Can you use Pb-Sn solder on PCBs w/Pb-free tinned pads?

[Syntax_Error]

As the title asks, "Can I use standard lead-tin solder with PCBs that come with pads tinned with lead-free solder?

[ales22]

Pb solder + Pb-free components, boards etc.: yes
Pb-free solder + Pb components... : no  perhaps yes, if you avoid some types of solder and it's hobby project. (e.g. SAC alloys should be ok, according to Kester's FAQ webpage.)
The reason should be, that common   some Pb-free solder is very sensitive to lead contamination and it may become brittle and eventually develop some defects. That's what I read somewhere.

EDIT: According to blueskull's post, only alloys containing bismuth are sensitive to Pb contamination. Also, as Dave (EEVBlog #180) and others say, don't bother with Pb-free soldering if you don't have to.

[Ian.M]

Apart from the smallest joints, its more a matter of regulatory approval, and for lab work and personal use, that's not really an issue.  I certainly wouldn't risk it for applications in high reliability industries, but a carefully hand-soldered Pb-free joint to a factory SnPb tinned component lead that didn't have any gobs of excess solder on it isn't going to be a problem.

[Syntax_Error]

Thank you both for your responses. My use is hobby/single design. The PCB manufacturer tins the pads w/Pb-free solder as a standard option, and my solder is standard 63/37 solder. I was worried I had a problem on my hands.

Thanks again.

[T3sl4co1l]

Pb-free solder + Pb components... : no
The reason should be, that common Pb-free solder is very sensitive to lead contamination and it may become brittle and eventually develop some defects. That's what I read somewhere.

I think it's okay with a tinge of Pb, actually.  References say >3% Pb stabilizes solder and platings against tin whiskers.  The main disadvantage would be a matte deposit from the wider "mushy" range (= don't nudge it while it's cooling, or you're much more likely to get a cold solder joint!).  I haven't heard of mechanical problems with oddball alloys like this -- but you tend to avoid them because they don't make good solder. 

A good solder solidifies all at once, as much as possible.  This is done by choosing a eutectic alloy: the lowest melting point composition, which is just enough of A and B that they effectively dissolve each other / precipitate at the same time.  Which leaves very little time for crystallization, so it freezes with a shiny finish, and instantly gains mechanical stability and strength.  The choice of eutectic, or nearly pure enough base metals that they still freeze quickly, tends to constrain the number of alloys that are best for soldering.  Example: tin-bismuth would seem an ideal replacement for tin-lead, but has much too low a melting point to be practical.

Tim