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Old 21st Jul 2019, 9:19 am   #1
John M0GLN
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Default Using Lead free solder.

Not sure if this should be in the 'Modern Technology' section or not.

I've just been looking through the service manual for my Marantz AV receiver and it says,

"When soldering use lead free solder, Sn-Ag-Cu."

Now is this just to comply with H & S regs or are there any technical reasons why they should not be mixed?

Thanks
John
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Old 21st Jul 2019, 9:35 am   #2
Jon_G4MDC
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Default Re: Using Lead free solder.

Don't mix them by my experience. You get a strange amalgam which is very similar looking to a dry joint.

If you can remove all the lead free apart from the surface layer then resoldering using Tin-Lead makes a good joint.
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Old 21st Jul 2019, 10:06 am   #3
Craig Sawyers
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Default Re: Using Lead free solder.

In my experience lead free solder makes a joint that looks dull and crystalline, almost indistinguishable from a dry joint.

That is why in aerospace, defence and critical care equipment leaded solder is still used for precisely that reason.

Craig
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Old 21st Jul 2019, 11:38 am   #4
emeritus
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Default Re: Using Lead free solder.

In a recent motoring column in a newspaper, a reader's problem with the radio of his new-ish car was attributed to poor solder joints.
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Old 21st Jul 2019, 11:45 am   #5
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Default Re: Using Lead free solder.

As per Jon's comments durability is fine as long as the majority of the modern solder is removed first. The story as told to me is that a very small %age of Pb in a finished joint is OK, as is your normal 30% or 40%. Somewhere in between these %ages however, is a dead zone where the joint is unsatisfactory and the Pb can even crystallise out of the alloy.

The magical world of metallurgy- I still can't quite cope with Pb and Sn having medium melting points, and Pb/Sn alloys having a low melting point..

A Pb/Sn solder with 1 or 2% of Cu is said to preserve the soldering iron tip for longer, but the melting point does shift upwards more than you expect, so perhaps not for soldering delicate components.

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Old 21st Jul 2019, 12:05 pm   #6
John M0GLN
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Default Re: Using Lead free solder.

Thank you all for your advice, I did solder a small capacitor into the Marantz a couple of years ago before reading the warning in the manual, normally I always get good shiny wet joints but these were exactly as you have suggested, they were two dull blobs, it's still working fine and they are in a non critical position so I'll leave them alone unless the fault re-appears, if it does or if I have any others to do I will remove the lead free solder first.

Thanks

John
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Old 21st Jul 2019, 5:41 pm   #7
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Default Re: Using Lead free solder.

In the past I have mixed them to some extent and obtained the dull joints as described. I have yet to come across a joint which failed, but, in the main, I don't use lead free at all unless there is good reason.
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Old 21st Jul 2019, 6:31 pm   #8
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Default Re: Using Lead free solder.

We had a lot of problems with lead free solder joints at the last place I worked until we switched to solder with some silver content, then the joints were good but still dull.
Played havoc with IPC620

Peter
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Old 22nd Jul 2019, 2:33 pm   #9
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Default Re: Using Lead free solder.

That maybe explains why I have not had problems as when I bought my lead free I chose that with good silver content thinking it may be of better quality, particularly for RF.
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Old 6th Oct 2019, 10:42 pm   #10
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Default Re: Using Lead free solder.

It is okay to add leaded solder to a lead-free solder joint. I do this when repairing Ericsson/Aastra/Mitel DECT phones with no problems and joints look as if only the leaded solder was used. Lead-free solder is horrible stuff which sets too quickly after the heat is taken off it.
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Old 7th Oct 2019, 10:31 am   #11
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Default Re: Using Lead free solder.

Quote:
Originally Posted by The Philpott View Post
The magical world of metallurgy- I still can't quite cope with Pb and Sn having medium melting points, and Pb/Sn alloys having a low melting point.
It's commonplace with any solution - table salt melts/solidifies at 801C. Water/ice at 0C. But brine (depending on concentration) may not freeze until -19C, lower than either!
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Old 7th Oct 2019, 12:42 pm   #12
ColinTheAmpMan1
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Default Re: Using Lead free solder.

Quote:
Originally Posted by kalee20 View Post
Quote:
Originally Posted by The Philpott View Post
The magical world of metallurgy- I still can't quite cope with Pb and Sn having medium melting points, and Pb/Sn alloys having a low melting point.
It's commonplace with any solution - table salt melts/solidifies at 801C. Water/ice at 0C. But brine (depending on concentration) may not freeze until -19C, lower than either!
Ah, yes, but while there is a similarity between alloys and solutions, metallurgy and solution physics are not the same.

Colin.

Last edited by ColinTheAmpMan1; 7th Oct 2019 at 12:43 pm. Reason: more clarity.
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Old 16th Oct 2019, 5:51 am   #13
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Default Re: Using Lead free solder.

Has anyone here got a decent looking joint with lead free here?,it seems rubbish to me,reminds me of the replacements for other banned stuff,creosote and two pack car paint come to mind,both replacements are total crap!!
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Old 16th Oct 2019, 7:07 am   #14
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Default Re: Using Lead free solder.

See post No 8 on this thread, the best we could get is to use lead free solder with some silver in it, lead free solders with no silver never gave a good joint.
Even with some silver we found we had to use additional flux to get a good joint, ie good mechanically and electrically but still dull.

Peter
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Old 16th Oct 2019, 9:56 am   #15
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Default Re: Using Lead free solder.

Depends a lot on the composition, some stuff is very brittle and not much good, i use sparkle esc, Japanese made, it's very good stuff, produces good joints every time.
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Old 16th Oct 2019, 10:45 am   #16
60 oldjohn
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Default Re: Using Lead free solder.

Quote:
Originally Posted by M3VUV51 View Post
Has anyone here got a decent looking joint with lead free here?,it seems rubbish to me,reminds me of the replacements for other banned stuff,creosote and two pack car paint come to mind,both replacements are total crap!!


Built in obsolescence ?


John.
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Old 16th Oct 2019, 3:48 pm   #17
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Default Re: Using Lead free solder.

There's nothing to stop you using leaded solder to repair consumer equipment, it's only intended to reduce the impact of large amounts of lead causing contamination of the environment. The odd joint is neither here nor there. These days very much less reaches landfill in any case. Multiple layers of sorting are in place, the scrap is too valuable!
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Old 16th Oct 2019, 9:31 pm   #18
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Default Re: Using Lead free solder.

Not much on TV so I thought I would investigate solders.

A charity shop purchase book on Metallurgy bought some years ago ("Metallurgy", E. Gregory, Blackie & Son, 1949 revised reprint of the 1932 original) only deals briefly with Tin-Lead solder, but does have a drawing showing the behavior for different proportions. More interesting is the comment on Tin itself, which is apparently unstable at room temperature and prone to disintegrate into powder below 19 C. I wonder if this is a factor in the difficulty often experienced in soldering old NOS components such as solder tags? If the "tinned" finish is in fact pure tin rather than a tin-lead solder, the change to the alpha tin allotrope would not be beneficial.

I wonder what proportion of other alloys need to be added to inhibit the formation of the alpha phase? The common lead free solders seem to consist of around 96% Tin. Possibly the reported unreliability is in part due to the progressive formation of the undesirable alpha allotrope if the mix isn't right.

When checking the composition of lead-free solders (I don't have any myself), I found the following in information about Multicore Lead-free solder on the RS web site.

"What are the differences between lead-free solder and leaded solder?

Lead-free solder is generally regarded as having a more positive environmental impact than leaded solder, and also as being safer for human use. However, lead-free solder also has potential production advantages. Lead-free solder can offer better lead spacing, which makes it more suitable for high-density components where pitches are tight. This means potentially better performance where space saving is a concern.

The advantages of lead solder are that it has a lower melting point, which is sometimes preferable for hand working components. Also, lower working temperatures reduces the risk of damage to components and circuit board.

Unlike lead-free solder, lead solder does not have a shelf-life and is less prone to losing quality after prolonged exposure to oxygen. However, many electronic application requirements exclude the use of lead solder, due to the toxicity of lead."


This is the first information I have seen that lead-free solder has a shelf life, and an admission that it does deteriorate on exposure to oxygen. I'll be sticking to my 60/40!


https://uk.rs-online.com/web/p/produ...-PRODUCT_GROUP
Attached Files
File Type: pdf Metallurgy of solder .pdf (120.6 KB, 14 views)

Last edited by emeritus; 16th Oct 2019 at 9:49 pm.
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Old 16th Oct 2019, 9:36 pm   #19
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Default Re: Using Lead free solder.

I had some small experience of lead-free solder, as I was working in the industry around the time it was introduced. Two things I noticed were:
  1. Lead-free solder melts at a higher temperature than 63/37. You will need a #8 bit (400 degrees?) if you are using a Weller iron, and plenty of flux (pay no any attention to claims of "no-clean", either).
  2. A good joint made with lead-free solder looks almost exactly the same as a bad joint made with lead-free solder.
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Old 16th Oct 2019, 10:11 pm   #20
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Default Re: Using Lead free solder.

I have witnessed, and bemoaned, the transition from leaded to lead-free solder in the electronics industry and have a few comments.

Firstly, I've never had a problem repairing lead-free joints with leaded solder. I routinely do this because it's quicker, cheaper and easier on the bench. I only ever work with prototypes, though, which are not expected to have a long service life. The joints look nice and shiny.

Secondly, there are many different lead-free alloys, and they're suitable for different purposes. In my experience, attempting to hand solder with cheap lead-free solder (which is basically just tin with a dash of copper) is a disaster. It's horrible stuff and just falls off in lumps. Get the stuff with silver in it. That works pretty much as well as leaded, though needs a slightly hotter iron and is expensive.

Most lead-free solder is used in automated PCB manufacture, and there the conditions are controlled so precisely that good joints result if sufficient care is taken.

A good lead-free joint is just as shiny and strong as a good leaded one, with the possible exception of tin whiskers. I see such good joints every day. However, for hobbyist repair and restoration use, don't worry about it. Just use leaded solder.

Chris
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