Active solid-state devices (e.g. – transistors – solid-state diode – Housing or package – With large area flexible electrodes in press contact with...
Reexamination Certificate
1999-04-22
2001-12-18
Williams, Alexander O. (Department: 2826)
Active solid-state devices (e.g., transistors, solid-state diode
Housing or package
With large area flexible electrodes in press contact with...
C257S689000, C257S712000, C257S658000, C257S732000, C257S719000, C257S699000, C361S310000, C361S310000
Reexamination Certificate
active
06331730
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor device for converting an AC output of an AC generator to a DC output. More particularly, the present invention relates to a semiconductor device which will be suitable for preventing defects of characteristics of a semiconductor chip which defects are induced when the semiconductor chip is pushed and fixed to a heat spreader (heat radiation plate).
In semiconductor devices according to the prior art for converting the AC output of AC generators to the DC output, the semiconductor chip is fixed, for example, to a flat portion of a bottom plate of a dent support electrode body, and the dent support electrode body is in turn pushed into a metal heat spreader having electrical conductivity and heat transferability, as described in JP-A-55-19828.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a semiconductor device which can prevent breakage resulting from deformation and can reduce the force acting on the semiconductor chip at the time of assembling, and can reduce the degree of deformation.
It is another object of the present invention to provide a semiconductor device which has long service life as well as high reliability.
It is still another object of the present invention to provide a semiconductor device which can be fabricated at a low cost of production.
The semiconductor chip portion of the conventional push-in type semiconductor devices described above is sealed by an insulating material for the purpose of insulation and protection. Though a silicone rubber has been used in many cases, an epoxy resin has been used, too, in some cases.
The heat spreader supporting/fixing structure of the semiconductor device by the push-in operation is achieved by boring a circular fitting hole having an inner diameter somewhat smaller than an outer diameter of the support electrode body in the heat spreader and fitting the support electrode body into this fitting hole by applying a load to the support electrode body.
Therefore, when the semiconductor device having the conventional structure is pushed into the heat spreader, a large force is applied to the semiconductor chip through the support electrode body, and the semiconductor chip is broken in some cases during this push-in operation. This problem can be solved, in principle, by interposing a sheet-like intermediate member between the support electrode body and the semiconductor chip, but this method is not desirable because the cost of production drastically increases due to the increase in the number of components and due to deterioration of the assembly working factor. In addition, the side wall of the dent support electrode body undergoes deformation to the inner peripheral side during the push-in operation and the insulating member is compressed. When an epoxy resin having a large Young's modulus is used for the insulating member, the force resulting from this deformation is transferred to the semiconductor chip, so that breakage of the semiconductor chip is more likely to occur.
Therefore, a push-in test is carried out by producing a prototype structure which reduces much more the force transferred from the support electrode body to the semiconductor chip during the push-in operation than in the conventional structure, and which is shown in FIG.
2
. In order to prevent the curve of the support electrode structure
3
by the compressive force applied from the heat spreader
4
, the support electrode body in this prototype structure is made thicker than in the conventional structure. The semiconductor chip is sealed by the epoxy type resin. The result of the experiment reveals that breakage such as the transverse crack from the outer peripheral side and the longitudinal crack from any surface including the upper or the lower surface is observed in some cases in the semiconductor chip
1
as shown in FIG.
2
. It is assumed that the breakage develops because the function of reducing the force applied from the support electrode body
3
to the semiconductor chip
1
is not sufficient.
Another problem occurs in that the insulating member
7
peels from the support electrode body
3
due to the contact of the support electrode body
3
with the heat spreader
4
during the push-in operation. This is because the support electrode body undergoes great deformation due to the force applied to it from the heat spreader
4
. When the semiconductor device is used in the environment in which the semiconductor chip is likely to be exposed to moisture, the moisture may enter from this peel portion and will invite the problem of the drop of the rectification operation due to the increase of a leakage current that flows in the opposite direction.
These problems can be solved by reducing the force applied to the semiconductor chip through the support electrode body and through the insulating material. They can be also solved by reducing deformation of the support electrode body due to the push-in operation in the proximity of the bonding surface between the support electrode body and the insulating member.
In a semiconductor device including a semiconductor chip, a support electrode body bonded to one of the ends of the semiconductor chip through a bonding member and equipped with a heat spreader fixing portion on the outer periphery thereof for supporting and fixing a heat spreader, a lead electrode body bonded to the other end of the semiconductor chip through a bonding member and an insulating member disposed at the bond portion between the semiconductor chip and the support electrode body and at the bond portion between the semiconductor chip and the lead electrode body, the semiconductor device according to the present invention has the following structural requirements.
(1): A first portion having a different outer diameter from that of the heat spreader fixing portion is formed on the support electrode body.
(2): In the construction (1) described above, the outer diameter of the first portion is not greater than 0.95 times the outer diameter of the heat spreader fixing portion.
This construction can solve the problems described above because the force transferred from the heat spreader is dispersed inside the support electrode body.
According to the result of the experiments and to the examination result by numerical analysis conducted by the inventor of the present invention, it has been found that if the outer diameter of the circular cylindrical shape or the maximum outer diameter of the circular truncated conical shape on the chip mounting surface side is not greater than 0.95 times the outer diameter of the support electrode body as shown in
FIG. 3
, the stress developing in the semiconductor chip is below the breaking stress limit.
(3): In the construction (1) or (2) described above, a cylindrical side wall is formed on the semiconductor chip mounting surface side of the support electrode body, and the inner diameter of the side wall on the opposite side to the support electrode body side is smaller than the inner diameter on the support electrode side.
This construction can prevent peel of the insulating member from the support electrode body. Further, a similar effect can be obtained by forming a lead protuberance portion on the lead extending up from the header surface of the lead electrode body in such a fashion that a part, or the entire part, of the protuberance portion comes into contact with the insulating member.
(4): In the construction (1) or (2) described above, the difference of thickness obtained by subtracting the thickness of the contact portion of the support electrode body, which is in contact with the heat spreader, from the thickness between the semiconductor chip mounting surface and its bank is from 0.07 to 0.25 times, or at least 0.47 times, the maximum outer diameter of the support electrode body.
According to the result of the experiments and the examination result by numerical analysis conducted by the present inventor, both transverse and longitudinal cracks of the semiconductor chip at the ti
Kitano Makoto
Miura Hideo
Nakajima Chikara
Terasaki Takeshi
Antonelli Terry Stout & Kraus LLP
Hitachi , Ltd.
Williams Alexander O.
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