Stock material or miscellaneous articles – All metal or with adjacent metals – Composite; i.e. – plural – adjacent – spatially distinct metal...
Reexamination Certificate
2002-10-31
2004-12-14
Moore, Margaret G. (Department: 1712)
Stock material or miscellaneous articles
All metal or with adjacent metals
Composite; i.e., plural, adjacent, spatially distinct metal...
C523S451000, C523S457000, C523S458000, C523S460000, C523S466000, C525S476000, C525S523000, C528S089000, C528S108000
Reexamination Certificate
active
06830825
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an epoxy resin composition for encapsulating semiconductors which contains substantially neither halogen-based flame-retarding agents nor antimony compounds and is excellent in solder reflowing resistance, flame retardance and high-temperature storage characteristics, and to a semiconductor device.
BACKGROUND ART
Hitherto, electronic parts such as diodes, transistors and integrated circuits have been encapsulated mainly with epoxy resin compositions. These epoxy resin compositions usually contain bromine atom-containing flame retarding agents, and antimony compounds such as antimony trioxide, antimony tetroxide and antimony pentoxide for the purpose of imparting flame retardance. However, with a worldwide increase of consciousness for environmental protection, there is a great demand for epoxy resin compositions having flame retardance which contain neither halogen-based flame-retarding agents nor antimony compounds.
Moreover, it is known that if semiconductor devices encapsulated with epoxy resin compositions containing halogen-based flame-retarding agents and antimony compounds are stored at high temperatures, halides produced owing to heat decomposition of these flame-retarding agents are liberated and corrode the bonding pad portions of semiconductor elements to damage the reliability of semiconductor devices. Thus, epoxy resin compositions are desired which can attain degree of flame retardance of V-0 in UL-94 without using halogen-based flame-retarding agents and antimony compounds as flame-retarding agents.
Corrosion resistance of bonding pad portions of semiconductor elements after semiconductor devices are stored at high temperatures (e.g., 185° C.) is called high-temperature storage characteristics, and as methods for improving the high-temperature storage characteristics, there are proposed a method of using diantimony pentoxide (JP-A-55-146950), a method of using antimony oxide and an organic phosphine in combination (JP-A-61-53321), and the like, and effects of these methods have been confirmed. However, some of epoxy resin compositions are still unsatisfactory for the high level recently required for high-temperature storage characteristics of semiconductor devices.
Various flame-retarding agents have been investigated for these demands. For example, metal hydroxides such as aluminum hydroxide, magnesium hydroxide and the like, and boron compounds have been investigated, but these compounds do not develop the effect of flame retarding unless they are used in large amounts, and, besides, they may deteriorate curability. Furthermore, under the present circumstances where surface packaging of semiconductor devices are generally carried out, if semiconductor devices which have absorbed moisture are exposed to high temperatures at the time of soldering, explosive stress of water vapor produced by vaporization causes cracking of package or delamination at the interface between semiconductor elements or lead frames and semiconductor encapsulating materials, resulting in troubles of the electrical reliability being severely damaged. Thus, a great task is to inhibit these troubles, namely, to improve solder resistance. Moreover, in view of the recent environmental problems, there is a tendency to use no lead in solders used for mounting of semiconductor devices, and, as a result, it is unavoidable that the temperature for solder reflowing treatment rises and it is considered that solder resistance required will become severer.
In order to improve the solder reflowing resistance, it has been attempted to add inorganic fillers in large amounts to epoxy resin compositions for encapsulation of semiconductors, thereby to reduce absorption of moisture and heat expansion of the semiconductor devices using the compositions and to increase strength of the semiconductor devices. Therefore, there are generally employed, for example, a means of using epoxy resins of low viscosity type or crystalline epoxy resins which are crystalline at room temperature, but which show extremely low viscosity at temperatures higher than melting point, thereby to inhibit reduction of fluidity of epoxy resin compositions at molding which is caused by increase of the amount of inorganic fillers added, or a means of using phenolic resins or epoxy resins in which the resin skeleton per se is hydrophobic and the cured products of which also show low moisture absorption.
Because of low glass transition temperatures, crystalline epoxy resins, hydrophobic epoxy resins and phenolic resins tend to deteriorate in high-temperature storage characteristics, and for improving the characteristics, there are requested compositions using neither halogen-based flame-retarding agents nor antimony compounds.
Furthermore, since the crystalline epoxy resins are low in viscosity, they are low in curability, and since the hydrophobic epoxy resins and the phenolic resins have a molecular structure long in distance between cross-linking points, cured products thereof are soft, and use of flame-retarding agents which hinder curing of the epoxy resins is difficult for increasing productivity by improving release properties at molding.
That is, it is demanded to provide an epoxy resin composition which maintains flame retardance, is excellent in moldability, solder reflowing resistance and high-temperature storage characteristics, and uses substantially neither halogen-based flame-retarding agents nor antimony compounds.
DISCLOSURE OF INVENTION
The present invention provides an epoxy resin composition for encapsulating semiconductors which contains substantially neither halogen-based flame-retarding agents nor antimony compounds and is excellent in moldability, flame retardance, solder reflowing resistance and high-temperature storage characteristics, and furthermore provides a semiconductor device made by encapsulating semiconductor elements with the epoxy resin composition.
The present invention is an epoxy resin composition for encapsulating semiconductors which comprises (A) an epoxy resin, (B) a phenolic resin, (C) a curing accelerator, (D) an inorganic filler and (E) a phosphazene compound as essential components, wherein the total weight of phosphate ion and phosphite ion contained in the phosphazene compound is not more than 500 ppm.
A more preferred embodiment is the epoxy resin composition for encapsulating semiconductors in which the phosphazene compound has a melt viscosity of 0.7×10
−2
to 5×10
−2
Pa·s at 150° C.
Another preferred embodiment is the epoxy resin composition for encapsulating semiconductors in which the phosphazene compound is a cyclic phosphazene compound represented by the following formula (1):
wherein n is an integer of 3-7, and R's denote same or different organic groups which are selected from alkyl groups, alkenyl groups, alkoxy groups, aryl groups, aryloxy groups, polyoxyalkylene groups, these groups in which at least one hydrogen atom is substituted with a group having N, S, O or F atom, amino groups, fluoroalkyl groups and fluoroalkyloxy groups. These phosphazene compounds may be used each alone or in admixture.
Another preferred embodiment is the epoxy resin composition for encapsulating semiconductors wherein at least n of 2n R's in the cyclic phosphazene compound represented by the formula (1) are phenoxy groups, or wherein at least one of 2n R's in the cyclic phosphazene compound represented by the formula (1) is an amino group or a polyoxyalkylene group.
Another preferred embodiment is the epoxy resin composition for encapsulating semiconductors in which the epoxy resin (A) is at least one resin selected from epoxy resins represented by the following formulas (2)-(6):
wherein R's denote hydrogen or an alkyl group of 1-4 carbon atoms and may be the same or different,
wherein R's denote hydrogen or an alkyl group of 1-4 carbon atoms and may be the same or different, a is 0 or a positive number of 1-4, and n is a positive number of 1-10 as an average value,
wherein R's denote hydrogen
Aihara Takashi
Fujieda Yoshio
Mizushima Ayako
Nikaido Hiroki
Oota Ken
Aylward D.
Moore Margaret G.
Smith , Gambrell & Russell, LLP
Sumitomo Bakelite Company Ltd.
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