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...
Reexamination Certificate
2000-09-13
2002-08-13
Dawson, Robert (Department: 1712)
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...
C156S329000, C252S514000, C252S519310, C524S398000, C524S588000
Reexamination Certificate
active
06433055
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a hot-melt silicone adhesive composition and more particularly to a hot-melt silicone adhesive composition containing an electrically conductive filler and a hydroxy-functional organic compound.
BACKGROUND OF THE INVENTION
Hot-melt silicone adhesives are useful in a variety of applications because they possess the processing advantages of hot-melt adhesives in combination with the performance advantages of silicones, such as thermal stability, good moisture resistance, excellent flexibility, high ionic purity, low alpha particle emissions, and good adhesion to various substrates. For example, hot-melt silicone adhesives are potentially useful in the medical, automotive, electronic, construction, appliance, and aerospace industries.
Hot-melt silicone pressure sensitive adhesive (PSA) compositions are known in the art. For example, hot-melt silicone PSA compositions comprising a silicone fluid and a silicone resin are disclosed in U.S. Pat. Nos. 5,371,128; 4,865,920; 5,328,696; 5,658,975; 5,578,319; 5,147,916; 5,246,997; 5,290,564; 5,162,410; 5,482,988; 5,352,722; and 5,300,299. Moreover, moisture-curable hot-melt silicone PSA compositions are disclosed in U.S. Pat. Nos. 5,508,360; 5,340,887; 5,473,026; 5,302,671; and 5,905,123. However, the preceding references do not teach the electrically conductive filler and the hydroxy-functional organic compound of the present invention.
Hot-melt adhesive compositions comprising a thermoplastic silicone block copolymer and an electrically conductive filler are also known in the art. For example, U.S. Pat. No. 4,820,446 to Prud'Home discloses an electrically conductive, potentially adhesive composition comprising a thermoplasitc block copolymer containing polysiloxane and urethane groups having elastomeric properties, and particles whose surface at least is electrically conductive. Furthermore, U.S. Pat. No. 4,822,523 to Prud'Home discloses an electrically conductive, potentially adhesive composition comprising a thermoplastic polyblock organopolysiloxane copolymer having elastomeric properties, and particles whose surface at least is electrically conductive. However, neither of the aforementioned patents teaches the hydroxy-functional organic compound of the present invention.
SUMMARY OF THE INVENTION
The present invention is directed to an electrically conductive hot-melt silicone adhesive composition, comprising:
(A) a hot-melt silicone adhesive;
(B) an electrically conductive filler in an amount sufficient to impart electrical conductivity to the composition, wherein the filler comprises particles having at least an outer surface of a metal selected from silver, gold, platinum, palladium, and alloys thereof; and
(C) an effective amount of a hydroxy-functional organic compound having a molecular weight up to about 1000 and containing at least one hydroxy group per molecule, provided that when the composition is curable, the compound does not substantially inhibit cure.
The silicone composition of this invention has numerous advantages, including good flow, low VOC (volatile organic compound) content, good adhesion, and unexpectedly superior electrical conductivity as evidenced by low contact resistance and/or volume resistivity.
The silicone composition of this invention has numerous uses, including die attach adhesives, solder replacements, and electrically conductive coatings and gaskets. In particular, the silicone composition is useful for bonding electronic components to flexible or rigid substrates. The composition of the present invention is also useful as a thermal interface material in semiconductor packages. For example, the silicone composition can be used as the thermal interface between heat-generating semiconductor elements, such as power transistors and integrated circuits, and substrates, lead frames, and heat-dissipating fins.
These and other features, aspects, and advantages of the present invention will become better understood with reference to the following description and appended claims.
DETAILED DESCRIPTION OF THE INVENTION
This invention pertains to an electrically conductive hot-melt silicone adhesive composition, comprising:
(A) a hot-melt silicone adhesive;
(B) an electrically conductive filler in an amount sufficient to impart electrical conductivity to the composition, wherein the filler comprises particles having at least an outer surface of a metal selected from silver, gold, platinum, palladium, and alloys thereof; and
(C) an effective amount of a hydroxy-functional organic compound having a molecular weight up to about 1000 and containing at least one hydroxy group per molecule, provided that when the organosilicon composition is curable, the compound does not substantially inhibit cure.
Component (A) of this invention is at least one hot-melt silicone adhesive. As used herein, the term “hot-melt” describes a silicone adhesive that is nonflowable at room temperature, but converts to a flowable state at an elevated temperature, for example, from about 50 to about 200° C. Component (A) can be any hot-melt silicone adhesive known in the art, provided the silicone composition formed by combining component (A) with components (B) and (C) exhibits improved contact resistance and/or volume resistivity compared with a similar silicone composition lacking only the hydroxy-functional organic compound. The hot-melt silicone adhesive can be a noncurable adhesive that becomes flowable at an elevated temperature and reverts to a nonflowable state upon cooling. Alternatively, the hot-melt silicone adhesive can be a curable adhesive that undergoes a curing (crosslinking) reaction after the adhesive has been applied to a substrate. Component (A) can be a single hot-melt silicone adhesive or a mixture comprising two or more different hot-melt silicone adhesives.
Hot-melt silicone adhesives suitable for use in the silicone composition of this invention include, but are not limited to, hot-melt silicone pressure sensitive adhesives comprising a silicone fluid and an organopolysiloxane resin; thermoplastic silicone-organic block copolymers; and moisture-curable hot-melt silicone pressure sensitive adhesives. Examples of the aforementioned hot-melt silicone adhesives and methods for their preparation are well known in the art. The U.S. patents cited in the Background section are hereby incorporated by reference to teach hot-melt silicone adhesives suitable for use in the silicone composition of the present invention.
Component (B) of this invention is at least one electrically conductive filler comprising particles having at least an outer surface of a metal selected from silver, gold, platinum, palladium, and alloys thereof. Fillers comprising particles consisting of a metal selected from silver, gold, platinum, palladium, and alloys thereof typically have the form of a powder or flakes with an average particle size of from 0.5 to 20 &mgr;m. Fillers comprising particles having only an outer surface of a metal selected from silver, gold, platinum, palladium, and alloys thereof typically have an average particle size of from 15 to 100 &mgr;m. The core of the particles can be any electrically conductive or insulative material that supports a surface consisting of the aforementioned metal and does not adversely affect the electrical properties of the silicone composition. Examples of such materials include, but are not limited to, copper, solid glass, hollow glass, mica, nickel, and ceramic fiber.
In the case of electrically conductive fillers comprising metal particles having the form of flakes, the surface of the particles may be coated with a lubricant, such as a fatty acid or fatty acid ester. Such lubricants are typically introduced during the milling process used to produce flakes from a metal powder to prevent the powder from cold welding or forming large aggregates. Even when the flakes are washed with a solvent after milling, some lubricant may remain chemisorbed on the surface of the metal.
The electrically conductive filler of this invention also incl
Kleyer Don Lee
Lutz Michael Andrew
Brown Catherine U.
Dawson Robert
Dow Corning Corporation
Milco Larry A.
Zimmer Marc S.
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