When we switch to lead-free solder, we will have two types of soldering to re-learn - hand soldering and re-flow soldering.
I recommend reading this seven page paper on lead-free soldering by Kester.
Some points in that Kester article are:
- lead-free solder flows more slowly
- lead-free solder requires more flux
- do not mix lead-free and leaded soldering equipment
- solder iron tip temperature should be much higher for lead-free alloys.
Unfortunately, we can not use higher solder iron tip temperatures for DPCB. The DPCB conductive ink melts at a lower temperature.
Hand soldering with lead-free solder
Lead-free solder does not wet the same was as leaded solder. Tin-lead solder joints either look proper or they don't. A cold solder joint can be spotted a mile away. For those of us using tin-lead solder for ten, thirty, or fifty, years, even a perfect lead-free solder joint just does not look good. We have to adjust our perspective of what a good lead-free solder joint looks like.
Here is something that was a bit surprising to me after 48 years of soldering; do NOT wet your sponge! We all grew up using a dampened sponge to wipe the solder iron tip clean. The water did not help cleaning the tip, it just prevents the sponge from burning a bit and stinking up the place.
So we have a couple of choices; get one of those tip-cleaners made up of coiled strands of sharp-edge copper, or just get a new sponge but do not 'wet' it. I have switched to 3M Scotchbrite Heavy Duty scouring pads. The heat of the iron does not seem to bother it at all.
Pre-tinning all through-hole component leads with lead-free solder is essential.
Because soldering lead-free solder requires higher temperature than our printed conductor can withstand, copper rivets are essential for all through-hole components. We can learn to solder the leads to the rivet quickly enough to not damage the printed conductor.
Reflow soldering with lead-free solder pastes
If you are not already familiar with solder paste and re-flow soldering, I recommend that you pause here and read the Wikipedia article on solder paste.