Learn to solder again – part 2

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.


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