July 2006
saw the introduction of the Lead Free directive. Which came 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
OSP 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
some
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. Some excellent photos of tin whiskers and a great deal of
detailed information can be found on the
NASA
web site.
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
The UK DTI have now produced a
very informative document can be downloaded from the DTI website.
RoHS_Regs_Draft_Guidance.pdf
The main section of the DTI
website dealing with RoHS Regulations can be found at
Other sites well worth a look at are;
Push Back
If you have any questions please
feel free to consult us on Lead Free issues.
