Test for Pb or Pb-free?

[glebert]

Anyone have a simple test they use to see if an amp was made with lead or lead-free solder? If I'm reflowing solder joints and want to add a little solder I really don't want to make the joint worse by mixing types. I've tried using temperature to tell, setting my iron to a temp that will melt my lead solder but not my lead-free but I don't know if that is a great way or not. I've heard that PCB marking such as ROHS (or lack thereof) really isn't indicative either way.

Thanks.
Greg

[mozz]

What year? They make swabs to check for lead. Anyways it won't matter if you mix it. Lead free sucks.

[glebert]

What year? They make swabs to check for lead. Anyways it won't matter if you mix it. Lead free sucks.

Right now I'm working on a '99 SVT CL (made in USA by SLM) and I've heard that the PCB connectors on these should get reflowed when you have them open. Really don't want to have to take this apart too many times...

[Enzo]

Mixing is not a problem.

[glebert]

Cool, thanks for the info guys. I guess I was misinformed on mixing solders.

[Enzo]

Lead free is mainly tin, lead solder is lead and tin.

[Mick Bailey]

I've never found there's a problem myself, but mixing results in a mystery alloy with undefined properties. I will sometimes remove any existing unleaded solder before resoldering a joint with leaded solder. For warranty repairs and critical applications (none of them audio related) though I use like for like. Remember when Tek scopes came with a little roll of silver-alloy solder inside for resoldering the DC restorer? If you resoldered it with regular leaded solder they said the joint would fail.

[Helmholtz]

Remember when Tek scopes came with a little roll of silver-alloy solder inside for resoldering the DC restorer? If you resoldered it with regular leaded solder they said the joint would fail.

I think the reason was the silver plated porcelain terminal strips. Regular solder would dissolve the silver plating and leave the bare porcelain, where nothing would attach to.
So it required a solder alloy with a saturated silver content.

[The Dude]

I agree with the above. I have no problem touching up lead free solder joints with the good ol' stuff. You can usually tell by eye when something is soldered with lead free solder. The joints are dull looking.

[pdf64]

My understanding is that in the UK and EU, it's a criminal offence to ‘contaminate’ lead free products by the use of leaded solder for repairs, or even to use a soldering iron bit that had previously been used with leaded solder.
High risk sectors are exempt though, eg nuclear, military, aerospace.

[Enzo]

Fortunately here in the USA lead solder is still OK.

[The Dude]

You certainly wouldn't want a visit from the solder police!

[tedmich]

to actually test 3M LeadCheck should work on solder FYI

[Jon Snell]

SMD lead free components use tin to connect the contacts to the silica substrate.
Lead will and does leach the tin away from the substrate making a possibly unstable component afterwards. I have had many PCBoards sent to me from other repair shops with unknown intermittant faults and have 95% of the time, traced the fault to poor components because of 60/40 leaded soldering.

Man made faults are the worst kind!
That is why I use lead free solders on lead free boards.

There is no issue with lead free solder if you use the correct soldering iron/hot air/IR rework station.
The issue comes when the sodering iron bit is too cold so the flux burns away too soon, making a dull cracked joint. Temperature is paramount!

Whoops typo corrected ...

[Mick Bailey]

SMD lead free components use tin to connect the contacts to the silica substrate.

Silver is also used, which embrittles the joint when using a regular lead/tin alloy. I'm suspicious of the contraction forces with SMD led-free reworking if an incompatible solder alloy is used - there's no 'give' as with a regular component lead. Joint contraction tearing used to be common in years ago anyhow with SMD/unleaded solder and caused a lot of subsequent failures, though techniques and alloys are better nowadays.

It's often not possible for the average engineer to know what alloy has been originally used anyhow and there are so many different unleaded alloys that reworking will almost certainly result in an indeterminate alloy being formed that has unknown properties. That's why the companies that do accredited and traceable repairs use XRF to determine the solder composition and match the correct solder alloy to the job and can certify the repair. In many ways (other than ROHS legislation) contaminating an unleaded joint with a different unleaded alloy is as bad as contaminating it with a lead/tin or lead/tin/silver alloy.