OL1.JUL–SC
Multichip packaging stays hot
The technology continues to shed its expensive custom image
The year 1993 may well be remembered as the year that multichip modules
entered the mainstream of packaging technology. The availability of
standard MCM products and the introduction of process refinements promise
to make the technology more cost-effective and practical for users.
The past few months have seen a continued rise in the introductions of
new multichip module products and processes. It appears that the
technology has finally emerged from the realm of laboratory curiosities
and technical conference papers into a mainstream practical packaging
technique.
On the standard products front Perhaps the biggest boost lately to the
MCM industry is the availability of low-cost ICs in MCM form. SMOS Systems
and Fujitsu Microelectronics, both of San Jose, CA, now have relatively
low-cost MCM packages for use in small computers, disk drives, consumer
electronic products, and telecommunications. The SMOS packages have
surface-mounted or chip-on-board mounted die on polyamide/epoxy glass and
come in standard quad flatpack (QFP) packages. They are designed for small
form factor packages: a two-chip device comes in a 184-pin package
measuring just 32 x 32 x 3.8 mm. In quantities of 10,000, this version
costs $13 to $15 each. A 232-pin package with four chips measures 40 x 40
x 3.8 mm and costs $21 to $24 each in 50,000-piece quantities. The
Fujitsu modules (see Fig. 1) combine analog and digital functions, using die
mounted on both sides of a multilayer ceramic substrate. Passive elements
can also be incorporated. Designed for low-power consumption, these 3-W
modules are also housed in QFPs. While early packages use wire bonding for
chip interconnects, Fujitsu plans to use flip-chip interconnects in future
versions. Pricing for the modules starts at $60 to $80 each in quantities
of 20,000 to 50,000. The military continues to demand MCMs for saving
space. In response, United Technologies Microelectronics Center (Colorado
Springs, CO) is now packaging its SmicronsMIT (Serial μ-coded
Monolithic Multimode Intelligent Terminal) products in MCM-C (ceramic)
packages. The single multichip package, which integrates the company's
MIL-STD-1553B protocol logic and bus transceivers, saves at least 43% of
the board space required for package mounting. The chip comes in two
versions, the SmicronsMIT-LX for +/-12 or +/-15 V operation, and the
SmicronsMIT-DX for +/-5-V operation. The device costs $550 each in
100-piece quantities.
Rapid prototyping While standard MCM products are beginning to
proliferate, most MCM parts will still be custom made. One of the key
concerns with custom MCMs has been the long lead time–typically
months–for turning around finished custom products. However, several
recent developments are trying to address that issue. Microelectronics
and Computer Technology Corp. (Austin, TX) and MicroModule Systems
(Cupertino, CA) have jointly announced a rapid prototyping service that
they say will make it possible to produce custom MCMs in two weeks instead
of several months. Key to the rapid prototyping process is MCC's Laser
Direct Write (LDW) technology, which uses a laser cutting and writing tool
to customize the substrate's circuit pattern. A thin-film MCM substrate,
developed by MicroModule, contains several generic, pre-fabricated
metallization and dielectric layers. A router software tool, developed by
MCC, selects the laser operations to transform the generic substrate into
custom circuitry. The process eliminates the need for costly custom
masking operations to image the substrate's circuit pattern. Mentor
Graphics' PCB Div. (San Jose, CA) and Toshiba Corp. (Tokyo, Japan) also
have an alternative to custom MCM modules. The companies have developed a
process to produce semicustom MCMs within 10 weeks from completion of
design to delivery, as opposed to 24 weeks for a traditional custom MCM
product. The process involves the imaging of circuit patterns on standard
substrates–either alumina nitride or alumina co-fired ceramic that
Toshiba stocks. These substrates have power and ground layers already in
place. Because forming the custom circuit pattern is the only additional
step required, prototyping time can be reduced substantially (see Fig. 2).
To help the user customize the circuit pattern, Mentor Graphics and
Toshiba have jointly developed a design kit to generate the schematic
design. The kit is based on Mentor Graphics MCM station software for
designing multichip modules. Special capabilities in the software include a
thermal analysis tool that determines if further thermal analysis of the
module is needed. Another capability is a pre-layout delay calculator that
enables users to run a timing estimate of traces before actual physical
layout.
Process improvements Other recent multichip module developments attempt
to alleviate the high cost of fabricating the packages. Pacific
Microelectronics Corp. (Beaverton, OR) has a new transfer tape process for
MCM-C technology. This process involves laminating a dielectric tape with
preformed vias onto a standard alumina or beryllia oxide substrate. The
laminated, metallized tape is then fired in an infrared kiln at 850
degreesC. According to Paul Danner, the company's president and CEO, the
transfer tape process provides a lower-cost alternative to MCM-D
(thin-film copper polyamide) techniques, but with better performance and
density characteristics than traditional co-fired ceramic and FR-4
laminate (MCM-L) techniques. The table compares key characteristics for
the processes. Prototypes can now be produced within 3 to 6 weeks. As an
added incentive, Pacific Microelectronics offers free IBM PC-compatible
software that asks for basic information on the user's design and
calculates non-recurring engineering costs and the size of the finished
package. Armed with this information, a prospective user can more easily
evaluate the cost of a MCM design for an application. Texas Instruments
also tries to apply a new twist to existing MCM technology with a new
process called MCM Laminate/Overlay, or MCM L/O. This technology applies
the thin-film overlay commonly used in high-performance MCM substrates
onto conventional pc-board laminates. It is based on a thin-film
manufacturing process known as high-density interconnect (HDI), developed
in conjunction with General Electric and the Advanced Research Projects
Agency. In the HDI process, bare ICs are set in wells in the substrate.
Then, the interconnect is laid over the tops of the ICs, using a plastic
laminate as a dielectric between the trace layers. This arrangement allows
heat to be dissipated through the substrate more quickly. Moreover, chips
can be interconnected without special preparation such as TAB lead bonds
or flip-chip bumps. Eliminating these steps cuts up to one-third of the
steps required for MCM fabrication. Texas Instruments eventually expects a
quick turnaround time for MCMs produced with the process: 6 to 8 weeks by
1994. –Spencer Chin
For more information from the companies mentioned in this report, call
the contact or circle the reader service number:
Fujitsu Microelectronics, Inc. San Jose, CA Betsy Taub 408-922-9200
Mentor Graphics Corp. Wilsonville, OR Sabina Merrill 408-451-5649
MicroModule Systems Cupertino, CA Howard Green 408-864-5986
Microelectronics and Computer Technology Corp. Austin, TX Cathy Martin
512-338-3746
Pacific Microelectronics Corp. Portland, OR Paul Danner 503-684-5657
SMOS Systems, Inc. San Jose, CA Dan Beck 408-922-0200
Texas Instruments Inc. Microelectronics Packaging Systems Dallas, TX
Customer Response Center 800-336-5236 ext 1507
United Technologies Microelectronics Center Inc. Colorado Springs, CA
Twila Gamble 719-594-8362
CAPTIONS:
Fig. 1. Standard MCMs continue to emerge, such as this module from
Fujitsu Microelectronics.
Fig. 2. Semicustom multichip modules produced by Toshiba use a alumina
nitride or alumina co-fired ceramic substrate (center) that has power and
ground layers already in place. Mentor Graphics offers a design kit to
help users develop the circuit pattern for the substrates.
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