Bright future ahead for ball grid arrays
The packages are becoming popular alternatives for high-density chips
More demanding density and performance requirements are creating wide interest
in ball grid arrays, whose solder ball leads ease assembly and save space. Both
discrete chips and multichip modules can use this technology.
Although multichip modules continue to occupy center stage in the world of
electronic packaging, another packaging technology–ball grid arrays–is at
least temporarily sharing the spotlight. Wooed by the density and ease of
assembly that BGAs offer, many companies are actively looking to package
high-pin-count chips in plastic or ceramic BGAs.
BGAs have been in development for years. However, Motorola Semiconductor's
announcement of its Ompac BGA package a year ago (see Electronic Products,
April 1993, p. 19), seems to have spurred the industry. The table lists some of
the BGA products available.
The key to the BGA is its array of solder balls underneath the package–a
pattern similar to the gold pins underneath a pin grid array. This arrangement
allows higher density than quad flatpacks, whose leads all reside on the
package's edge. Because it does not have the thin, fragile leads of QFPs, BGAs
are easily assembled on the pc board with standard surface-mount assembly
equipment. With its smaller footprints and very short electrical
interconnections, electrical performance for the BGA is also better than that
of a QFP.
Motorola Semiconductor (Phoenix) not only has tooled plastic BGAs, but also
ceramic BGAs having a 25-mil pitch and 420 pins for static RAMs, as well as
21-mm ceramic BGAs for application-specific ICs. Unlike the plastic BGA, the
ceramic BGA is hermetic and thus can withstand more environmental extremes.
Altera is announcing a programmable logic device with over 8,000 gates in a
plastic BGA (see Outlook section, p.xxx).
National Semiconductor is now qualifying 225- and 313-pin ASICs in BGAs (see
photo). The company is actively trying to establish the thermal and electrical
performance characteristics of the package. “Beyond the form factor of the
package, which is JEDEC-registered, there needs to be other standards regarding
the physical, thermal, and electrical characteristics of the package,” says
Jack Velani, director of package technology for National Semiconductor.
Domestic companies are not the only ones pursuing BGAs. According to TechSearch
International, a packaging consulting firm in Austin, TX, major Japanese
companies are also evaluating BGAs. They include Fujitsu, Hitachi, Mitsubishi,
Matsushita, NEC, and Toshiba. In Europe, Ericsson is using a ceramic BGA to
package an ASIC and two RISC processors, while Bosch Blaupunkt and Valtronic
are supplying plastic BGAs.
While BGAs are well suited for single-chip packages, multichip modules also
readily lend themselves to the package. For instance, Pacific Microelectronics
(Portland, OR) is using BGA technology to form the interconnects in its MCMs
made through the company's transfer tape process (see Electronic Products, July
1993, p. 17), which uses a perforated dielectric tape to create the substrate's
circuit pattern. The BGA technology enables Pacific Microelectronics to
manufacture MCMs having as many as 265 pins in a 1.2-in.
Aside from the newness of BGAs and the lack of standards for them, designers
face other technical challenges. While the packages are easier to place than
fine-pitch devices, they are difficult to inspect after soldering. The lack of
access to the leads makes rework difficult–the entire module must be removed
if a solder joint is defective. Cooling could also present a problem, since
heat sinks for BGAs are not yet available.
–Spencer Chin
PHOTO CAPTION:
National Semiconductor is now qualifying 225- and 313-pin ASICs in ball grid
arrays.
Advertisement
