Contract Bumping is Increasing
John Baliga, Associate Editor -- Semiconductor International, 3/1/1999
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In its 1997 Roadmap, the SIA announced that flip-chip technology development would finally have to start in earnest. After 30 years of being the technology of the future, it is expected to be a technology of the near future.
| Company News | |
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ZiLOG (Campbell, Calif.) announced it will outsource its assembly operations, closing its assembly facility in The Philippines. The company's final testing operations in Sucat, The Philippines, will remain open. Sharp Corp. (Tokyo) has licensed Tessera's (San Jose, Calif.) mBGA chip-scale packaging technology. Dense-Pac Microsystems Inc. (Garden Grove, Calif.) has begun shipping production quantities of its new memory stacking devices, used to produce 512 MB memory modules. The company announced the availability of stacked devices for manufacturing of 1 GB PC-100 memory modules. The company also recently received $2.7 million in orders from a single customer. GiGA North America (Thousand Oaks, Calif.) recently introduced a 155Mb/s, two-chip coded-mark-inversion interface chip set in 28-pin SSOP packages. The transmitter and receiver chips are packaged separately to reduce cross-talk. HIG Capital Management (Miami) has completed its buyout of Surface Mount Taping Corp. (SMT, Austin, Texas). SMT initiated the buyout to gain capital resources. Universal Instruments Corp. (Binghamton, N.Y.) has acquired Alphasem. Alphasem will continue to operate as Alphasem and remain in Berg, Switzerland. Financial details of the transaction were not disclosed. Kulicke and Soffa Industries (Willow Grove, Pa.)
announced plans to move its ball bonder manufacturing operations to Asia.
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Flip-chip technology has come in various forms and metallurgies. Gold wire bonders have been adapted to deposit gold stud bumps. Under bump metalizations of different kinds have been evaporated, sputtered or plated. The bumps themselves have been C4, solder or nickel-gold. Conductive thermoset polymer bumps have also entered the mix recently. Bumping is a mature area of technology.
Until now, flip-chip has been relegated to high-performance and specialty applications. An indication that it may be ready to take a big hold on the industry is an increase in contract bumping providers.
The following companies are among those currently providing contract bumping
services: Flip Chip Technologies (Phoenix), Unitive Electronics (Research
Triangle Park, N.C.), Focus Interconnect (Austin, Texas), IC Interconnect
(Colorado Springs, Colo.) Pac Tech (Nauen, Germany), Chipbond (Hsinchu, Taiwan),
APTOS (Milpitas, Calif., a second facility to be in Taiwan), FUPO Electronics
(Hsinchu), APACK (Hsinchu), MicroFab Technology (Singapore) and Polymer Flip
Chip Corp. (Billerica, Mass.).
Underfill First?
One of the most time-consuming processes in flip-chip packaging is underfilling. If it can be avoided, it usually is. The underfill material is deposited around the edge of the attached chip, and it wicks between the substrate and chip until the area is filled.
Fig. 1. No flow-fluxing underfill material is applied before flip chip attach.
In addition, the substrate is typically treated with a flux material before chip attach, and the flux residue is cleaned between attach and underfill. Not only does this take more time, but it also consumes more chemicals.
To streamline the flip-chip process, Emerson & Cuming (Billerica, Mass.) has developed a series of materials it calls no flow-fluxing underfills. The AMICON E materials are designed to be applied directly to the substrate after a standard cleaning step (see Figure). The chip is then placed on top of the material, with enough force for the solder balls to touch the contact pads.
The materials have adhesive strength sufficient to hold the chip in place during reflow, and they perform the fluxing function of preparing the bonding pads. Some of the materials are designed to cure during reflow. Others do not cure during reflow, simplifying rework to the point where the material need not be removed.
The reliability and handling characteristics for the materials are comparable
to industry standard materials. Materials like these are able to reduce process
time and consumables used as well as simplify flip-chip assembly.
