heat. The biggest problem is usually holding everything in place - a dab of hot melt glue might help to keep stuff aligned while you solder.

Dave

 

Offline Antwan

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Re: Soldering PCBs
« Reply #3 on: November 04, 2018, 07:27:16 am »
What Dave said. The Romans got it right with solder ratios 2000odd years ago - then the environmentalists got involved

The lead solder is still available for home use and military applications.

Offline ChrisJC

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Re: Soldering PCBs
« Reply #4 on: November 04, 2018, 08:12:58 am »
Get some solder wick too. You will find that you get too much solder in there, shorting stuff together. You can 'suck' it out with solder wick.

Also get a temperature controlled soldering iron. Not one of those shite things for a fiver.

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Offline Flotsam

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Re: Soldering PCBs
« Reply #5 on: November 04, 2018, 05:56:52 pm »
I've been designing and repairing electronics for 4 decades. You need to use thin cored solder or fluxed solder paste. Don't even think about lead free. it's worth setting up a magnifier and light, the better the quality the better the chances. Buy or borrow a micro tipped soldering iron. Don't try and lift the component in one go. It's better to cut the leads of or break the connector up and de-solder and remove one lead at a time.

Offline SamT

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Re: Soldering PCBs
« Reply #6 on: November 04, 2018, 07:55:22 pm »


Don't try and lift the component in one go. It's better to cut the leads of or break the connector up and de-solder and remove one lead at a time.

Interesting.. all the vids Ive watched show people lifting the port off in a oner. One uses a little hot air gun (prob one of those gas ones) One uses a hot air gun (looks like a diy paint stripper) from below which looks well dodge. and another uses one of those plunger sucker things and an iron.

The component has 4 attachment lugs on each corner and about 8 tiny weeny connectors off the back.

Not sure youd be able to cut them really.

Am starting to gather some of the kit from ebay.

Got a mini blow torch. Already have some of that copper ribbon stuff for cleaning off the old solder.

I have some fine guage solder that has a flux core but no idea if its 60:40 or what.

Ebay seems awash with loads of different types of flux but all the vids show something very liquid being applied.

I know to clean up after with alcohol on an ear bud.

Anyone care to link to an appropriate flux on ebay.

What is solder paste and how is it used?

Might know someone with binocular microscope. Need to get in touch.

Another thing... folks seem to talk about setting the iron to the right temperature.  My various irons have never had this function.  But what kind of temps.. how do you judge that. I wouldn't know where to start.

How much should I spend on a vari-temp iron? Any recommendations/ebay links




Offline Addy

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Re: Soldering PCBs
« Reply #7 on: November 04, 2018, 09:19:53 pm »
Not a bad video. There are plenty more showing all types of butchery.
The use of a hot air gun enables the whole lot to be taken off in one go but it's not imperative and can be done by firstly removing as much from the anchors as possible using solder wick. Eventually, you should be able to remove 'enough' to release the frame.

Perhaps the single most important point is not to strain the connection 'fingers' on the PCB itself. They will tear up if you apply any form of leverage.
A fine scalpel *could* be used to sever the connector fingers as far from the PCB as possible and then remove the individual slivers with the iron, but tricky to avoid damage to the PCB.

There's no harm in 'flooding' the pins with solder so that they all heat together, minimising the risk of damage.

When soldering back on, you'll need a pretty fine iron to solder the fingers singly.
Alternatively, once the connector is in position and the frame is anchored, flood the pins again and ten remove surplus with solder wick.

Why?

Offline Mr Mike

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Re: Soldering PCBs
« Reply #8 on: November 05, 2018, 07:16:15 am »
I used these Flux pens and they work well:

Stannol 830321 Mini-Fluxer X33S-07i Flux Pen 10ml

Electrolube SMF12P Surface Mount Rework Flux Pen 12ml

A big thing to watch for it too much heat on the little pads, that can also lift them and then its knackered. Not essential, but if you can borrow / get you hands on a hot air soldering station it really makes life easier to take it all off in a one go.

I don't know how much experience you have with this sort of thing, but if not much - it just might be better to get it fixed at the multitube of phone repair shops. If you already have the spare connector, take it along and ask - it would be a quick job and I can't see it costing much.

Offline droid

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Re: Soldering PCBs
« Reply #9 on: November 05, 2018, 07:57:47 am »
Sounds like my futile attempts at motorcycle 'maintainance'

5 hours frigging about, create 3 new problems, phone the dealer...... :lol:
No longer 'Exceptionally antagonistic' 'Deliberately inflammatory'

Offline Flotsam

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Re: Soldering PCBs
« Reply #10 on: November 05, 2018, 08:36:34 am »
Forget about trying to de-solder using wick. The solder actually holding the component will not be soaked up with the wick. You will only have a couple of goes at doing this without destroying the PCB tracks and pads.

Offline prahja

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Re: Soldering PCBs
« Reply #11 on: November 05, 2018, 12:09:54 pm »
It’s an easy job with the right tools. Nigh on impossible without them. Find someone with a hot air station and who has done smt soldering. Otherwise it’ll be easy to destroy the board.

Also worth noting not all flux, by any means, is soluble in alcohol - some leaves a hideous sticky, mildly conductive residue if you use alcohol....

Offline SamT

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Re: Soldering PCBs
« Reply #12 on: November 05, 2018, 01:19:12 pm »
some leaves a hideous sticky, mildly conductive residue if you use alcohol....

OK, thanks for the tip - but more useful would be to explain which  :shrug:

Offline Mr Mike

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Re: Soldering PCBs
« Reply #13 on: November 05, 2018, 01:22:06 pm »
IPA cleans most normal fluxes with no problem. I would say, don't buy cheapo Ebay stuff, only a branded name fluxes.

Offline SamT

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Re: Soldering PCBs
« Reply #14 on: November 05, 2018, 01:39:57 pm »
Indian Pale Ale ??

(so many goddam TLAs,  - SMD, PCB, RMA,  RMG).

You lot are worse that computer programmers..  :wall:

Offline Mr Mike

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Re: Soldering PCBs
« Reply #15 on: November 05, 2018, 01:48:35 pm »
Indian Pale Ale ??

(so many goddam TLAs,  - SMD, PCB, RMA,  RMG).

You lot are worse that computer programmers..  :wall:

I knew someone would say that - Iso-Propyl Alcohol, but not of the double type.

Offline prahja

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Re: Soldering PCBs
« Reply #16 on: November 05, 2018, 02:14:54 pm »
some leaves a hideous sticky, mildly conductive residue if you use alcohol....

OK, thanks for the tip - but more useful would be to explain which  :shrug:

You’d have to look on the manufacturer’s soec sheet. There are so many fluxes - some have their own solvent/removers. Some are water soluble.

As an example - I use rosin core solder and mg chemicals rosin flux which is soluble with isopropyl alcohol. I also use mg chemicals no-clean flux which is not soluble with IPA for when I cant soak the board in ipa (eg when I have pots with alcohol soluble grease installed). I build a lot of modular synthesisers!

But you really need to check the spec sheets....

A hot air work station can be had on ebay for £30 which is what the guy in the video isusing.

Offline bograt

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Re: Soldering PCBs
« Reply #17 on: November 05, 2018, 04:15:28 pm »
I use flux cored solder for the circuit board, no need for any additional flux there. For 'tinning' the bit (coating the souldering iron) a dip in Fluxite is good, if you're ever in Chapel-en-le-Frith give me a P.M. and I can let you have some, I've got loads. (I can't post it as I live over a mile from the nearest post box and have been stopped from driving because of the stroke).
 For cleaning out old solder, use a 'sucker' as already descrubed for the bulk of it and wick to finish off.
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