Active solid-state devices (e.g. – transistors – solid-state diode – Housing or package
Reexamination Certificate
2001-01-04
2002-05-07
Clark, Jhihan B (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Housing or package
C257S693000, C257S737000
Reexamination Certificate
active
06384471
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of connections in BGA, or “Ball Grid Array” packages in printed circuit cards, and more particularly concerns PGBA, or “Plastic BGA” packages.
BACKGROUND OF THE INVENTION
The standard “cavity down” type of PBGA package comprises a cavity in which an integrated circuit, also called a “chip,” is housed.
In this type of package, the areas for connecting the chip to the package and the areas for connecting an array of solder balls to the package are disposed on the same level of the package, generally corresponding to the bottom surface of the package, i.e. the surface that faces the printed circuit card when the package is mounted on the card.
The ball array connects the chip to the printed circuit card both electrically and mechanically.
In order to protect the active surface of the chip constituted by a semiconductor layer, and the connections, for example bonding wires, both mechanically and from the environment, an encapsulating material is used, for example a thermosetting and electrically neutral resin, which coats the outside of the chip and its connections.
Such a method is specifically described in U.S. Pat. No. 5,397,921A.
This method, applied to the BGA package described above, has the drawback that the height of the wires thus coated by the resin must be compatible with the height of the balls, which is typically on the order of 0.6 mm for a pitch between the balls on the order of 1.27 mm.
This imposes the near exclusive use of the “gold”, or “ball bonding” technique, and the package must include an “electrolytic gold” metallization, requiring the use of “feeders,” which after metallization leave remaining wire ends that are equivalent to antennas for high frequencies, particularly for clock signals.
In addition to controlling the wiring loops of the wires, it is also necessary to control the height of the coating so that the wires are completely covered.
In general, a line of highly viscous adhesive is deposited around the areas for connecting the wires to the package in order to serve as a wall for retaining the coating resin, which by contrast is very fluid in nature, so that it properly coats the wires and the chip.
This wall also makes it possible to prevent an overflow of the coating resin in the areas for connecting the balls to the package.
Another drawback relates to the phenomenon of the “collapse” of the balls when the package is assembled to the printed circuit card.
In essence, during assembly, the superficial tensile forces of the alloy constituting the balls, typically remelted tin-lead, causes the balls to collapse onto the card.
Thus, a ball typically having a height of 0.6 mm for a pitch of 1.27 mm and an initial diameter before assembly of 0.76 mm will decrease in height by about 0.2 mm. This phenomenon is amplified, particularly when an integrated heat sink covers the top surface of the package; this can result in short-circuiting between the balls.
SUMMARY OF THE INVENTION
The specific object of the invention is to eliminate the aforementioned drawbacks.
To this end, the subject of the invention is a package for an integrated circuit of the type comprising a cavity in which the integrated circuit is mounted, the active surface of the integrated circuit being electrically connected to the package on the level of connection of a ball array to the package, providing a mechanical and electrical link between the integrated circuit and a printed circuit card to which the package must be assembled. The package is characterized in that it comprises an additional layer that is rigid and electrically neutral, attached to the level of connection of the integrated circuit and the balls and containing the balls.
The invention has the particular advantage of simultaneously facilitating the mounting of the balls onto the package, also called the “ball bonding” of the package, and of protecting the connections and the card.
It also makes it possible to guarantee a predefined distance of the package from the card, thus playing the role of a spacer between the package and the card.
REFERENCES:
patent: 5293072 (1994-03-01), Tsuji et al.
patent: 5420460 (1995-05-01), Massingill
patent: 5583378 (1996-12-01), Marrs et al.
patent: 5844168 (1998-12-01), Schueller et al.
patent: 5844315 (1998-12-01), Melton et al.
patent: 6060778 (2000-05-01), Jeong et al.
Patent Abstracts of Japan, vol. 1998, No. 09, Jul. 31, 1998 & JP 10 112472 A (Toshiba Corp.) Apr. 28, 1998 Abstract, Figs 1,3,9A-9E.
Patent Abstracts of Japan, vol. 1996, No. 08, Aug. 30, 1996, & JP 08 097314 A Dainippon Printing Co., Apr. 12, 1996; Abstract; Figs 4A-4G.
Patent Abstracts of Japan, vo. 1998, No. 14, Dec., 31 1998 & JP 10 256424 A (Toshiba), Sept. 25, 1998 -Entire Document.
Patent Abstracts of Japan, vol. 1996, No. 08, Aug. 30, 1996 & JP 08 088293 A (Mitsui High Tec Inc), Apr. 2, 1996, Abstract, Figs 4,5.
Patent Abstracts of Japan, vol. 1997, No. 01, Jan. 31, 1997 & JP 08 250835 a, Sep. 27, 1996, Abstract.
Petit Claude
Stricot Yves
Bull S.A.
Clark Jhihan B
Kondracki Edward J.
Miles & Stockbridge P.C.
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