Mixture of solder (lead and leadfree) when repairing old equipment?

[nightfire]

Situation: I am in germany, where due to RoHS leaded solder (at least officially) is hard to come by.

As I have currently a project of repairing (and understanding) some old lab power supply build around 1987, I would have the generic question of the best approach of solder to use.
As this probably applies to lots of other old gear that uses leaded solder, I put this thread standalone, as other folks probably are in the same situation...

Anyway, the gear in my case is from 1987, very probably build with leaded solder. (Fun fact: on the website of the manufacturer it says under RoHs statement: Our equipment is intended for military use, so no exempt from RoHS regulations)

Questions here:

a) To which extent is leaded solder needed with material characteristics for maybe vibration dampening? The Lab Power supply in my case is intended to be used in a military context, but is not ruggedized, rather a mechanical high-quality version of a standard linear lab power supply, build with all discrete parts, no SMD.
b) should i use leaded solder for work like recapping?
c) What would be the consequences of mixing solder types, especially with maybe soldering joints that have not been thouroughly cleaned from previous solder when desoldering a component?
d) should I have separate soldering irons/tips for using leaded and unleaded solder?

Apologies when a similar thread is still open where this exact question has been discussed concisely- in that case, could someone point me  to that thread?

[2N3055]

Situation: I am in germany, where due to RoHS leaded solder (at least officially) is hard to come by.

As I have currently a project of repairing (and understanding) some old lab power supply build around 1987, I would have the generic question of the best approach of solder to use.
As this probably applies to lots of other old gear that uses leaded solder, I put this thread standalone, as other folks probably are in the same situation...

Anyway, the gear in my case is from 1987, very probably build with leaded solder. (Fun fact: on the website of the manufacturer it says under RoHs statement: Our equipment is intended for military use, so no exempt from RoHS regulations)

Questions here:

a) To which extent is leaded solder needed with material characteristics for maybe vibration dampening? The Lab Power supply in my case is intended to be used in a military context, but is not ruggedized, rather a mechanical high-quality version of a standard linear lab power supply, build with all discrete parts, no SMD.
b) should i use leaded solder for work like recapping?
c) What would be the consequences of mixing solder types, especially with maybe soldering joints that have not been thouroughly cleaned from previous solder when desoldering a component?
d) should I have separate soldering irons/tips for using leaded and unleaded solder?

Apologies when a similar thread is still open where this exact question has been discussed concisely- in that case, could someone point me  to that thread?

Mixing solder is very bad (as in adding lead free on top of existing leaded solder). It will leave you with a very brittle mix of solder.  Separate solder tips are not really necessary if you clean them well and rewet with solder you are going to use. To avoid that you could have separate tips. Separate tips are also used in ROHS where there is testing that will show minutest traces of lead...

In short, simplest and best is to find leaded solder and repair leaded equipment with it.. Separate tip would be nice, but not strictly necessary if you clean them really well at change back and forth. Make note it will leave trace residue of lead on tip that can be detectable with ROHS testing, although wont make practical difference (if cleaned well).

This is "hobby" advice.  For pro use, leaded equipment should be repaired only with proper leaded formulations (as original) and new lead free with lead free. No equipment should be shared (tips, cleaners ..)

[jeremy]

I have never had a problem mixing as long as bismuth is not involved. Bismuth/Lead alloys are very soft with low melting points and you can just pull SMD parts off PCBs with tweezers in some circumstances.

I think for a hobbyist the risks are way overblown; it’s not like your equipment is going to experience large repeated shocks or heavy vibration… I’m also not convinced I have ever seen a failure due to mixing of alloys that would have not occurred with unmixed alloys (in hobbyist equipment).

[janoc]

I have never had a problem mixing as long as bismuth is not involved. Bismuth/Lead alloys are very soft with low melting points and you can just pull SMD parts off PCBs with tweezers in some circumstances.

I think for a hobbyist the risks are way overblown; it’s not like your equipment is going to experience large repeated shocks or heavy vibration… I’m also not convinced I have ever seen a failure due to mixing of alloys that would have not occurred with unmixed alloys (in hobbyist equipment).

The joint brittleness described above is a real thing - but unless the device in question is going to be exposed to vibrations (e.g. in a car or as a part of a household appliance which has a motor - washing machine or something like that), it is likely to be fine.

I am routinely doing the opposite to what the OP describes - repairing electronics that has been soldered using lead-free solder (99% of commercial stuff from the last 20 years or so) with leaded solder and never had a joint fail on me either.

Of course, it is not acceptable to do so as soon as RoHS compliance is involved or where utmost reliability is required but DIY/personal use it is fine.

[janoc]

d) yes, otherwise the the soldering tip might get damaged by solder corroding the covering layers of the tip

Given that the OP is using lead-free solder already, then they likely have a tip with the proper plating. Leaded solder won't corrode a lead-free tip, it is the lead-free solder that is known to eat tips intended for leaded for lunch because they don't have as good plating.

Having separate tips is required only if you care about RoHS compliance (not a concern for personal stuff) or must have the best possible reliability due to avoiding mixing of the alloys (probably doesn't matter for personal projects).

[Spectrum]

Using 60/40 (or 60/38/2Cu) alloy for limited repair (NOT board construction) is also allowed by RoHS regulation. In fact, you can still safely buy all the 60/40 alloy you want, if it were illegal, it wouldn't be possible. A repair is always visible compared to a virgin board.
As I think, if I have to repair joints with lead-free alloy, first I eliminate the alloy present and then I go back up with an excellent quality 60/40 alloy (STANNOL, Felder, BW Billiton,Weller etc ..).
I know repairmen who mix the two alloys to save time, but I am not.
No need to keep separate tips for the two alloys, as long as quality equipment is used. The lead-free alloy uses higher temperatures and therefore is more damaging to the life of the tips, but that's another story.

[nightfire]

Thanks for all the input so far!
In my situation, I do this as a hobby project, so my usual trustworthy suppliers that cater to private customers do not have leaded solder available.
Also I do not need big amounts of it, as the stuff I probably also will repair in the future is not very big.

From what I have read so far, I conclude:

- Repair with leaded solder is always allowed under RoHS conditions, additionally for hobby use
- Soldering tips can be kept separate for leaded and unleaded, but with good cleaning, there is no need to do so (for hobby usage)
- newer soldering tips consist of a better material to be able to keep up with unleaded solder (My soldering iron is about one year old, so no worries here)
- do not mix leaded and unleaded solder->clean the pcb after desoldering parts thouroughly, better use same solder type as the manufacturer did

Currently I am going for some smaller amounts of old solder, from what I learned from some search is that for electronics use, the flux should be of the F-32 type, because  that is essentially "no-clean". The older standard F-26 means some slight agressiveness, so that stuff requires some cleaning afterwards.
(And for the germans: The old designation of Stannol "Bastlerlot is intended rather for metalworks and has a quite aggressive flux- therefore should not be used on electronics)

[Ian.M]

Why wouldn't you use as close as you can to the same solder alloy as the original for any repair work?   While Sn/Pb based solder alloys tolerate a moderate shift in composition (due to mixing) away from the Sn63/Pb37 eutectic without gross changes in their electrical and mechanical characteristics, the same is *NOT* true of common post-ROHS Pb-free solder alloys.  As little as 0.5% Pb contamination can halve the fatigue life of the joint ([ref]).

Lets suppose you repair one joint on a post-ROHS board with Sn/Pb solder - you suck off the Pb-free alloy and remake the joint properly - or the same on a pre-ROHS board with Pb-free solder, then in the future, anyone touching up joints is likely to carry lead contamination from a Pb containing  joint to other  Pb-free joints retouched after it, leading to premature failure.

The ROHS limit is Lead (Pb): < 1000 ppm. That is a 0.1% limit on Lead concentration.

You don't *NEED*  different irons or tips for pre and post-ROHS soldering - Start with a tip that has been used for Sn/Pb solder, wipe your tip as clean as possible, and tin it generously with Pb-free solder, and you've just reduced the Pb concentration by at least a factor of ten by simple dilution.  Repeat two more times, and as long as your Pb-free solder's trace Pb content is well under the ROHS limit, your tip is certain to be under the limit as well.

Its almost always OK to simply wipe and tin twice then wipe.  You don't start from 100% lead, and the reduction per wipe/tin is usually more than a factor of ten + any traces will be further diluted in the first joint so it meets the limit.   

Going the other way is easy, wipe off the Pb-free solder, re-tin with Sn/Pb and wipe off excess solder and it will be close enough, as long as the Pb-free solder wasn't an exotic low melting point alloy.

Of course, in a commercial setting its good practice to have separate bits, and separate tools makes sense as then you can color code everything including the solder reels and avoid mix-ups, but if you have to switch from non-ROHS to ROHS compliance doing field repairs, with a limited toolkit, clean the iron properly and you will be OK as long as you have the correct solder.

[tooki]

Will Digi-Key or Mouser ship you leaded solder from USA? (I haven’t tried doing it recently, but neither website stops me from adding it to my cart.) One large roll of leaded solder and some flux would probably get you over the minimum for free shipping.

[Audiorepair]

It is not difficult to get leaded solder in Germany or most other EU countries.

https://de.farnell.com/multicore-loctite/dlmp24-250g-reel/l-tdraht-lmp-0-56mm-250g/dp/419552?ost=419552

[james_s]

I use 60/40 leaded solder for everything, it just works better and at the scale I'm working with it is no issue at all. Buy a roll, imported if you have to and you'll probably have a lifetime supply.

[Audiorepair]

https://de.farnell.com/stannol/hf32-3500-1-0mm-250g/l-tdraht-60-40-183grad-250g/dp/817612

[nightfire]

Will Digi-Key or Mouser ship you leaded solder from USA? (I haven’t tried doing it recently, but neither website stops me from adding it to my cart.) One large roll of leaded solder and some flux would probably get you over the minimum for free shipping.

Will probably give some issues at import at customs check, as I am a private user.
I remember the trouble we had as we wanted to get at my last employer a replacement for a serial console server that was not RoHS compliant and the spare part would have been needed to import in the EU from the US.... Was not nice and a bit of drama...

Anyway, a visit on ebay hopefully solved the issue, got some old stock from another hobbyist...

[tooki]

Will Digi-Key or Mouser ship you leaded solder from USA? (I haven’t tried doing it recently, but neither website stops me from adding it to my cart.) One large roll of leaded solder and some flux would probably get you over the minimum for free shipping.

Will probably give some issues at import at customs check, as I am a private user.
I remember the trouble we had as we wanted to get at my last employer a replacement for a serial console server that was not RoHS compliant and the spare part would have been needed to import in the EU from the US.... Was not nice and a bit of drama...

Anyway, a visit on ebay hopefully solved the issue, got some old stock from another hobbyist...

What customs inspection? Both of those distributors ship with customs pre-cleared.

[janoc]

It is not difficult to get leaded solder in Germany or most other EU countries.

https://de.farnell.com/multicore-loctite/dlmp24-250g-reel/l-tdraht-lmp-0-56mm-250g/dp/419552?ost=419552

Unless you are a business many distributors will not sell leaded solder to private persons. It is stupid.

[janoc]

What customs inspection? Both of those distributors ship with customs pre-cleared.

Not true, at least for Digikey. Digikey ships from the US and there is always custom clearance involved. Depending on the country you are in, you even get charged by UPS (or who they use for shipping/doing the paperwork) for the customs declaration fee, despite no customs being due. It is a royal PITA + about 20€ fee to UPS. I am avoiding Digikey for that reason.

Mouser ships from EU warehouses for most things (and indicates where the goods will come from the US/UK if that's the case) so you don't get these issues but not Digikey.

[tooki]

At work, we order from Digi-Key and Mouser regularly and never, ever run into that issue. If you’re getting charged on delivery, then you didn’t select a shipping and currency combination that produces DDP incoterms for your country.

Note that if you last ordered many years ago, it changes. Both Mouser and Digi-Key have expanded their DDP availability over the years.

You’re absolutely wrong about Mouser shipping from “EU warehouses” because, like Digi-Key, Mouser only maintains a single warehouse, and it’s in USA.

The one that works the way you describe (with both EU and US warehouses) is Farnell.

[2N3055]

At work, we order from Digi-Key and Mouser regularly and never, ever run into that issue. If you’re getting charged on delivery, then you didn’t select a shipping and currency combination that produces DDP incoterms for your country.

Note that if you last ordered many years ago, it changes. Both Mouser and Digi-Key have expanded their DDP availability over the years.

You’re absolutely wrong about Mouser shipping from “EU warehouses” because, like Digi-Key, Mouser only maintains a single warehouse, and it’s in USA.

The one that works the way you describe (with both EU and US warehouses) is Farnell.

That probably depends on the country. To Croatia, Digikey only offered Carriage Paid To (CPT) last time, a month or so ago.
That means I did have to pay customs clearing and duties..
Mouser sends DDP and it just comes to my door, but I do get EU invoice from their EU subsidiary.

Maybe Switzerland has different customs regime with USA...?

[tooki]

It definitely depends on the country, absolutely.

I don’t think it has anything to do with any customs treaties. Digi-Key and Mouser (and Farnell) have been expanding their DDP offerings over the years. At least with Digi-Key, it’s very easy to see which incoterms apply, since they’re shown in the country/currency/language switcher.

Switzerland was already DDP from Digi-Key when Swiss authorities enacted a law requiring foreign shops that sell over CHF100K/year to consumers in Switzerland to collect Swiss VAT and hand it over to the tax authority. Since they have to calculate the applicable Swiss VAT in order to collect it, and the fact that as long as no items with special customs restrictions are involved, VAT is all the delivery companies/post were collecting anyway (plus their fees for the “service”), this had the effect of eliminating many of the surprise bills, since it’s effectively requiring DDP incoterms for consumers.

[strawberry]

The joint brittleness described above is a real thing - but unless the device in question is going to be exposed to vibrations (e.g. in a car or as a part of a household appliance which has a motor - washing machine or something like that), it is likely to be fine.

case bending and thermal expansion will crack any solder on PCB

[janoc]

The joint brittleness described above is a real thing - but unless the device in question is going to be exposed to vibrations (e.g. in a car or as a part of a household appliance which has a motor - washing machine or something like that), it is likely to be fine.

case bending and thermal expansion will crack any solder on PCB

Sure, but there is a difference in how long that will take. Those mixed alloys take significantly less stress for it to happen.

[Spectrum]

That probably depends on the country. To Croatia, Digikey only offered Carriage Paid To (CPT) last time, a month or so ago.
That means I did have to pay customs clearing and duties..
Mouser sends DDP and it just comes to my door, but I do get EU invoice from their EU subsidiary.

Maybe Switzerland has different customs regime with USA...?

Wonder Croatia, Supercountry... I would like to live there

[2N3055]

That probably depends on the country. To Croatia, Digikey only offered Carriage Paid To (CPT) last time, a month or so ago.
That means I did have to pay customs clearing and duties..
Mouser sends DDP and it just comes to my door, but I do get EU invoice from their EU subsidiary.

Maybe Switzerland has different customs regime with USA...?

Wonder Croatia, Supercountry... I would like to live there

Glad you like it so much  ... But it is far from perfect when you live here....Nice nevertheless..

[Haenk]

I'd really use leaded solder for this type of repair.

60/40 is still available on ebay. Or (just a random search result): https://elw-elektronik.com/
Or Farnell: https://de.farnell.com/c/werkzeuge-werkstattbedarf/lottechnik/lotdraht-lotzinn?lotlegierung=60-40-sn-pb

[JohanH]

I've bought Cynel leaded solder on Ebay. It is Polish and good quality. Also smells good