JP4003285B2 - Film adhesive excellent in reflow resistance, lead frame and semiconductor device using the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a film adhesive used as an adhesive member in a semiconductor package, a lead frame using the same, and a semiconductor device. In particular, the present invention relates to a film adhesive excellent in reflow resistance.
[0002]
[Prior art]
For semiconductor packages, a base film is used to connect the lead frame and the chip in a LOC (lead on chip) structure, a COL (chip on lead) structure, or a frame tab structure, and to connect the inner lead and the heat spreader in a composite lead frame with a heat sink. The joining member which consists of a composite film which apply | coated the adhesive agent to the one side or both sides of this is used.
Conventionally, a thermosetting adhesive such as an epoxy type or a rubber-modified epoxy type, or a heat resistant hot melt adhesive such as polyimide or polyamideimide has been used for joining a semiconductor lead frame and a semiconductor element. When a package is assembled using these adhesives, there is a problem in that moisture in the adhesive that performs heating such as solder reflow after moisture absorption evaporates and expands and the package expands.
In order to cope with this problem, an adhesive having excellent reflow resistance that does not swell due to heating after moisture absorption is desired.
Conventionally, attempts have been made to leave a solvent from the viewpoint of lowering the bonding temperature or improving workability. For example, the solvent is consciously left to soften the resin (Japanese Patent Laid-Open No. 3-64386), the solvent is used as a processing aid in the melt processing of polyimide (Japanese Patent Laid-Open No. 60-118741), However, there is no suggestion that the reflow resistance is improved when used in a semiconductor package.
[0003]
[Problems to be solved by the invention]
The present invention solves such problems, and provides a film-like adhesive having excellent reflow resistance used as an adhesive member in a semiconductor package, a lead frame using the same, and a semiconductor device. .
[0004]
[Means for Solving the Problems]
As a result of intensive studies, the present inventors have found that an adhesive layer formed from an adhesive composition obtained by mixing a specific solvent in a specific amount of a heat-resistant resin varnish has excellent reflow resistance, and completes the present invention. It came to.
In the adhesive composition of the present invention, a heat-resistant resin having a glass transition temperature of 250 ° C. or lower and a solvent having a boiling point of 250 ° C. or higher are 3 to 30% by weight with respect to the resin, and a coupling agent is 10 with respect to the resin. It is characterized by comprising a solvent having a weight% of not more than 100% by weight and a filler having a boiling point lower than 250 ° C.
The adhesive composition can be a film adhesive excellent in reflow resistance, and the adhesive composition can be a film adhesive excellent in reflow resistance formed on at least one surface of a substrate. it can.
The adhesive layer is used on a lead frame, and a semiconductor element can be mounted on the lead frame to form a semiconductor device.
[0005]
That is, in the present invention, a heat-resistant resin having a glass transition temperature of 250 ° C. or lower and a solvent having a boiling point of 250 ° C. or higher are 3 to 30% by weight with respect to the resin, and a coupling agent is 10% by weight or less with respect to the resin. Provided is an adhesive composition excellent in reflow resistance, characterized in that the filler comprises a solvent of 100% by weight or less with respect to the resin and has a boiling point lower than 250 ° C., and a lead frame and a semiconductor device using the adhesive composition To do.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
The adhesive used in the present invention is desirably a heat-resistant adhesive mainly composed of a heat-resistant thermoplastic resin having a glass transition temperature of 250 ° C. or lower, preferably 150 to 250 ° C. For that purpose, a polyimide adhesive and a polyamide are used. An adhesive is preferred.
Here, the polyimide includes a resin having an imide group such as polyamide imide, polyester imide, and polyether imide.
[0007]
In the present invention, the solvent remaining in the adhesive layer is a solvent having a boiling point of 250 ° C. or higher, preferably 50 ° C. or higher. Examples of the solvent include sulfolane and glycerin. A solvent having a boiling point lower than 250 ° C. is preferably used as a solvent for dissolving the adhesive, and a solvent having a boiling point of 250 ° C. or higher is added to the adhesive solution to produce a film adhesive.
In the present invention, the amount of residual solvent was calculated from the weight change before and after drying after the film was dried at 300 ° C. for 30 minutes.
If the residual solvent amount is less than 0.5%, the effect of improving the reflow resistance is small, and if it exceeds 10 wt%, foaming at the time of adhesion becomes remarkable, which is not preferable.
[0008]
In the present invention, the evaluation of reflow resistance is carried out by sticking a film adhesive on a copper plate, immersing it in water in a greenhouse for 24 hours, and then leaving it on a hot plate at a predetermined temperature for 20 seconds. The temperature at which foaming occurs for the first time in the periphery of the film was taken as the foaming temperature and used as an index of reflow resistance.
The heat-resistant adhesive used in the adhesive member of the present invention may be used alone, or may be applied or impregnated on a base material such as a base film or a sheet. In addition, when the heat-resistant adhesive is used alone, it may be directly applied to an adherend such as a semiconductor chip or a lead frame, or may be applied to the adherend in the form of a sheet in advance and used after thermocompression bonding. May be.
[0009]
The substrate used in the present invention is a film, glass cloth, carbon fiber cloth, cloth such as polyaramid cloth, metal foil such as copper foil, aluminum foil, and stainless steel foil.
Examples of the heat resistant film used as the base film include films of engineering plastics such as polyimide, polyamide, polysulfone, polyphenylene sulfide, polyether ether ketone, and polyarylate. The glass transition temperature (Tg) of the heat resistant film is higher than that of the heat resistant adhesive used in the present invention, preferably 200 ° C. or higher, more preferably 250 ° C. or higher. A heat-resistant film having a water absorption of 3% by weight or less, preferably 2% by weight or less is used.
Therefore, the heat resistant film used in the present invention is preferably a polyimide film from the viewpoint of Tg, water absorption, and thermal expansion coefficient. A film having physical properties of Tg of 250 ° C. or higher, water absorption of 2% by weight or less, and thermal expansion coefficient of 3 × 10 −5 / ° C. or less is particularly preferable.
The heat resistant film is desirably subjected to a surface treatment in order to increase the adhesive force with the adhesive. As the surface treatment method, any chemical treatment such as alkali treatment, silane coupling treatment, physical treatment such as sandblasting, plasma treatment, corona treatment, etc. can be used, depending on the type of adhesive. The most suitable process may be used. In applying the heat resistant adhesive in the present invention, chemical treatment or plasma treatment is particularly suitable as the surface treatment applied to the heat resistant film.
[0010]
In the present invention, the film adhesive can also be obtained by applying and drying a heat resistant adhesive on one side or both sides of the substrate. The heat resistant adhesive applied to both sides may be the same or different.
The method for applying the heat resistant adhesive (varnish) to the heat resistant film is not particularly limited. You may apply by any method, such as a doctor blade, a knife coater, and a die coater. Moreover, although it may coat through a film in a varnish, since control of thickness is difficult, it is unpreferable.
[0011]
In the present invention, when a film coated with a heat-resistant adhesive is heat-treated for solvent removal or imidization, the heat treatment temperature differs depending on whether it is a polyamic acid varnish or a polyimide varnish.
In the case of a polyamic acid varnish, a temperature equal to or higher than Tg is required for imidization, but in the case of a polyimide varnish, any temperature may be used as long as the solvent can be removed.
You may add and use fillers and coupling agents, such as ceramic powder, glass powder, silver powder, copper powder, rubber particles, and resin particles, to the adhesive of this invention.
As the rubber particles, silicone rubber particles are preferable from the viewpoint of heat resistance, and in particular, core-shell structure or surface-treated particles are preferable from the viewpoint of adhesiveness and compatibility with the adhesive resin.
[0012]
As the coupling agent, coupling agents such as vinyl silane, epoxy silane, amino silane, mercapto silane, titanate, aluminum chelate, zirco aluminate are used, but silane coupling agents are preferable, and epoxy silane coupling agents are particularly preferable. preferable.
[0013]
【Example】
Hereinafter, the present invention will be described in detail by way of practical examples, but the present invention is not limited to these ranges.
Example 15 g of carboxy-terminated polyester having a molecular weight of 1500 consisting of adipic acid and hexanediol in a 1000 m1 four-necked flask equipped with a stirrer, thermometer, nitrogen gas inlet tube and distillation tube, bisphenol A bistrimellitic dianhydride 25 g, 110 g of sulfolane, 0.09 g of 3-methyl-1-phenyl-3-phospholene-1-oxide were added, and the temperature was raised to 200 ° C. while stirring in a nitrogen atmosphere. After adding 4.7 g of diphenylmethane diisocyanate (MDI), the mixture was reacted at 200 ° C. for 1 hour, and then cooled to room temperature. The obtained copolymer reaction liquid was poured into methanol, and the resulting precipitate was separated, pulverized with a mixer, washed with water, and dried to obtain a polyesterimide powder having a polyester content of 60 wt%. The obtained polyesterimide powder was measured using gel permeation chromatography (hereinafter abbreviated as GPC; the eluent is MDF, the liquid speed is 1 ml / min, and the detection is a UV detector). The weight average molecular weight is in terms of polystyrene. 230,000.
30 g of this polyesterimide powder and 0.9 g of γ-glycidoxypropyltrimethoxysilane (hereinafter abbreviated as CPL) (the amount of CPL: 3% by weight) were added, and 86.4 g of cyclohexanone and 3.6 g of sulfolane were added. The varnish was adjusted.
The above varnish is applied to one side of a 50 μm-thick polyimide film (UPILEX S, manufactured by Ube Industries, Ltd.) to a thickness of 25 μm, and heat-treated at 100 ° C. for 15 minutes and further at 250 ° C. for 15 minutes. A film with an adhesive was obtained.
The glass transition temperature by the penetration method of the adhesive layer was 155 ° C.
The obtained heat-resistant film with a heat-resistant adhesive layer is cut into a size of 10 mm × 20 mm, and this is pressure-bonded to a copper alloy as a lead frame material under conditions of temperature: 180 ° C., pressure: 3 MPa, and time: 3 seconds. Then, it was immersed in water in a greenhouse for 24 hours. When the water-absorbed copper plate with a film was placed on a hot plate at a predetermined temperature for 20 seconds and the foaming temperature was measured, it was 200 ° C.
[0014]
【The invention's effect】
The film adhesive of the present invention has excellent reflow resistance after moisture absorption.

Claims (4)

A solvent having a glass transition temperature of 250 ° C. or less and a coupling agent of 10% by weight or less with respect to the resin, and a boiling point of 3 to 30% by weight with respect to the resin of 250 ° C. or more. A film-like adhesive formed from a varnish prepared with a solvent lower than 250 ° C. , wherein the residual solvent amount of the film-like adhesive is 0.5 to 10% by weight and excellent in reflow resistance. The film adhesive excellent in reflow resistance according to claim 1, wherein an adhesive layer formed from the varnish is formed on at least one surface of the substrate.   A lead frame comprising the film adhesive according to claim 1.   A semiconductor device having a semiconductor element mounted on the lead frame according to claim 3.