OL1.MAR–SC
From Nepcon West: MCM improvements keep coming
Papers presented at last month's Nepcon West exhibit in Anaheim showed
that the quest continues for ever-faster chip operating speeds and
denser, lighter packages. And, as in the past few years, many of the
papers discussed emerging multichip module technologies. Memory cards also
made a strong showing. One paper discussed a new MCM substrate material:
diamond. Recent reductions in the cost of 4-in.-diameter and larger
diamond substrates have made this material a practical choice for both
two- and three-dimensional MCM substrates. The Nepcon paper was coauthored
by Dean Schaefer of E-Systems (Dallas), Thomas Moravec of Norton Diamond
Film (Northboro, MA), and Richard Eden, an independent consultant in
Thousand Oaks, CA. They asserted that diamond is ideal for many electronic
packaging applications because of its high thermal conductivity, typically
2,000 (W/m)
fabricate MCMs with more densely spaced interconnects than other
substrates like silicon and alumina.
Another paper addressed the development of 3D multichip substrates. In
“HDI Stacked Multichip Module Technology's Impact on System Design,”
researchers at General Electric's Corporate Research Center in
Schenectady, NY, and others described GE's efforts to develop a 3D
high-density interconnect (HDI) process for MCMs that can interconnect
individual dice in a stack to achieve very high density. Like stacking
technologies from Irvine Sensors and Dense-Pac Microsystems (see Electronic
Products, Feb., p. 15), the General Electric process (see diagram) can
reduce the size and weight of many multichip modules. One demonstration
for the process is a 16-Mbit static RAM module containing four 2D modules
laminated into a single stack with HDI interconnects on both sides.
Researchers at the Microcomputer and Computer Technology Corp. (MCC) of
Austin, TX, presented a paper “Design of MCMs for Insertion into Standard
Surface Mount Packages.” The paper explores the advantages and tradeoffs
of inserting small multichip modules in surface-mount packages, based on
using a 80486-based PC board with a cache controller. According to
researchers Peter Sandborn, Hassan Hashemi, and Linda Bal, the multichip
packages were, perhaps not surprisingly, more expensive than individually
packaged chips. However, when overall system cost–comprisingassembly,
test, and performance–is factored in, the multichip packages were often
less ex pensive than the single-chip solutions. Implementing multichip
modules in standard packages could accelerate the use of MCMs in
high-volume applications. Outside of multichip modules, memory cards,
driven by the rapidly growing laptop and notebook computer market, have
also grown in importance. One of several papers addressing memory cards
was “An Overview of PCMCIA Packaging and Card Assembly Process,” from IBM
Canada in Toronto. The paper discussed the Personal Computer Memory Card
International Association (PCMCIA) standard for memory card packaging. The
thin cards can encompass chips in tape-automated bonded (TAB),
wire-bonded, flip-chip attach, and thin plastic flatpack formats. Cards
meeting the PCMCIA standard typically pack in 8 to 12 leads per square
centimeter, higher than existing pc cards. Other advantages of these cards
include interchangeability and portability. On the downside, the thin
cards are difficult to handle and encapsulate. –Spencer Chin
CAPTION:
Like several other multichip module processes, General Electric's HDI
process stacks chips to increase packaging density.
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