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At Nepcon West:
IC packages take on new forms
As packaging requirements become more complex, the universe of IC packages continues to expand to meet the need. At the upcoming Nepcon West show* in Anaheim, several technical papers will focus on some of the more innovative packages.
One of the most interesting developments is the SLICC (Slightly Larger than IC Carrier) package, discussed in a paper by Motorola's Land Mobile Products Sector (Fort Lauderdale, FL). This package takes advantage of the volumetric efficiency afforded by direct chip attachment to pc boards. At the same time, it has the testing, assembly, and repair advantages of ball grid arrays (BGAs). Motorola asserts that the SLICC will be cost effective for packages having 30 to 150 pins, such as microprocessors and microcontrollers.
The package comprises a solder-bumped IC that is reflow soldered to a thin pc-board chip carrier and underfilled using conventional flip-chip processes. Each I/O in the chip interfacing with outside circuitry is routed to the carrier's bottom-side via plated-through-holes, into a pad array. These pads are bumped with 0.020-in.-diameter solder spheres. The diagram shows a schematic of the SLICC.
The virtues of the BGA
Over the past year, BGAs have emerged as a viable packaging technology because of their high interconnect density, low profile, light weight, and lower cost than such packages as quad flatpacks (QFPs). Two papers, one by Amkor Electronics (Chandler, AZ) and the other by Hestia Technologies (Sunnyvale, CA), expand on the virtues of BGAs.
Amkor's paper asserts that the packaging limits of BGA technology have yet to be realized. While present MCMs based on BGAs have just two to four ICs and a few passive components, future BGA MCMs could contain as many as 20 ICs. Pin counts that now range between 169 to 313 are expected to run from 600 to 1,000 in the future.
Hestia's paper says that BGA technology is particularly suited for MCMs based on thick-film laminates, otherwise known as MCM-L. Because of their small size and very short electrical paths, BGAs can improve the performance of laminate-based MCMs to a level competitive with costlier ceramic- or thin-film-based MCMs, says the company. While tooling for BGAs is relatively limited, it is less expensive than the trim-and-form tooling for packages like QFPs and plastic leaded chip carriers (PLCCs), according to Hestia.
Among the many papers on multichip modules is one describing various approaches to fabricating three-dimensional MCMs by TechLead Corp. (Evergreen, CO). One approach, from Dense-Pac Microsystems (Irvine, CA), uses a thin, stackable ceramic chip carrier with a center cavity for wire bonding the die. Metallization layers reside atop the die. Once wire bonding is completed, the cavity is filled with a polymer and the chip is tested. The three-dimensional MCM structure is achieved by stacking individual carriers, typically two to eight high.
Another three-dimensional approach described in TechLead's paper is a custom low-temperature cofired ceramic (LTCC) structure developed by Harris Corp. (Melbourne, FL). This MCM structure has vias around the edge of each layer soldered together to create the Z-axis interconnections. The paper says that this approach is economical but does not permit easy replacement of defective layers.
–Spencer Chin
* The Nepcon West show will take place at the Anaheim Convention Center in Anaheim, CA, from February 27 through March 4. For more information, contact Barbara Axelson at the Reed Exhibition Companies (Des Plaines, IL) at 708-299-9311.
CAPTION:
The SLICC (Slightly Larger Than IC Carrier) combines flip-chip and ball grid array technology to house parts such as microprocessors and microcontrollers.
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