Forum on reliability for Pb-free electronics
Werner Engelmaier
“I recently participated in a very focused forum on the reliability issues in electronic assemblies
resulting from the RoHS Pb-ban.”
Forum on reliability for
Pb-free electronics
In my past columns on reliability I always knowing each other much beforehand, the materials become available, e.g. higher heat
concentrated on essentially pure technical aim was here to bring together more dif- resistant laminates, better Pb-free solders,
contents. This column is somewhat of a ferent departments from each company, to etc., new questions arise. First, the PCB
deviation from that past. limit the total number of participants and to production process needs to be matched
I recently participated in a very focused match companies with similar interests but to these, and as always, if you want to buy
forum on the reliability issues in electronic no competition conflicts. The aim was to something, you have to pay for it. New specs
assemblies resulting from the RoHS Pb-ban. bring R&D together with production tech- and requirements need to be added, while
This forum, actually two forums in the nology as well as purchasing. Just imagine with some of these we open a can of worms,
south and north of Germany, organized un- the upcoming discussions about balancing e.g. higher tool costs due to increased drill
der the auspices of the Fraunhofer Institute material quality, cost and influence on assem- wearout with high Tg materials.
by Thomas Ahrens, included an expert-quar- bly quality and reliability. The purely statistical approach, a la
tet of four experts in the field of reliability From the researcher’s point of view, the MIL-HDBK-217, enables us to describe the
but coming to it from different directions. questions raised were to the point, showing principles of reliability but fails at modern
The forum participants came from the that even from a profound background we requirements of “ppm defect rates over
automotive, aerospace and military indus- lack common knowledge and experience lifetime” when the numbers of devices to be
tries, all industries with extended lifetime about materials properties in the lead-free tested become large.
expectations mostly in harsh environments. electronics era; at the moment we are just Therefore, the current approach to
While this forum was held in two different beginning to gather and interpret research reliability is that of addressing the physics-
locations with similar programs, in both results and field experience, as lead-free and of-failure by increased measurement and
cases these mentioned application categories RoHS compliant products grow into and analysis efforts, addressing load and damage
were present. Contrary to other reliability within the market. mechanisms, and understanding the elec-
congregations, where participants come The need for ‘recipes’ is clearly under- tronic assembly as an electrically, thermally
widespread from different companies not stood, but the message is that even as new and mechanically active system put together
from various materials which are from a first
approach not really compatible.
Both approaches however need to be
combined to get an overall picture and
to enable us to give the end user what is
needed: an indication of reliability and
safety in the use of electronics.
When one looks at the totality of the
reliability concerns for electronic products,
one invariably has to deal with what is
referred to as the reliability ‘bathtub’ curve,
shown in Figure 1.
The curves are plotted in a log-log graph
of the failure rate versus operating time.
The failure rate is given in FITs [1 FIT = 1
failure in 10
9
device-hours], a unit devel-
oped at Bell Telephone Laboratories in the
1920’s to get a handle on the reliability
assessment of large numbers of nominally
identical components. The ‘bathtub’ curve
Figure 1. Reliability ‘bathtub’ curves for ‘typical’ electronic component without solder attachment and separately for
the surface mount solder joints.
44 – Global SMT & Packaging – September 2008 www.globalsmt.net
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