July 2006 will see the
introduction of the Lead Free directive. Which comes into play under the
new RoHS Restriction of Hazardous Substances Directive.
Quite where it will all end up is still a big
puzzle some large users are successfully making the change, but it's anyone's
guess as to what we will all end up using. Little doubt that Lead is hazardous
in the wrong places, but questions remain as to whether circuit boards
are the wrong place. Lets hope that its replacement is less toxic and
can be proved to work reliably.
We noticed with great interest that some of the
early companies that changed over to an almost pure tin solder, have
suffered irreparable damage to their plant. It appears that once
stainless steel has lost its protective oxide film, molten tin readily dissolves
it.
As a PCB manufacturer Lead free isn't a big
problem, tin, gold, silver, and organic finishes all comply. The
downside is mainly on the assembly side, as tin lead HASL finish
was a very good all rounder. It gave boards a good shelf life followed
by problem free assemble and a long joint life for the components. Thick
tin along with silver were rejected years ago because of high risk of
the metal migrating across the circuit board, creating metal shorts. All
that's required is a little moisture combined with electricity and the
fun begins. Thin silver, gold, and tin along with organic coating all
have short shelf lives and quickly become difficult to solder. Most
boards can stripped and reworked so it's not all bad.
The IPC have a Lead Free Forum that's starting
to get some input, if you are after more information its well worth a
look and can be found at;
www.ipc.org
Other sites worth a look at are;
www.lead-free.org/
and www.smartgroup.org/
If you have any questions please
feel free to consult us on Lead Free issues, it coming fast and looks
like it's here to stay.
