[sdiy] stupid solder

[Tony Clark]

> So if I use lead-free solder with PCBs that has been plated with
> regular solder, I'm making things worse by mixing 2 types?

   Possibly.  There are, of course two areas where you do need to be 
concerned.  One would be the PCB, the second would be the components.  
Depending on what processes your board house is using, your PCB may in 
fact already be lead-free.  There are two widely used plating methods 
for PCB, one is tin-lead, the other is just tin.
   For SMOBC (soldermask over bare copper) processes, it is most likely 
that you will get a tin plate, but not necessarily.  You should ask and 
see what processes your board house is using and/or what processes are 
available to you upon request.
   If they do not do pure tin reflow, you could request that you get bare 
copper pads on your boards, but that may be more difficult to deal with 
since oxidation will most definately rear its ugly head!
   As for components, most are probably lead-free, especially in the SMT 
arena (which I know you're into).  It's mostly axial-leaded parts that 
may still use tin-lead mixtures.

> __reflow, which is a controlled temperature environment, 
> __something that's 
> __not achievable with a soldering-iron!  So it is quite 
> 
> how about hot-air soldering iron? Will it make better results?

   Possibly.  However, as I mentioned before, ideally you need to setup a 
temperature "profile", which includes a pre-warming period followed by 
reflow, followed by a cool-down.  Possibly this would be easier to 
achieve with a hot-air iron as you can easily adjust the temperature by 
controlling the distance of the iron.

> I've seen many times solder points broken in car radios due
> to vibrations.
> But I doubt I'll ever make modular for cars (don't even have a car) :)

   Yep, I've seen it too.  And in most cases, the joints didn't look well 
to begin with (and I'm pretty sure that they aren't using lead-free!).  I 
had to repair a power-amp once where a whole Molex connector came 
completely free!

> __in seconds as with soldering irons!  So the most likely 
> __problem is that 
> __your solder joints are cooling too quickly.  You might try 
> 
> well... the best (most shiny, or rather the least matt) results I got
> at super-quick soldering, when I heated the pad, and component
> lead (how do you call a "lead" of leadless component?) for couple
> of seconds, then apply solder and runaway with the iron.
> I mean, solder is melt only for really short moment, maybe fraction
> of a second.

   Right, well you've got the trick there, to pre-heat the pad and lead 
before applying the solder.  Even in reflow ovens, the actual reflow 
period is relatively short compared to the overall time the board is in 
the oven.
   I don't know what your soldering iron is, but typical ones we use here 
at work aren't variable temperature.  The tips are rated at 700F (371C) 
which is WAY higher than in reflow ovens 230C (446F) tin-lead or 270C 
(518C) for lead-free.  Much better would be to use a setting around 500F 
for tin-lead and 600F (315C) for lead-free, but you'll definately need to 
preheat the board first, especially if you have any thermal-relief pads 
on the PCB!

> I tried also flooding everything in resin flux, but it didn't prove
> to be usefull.

   Resin probably isn't aggressive enough for lead-free.  Most likely you 
should switch to a water-soluable organic flux.

   Cheers,

   Tony

-----------------------------------------------------------------------
         The E-Music DIY Archive - New Site Coming Soon!
-----------------------------------------------------------------------

"We wouldn't want to ship something that doesn't work"
   - Carl Stork, general manager, Microsoft Windows division
     Excerpt from EE Times April 2, 2001