IC packaging technology retrospective—part 4
Joe Fjelstad
IC packaging technology
retrospective—part 4
The electronics industry’s mantra has for the industry embraced the concept, and system in package (SiP) solutions.
many years been “Smaller, Faster, Lighter, BGA technology took off in a significant The lack of KGD was among the
Better and Cheaper.” However, as I/O way. Around the same time the BGA was major causes for the early MCM industry’s
counts continued to rise on the chip and introduced, the electronics industry was demise. The concern of compound yield
thus the IC package, peripherally leaded trying to define and implement what many and expense loomed large in spite of the
devices found themselves unable to keep considered the “ultimate solution” for promise, so the technology faded from
pace. The packages were getting too large manufacturing electronics, the multichip the commercial world but was still being
and the lead too long, and both cost and module, or MCM. In truth, MCMs were worked and, as was shown earlier, not
performance were suffering as a result. It not all that new. The technology had deep forgotten completely. While the industry
was clear that something new on the IC roots in time, both in the hybrid circuit in- continued to look for ways to procure good
packaging front was going to be required. dustry and in the Marley patent described die in unpackaged formats, in the early
SO and TSOP packages were still satisfacto- in the previous part of this series. Marley 1990s creative thinkers and innovators in
ry for lower I/O, but for higher pin counts showed clear early thinking along the line a few companies, big and small, in the US,
the pin grid array (PGA), which had been of what was being now called the MCM; Europe and Asia, saw opportunity to pro-
used primarily for microprocessors, was however, the big challenge was going to be vide packages that were near the size of the
reinvented to become the ball grid array or how to make what was largely a military chip to solve the cost problem by providing
BGA, and the BGA has been a huge suc- technology into a commercial one. Perhaps standards. One of the early leaders was
cess in the world of IC packaging. This did the most daunting of the challenges for Tessera, a small company formed princi-
not spell the end of the PGA however. The MCMs was the availability (or lack thereof) pally by IBM veterans Tom DiStefano and
PGA, which IBM had actually employed of known good die (KGD). Igor Khandros. Together they conceived
as the format for the modules used in the A number of schemes were developed and developed a new chip size package
IBM 360 computer when it was introduced in the late 1980s and early 1990s, includ- that provided the benefits of flip chip in a
in the early 1960s, remains a popular ing some involving the plating of intercon- protected and easily tested and assembled
format with the pin pitch decreased and nections onto chips in a planar fashion at format along with solder joint reliably.
the height lowered for socketable devices, AT&T, Raychem’s Advanced Packaging These and other similar devices were
primarily microprocessors, but we will see Technologies group, Unistructure and manufactured at near the size of the die
later how it has worked its way into other General Electric. Today these concepts are and so became known as chip scale (or chip
fewer I/O package applications as well. being revisited by companies like Casio, size) packages or CSP. At about the same
Area array constructions provided more FreeScale and Imbera for multichip assem- as Tessera was emerging on the East coast,
I/O in less space than QFPs, even when bly with some success as a less expensive a small Silicon Valley company, M-pulse
area array I/O pitch was coarser. It also alternative to building an entire system on (later ChipScale Inc.), was also working on
had lower electrical parasitics, thus in the a chip (SoC), however in the mid 1990s the methods for making packaged ICs at near
late 1980s and early 1990s, BGAs began MCM concept was generally abandoned. chip size. The company, founded by Wen-
showing up in greater numbers. Still, area That being the case then, in recent years dell Sander, (who had earlier been the key
array technology took a while to catch hold the MCM has been reborn in the form of designer of the Apple III), was developing
as the industry grappled with quality as- various wire bonded and flip chip multi- a method for packaging few I/O devices
surance and reliability engineers’ concerns chip packages along with various stacked directly on the wafer by creating peripheral
regarding the myriad of blind interconnec- chip and system in package structures leads around the chips. It was, in fact, an
tions that resided beneath the package. which were being built in relatively small early version of wafer level packaging.
Fortunately, once comforted by actual expe- volumes by such companies as Dense Pac, Since the emergence of the CSP, a wide
rience that reliable interconnections could Irvine Sensors and Stack Tech. In general range of chip scale and chip size package
be readily made with good yield, even these newer generation devices are often structures have been developed having
better than fine pitch lead frame devices, referred to as either multichip packages or both peripheral and area array leads.
4 – Global SMT & Packaging – June 2009 www.globalsmt.net
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