IC packaging technology retrospective—part 3
contacts) onto organic PCB substrates. The
coefficient of thermal expansion (CTE)
mismatch between ceramic and FR4 was
nearly 3X, and the result was a lot of solder
joint failure. When it was clear what the
cause was, the industry took a few different
paths to a solution. One was to try and
match the CTE of substrate and board,
another was to socket the ceramic compo-
nents, which added cost, and a third was
to try and make component leads more
compliant. This latter solution is the one
that was ultimate winner, but there were a
number of different lead shapes explored
including I-lead, J-lead and gull wing. The
I-lead was in essence a dual-in-line package
with sawed off leads, the J-lead roll formed
the leads under the package and the gull
wing was a gentle S-shaped lead that ex-
!
tended from the edge of the package. This
Figure 2. Examples of surface mount packages are illustrated above. Clockwise from the upper left are SOP,
design feature increased the component’s
TSOP, PLCC and QFP packages
footprint, but it also made inspection of
the solder joint much easier. The first for some of the myriad different package its steady progress possible. Peripherally
generation of volume, commercial, surface names that now pepper industry IC pack- leaded components will continue to be
mount IC packages were developed at aging literature. used for the foreseeable future. However,
Philips in Switzerland, and the term SO One of the concerns of early surface unless they are laid out with an eye to the
or ‘Swiss outline’ was originally applied to mount was getting the delicate leads to benefit of standard grids as described in
describe them; however the term morphed hold shape. Alloy 42, which was and still Part 2, they may find themselves relegated
to become ‘small outline.’ The SO pack- is used to match the CTE of ceramic, was to a niche, if the concept latches on. This
age, which had leads on only two sides, was used in early plastic TSOPs, perhaps to series will continue in Part 4.
followed logically by components that had help ameliorate the concern. However,
leads on all four sides. Plastic leaded chip Alloy 42 turned out to be a problem when Verdant Electronics founder and president
carriers (PLCC) and quad flat packages it came to board level reliability due the Joseph (Joe) Fjelstad has more than 35 years of
(QFP) followed (Figure 2). repeat issue of a bad CTE mismatch with international experience in electronic intercon-
Over the last 20-plus years, peripher- the PCB. (Note: Global SMT & Packaging nection and packaging technology in a variety
ally leaded surface mount packages have columnist and renowned reliability expert of capacities from chemist to process engineer
continued to evolve, even as area array Werner Engelmaier was among the first to and from international consultant to CEO. Mr.
packaging has made it mark. Using the raise the ‘red flag’ predicting this problem Fjelstad is also a well known author writing on
80% Rule, lead pitches continued to in advance of its wider recognition.) As the subject of electronic interconnection technol-
shrink over time until they reached a prac- a result of the experience, nearly all lead ogies. Prior to founding Verdant, Mr. Fjelstad
tical limit at 0.5 mm pitch. Now the family frames of today are made from copper. co-founded SiliconPipe a leader in the develop-
of different peripherally leaded packages In summary, surface mount technology ment of high speed interconnection technologies.
includes the SOT (small outline transistor), offers significant benefits to the electronic He was also formerly with Tessera Technologies,
the TSOP (thin small outline package) industry and will continue to be a vital a global leader in chip-scale packaging, where he
and the increasingly popular QFN (quad technology in the future. However, it has was appointed to the first corporate fellowship
flat no-lead) package. There are a host of been its long-standing partnership with for his innovations.
variations on these packages that account IC packaging technology that has made
2009
Do you have a process or technology or a really strong case
call
study that you want to share with Global SMT & Packaging’s
readers? Global SMT & Packaging is currently seeking technical
articles and case studies for publication in its print magazines
for
and website. We are specifically looking for papers that offer a
‘real’ manufacturing solution and that have not been previously
published in another magazine or journal. For editorial
papers
guidelines, contact editor@globalsmt.net.
www.globalsmt.net Global SMT & Packaging – May 2009 – 5
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