Active solid-state devices (e.g. – transistors – solid-state diode – Housing or package – Insulating material
Reexamination Certificate
1998-11-30
2002-04-23
Tran, Minh Loan (Department: 2811)
Active solid-state devices (e.g., transistors, solid-state diode
Housing or package
Insulating material
C257S707000, C257S706000, C257S778000, C257S710000, C257S720000, C257S712000, C257S713000, C257S719000, C257S779000, C257S780000, C257S758000
Reexamination Certificate
active
06376907
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a semiconductor device provided with a package of the ball grid array (BGA) type and comprising semiconductor chips connected by a flip-chip process to a resin substrate with a number of solder ball terminals.
2. Description of the Prior Art
Packages for packaging semiconductor chips have recently been provided with an increasing number of base pins (lead wires). As one of such packages, there has been provided a package of the pin grid array (PGA) type in which pins are disposed into the shape of a grid on the overall backside of the package. In the PGA type package, a ceramic substrate is provided with a number of base pins embedded therein and includes a mounting portion on which a number of electrode pads are provided. The pins are connected via conductor patterns to the electrode pads respectively. A semiconductor chip is mounted onto the mounting portion of the substrate by a flip-chip process.
In mounting the semiconductor chip by the flip-chip process, it is important to be able to dissipate or radiate heat produced by the mounted chip not only from a mounted side thereof but also from its backside opposite the mounted side. For this purpose, a container-shaped cover plate is made of a metal such as aluminum, for example. The cover plate is bonded to an upper side of the semiconductor chip and further at a periphery thereof to the substrate. Heat produced by the semiconductor chip is transferred from the backside or upper side thereof via an adhesive agent to the cover plate, from which the heat is radiated outward. The cover plate serves to mechanically and electrically protect the semiconductor chip as well as to radiate heat therefrom.
Various packages of the ball grid array (BGA) type have recently been developed instead of the above-described PGA type packages. The BGA type packages have recently drawn attention as those of the surface mounting type. In the BGA type packages, a number of ball-shaped solder terminals (solder balls) are provided on connecting terminal conductors disposed into the shape of a grid, instead of the pins. The solder balls are disposed opposite the connecting terminal conductors respectively when the BGA type package is mounted on the printed board. The solder balls are soldered in the block by reflow processing to be electrically connected to the respective conductors.
The soldered terminals are sometimes subjected to mechanical stress in the BGA type package since the BGA type package is mounted on the substrate without using terminals so as to be closely adherent to the substrate. The package needs to be rendered large in size with increase in the size of the semiconductor chip. However, when a large-sized ceramic substrate is mounted on the printed board, mechanical stress due to changes in the temperatures of the substrate and the board is increased to such an extent that the stress cannot be ignored. The solder terminals located particularly at ends of the package are subjected to a larger stress than those located at the center of the package. This sometimes results in occurrence of cracks in connecting portions of the solder or in disconnection or circuit opening.
The above-described drawbacks result from the difference in coefficients of linear expansion between the printed board and the ceramic. To overcome the drawbacks, the prior art has proposed use of a resin substrate as the substrate of the package on which the semiconductor chip is mounted. By the use of the resin substrate, the mechanical stress to which the connecting portions of the solder is subjected can be eased or reduced. Furthermore, the size of the substrate of the package can be increased, so that the limitation in the size of the semiconductor chip can be reduced.
However, stress between the resin substrate and the radiating cover plate sometimes warps the substrate when the cover plate is attached to the resin substrate. Particularly when the cover plate is made of a metal such as aluminum, the stress deforms the resin substrate while the bonded cover plate is being cooled. This stress adversely affects the semiconductor chip, resulting in a new drawback.
It is important to maintain a desirable heat conductivity between the cover plate and the semiconductor chip so that heat generated by the semiconductor chip is efficiently radiated through the cover plate. Accordingly, the heat conductivity of the cover plate needs to be taken into consideration. In view of this, a process as shown in
FIGS. 14 and 15
is employed, for example. Prior to a step of attaching a cover plate
1
to a resin substrate
2
, a predetermined amount of paste
3
with high heat conductivity is applied to an inside of the cover plate
1
by a dispenser
4
(see FIG.
14
). In this state, the cover plate
1
is bonded by an adhesive agent
7
to the resin substrate
2
on which the semiconductor chip
5
has been mounted (see FIG.
15
). The inside portion of the cover plate
1
to which the paste
3
is applied is maintained in contact with the semiconductor chip
5
.
The step of applying the paste
3
to the cover plate
1
is an independent step in an ordinary assembly line since only the cover plate is processed in the step. Furthermore, this step requires new equipment depending upon conditions such as the shape and size of the cover plate
1
, resulting in an increase in the cost.
Furthermore, when having a low viscosity, the paste
3
overflows a predetermined applying area on the inside of the cover plate
1
, so that it becomes difficult to suitably apply a necessary amount of paste
3
to the cover plate.
SUMMARY OF THE INVENTION
Therefore, an object of the present invention is to provide a semiconductor device provided with the BGA type package including a cover plate wherein the above-described drawbacks due to warp of the substrate can be prevented.
Another object of the invention is to provide a semiconductor device provided with the BGA type package wherein a high-temperature conductive paste can, even if it has a low viscosity, be applied to the cover plate without overflowing and can readily be applied by the conventional equipment with no specific equipment being required.
The present invention provides a semiconductor device comprising a substrate made of a resin and having one side on which a number of solder ball terminals are provided and the other side on which a chip mounting portion electrically connected to the solder ball terminals is provided, and a cover plate made of a metal and attached to a semiconductor chip so as to cover and come into contact with the same under a condition where the semiconductor chip is connected to the resin substrate by a flip-chip process, the cover plate including a base brought into contact with the semiconductor chip and a peripheral portion provided with a plurality of bonding portions where the cover plate is bonded to the substrate, the bonding portions being discontinuous to each other.
According to the above-described construction, the cover plate includes a plurality of the peripheral discontinuous bonding portions where the cover plate is bonded to the substrate to which the semiconductor chip is connected. Stress due to temperature changes occurs between the substrate and the cover plate when the cover plate is bonded to the substrate. However, the above-described construction can reduce the stress as compared with the conventional construction in which the cover plate has a continuous bonding portion. Consequently, the warp of the substrate due to the bonding of the cover plate thereto can be reduced even when the substrate is made of a resin. Furthermore, even when a large-sized substrate is used, the structure of the semiconductor device can be rendered practically durable.
In one preferred form, the bonding portions are arranged into an axial symmetry. Consequently, since the stress is evenly shared by the bonding portions, the stress can efficiently be dispersed.
In another preferred form, the cover plate includes at least one connectin
Hosomi Eiichi
Takano Eiji
Takubo Chiaki
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Kabushiki Kaisha Toshiba
Thai Luan
Tran Minh Loan
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