Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Utility Patent
1998-08-14
2001-01-02
Cain, Edward J. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S493000, C524S494000
Utility Patent
active
06169136
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a thermosetting resin potting composition for highly-integrated semiconductor devices to form a protective layer thereon.
In order to protect large-sized semiconductor chips such as large scale integrated circuits (LSI) and very large scale integrated circuits (VLSI) from moisture and the like, a thermosetting resin potting composition is applied to form a protective layer. In case a thermal expansion ratio of the thermosetting resin potting composition is quite different from that of the semiconductor chip, thermal stress is generated therebetween at the heating step after the application of the potting composition, and the thermal stress may damage the semiconductor chip. In order to suppress the thermal stress as small as possible, the thermosetting resin potting composition is required to have a thermal expansion ratio close to that of the semiconductor chips. In other words, the thermosetting resin potting composition is required to have a low thermal expansion ratio. The thermal expansion ratio of the thermosetting resin potting composition can be successfully lowered by increasing the content of the inorganic filler in the thermosetting resin potting composition. However, in this case, there is a problem as follows. That is, when the content of the inorganic filler in the potting composition is increased, the melt viscosity of the potting composition is also increased, and as a result, the flowability of the potting composition is lowered. The potting composition with low flowability cannot be satisfactorily applied onto the surface of the semiconductor chips. In order to solve this problem, various attempts have been conducted to increase a packed density of the inorganic filler without increasing its viscosity. For example, there has been an attempt that sphere silica particles are contained in the inorganic filler. There has been another attempt that sphere silica particles with particles having a continued particle size distribution are contained in the inorganic filler. However, these attempts have not been successful.
SUMMARY OF THE INVENTION
The present invention was made to overcome the problem residing in the prior art that the potting composition has poor flowability when its melt viscosity is increased by increasing the content of the filler containing sphere silica particles.
Therefore, it is an object of the present invention to provide a thermosetting resin potting composition which has a low thermal expansion ratio by increasing the content of the inorganic filler containing sphere silica particles, while having low melt viscosity and good flowability.
According to an aspect of the present invention, a thermosetting resin potting composition includes an inorganic filler containing silica powder as a main component. The silica powder comprises at least one particle group with respect to a particle size distribution, and the particle group has an average particle diameter of 0.01 to 10 &mgr;m, and a coefficient of particle diameter variation of 10 percent or less.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION
In general, a thermosetting resin potting composition has a low thermal expansion ratio when it contains large amount of an inorganic filler. However, it has been considered to be difficult to give excellent flowability to the potting composition when it contains large amount of inorganic filler. In order to solve this problem, the present inventors have conducted hard studies, and have found that it is possible to give excellent flowability to a thermosetting resin potting composition even if it contains large amount of an inorganic filler. This has been attained by using an inorganic filler containing sphere silica particles with sharp distribution in particle size.
Preferably, the sphere silica particles have two or more particle groups with respect to a particle size distribution. In the particle size distribution, it is more preferable that the average particle diameter of the larger particle group is 1.4 times or larger than its adjacent smaller particle group.
The preferable content of the inorganic filler is 60 to 90 weight percent of the total weight of the thermosetting resin potting composition. The preferable content of the sphere silica powder is 5 to 100 weight percent of the total weight of the inorganic filler.
The sharpness of the particle size distribution is expressed by a coefficient of particle diameter variation obtained from the following formula:
Coefficient of particle diameter variation (%)=(standard deviation/average value)×100
As sharper the particle size distribution of the sphere silica particles becomes, the melt viscosity of the potting composition can be lowered, even if the use amount of inorganic filler is increased. As a result, the potting composition has better flowability. In the present invention, the coefficient of particle diameter variation of the sphere silica particle groups should be 10 percent or less, and preferably 8 percent or less, and more preferably 6 percent or less.
When the average particle diameter is too small, the thermosetting resin potting composition has poor strength. Therefore, the minimum average particle diameter of the particle group should be 0.01 &mgr;m, and preferably 0.03 &mgr;m, and more preferably 0.05 &mgr;m. On the other hand, when the average particle diameter is too large, the thermosetting resin potting composition in the form of liquid does not sufficiently enter the minute spaces of 50 &mgr;m or smaller of the surface of the semiconductor chip. Therefore, the maximum average particle diameter thereof should be 10 &mgr;m, and preferably 5.0 &mgr;m, and more preferably 3.0 &mgr;m.
Preferably, sphere silica particles have a complete sphere shape as round as possible. The sphericity of the particles is expressed by a ratio of the longest particle diameter against the shortest particle diameter. Assuming that the particle has a complete sphere shape, the ratio is 1.00. When inorganic filler containing large amount of the sphere silica particles with the ratio of larger than 1.20 is used, the melt viscosity of the thermosetting resin potting composition is increased, and as a result, its flowability becomes poor. Therefore, the ratio is desired to be 1.00 to 1.20, and preferably 1.10 or less, and more preferably 1.05 or less.
The thermosetting resin potting composition additionally has high strength and humidity resistance when the sphere silica particles in the inorganic filler comprise two or more particle groups with different average particle diameters from each other. In this case, two or more raw material sphere silica particles are mixed with each other. Specifically, in accordance with the required strength of the potting composition, the average particle diameter of the sphere silica particles to be a main component of the filler is determined. Then, another sphere silica particles having smaller average particle diameter are selected, and mixed with the main component. In the mixed sphere silica particles, the spaces between the larger particles are filled with the smaller particles, whereby the packed density of the filler is increased. Thus-obtained filler gives high strength and humidity resistance to the potting composition. For example, when the main component of an inorganic filler is sphere silica particles with an average particle diameter of 1.5 &mgr;m, higher strength is obtained by being mixed with another sphere silica particles having an average particle diameter of 0.3 &mgr;m, as compared with the case where the sphere silica particles of the main component are used alone. In this case, each particle group preferably has a sharp particle size distribution. If the particle groups having a wide particle size distribution are mixed with each other, a complicated arrangement is required to obtain an ideal mixing ratio, because of their particle size distributions overlapping with each other.
When the different particle groups are used as sphere silica particles, it i
Iriguchi Jiro
Oishi Hideki
Shimizu Shuji
Yamamoto Yasuhiro
Cain Edward J.
Nippon Shokubai Co. , Ltd.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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