Lead Free Solder – Some of it’s Characteristics and Problems and How to Deal With Them – RoHS

Since the RoHS legislation came into force in Europe the nature of electronics manufacturing, and soldering in particular has changed forever. RoHS compliance and lead free solder presents many new challenges to businesses involved in pcb manufacturing.

No-one seriously disputes that lead free solder is healthier for everyone involved in pcb assembly, but unleaded solder does present certain problems. Lead free solder does not flow as easily as leaded solder and the soldered joints on a pcb board look different on a leaded board, when compared to a board built using lead free solder.

The first thing you will notice is the lack of top fill on your through-plated pcb boards. It is rare to get more than a 75% fill on your pcb boards.

The second thing you will notice is that your lead free solder joints are not as shiny as the old style leaded joints that you will have been used to. This is simply down to the actual mix of lead free solder and should not be a cause for undue concern.

Does lead free solder melt at the same temperature as leaded solder?

No! Unleaded solder will melt at a higher temperature, the exact temperature will vary depending on the solder mix you choose to use. One common mix is 99% Tin, Copper 0.7%, and Silver 0.3%. This melts and flows without much difficulty at 275 degrees.

Preparing to use lead free solder for the first time.

Who has to use unleaded solder?

Almost all electronics assembly will have to be done using lead free processes. (See my article on RoHS compliance for more details).

What about soldering equipment?

It is very likely that most of your soldering equipment will need either replacement or adjustment to prepare it for lead free service.

At the very least your soldering irons will require new tips to avoid contamination issues, and you may find that you need to replace the entire soldering iron if you find it has trouble reaching the new higher temperature that is required for lead free soldering.

Bigger soldering equipment such as a wave soldering machine will probably need to have their soldering baths replaced and you may want to consider replacing the flux you use, as the pcb boards that you will now be soldering will be lead free as well.

Solder pots and other hand operated solder equipment can either have their baths replaced, or for a cheaper option you could try emptying them of solder, cleaning the bath, and coating it with a layer of oxide paint. Once it is dry you can fill your bath with new lead free solder and you are ready to start soldering again.