Lead-Free or not to be, that is the question.
By Dave Corey
The Hot Air Solder Leveling (HASL) process has
been the preferred coating procedure utilized by
the Printed Circuit Board (PCB) Industry for the
past 25 years. With new regulations for the
elimination of lead from solder, the HASL
process has not lost its popularity or
feasibility and still remains the preferred
coating of PCB manufactures worldwide. With the
electroless nickel/gold process having a less
desirable solderability of components and silver
process having an additional decrease in shelf
life, the new lead-free HASL process is now a
viable lead-free alternative.
With that being said, HASL equipment and alloy
manufacturers have been on the move developing
lead-free products to work with the impending
lead-free requirements. Currently, due to the
lack of installed lead-free HASL systems in the
field, there has been a great deal of
speculation regarding the new lead-free HASL
process. We just dont have enough data yet. As
of November 2004, a handful of PCB manufacturers
located in Texas have taken the necessary steps
to convert their process to the new lead-free
alloy and HASL System. In addition, a few of
these fabricators have kept their tin-lead HASL
systems in operation in order to provide both
finishes for now.
ACS would like to commend these fabricators for
having the valor to take the necessary proactive
steps. Their actions will not only better
themselves, but will also benefit the PCB
industry as a whole. Up until now, we havent
had any factual data to support or dispel past
or present speculation of the burning question:
Will lead-free work? The results these
fabricators have experienced with the lead-free
process have been very encouraging and
promising.
The two most Frequently Asked Questions here at
ACS are:
Q: Can it be done and are their any current
acceptable lead-free alloys available to the
industry today?
A: Absolutely! ACS has investigated a variety of
lead-free alloy manufactures, in addition to,
the different versions of lead-free alloy
available. The two major lead-free alloys are
tin-nickel-copper (Sn-Ni-Cu) and
tin-silver-copper (Sn-Ag-Cu). Upon completion of
our investigation,
ACS decision was to work closely with the Nihon
Superior SN100CL tin-nickel-copper (Sn-Ni-Cu)
lead-free alloy in concurrence with the
Lantronic Model TT30 Lead-Free HASL System. To
this date, all installations conducted by ACS
have been with the Nihon Superior SN100CL
lead-free alloy. The lead-free installations
have been very successful and concluded with a
smooth, trouble-free transition with very little
interruption in production.
Q: What about thermal shock, delamination, and
Z-axis expansion?
A: With the newly designed solder pot of the
Lantronic Model TT30 Lead-Free System, ACS was
able to successfully run a solder pot
temperature of 495ºF. The solder pot is
designed to generate a significant amount of
solder flow which eliminates the need to double
cycle every PCB, unlike other competitive
lead-free HASL systems. In addition, Lantronic
has specially designed their LanTroFlow
heating system which provides a steady flow of
heated air to the air knives. The LanTroFlow
heating system gives fabricators the ability to
run a consistent air knife temperature of 500°F.
When working with the eutectic 63% - 37%
tin-lead (Sn-Pb) HASL alloy, the standard solder
pot temperature of the Model TT30 is 485ºF. As
previously mentioned, with the Nihon Superior
SN100CL lead-free alloy, fabricators are able to
run a solder pot temperature of 495º F, this 10º
increase in solder pot temperature is minimal.
The aforementioned fabricators have not
experienced any issues with thermal shock,
delamination, or Z-axis expansion to date.
To everyones surprise the surface finish was
comparable. You could not tell the difference
between the tin-lead and lead-free alloy. The
finish is very similar to that of eutectic 63% -
37% tin-lead (Sn-Pb) alloy. The other surprise
and advantage of the Nihon Superior SN100CL
lead-free alloy was the flow characteristics,
through-hole clearance, the uniformity and
flatness of the cooper pads as well as the
overall smooth shiny finish. In addition,
exceptional solderability in assembly has been
achieved. Copper leaching and extraction of
copper from the solder pot is still under
evaluation as well as XRF measurements. ACS will
keep you posted.
Conclusion
Time is of the essence, and procrastinating
until the last minute can lead to playing catch
up or even loss of work to your competition. As
we move ahead into the next generation of HASL
finishes, be confident in knowing that the
transition is brief and undisruptive. Your
current pre-clean and fluxing applications need
no modifications. ACS is available to assist you
with this procedure. As previously mentioned,
with the lead-free deadline now in place, PCB
manufactures must embark on the necessary steps
to convert their existing HASL systems from the
current eutectic 63% - 37% tin-lead (Sn-Pb) HASL
alloy, to the new lead-free (Sn-Ni-Cu) HASL
alloy.
ACS can be reach at 479-846-2403 or visit their
Web site at
www.acs-tech.com - click on Lantronic logo
for HASL info. |