Semiconductor device manufacturing: process – Packaging or treatment of packaged semiconductor – Including contaminant removal or mitigation
Reexamination Certificate
1999-07-30
2001-07-17
Bowers, Charles (Department: 2813)
Semiconductor device manufacturing: process
Packaging or treatment of packaged semiconductor
Including contaminant removal or mitigation
C438S118000, C438S121000, C438S125000
Reexamination Certificate
active
06261866
ABSTRACT:
FIELD OF INVENTION
This invention relates to a method of sealing a chip carrier and lid and an apparatus for holding, heating and joining them.
BACKGROUND OF INVENTION
Micro-mechanical gyroscopes and accelerometers must be sealed in a vacuum or inert atmosphere to operate. Two methods of vacuum sealing sensors are in use. In one method a lid with a small hole in it is welded on a chip carrier after a sensor is mounted inside. The chip carrier is then placed in a vacuum chamber and heated for several hours to drive out moisture and activate a getter element. Sealing is accomplished by dropping an indium ball on the lid, which melts and plugs the small hole as the chip carrier cools under vacuum. In the second method, oversized lids and chip carriers are placed in compartments of graphite trays. The lid tray is suspended above the chip carrier tray in a vacuum chamber and heated by passing an electric current through it. At the end of the degas time, the chip carrier tray is raised. Holes in the bottom of the lid tray allow the chip carriers to contact the lids. When this occurs, a braze preform on the chip carrier melts and seals the lid to the chip carrier. These methods of sealing require significant touch labor and processing time. They also yield packages that are less than sufficiently robust for military applications. The indium ball seal can soften and leak at temperatures above 125° C., while the oversize lid flexes and cracks its braze seal when subjected to high acceleration, e.g., a gun launch. The chip carrier with the weldable seal ring that is used in the indium ball process is expensive. In addition, in both approaches the sealing preform is added to the chip carrier after the chip is bonded into the carrier so that the chip can be damaged or contaminated during that process.
BRIEF SUMMARY OF THE INVENTION
It is therefore an object of this invention to provide an improved method of sealing a chip carrier and lid and an apparatus for holding, heating and joining them.
It is a further object of this invention to provide an improved method of sealing a chip carrier and lid and an apparatus for holding, heating and joining them which requires less touch labor and processing time and is less expensive.
It is a further object of this invention to provide an improved method of sealing a chip carrier and lid and an apparatus for holding, heating and joining them which yields a more robust product.
It is a further object of this invention to provide an improved method of sealing a chip carrier and lid and an apparatus for holding, heating and joining them which is better sealed, less likely to leak and can withstand higher acceleration force.
It is a further object of this invention to provide an improved method of sealing a chip carrier and lid and an apparatus for holding, heating and joining them which avoids the risk of contamination and damage attendant on applying the sealing preform to the carrier after the chip is bonded in place.
The invention results from the realization that a truly simple, yet effective sealing of a chip carrier and lid can be achieved by mounting the chip carrier in an inverted position with the lid mounted inverted, below and facing the chip carrier, then heating them and bringing them together to join them at the sealing preform carried by the lid.
This invention features a method of sealing a chip carrier and lid including mounting a chip carrier in an inverted position and mounting a lid having a sealing preform in an inverted position beneath and facing the chip carrier. The chip carrier and lid are heated to melt the sealing preform and the chip carrier and lid are moved together to join them at the sealing preform
In a preferred embodiment there may be an evacuating space around the lid and carrier, the chip carrier may be heated to degas it, and the lid may include a getter. The method further includes heating the getter to activate it to evacuate the chip carrier. The moving of the chip carrier and lid together may include lifting the lid out of its mounting into contact with the carrier.
This invention also features a chip carrier and lid sealing apparatus including an upper holder for mounting at least one chip carrier in an inverted position and an upper heater for heating the chip carrier. A lower holder mounts at least one chip carrier lid with a sealing preform in an inverted position facing the chip carrier and a lower heater heats the lid and sealing preform. A drive mechanism moves the upper and lower holders together to join the carrier and lid with the sealing preform.
In a preferred embodiment the upper holder may include a cavity for receiving the chip carrier and a retainer for securing the chip carrier in the cavity. The retainer may include a keeper block and a spring for urging the keeper block against the chip carrier to secure it in its cavity. The lower holder may include a cavity for receiving the chip carrier lid. There may be a degas heat source for heating the chip carrier to degas it. The drive mechanism may include a drive device for moving at least one of the holders toward the other. The drive device may move the upper holder toward the lower holder. The drive mechanism may include a lifter device for lifting the lid out of the cavity to meet the chip carrier.
REFERENCES:
patent: 4382327 (1983-05-01), Bardens
patent: 5688708 (1997-11-01), Kato
patent: 0472866 A2 (1992-03-01), None
Marinis Thomas F.
McEleney Cathy
Romano Gregory M.
Berezny Nema
Bowers Charles
Iandiorio & Teska
The Charles Stark Draper Laboratory Inc.
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