Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
1999-10-20
2001-10-16
Mayes, Curtis (Department: 1734)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S308200, C156S309900, C156S330900, C428S346000
Reexamination Certificate
active
06302991
ABSTRACT:
BACKGROUND OF THE INVENTION
(a) Field of the Invention
The present invention relates to a composite film which has excellent punching capability and is useful as a bonding element for semiconductor packaging.
(b) Description of Related Art
In semiconductor packaging, a bonding element which is a composite film produced by coating one or both sides of a base film with adhesives is used for bonding chips to lead frames to form LOC (lead on chip) or COL (chip on lead) structures or window-tub structures, or for bonding inner leads to heat spreaders to form composite lead frames with heat sinks attached. The bonding element is generally applied to the lead frames by punching out the bonding element from the composite film over the lead frames and pressing the bonding elements to required parts of the lead frames. However, the yield rate of the resulting lead frames with composite film attached is low since flashes are frequently formed at the punched edges of the composite film.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a composite film which is so excellent in punching capability as not to form flashes at the time of punching and are useful as bonding film in semiconductor packaging.
Another object of the present invention is to provide a lead frame with composite film bonded to the required parts of the lead frame by punching the composite film of the present invention and is reliable when used in semiconductor packages.
As a result of studies in the relationship between the properties of composite film and flashes, we have found that flashing can be effectively prevented when there exists specific relation between the thickness T of composite film and the edge tearing strength R and have completed the present invention based on the finding.
That is, the present invention provides a composite film, comprising a base film and an adhesive layer on at least one side of the base film, the composite film having a thickness of T (&mgr;m), the base film having an edge tearing strength of R (kg/20 mm), the adhesive layer having a total thickness of A, the base film having a thickness of B, T being related to R by a numerical formula R>0.6T-8 when T≦60, or by a numerical formula R≧28 when T>60, and A/B being 0.5 to 1.4.
The present invention further provides a lead frame with a composite film attached, comprising a lead frame body and a composite film applied to the lead frame body, the composite film being punched out from the composite film of the present invention.
The present invention further provides a method of producing a lead frame with a composite film attached, comprising punching out a composite film from the composite film of the present invention, pressing the punched out composite film to a lead frame body, with one adhesive layer contacting a surface of the lead frame body.
Herein, the edge tearing strength of base film is measured according to JIS C 2318.
Flashes, which tend to be formed at the edges of punched composite film comprising a base film and an adhesive layer on at least one side of the base film, can be extremely decreased by using a composite film wherein T and R are related to each other by the above numerical formula and the ratio of the thickness A of the adhesive layer to the thickness B of the base film, A/B, is within the above-described range.
THE PREFERRED EMBODIMENTS OF THE INVENTION
The composite film of the present invention is produced by applying adhesives to one or both sides of a base film, followed by drying. The adhesives applied to both sides of the base film may be identical with or different from each other.
The desirable adhesives are heat resistant adhesives which contain as main components heat resistant thermoplastic resins and have a glass transition temperature (Tg) of 150 to 350° C., a water absorption of 3% or less and a broadening length of 2 mm or less, and, therefore, polyimide adhesives and polyamide adhesives are suitable.
Herein, the term “polyimide” means not only polyimide but also any other resin containing imide bonds, such as polyamideimide, polyesterimide or polyetherimide.
If the glass transition temperature is beyond the above-described range, or the water absorption is more than 3% by weight, or the broadening length is longer than 2 mm, the resistance to reflow cracking of packages tends to be decreased.
The water absorption of the heat resistant adhesives is more preferably 2.5% by weight or less, particularly preferably 2.0% by weight or less. The broadening length is more preferably 1 mm or less, particularly preferably 0.5 mm or less.
In addition, fillers, such as ceramic powder, glass powder, silver powder, copper powder, resin powder, gum powder and coupling agents may also be added to the heat resistant adhesives. The heat resistant adhesives may also be used after impregnating with it a base sheet, such as glass fabric, aramid fabric or carbon fiber fabric.
Usable examples of the coupling agents include; vinylsilanes, such as vinyltriethoxysilane, vinyltrimethoxysilane and &ggr;-methacryloxypropyltrimethoxysilane; epoxysilanes, such as &ggr;-glycidoxypropyltrimethoxysilane, &ggr;-glycidoxypropylmethyldiethoxysilane and &bgr;-(3,4-epoxycyclohexyl)ethyltrimethoxysilane; aminosilanes, such as &ggr;-aminopropyltriethoxysilane, &ggr;-aminopropyltrimethoxysilane and N-phenyl-&ggr;-aminopropyltrimethoxysilane; mercaptosilanes, such as &ggr;-mercaptopropyltrimethoxysilane; and coupling agents such as titanates, aluminum chelates and zircoaluminates.
Of these, silane coupling agents are preferred with epoxysilane coupling agents being particularly preferred.
Herein, “broadening length of an adhesive” defines a width by which a film of the adhesive of 19×50 mm and 25 &mgr;m thick is broadened out perpendicularly from the middle of each side of the film by pressing the film at 350° C. at 3 MPa for one minute.
The base film to be used in the present invention, preferably, is a heat resistant film made of an engineering plastic, such as polyimide, polyamide, polysulfone, polyphenylenesulfide, polyetheretherketone or polyarylate. The thickness of the base film is preferably 5 to 150 &mgr;m, more preferably 20 to 125 &mgr;m.
The glass transition temperature (Tg) of the heat resistant film is preferably higher than the Tg of the adhesives to be used in the present invention, and is preferably 200° C. or higher, more preferably 250° C. or higher. The heat resistant film preferably has a water absorption of 3% by weight or less, more preferably 2% by weight or less.
Therefore, polyimide film is suitable as the base film to be used in the present invention because of the high Tg, the low water absorption and the low thermal expansion coefficient thereof. The particularly preferred film has a Tg of 250° C. or higher, a water absorption of 2% by weight or less and a thermal expansion coefficient of 3×10
−5
/° C. or less.
To increase the adhesion force between the base film and the adhesives, it is preferable to surface treat the base film. The surface treatments applicable in the present invention are not limited and include, for example, chemical treatment, such as alkali treatment and silane coupling agent treatment, physical treatment, such as sand blasting, plasma treatment or corona treatment, and it is possible to select one or more treatments that are the most suitable for the adhesives used. In cases where heat resistant film is used as the base film and adhesive layers of heat resistant adhesive are applied thereto, chemical treatment or plasma treatment is particularly suitable.
The method of forming the adhesive layers on the base film is not particularly limited, and an example of suitable methods comprises applying adhesive varnish to the base film and drying to remove solvents. The method of applying the adhesive varnish to the base film is not particularly limited, and may be any one using a doctor blade, a knife coater or a dye coater. The application may also be performed by dipping the base film in adhesive varnish, but it may be difficult to contr
Matsuura Hidekazu
Nomura Yoshihiro
Antonelli Terry Stout & Kraus LLP
Hitachi Chemical Co. Ltd.
Mayes Curtis
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