January 24,
2007
Problems
with Lead-free Manufacturing are Getting Solved
Manufacturers
in the electronics industry have struggled with the conversion to lead-free
components, but some of these problems are finally getting solved. Finding
lead-free components is easy enough now, since component manufacturers were
quick to convert in time for the July 2006 European Union RoHS deadline. The
problems that remain have to do with those companies in the aerospace, defense
and medical device industries that are exempt from RoHS laws. Many of those
companies now find that it’s difficult to get leaded parts, so they are forced
in many instances to begin using leaded versions of components.
The
problem could be solved to some degree if the exempt manufacturers switched
over to lead-free parts and crossed their fingers that there would not be any
reliability problems – such as tin whisker growth – with the lead-free parts.
But the situation is further complicated by the fact that some of the parts
these companies work with are lead-free, while others contain lead. That can
cause problems during the manufacturing process since the reflow temperature of
solder for leaded parts is different from the reflow temperature for lead-free
parts.
This
problem of mixed parts is further complicated by the fact that many component
manufacturers did not change part numbers when they switched from leaded parts
to lead-free parts. Instead of issuing new part numbers, about 30 percent of
component manufacturers simply noted the switch from leaded to lead-free by
manufacturing lot number or date. Thus, in order for product manufacturers to
know if the part is leaded or lead-free, they have to know what lot number or
date indicates a change from leaded to lead-free. When you have hundreds – even
thousands – of parts in your product, checking each individual component for
its leaded or lead-free status is no small undertaking. This problem is not
isolated to the exempt manufacturers. Plus, all manufacturers now – exempt or
not – have to determine the exact status of subassemblies as well as checking
each individual part.
There are two solutions that have arrived
to help manufacturers through the thorny problems with manufacturing that
involves both leaded and lead-free parts and sub-assemblies. For one, The
International Electronics Manufacturing Initiative (iNEMI) has formed a group
of industry engineers to propose solutions. The High-Reliability RoHS Task
Force has recently published guidelines regarding assembly processes and
reliability requirements for RoHS subassembly modules. On the solder reflow
problem, the Flomerics Group in the UK has released a Flo/PCB thermal
simulation software which is designed to help solve thermal problems in reflow
processing associated with the use of lead-free solders.
iNEMI’s
concern is that subassemblies such as hard disk drives and power modules may or
may not be lead-free and thus they might not be compatible with the products
they are used in. “It is very likely that manufacturers will use subassemblies
that contain both tin-lead and lead-free components, which causes reliability
concerns due to the differences in processing temperatures and materials,” says
Thilo Sack, principle engineer, corporate technology for Celestica Inc. and
co-chair of the High-Reliability RoHS Task Force. “It is the task force’s
position that if RoHS6 subassemblies are to be used in RoHS5 products, the
RoHS6 subassemblies should be thoroughly qualified to ensure that they will
meet the higher reliability requirements of the RoHS5 products.”
The
task force have produced guidelines to help manufacturers through the confusing
manufacturing problems that appeared when lead-free components and
subassemblies came to market. The guidelines include specific suggestions such
as “Lead-free finishes on leaded and discrete components should only be used
when these finishes include suitable tin whisker mitigation practices as
defined in the IPC/Joint Electron Device Engineering Council (JEDEC) joint
publications JP002.” The guidelines are available for download at
http://thor.inemi.org/webdownload/projects/ese/High-Reliability_RoHS/High_Rel_position_061206.pdf
The
Flomerics Flo/PCB software simulates the reflow process in manufacturing and
predicts the temperatures at any point in the printed circuit board during the
entire reflow process. This is designed to make it possible to optimize oven
settings and thermocouple attachment points prior to a physical profiling run.
It is also designed to allow board designers to investigate the effects of
component layout on the solder ability of the PCB assembly. Design engineers
can use the simulation to evaluate the thermal gradients generated by different
component layouts at an early stage in the design process when changes can be
made inexpensively.
Visit SourceESB.com for all your sourcing needs.
We would like to hear from
you. Please e-mail article feedback or
comments to esbideas@SourceESB.com