Active solid-state devices (e.g. – transistors – solid-state diode – Housing or package
Reissue Patent
1994-04-14
2001-03-06
Font, Frank G. (Department: 2877)
Active solid-state devices (e.g., transistors, solid-state diode
Housing or package
C257S689000, C257S690000, C257S704000, C257S731000, C257S723000, C257S668000
Reissue Patent
active
RE037082
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention provides a novel package for RF transistors which offers improved stability to wave and vapor phase soldering.
2. Description of Related Art
Hybrid RF power, semiconductive devices, or packages, are well-known in the art. Typically such devices or packages include a transistor and an input capacitor mounted upon appropriately metallized surfaces of a beryllia substrate including a lead frame arrangement bonded to the metallized areas which includes input, output and ground portions or members. Appropriate wire bonds extend from the active portions of the transistor and capacitor to the various lead portions as is well understood. Such hybrid devices, or packages, may be characterized as having an input circuit and output circuit and a common circuit which includes common lead inductance.
The beryllia substrate is electrically insulating but thermally conducting and is usually mounted upon a relatively massive metallic heat sink. Appropriate ground connections may be made to the grounded heat sink. Further, the input and output circuits usually comprise microstrip conductor means which include a metallic strip mounted on an insulating substrate whose impedance are matched to those of the input and output circuits of the transistor. In addition, the microstrip circuit devices may also be grounded to the metallic heat sink, for example, by wrap around metallizations.
The RF transistor packages have protective caps sealed over the active silicon device with epoxy. Automated package assembly techniques, such as wave soldering and vapor phase soldering, employ temperatures and conditions which often cause breakdown of the epoxy and leakage of the solder into the active region of the device. In addition, when soldering onto a gold lead, the solder and solder flux may leach and travel along the gold underneath the epoxy. Equipment manufacturers must therefore rely on hand soldering of devices into boards after automatically inserting and soldering all other components.
There remains a need, then, for an improved package which will permit total automation of the assembly process.
SUMMARY OF THE INVENTION
An RF transistor package is provided, exhibiting superior stability to wave and vapor phase soldering. The improved device has a barrier of nickel oxide in proximity to, and encircling, the active region, thereby preventing solder from penetrating the epoxy/cap interface. This barrier is formed by placing a photoresist material over nickel or nickel-plated leads prior to gold plating. A narrow ring or annulus of nickel without gold plating then surrounds the active area. This unplated region is oxidized during assembly of the package, creating the nickel oxide barrier, and a cap sealed to the ring area with epoxy. The nickel oxide barrier resists migration of solder, thereby maintaining the integrity of the package.
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Font Frank G.
Galanthay Theodore E.
Jorgenson Lisa K.
Larson Renee M.
Ratiff Reginald
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