Title
IC packaging technology retrospective—part 2
Joe Fjelstad
IC packaging technology
retrospective—part 2
In the first part of this retrospective, seen ment and testing systems could plan ahead to greater order and ease of design. With
in the February 2009 issue of Global SMT for anticipated miniaturization which had the proliferation of odd components types
and Packaging, some of the early origins become and still is a prime objective and and lead pitches that stem from the 80%
and issues of IC packaging were reviewed. feature of each new generation of electron- rule, the designer is faced with a wide, even
The column left off noting that surface ic products. The idea worked satisfactorily mind numbing, range of choices that pres-
mount brought with it significant advan- for some time. In fact, it worked well as ent significant challenges to the designer.
tages to IC packaging but also that there long as peripherally leaded components To better appreciate this, some additional
was need to provide guidance for future were dominant. Unfortunately, it appears background information is helpful.
development. The result of that effort is that the originators of the concept did not The industry is presently compelled to
something that is now known as the ‘80% look far enough ahead to foresee, or at deal with legacy component lead pitches
rule.’ This is a matter that warrants more least fully consider, the advent of area array because of the long established precedent.
detailed discussion, and this will be the packaging and what it represented. The The now registered and accepted range of
primary subject of this part of this short result has been a legacy of missed oppor- options include 0.100” (2.54 mm), which
series on IC packaging history. tunity, one which has created an ongoing was the original single de facto standard
The 80% rule was established specifi- challenge for the electronics industry both for IC components. It has the advantage of
cally for surface mounted packaging tech- in design and manufacture. allowing the designer to lay out his entire
nology at a time when peripheral leaded The seemingly unanticipated fact is design using that value as a fundamental
packages were dominant. The objective was that area array packaging offers significant pitch. (At the same time there was a metric
to provide a forward looking roadmap so benefits when it comes to electronic design, equivalent pitch of 2.5 mm in the Eastern
that those involved in the design of elec- especially if one designs exclusively with Block, which looked similar but was not
tronics components, manufacturing equip- such components. The opportunities relate compatible.) From this point it quickly
went downhill because apparently no one
had considered fully the considerations.
The next lead pitch was 0.075” and then
0.050”, at which point, given the increas-
ingly global nature of the electronics
industry, the US, which had been the
early standard setter, agreed, under the
aegis of the American Electronics As-
sociation (AEA) and its Joint Electronic
Device Council (JEDEC), that all future
component lead pitches would be metric.
Thus the last legacy inch-based component
lead pitch of 0.050” became 1.27 mm, and
the first full metric pitch of 1.0 mm was
established, which, perhaps coincidently,
perhaps not, is approximately 80% of 1.27
! mm. From this point on the 80% rule has
been in effect. The component pitches
Area array components based on the 80% rule increase routing complexity requiring more sophisticated routing
for IC packages that followed in service
tools. Note that only two of the five grid pitches derived from the concept have ability to conform to a common
grid based on the smallest defined lead pitch for component I/O (in this case 0.5mm). In contrast, on the right
of the new convention were 0.8 mm, 0.65
can be seen a number of components based on the use of a common grid pitch where it can be seen that every
mm, 0.5 mm, 0.4 mm and 0.3 mm. The
component lead falls on grid allowing for high efficiency ‘Manhattan routing’ of circuits. key thing to remember is that the 80%
4 – Global SMT & Packaging – March 2009 www.globalsmt.net
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