Article as seen in
Circuitree Magazine, July 1996, by John S. Eddy, President and
Co-founder of Eddy Electronics Mfg. Ltd.
With environmental
concerns and increasing regulations on industrial pollution, lead
is looming large as a major problem for the PCB and electronics
industry.
Environmental problems
are compounded by widely differing and uneven environmental
regulations and practices across the globe that have led to
political and financial obstacles for our industry.
Most PCB manufacturers
live with some fear that the consequences of these practices could
overtake them suddenly in some change in law or environmental
policy.
As a conscientious
industry in the developed world, PCB manufacturers are already
pursuing ways to reduce lead consumption in our industry and with
the threat of unfair offshore competition, it is of even greater
concern. If lead in electronic products can be reduced, we can
also reduce the threat of lost contracts, jobs, and
competitiveness. If lead consumption is to be reduced, PCB
manufacturers can benefit the most by leading the way.
There has been much
development in lead free solders and interconnects. Conductive ink
has been promoted for years but has failed to gain broad
acceptance, especially as a replacement for copper traces. Indium
solders show great promise but are very costly. Tin-bismuth
solders are considered safe but oxidize easily and lack ductility.
Even if there is no immediate replacement for tin-lead solder,
there is considerable interest in replacing it. Wave solder
machines, their fumes and waste materials are considered health
and safety hazards.
Perhaps the greater
impact on the consumption of lead is not in the soldered
connections, but rather in the printed circuit itself. The
processes required for putting lead on the printed circuits are
inefficient and, in themselves, present occupational hazard and
waste treatment problems that are out of all proportion to any
value they add.
A promising new
development now exists in Canada where Eddy electronics Mfg. Ltd
has developed a manufacturing process which is lead-free. Standard
and non-value adding process steps have been abandoned and only
simpler and cleaner steps are in place.
Manufacturing starts
in a very conventional way with the normal drilling and
electroless copper. Then, Eddy Electronics panel plates the copper
to the specified thickness in a pyrophosphate bath. Pyrophosphate
is preferred for its ductility and strength. Lamination and
imaging follow to produce a "tent and etch" bare copper printed
circuit. The last wet process step is an efficient immersion
silver bath which is self regulating and produces a layer 2-4
microns thick. Solder mask and overlay are of course normal, and
the silver provides excellent adhesion with a low profile relative
to solder plated PCBs.
The cost of waste
management is far less in the absence of lead. Hot Air Solder
Leveling, once favored for low solder profile and relative
cleanliness, has been identified by the October Project consortium
as a process to be eliminated.
This process offers
other advantages including: Copper bearing waste is free of lead
and recycling can proceed on-site at a PCB plant. Phototool film
with its silver emulsion can be used as a valuable resource rather
than a waste treatment problem.
High quality PCBs are
manufactured with this process that are comparable to common SMOBC
types with the added benefit of wide design latitude. Very fine
features and very large copper areas can be manufactured reliably
with no concern for plating densities or warpage. Eddy Electronics
has manufactured PCBs with .003 lines and .004 spaces.
As the only solder on
the finished product is applied by the assembler, many different
combinations of solder or conductive ink may be used. Tin-lead
solder may also be used. The low profile nature of the product
allows accurate placement of solder pastes for SMD applications.
Eddy Electronics'
product is a little different but has been gaining acceptance in
local and export markets for more than ten years. Many similar
approaches to the same end exist and are under development.
Organic coatings, like Entech, and various electroless and
immersion coatings have emerged over the past few years. With
future environmental sensibilities, acceptance of all of these
approaches are likely to grow.
A lead-free printed
circuit allows manufacturers to choose solders or bonding systems
according to their own criteria and makes a lead free electronic
product a viable option. Even if lead free is not the way they
choose to go, the benefits ot PCB fabricators can hardly be
ignored.
