Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Including a second component containing structurally defined...
Reexamination Certificate
1998-11-20
2002-04-02
Chen, Vivian (Department: 1773)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Including a second component containing structurally defined...
C428S402000, C428S403000, C428S404000, C428S457000, C106S287340, C106S481000, C423S335000
Reexamination Certificate
active
06365269
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to plastic compositions for sheathing a metal body and/or a semiconductor body. The plastics have at least one polymer, in particular a duroplast (thermosetting plastic), and at least one filler. The invention also relates to method for producing fillers and to the fillers themselves. Finally, the invention also relates to plastic composite bodies, which have a base body comprising a metal and/or semiconductor material and have a sheath that has at least one filler and a polymer. Finally, the invention also pertains to a method for detecting the presence of a filler according to the invention in a plastic composite body.
In plastic composite bodies, such as semiconductor components, which have a base body of metal, such as a lead frame, and bodies of semiconductor material, such as a microchip, undesirable failures often occur under actual environmental conditions. In the prior art, this is ascribed above all to a different coefficient of thermal expansion for the material of a sheath of the base body and for the base body itself.
To compensate for differences in the coefficient of thermal expansion of the sheath and of the base body, the prior art often admixed quartz glass with the basic material of the sheath. It is problematic that with the polymers used to fabricate the sheath, adding quartz glass still cannot attain an adequate reduction in the coefficient of thermal expansion of the sheath. If the proportions of quartz glass in the sheath material are too high, problems also occur in molding the sheath.
In the prior art, a different course is therefore fundamentally recommended, namely the development of sheathing materials that adhere better to the base body. Here it is problematic that the polymers developed for this purpose are very expensive and can therefore not be considered for use on a mass production scale.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide suitable plastic compositions, fillers, methods for producing suitable fillers, and plastic composite bodies, which overcome the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and which assure reliable operation of the plastic composite bodies, even under changing environmental conditions.
With the foregoing and other objects in view there is provided, in accordance with the invention, a plastic composition for sheathing a metal and/or semiconductor body, comprising:
at least one polymer, in particular a duroplast, and at least one filler;
the filler having spherical SiO
2
particles with a graduated diameter distribution defining individual diameter stages, and wherein a standard deviation in a mean diameter of the SiO
2
particles of at least one diameter stage is less than 10%.
In accordance with an added feature of the invention, the standard deviation in the mean diameter of the SiO
2
particles of at least one diameter stage is less than 5%, and preferably even less than 1.7%.
In other words, it is a first aspect of the invention to provide a filler for the polymer forming the sheath, where spherical SiO
2
particles with a graduated diameter distribution are used, and the standard deviation in the mean diameter of the SiO
2
particles of at least one diameter stage is less than 10%. Depending on the quality of the production process of the spherical SiO
2
particles, standard deviations of the mean diameter of less than 5% and less than 1.7% can also be attained.
In accordance with an additional feature of the invention, a quantity of SiO
2
particles of at least one diameter stage and the mean diameters of the individual diameter stages are selected such that a packing density of the SiO
2
particles of at least 90% results. A packing density of better than 95% can be achieved by proper selection of these parameters. This results in a plastic composition which has the requisite rheological properties from rolled processing with a low proportion of polymer. The spherical fillers may be provided in bimodal or trimodal particle size distributions. For such a filler, beginning with the most precisely possibly specified primary particle diameter, smaller particles are admixed, whose diameters fit precisely into the interstices thus created in the packing of the primary particles. For a primary particle diameter of d=40 &mgr;m, interstices are created that are optimally filled up approximately with secondary beads or balls 9 &mgr;m in diameter. The residual voids that then still remain can be filled with a further fraction of correspondingly smaller particles. By using SiO
2
particles with a low standard deviation of the mean diameter within a diameter stage, it becomes especially easy to classify the corresponding particles in the smaller diameter stages. It is advantageous that the improvements in the properties of the plastic composition result regardless of which material makes up the primary component of the polymer.
With the above and other objects in view there is also provided, in accordance with an alternative feature of the invention, a plastic composition for sheathing a metal and/or semiconductor body, comprising:
at least one polymer (e.g. duroplast) and at least one filler;
the filler comprising spherical SiO
2
particles each having an interior with a center and a surface, and wherein an index of refraction in the interior of at least one of the SiO
2
particles increases from the center to the surface.
The same advantages as noted above are obtained in the use of spherical SiO
2
particles as a filler in which the index of refraction in the interior of at least one SiO
2
particle increases in a direction from its center to its surface. It has been found that when SiO
2
particles that have this characteristic are used, plastic compositions that can be processed especially well can also be produced.
The course of the index of refraction or the optical coefficient of refraction in the interior of a spherical SiO
2
particle of a sheathing material according to the invention is measured using contrast variation in a suspension of the spherical SiO
2
particles. Precisely in spherical SiO
2
particles with diameters up to about 100 nm, the courses according to the invention of the optical index of refraction can be readily determined. The method for measuring the index of refraction is based on the fact that the optical contrast of a suspended particle depends on the quantitative difference between the index of refraction of the particle and the index of refraction of the dispersing agent. If the indices of refraction of the particle and of the dispersing agent have the same value, then the contrast equals zero and thus the particle is optically imperceptible. It is possible to vary the optical contrast to suspended particles if the index of refraction of the dispersing agent can be varied continuously by the addition of a miscible second substance. If the dispersing agent is formed by hexane, then benzene can for instance be added as a second substance. If the index of refraction of the particles differs from the index of refraction of the peripheries of the particles, then the contrast of the “shells” of the particles can be reduced to zero by the choice of a suitable index of refraction of the dispersing agent. Then only a nucleus of the particles remains optically observable. In particles with a nonhomogeneous course of the index of refraction, a variation in the optically observable particle size can be attained. By varying the proportions of dispersing agent and second substance, the course of the index of refraction can thus be measured in the interior of the spherical SiO
2
particles. For the measurement, a particle size determination is done using a scattered light method, while the index of refraction of the dispersing agent is being varied. From the association between the index of refraction of the dispersing agent and the measured particle diameter, the radius-dependent course of the index of refraction inside the particle
Atzesdorfer Alexandra
Heckmann Klaus
Thumbs Josef
Greenberg Laurence A.
Infineon - Technologies AG
Lerner Herbert L.
Stemer Werner H.
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