Joe,

I will respond to your points in the order in which you raise them.

1.  Paper phenolic laminates

The answer to your question is that boards constructed with these laminates
are being soldered with the stabilised Sn-0.7Cu solder.

One of the driving force for the adoption of leadfree solders by the Japanese
industry has been the legislation on recycling of domestic appliances.   The
need for products like these to be very cost competitive means that at far as
possible lower cost board materials are used for the electronics in these
products.   Thus probably the majority of the circuitry soldered with the
stabilised Sn-0.7Cu eutectic so far has been on these cheaper types of
laminate.    Obviously your concern is about thermal degradation of such
laminates with higher preheats, soldering temperatures and contact times.  As
it turns out, however, these less heat tolerant materials tend to be used
mainly for single sided boards.  Because there is not the need to fill plated
through holes, preheats need not be as high nor contact times as long as with
plated through hole boards.   The experience is therefore that these cheaper
laminates survive leadfree soldering without degradation that affects service
reliability.   Solder bath temperatures above 255C (490F) are usually not
required.  And the preheat for a single sided board need be only about 100C
(212F) topside.     The plated through hole boards that do require a bit more
preheat and contact time to get a hole fill are usually made of materials
that can better tolerate these conditions.

2.  Cost

There are additional costs associated with going to leadfree soldering, just
as there have been costs associated with any of the changes in manufacturing
technology the electronics industry has had to accommodate.    That increase
in costs is, of course, one of the factors that has prompted the vigorous and
very appropriate discussion in this forum about the merits or otherwise of
changing to leadfree.   As someone representing the supplier side of the
industry it is not appropriate for me to enter into the debate on whether or
not the industry should incur the costs involved in moving to leadfree.   A
supplier's role can be only to provide service to their customers.   All that
the suppliers have been trying to do is to prepare to meet the needs of their
customers for product and technical support IF it turns out that they do need
to go to leadfree soldering.

For a start the cost of all leadfree solders must reflects the higher tin
content.   You are replacing the 37% of relatively cheap lead in the
conventional solders with more expensive tin and some other elements all of
which are more expensive than lead.  And, at this stage in the introduction
of leadfree, suppliers have to look for some return on the massive investment
they have made over the past decade in developing suitable materials and
processes so that they will be ready should their customers need to change.

On top of that those converting to leadfree may in some cases need to upgrade
or even replace equipment.   Wave soldering machines running with the
Sn-0.7Cu solder need plenty of preheat capacity and good control of process
parameters such as temperatures and conveyor speed.    Probably most of the
machines installed at the moment already meet those requirements but if they
do not then an upgrade will be required.    The main requirement for reflow
ovens for the higher melting point leadfree alloys such as the Sn-Ag-Cu
ternary eutectic is plenty of heat capacity, temperature gradients as flat as
possible, which probably means forced convection, and enough zones that at
least two can be spared for the reflow stage.   Again, many companies already
have this sort of reflow oven installed but if not they might be looking at
an upgrade.

I do not think that anyone is trying to pretend that the move to leadfree, if
it occurs, will be made as a cost saving exercise.    In some countries the
move will be in response to legislation.   In the US, however, it will
probably be a marketing decision arising from a judgement on the perceived
value to the company of being able to promote a "clean green" image.

3.   Operating Costs

Because even the most advanced users of leadfree soldering are still in a
relatively early part of the learning curve it is difficult to get an
estimate of operating costs.
Apart from any amortisation of the capital costs of any equipment upgrades
required the main additional operating cost is likely to be the higher cost
of the solder.   There may be a small increase in power usage associated with
higher heat inputs required.  After process and design optimisation
production yields are close to those obtained with conventional Sn-Pb solder.

4.   Dross production

Drossing characteristics are one of the factors that needs to be taken into
account when selecting a leadfree solder for wave soldering.   Elements in
some of the leadfree solders being promoted increase dross production.
Users report that the stabilised Sn-0.7Cu eutectic with which Nihon Superior
has most experience actually has a slightly lower drossing rate that than
63/37 Sn-Pb solder and the dross tends to be "drier", i.e. with less
entrained solder.    Data collected for one line that was converted from
63/37 Sn/Pb to the stabilised Sn-0.7Cu eutectic was that, following normal
dedrossing procedures, about 1.0kg/8 hour shift was collected from the
stabilised Sn-0.7Cu solder compared with about 1.5kg/8 hour shift for 63/37.
  These results are for a dual wave machine operating at 255C operating in
air.

5.  Pot life

You have hit on a very important point in the selection of leadfree alloys
for wave soldering.

The rate at which copper is picked up from the boards and components soldered
depends to some extent on the content of copper and other elements in the
leadfree alloy used.   The copper content of alloys with a lower copper
content tends to rise fairly quickly so that the alloy is soon out of
specification and the pot needs to be replaced.     The rate of copper pick
up by the Sn-0.7Cu eutectic is lower than that for alloys with a lower copper
content.   And being essentially a binary alloy it is fairly easy to keep the
bath composition in balance.  There are solder pots running with the Nihon
Superior stabilised Sn-Cu eutectic alloy that have been in commercial
three-shift operation for some two years without the need for replacement of
the solder and the indications are that with proper management they will
continue to operate in this way indefinitely.    In theory this maintenance
of the composition of the solder in the pot is possible with all leadfree
solders but for those with more than two critical constituents it starts to
become difficult to manage in practice and more frequent pot changes seem to
be required.

Of course the pot life is affected by the pick up of other elements.  At this
stage in the process of conversion to leadfree many of the components that
have to be soldered still have lead-containing solderable finishes so that
there is pick-up of lead.    Simple calculations show that an impurity in a
solder bath reaches an equilibrium level when the rate at which it is being
picked up from the work being soldered is just balanced by the rate at which
it is being carried out of the bath in the solder on the joints and in the
dross skimmings.  The capacity of the bath will determine how long it takes
to get to that equilibrium level but not the actual level.   If you are lucky
the equilibrium level is less than the level at which the impurity causes a
significant deterioration in joint quality.   The tolerance of impurities
like lead is therefore another consideration in selecting a leadfree alloy
for wave soldering.  For some there is significant deterioration of joint
properties at quite low levels of lead contamination.    Our experience is
that the Sn-0.7Cu eutectic can tolerate levels of lead contamination higher
than the equilibrium level usually reached with the current mix of component
finishes so that pot life is not detrimentally affected.    Of course each
case has to be assessed and the normal practice when commissioning a leadfree
line is to undertake frequent analysis of the solder in the pot over the
first few month to determine what the trends in contamination are.


Sorry about the length of this e-mail but you raised some important points.

Regards
Keith Sweatman
Nihon Superior Co Ltd

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