Stock material or miscellaneous articles – All metal or with adjacent metals – Composite; i.e. – plural – adjacent – spatially distinct metal...
Reexamination Certificate
1998-11-03
2001-06-05
Dawson, Robert (Department: 1712)
Stock material or miscellaneous articles
All metal or with adjacent metals
Composite; i.e., plural, adjacent, spatially distinct metal...
C523S424000
Reexamination Certificate
active
06242110
ABSTRACT:
The present invention relates to an epoxy resin composition for encapsulating a semiconductor, superior in flame retardancy and reliability, as well as to a semiconductor device using the composition.
Electronic parts such as diodes, transistors, integrated circuits and the like have been encapsulated mainly with epoxy resin compositions. These epoxy resin compositions contain, as a flame retardant, a halogen-based flame retardant and antimony trioxide so that the compositions can show good flame retardancy. Meanwhile, it is requested to develop, from the standpoint of environmental sanitation, an epoxy resin composition of excellent flame retardancy using neither halogen-based flame retardant nor antimony trioxide.
For the above request, metal hydroxides (e.g. aluminum hydroxide and magnesium hydroxide) and boron compounds have been investigated. They, however, must be added in a large amount in order to show flame retardancy, and contain a large amount of impurities and have a problem in moisture resistance; therefore, they have found no practical application yet. Red phosphorus-based flame retardants are effective even when added in a small amount and are useful to obtain a flame-retardant epoxy resin composition; however, red phosphorus reacts with a very small amount of water to generate phosphine or corrosive phosphoric acid and has a problem in moisture resistance, making impossible its use in an epoxy resin composition for encapsulating a semiconductor which has a severe requirement for moisture resistance. Hence, it was tried to coat red phosphorus particles with aluminum hydroxide, a metal oxide, an inorganic compound or an organic compound (e.g. a thermosetting resin) to stabilize red phosphorus; however, such an approach still has a problem in moisture resistance. Thus, no epoxy resin composition for encapsulating a semiconductor has been developed yet which uses neither halogen-based flame retardant nor antimony trioxide but which has both flame retardancy and moisture resistance.
In view of the above situation, the present invention provides an epoxy resin composition for encapsulating a semiconductor, which is free from any flame retardant and yet superior in flame retardancy and reliability, and also a semiconductor device using the composition.
The present inventors made an intensive study in order to solve the above-mentioned problems of the prior art. As a result, the present inventors found out that use of a particular epoxy resin and a particular phenolic resin in combination can provide an epoxy resin composition for encapsulating a semiconductor which is free from any flame retardant and yet superior in flame retardancy and reliability. The present inventors also found out that the epoxy resin composition can have higher flame retardancy by controlling its reactivity. The present invention has been completed based on these findings.
The present invention provides an epoxy resin composition for encapsulating a semiconductor, comprising as essential components:
(A) a phenolic resin containing, in the total phenolic resin amount, 30 to 100% by weight of a phenolic resin of novolac structure containing, in the molecule, a biphenyl derivative and/or a naphthalene derivative,
(B) an epoxy resin containing, in the total epoxy resin amount, 30 to 100% by weight of an epoxy resin of novolac structure containing, in the molecule, a biphenyl derivative and/or a naphthalene derivative,
(C) an inorganic filler, and
(D) a curing accelerator.
In the present epoxy resin composition for encapsulating a semiconductor, it is preferable that the ratio of the number of phenolic hydroxyl groups of total phenolic resin to the number of epoxy groups of total epoxy resin is larger than 1 but not larger than 2.
The present invention also provides a semiconductor device obtained by encapsulating a semiconductor with the above epoxy resin composition.
The present inventors found out that use of a particular epoxy resin and a particular phenolic resin in combination can provide an epoxy resin composition superior in flame retardancy and reliability and also that the epoxy resin composition can have higher flame retardancy by controlling its reactivity.
In the present invention, the particular phenolic resin refers to a phenolic resin of novolac structure containing, in the molecule, a biphenyl derivative and/or a naphthalene derivative, and the particular epoxy resin refers to an epoxy resin of novolac structure containing, in the molecule, a biphenyl derivative and/or a naphthalene derivative. They each contain, in the molecule, an aromatic ring(s) of a biphenyl derivative and/or a naphthalene derivative.
A phenolic resin or an epoxy resin each containing, in the molecule, an aromatic ring(s) of biphenyl derivative and/or naphthalene derivative has a large bond energy between molecules and hardly causes decomposition when burnt, expressing flame retardancy. As the number of aromatic rings in the molecule of the phenolic resin or the epoxy resin is larger, the resin is more resistant to combustion and has higher flame retardancy; for example, the resin containing anthracene is more resistant to combustion than the resin containing naphthalene. However, such a resin having a larger number of aromatic rings has too high a softening point and inferior flowability. Therefore, as the aromatic ring, a biphneyl derivative and a naphthalene derivative are best in view of the balance of flame retardancy and flowability.
The present epoxy resin composition can have higher flame retardancy by controlling its reactivity. That is, the present epoxy resin composition can have higher flame retardancy when the ratio of the number of phenolic hydroxyl groups of total phenolic resin to the number of epoxy groups of total epoxy resin is allowed to be larger than 1. The reason might be that in the cured resin composition, there are residual hydroxyl groups which have not reacted with epoxy groups and, when the cured resin composition is burnt, these hydroxyl groups cause a dehydration reaction (an endothermic reaction) between themselves. The ratio of the number of phenolic hydroxyl groups of total phenolic resin to the number of epoxy groups of total epoxy resin is preferably not larger than 2. The ratio of larger than 2 reduces the above-mentioned reactivity of epoxy resin composition strikingly. The ratio is more preferably 1.1 to 1.5.
In the combination of a general-purpose phenolic resin (phenolic novolac) and a general-purpose epoxy resin (o-cresol novolac type epoxy), as the ratio of the number of phenolic hydroxyl groups of total phenolic resin to the number of epoxy groups of total epoxy resin is made larger, the combination tends to have higher water absorption and lower moisture resistance. In contrast, in the combination of the particular phenolic resin and the particular epoxy resin according to the present invention, neither large increase in water absorption nor reduction in moisture resistance is seen. This is presumed to be because the particular phenolic resin and the particular epoxy resin of the present invention both have hydrophobic aromatic rings and further because in the combination of these resins, the distance between crosslinked molecules is larger than in the combination of the general-purpose phenolic resin (phenolic novlac) and the general-purpose epoxy resin (o-cresol novolac type epoxy) and resultantly no large increase in water absorption is seen.
In the present invention, the particular phenolic resin refers to a phenolic resin of novolac structure containing, in the molecule, a biphenyl derivative and/or a naphthalene derivative. The phenolic resin of novolac structure containing, in the molecule, a biphenyl derivative is specifically represented by the formula (1):
The phenolic resin represented by the formula (1) is a resin obtained by reacting phenol and e.g. a bismethoxymethylenebiphenyl. In the formula (1), n is 1 to 10. When n is 11 or larger, the resin has too high a viscosity and has reduced flowability. For obtaining flame retardancy, it is desired that th
Iji Masatoshi
Iwasaki Shinichi
Kiuchi Yukihiro
Aylward D.
Dawson Robert
Smith Gambrell & Russell
Sumitomo Bakelite Company Limited
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