Lead Free Solder

So, you’re wondering if lead-free solder would be the best choice for your project. You want to be environmentally friendly and think using lead-free solder would be a big help.  Woe is to the technician that loves the lead-free realm!  Let’s take a closer look and I’ll explain why lead-free isn’t all that it’s cracked up to be in the world of electronics.

First of all, lead-free solder was not the idea of any technician that I know, have known, or have heard of in my thirty years in the electronics industry.  The European Union Electrical Waste and Electronic Equipment, or (WEEE), “yes, it has that acronym”, and Restriction of Hazardous Substances Directive or (RoHS), came into effect prohibiting the inclusion of large quantities of lead in almost all consumer electronics produced in Europe. 

 

Most manufacturers in the U.S. still use tin/lead solder.  Some may receive a tax break if they reduce the lead content in their formulations. 

Lead-free solders on the commercial market may contain some amount of tin, copper, silver, bismuth, indium, zinc, antimony, and small amounts of other trace metals.

Most lead-free solders have a much higher melting point than conventional lead based solders with tin.   The temperature difference may be as much as 20 degrees Celsius higher in some formulations. 

Lead-free solder poses a unique challenge to the technician or manufacturer of electronic components when using lead-free solder.  Solder pots and wave soldering machines must remain completely free of any tin/lead solder due to the contamination that the lead will introduce to the lead-free environment.  Solder pots can literally blow out their sides when tin/lead and lead-free solders are mixed.

When using lead-free solder you may notice that the resulting joint does not display a shiny appearance as the tin/lead solder will.  You should observe a dull, grainy appearance after the joint has cooled and has been cleaned.  This is normal in lead-free soldering.  When using lead-free solder the solder tip must remain completely clean and uncontaminated from any tin/lead solder.  A small amount of lead-free solder must be placed on the unused tip to reduce extreme oxidation caused by the lack of lead in the solder.

Example of a lead-free soldered joint

Tin/lead solders were initially introduced to help prevent the effects of “whiskering”.  This is a phenomenon caused by the tin in the solder.  Tin will actually grow tiny fine little whiskers over time if left unchecked and can cause short circuits in electronics.  Lead-free solders have this potential for causing whiskering.  Shown below is an example of this phenomenon under a microscope magnified many times.

Lead-Free solder whiskering

I prefer to stick with my tried and true tin/lead solder.  Unless you decide to move to Europe in the near future, I recommend that you stick with standard solder and leave worrying about the environment to the solder illiterate out there in the world.  They may never know what we go through to ensure their electronics function properly the first time and continue to function for many years.

Lead-free solder is a fine concept.  However, in actual applications it’s not as reliable as we would like it to be.  Lead-free soldered joints have a tendency to crack under stress and loads.  They don’t provide high reliability in most aviation and medical applications either.  That’s why we use tin/lead formulations in most of our electronics in the U.S. and other non RoHS compliant nations. 

But, if you’re dead-set on using lead-free solder in your own applications, I highly recommend that you do thorough research and get trained up on how to use this solder the correct way.  Mixing your lead-free solder with tin/lead solder on a circuit board may have unwarranted effects in the long run. 

Shown below is an example of the differences between tin/lead and lead free.  You will notice that the joint on the left is shiny and smooth while the one on the right is dull and grainy.  The shiny one is tin/lead and the dull one is obviously lead-free.  

Comparison of tin/lead to lead-free

  

If you mix lead-free with tin/lead solder you may cause more damage soldering the components to the board than the initial damage that caused you to rework the circuits in the first place.

Take care and good luck on your lead-free journey if you so choose this dangerous and windy path.