Cover tape for packaging chip type electronic parts

Abstract: A cover tape (1) for packaging of chip type electronic parts, which tape comprises an outer layer (2), an intermediate layer (4) and an adhesion layer (5) and which is heat-sealable to a plastic carrier tape having at given intervals pockets for accommodation of chip type electronic parts, the outer layer being a biaxially oriented film (2), the intermediate layer (4) being a polyolefin film which causes its own cohesive failure to enable peeling, and the adhesion layer (5) being a dispersion of conductive fine powders of tin oxide or the like in a thermoplastic resin. In the cover tape (1), the adhesion layer (5) is rendered antistatic by the conductive fine powders.

Description: The present invention relates to a cover tape heat-sealable to a plastic carrier tape having at intervals pockets for accommodation of chip type electronic parts, to a cover tape and carrier tape combination and to the use of an intermediate layer in a cover tape. Cover tapes constitute one component of packaging materials which are used for storage, transportation and mounting of chip type electronic parts and which allow arrangement and removal of said electronic parts to protect them form contamination and to mount them on an electronic circuit substrate. In recent years, chip type electronic parts used for surface mounting, such as ICs, transistors, diodes, condensers, piezoelectric resistors and the like have been supplied in packaging materials consisting of a plastic carrier tape having at given intervals pockets formed by embossing so as to accommodate chip type electronic parts of particular shape and a cover tape heat-sealable to the carrier tape. The electronic parts contained in the packaging materials are automatically taken out after peeling the cover tape of the package, and are mounted on the surface of an electronic circuit substrate. The strength when the cover tape is peeled off from the carrier tape is called "peel-off strength". When the peel-off strength was too low, there was a problem that the cover tape was separated from the package at the time of the package transfer and the contents, i.e., the electronic parts fell off. When the peel-off strength was too high, there occurred a phenomenon that the carrier tape underwent vibration in peeling the cover tape and, as a result, the electronic parts jumped out of the pockets right before their mounting, i.e., jumping trouble. As a material for the carrier tape, there have conventionally been used polyvinyl chloride (PVC) sheet, polystyrol sheet, polyester (PET) sheet, polycarbonate sheet, acrylic sheet and other sheets, all of easy sheeting. Meanwhile, as a cover tape heat-sealable to the carrier tape, there have generally been used a composite film obtained by laminating a polyethylene-modified film or a ethylene-vinyl acetate copolymer (EVA)-modified film which is heat-sealable for a PVC or polystyrol sheet to a biaxially oriented polyester film. In the conventional cover tape, however, the peel-off strength was greatly affected by the sealing conditions such as sealing temperature, sealing pressure and the like, and the fluctuation in sealing conditions made it difficult to control the peel-off strength in an appropriate range as mentioned above; further, the peel-off strength was also affected by temperature and humidity depending upon the storage conditions of the conventional cover tape or the storage conditions after sealing, whereby the peel-off strength was increased or decreased with the lapse of time and, in some cases, deviated from an appropriate range. There are two types of cover tapes which differ in peeling mechanism; one is an interface peeling type and the other is a cohesion peeling type. In the case of the interface peeling type, it was difficult to satisfy two contradictory properties of "strong adhesion and easy peeling" which are basic requirements for cover tapes, because the sealing surface and the peeling surface are the same; the peel-off strength was affected by the surface condition of a carrier tape to which a cover tape was to be sealed, and consequently fluctuated and thus it was difficult to control the peel-off strength in an appropriate range as mentioned above; the peel-off strength was also affected by temperature and humidity depending upon the storage conditions of a cover tape or the storage conditions after sealing; whereby the peel-off strength was increased or decreased with the lapse of time and, in some cases, deviated from an appropriate range. Meanwhile, in the case of the cohesion peeling type, by using a film as disclosed in Japanese Patent Publication No. 12936/1986, it was possible to produce a cover tape wherein the sealing surface and the peeling surface were different and the peel-off strength was obtained by the cohesive strength of the adhesion layer; this cover tape showed excellent properties which were stable even with the lapse of time. However, the cohesive strength of the adhesion layer was not so large; therefore, when the cover tape as a product was stored in a rolled state particularly at high temperatures in summer, etc., the biaxially oriented film caused blocking with sealing surface at the core portion, which caused insufficient sealing, significant reduction in transparency, etc. Further, regarding "strong adhesion and easy peeling", easy peeling could be attained by cohesion peeling, but strong adhesion still had a problem because the adhesion layer did not strongly adhere to a carrier tape and the adhesion was greatly affected by the sealing surface condition and sealing width of the carrier tape. With the significant improvement in surface mounting technique in recent years, electronic parts to be surface-mounted have come to be made in chips of higher capability and smaller size. In such a movement, the electronic parts, when transferred in a package, have undergone vibration and contact with the embossed inner surface of the carrier tape of the package or the inner surface of the cover tape of the package, and the resulting friction has generated static electricity; static electricity has been also generated when the cover tape was peeled off from the carrier tape; this static electricity has generated sparks which cause destruction and deterioration of the electronic parts. Thus, the electronic parts have had troubles due to static electricity, and it has been the most important task to develop an antistatic measure for packaging materials such as carrier tape and cover tape. The antistatic treatment for a carrier tape has hitherto been effected by incorporation or coating of carbon black into or on the carrier tape material used, and the effect has been satisfactory. However, no sufficient measure has yet been taken for the antistatic treatment for a cover tape, and currently there is merely effected, for example, coating of an antistatic agent or a conductive material on the outer layer of the cover tape. This treatment, however, has not been sufficient for the protection of electronic parts to be contained by sealing, because the treatment is applied to the outer side of the cover tape, and the treatment was ineffective particularly for the static electricity generated by the contact of the inner surface of the cover tape with the electronic parts. The antistatic treatment for the inner surface of the cover tape, i.e. the adhesion layer of the cover tape can be effected by coating or incorporation of an antistatic agent on or into the adhesion layer. In the case of incorporation, however, the antistatic agent incorporated into the adhesion layer has bled onto the inner surface of the cover tape and invited unstable sealing and many troubles due to poor sealing; moreover, the antistatic effect has decreased with the lapse of time, has been greatly affected by the conditions under which the package was used, i.e., temperature and humidity, particularly humidity, and has significantly decreased under a low humidity such as 10% R.H.; thus, no sufficient effect has been obtained. Meanwhile, the incorporation of a conductive material into an adhesion layer has been technically difficult, because the adhesion layer has been formed by laminating an extruded film or the like to an outer layer; moreover, the incorporation has significantly reduced the transparency of the resulting cover tape, making the cover tape usability questionable. The coating of a conductive material on an adhesion layer has not been effected in fact, because the selection of a binder stably bondable to the carrier tape has been difficult, and because the adhesion layer is covered and hidden by the coating. The present invention makes it possible to provide a cover tape whose adhesion layer has been subjected to an antistatic treatment, whose peel-off strength is only slightly affected by the sealing conditions and shows small change with the lapse of time, and whose sealing property is stable. The present inventors found that a composite film comprising (a) an outer layer consisting of a biaxially oriented film (b) an intermediate layer provided between said outer layer and an adhesion layer to be described later, comprising a polyolefin film which facilitates peeling by its own cohesive failure when said composite film which has been used as a cover tape sealed to a carrier tape is peeled, and (c) an adhesion layer coated on said intermediate layer, comprising a thermoplastic adhesive of heat seal lacquer type in which conductive fine powders have been dispersed, is transparent and can be used as a cover tape having good properties. The above finding has led to the completion of the present invention. The present invention therefore provides a plastic carrier tape and a cover tape for packaging of chip type electronic parts, which cover tape is heat-sealable to the plastic carrier tape which has at intervals pockets for the accommodation of chip type electronic parts, the cover tape comprising an outer layer of a biaxially oriented film consisting of a polyester, a polypropylene or a polyamide (nylon), an intermediate layer and an adhesion layer, wherein the adhesion layer consists of a dispersion of conductive fine powder in a thermoplastic resin, the conductive fine powder consisting of tin oxide, zinc oxide, titanium oxide, carbon black or a Si-based organic compound, or two or more thereof, in an amount of 10 to 1000 parts by weight per 100 parts by weight of the thermoplastic resin and the intermediate layer consists of a polyolefin film which facilitates peeling by its own cohesive failure, and the adhesion strength between the adhesion layer and the sealing surface of the carrier tape being greater than the cohesive strength of the intermediate layer of the cover tape when the cover tape has been heat-sealed to the carrier tape. In a cover tape according to the invention as described above the intermediate layer provided between the outer layer and the adhesion layer is a polyolefin film which advantageously comprises (a) 55 to 95% by weight of at least one ethylene polymer selected from polyethylenes having a density of 0.91 to 0.93 g/cm³ and ethylene-vinyl acetate copolymers containing 10% by weight or less of vinyl acetate, (b) 5 to 30% by weight of a polystyrene and (c) 0 to 20% by weight of a styrene-butadiene-styrene or styrene-isoprene-styrene block copolymer having thermoplastic elastomeric properties. The adhesion layer, of a cover tape according to the invention as described above, comprises a dispersion of conductive fine powders comprising tin oxide, zinc oxide, titanium oxide, carbon black or a Si-based organic compound, or two or more thereof, dispersed in a thermoplastic resin, advantageously polyurethane resin, acrylic resin, polyvinyl chloride resin, ethylene-vinyl acetate copolymer resin or polyester resin, or two or more thereof. The amount of the conductive fine powders added is 10 to 1,000 parts by weight per 100 parts by weiqht of the thermoplastic resin of the adhesion layer. After heat-sealing of the cover tape to the carrier tape the adhesion strength between the adhesion layer of the cover tape and the sealing surface of the carrier tape is larger than the cohesive strength of the intermediate layer of the cover tape. The cohesive strength of the intermediate layer of the cover tape is advantageously 10 to 120 g per mm of sealing width, and the visible light transmittance of the cover tape is advantageously 10% or more. In other embodiments the invention provides the use, as an intermediate layer in a cover tape comprising an outer layer, the intermediate layer, and an adhesive layer, of a material, preferably a polyolefin-based material, that will suffer cohesive failure when the cover tape is peeled from a substrate to which it is adhered. The invention will now be described, by way of example only, with reference to the accompanying drawings in which: Fig. 1 is a sectional view showing an example of the layer constitution of a cover tape of the present invention. Fig. 2 is a sectional view showing the state where a carrier tape and cover tape according to the present invention have been bonded together. Fig. 3 is a sectional view showing the state of a carrier tape where a cover tape of the present invention has been bonded to the carrier tape and then peeled therefrom. Fig. 4 is a sectional view showing the state of a cover tape of the present invention where the cover tape has been bonded to a carrier tape and then peeled thereform. The constitutional elements of the cover tape 1, of the present invention, are explained with reference to Fig. 1. The outer layer 2 is a biaxially oriented film consisting of biaxially oriented polyester film, biaxially oriented polypropylene film or biaxially oriented polyamide (nylon) film, and preferably has a thickness of 6-100 µm, transparency and high rigidity. When the thickness is less than 6 µm, the rigidity is reduced. When the thickness exceeds 100 µm, the hardness becomes high, making the sealing unstable. The surface of the outer layer 2 contacting with the adhesive layer 3 can be, if necessary, subjected to a surface treatment such as corona treatment, plasma treatment, sandblasting treatment or the like to increase the adhesion strength to the adhesive layer 3. The exterior surface of the outer layer 2 may be coated with a surfactant, conductive powders or the like in order to impart an antistatic property to said surface. The intermediate layer 4 is a polyolefin film which advantageously comprises (a) 55-95% by weight of at least one ethylene polymer selected from polyethylenes having a density of 0.91-0.93 g/cm³ and ethylene-vinyl acetate copolymers containing 10% by weight or less of vinyl acetate, (b) 5-30% by weight of a polystyrene and (c) 0-20% by weight of a styrene-butadiene-styrene or styrene-isoprene-styrene block copolymer having thermoplastic elastomeric properties and which causes its own cohesive failure to enable peeling when the cover tape which has been sealed to a carrier tape is peeled. The surface of the intermediate layer 4 contacting with the adhesion layer 5 may be, if necessary, subjected to a surface treatment such as corona treatment, plasma treatment, sandblasting treatment or the like to increase the adhesion between the intermediate layer 4 and the adhesion layer 5. The adhesion layer 5 comprises a transparent thermoplastic resin of heat-sealing lacquer type (e.g., polyurethane resin, acrylic resin, ethylene-vinyl acetate copolymer resin, polyvinyl chloride resin, polyester resin), and there is selected one single resin or a mixed resin each of which is heat-sealable to a plastic carrier tape 6 to which the adhesion layer 5 is to be bonded. Because of the presence of this heat-sealing adhesion layer which covers the intermediate layer wherein cohesion peeling takes place, blocking of the intermediate layer and biaxially oriented film can be prevented, when the cover tape is stored at high temperatures and, at the same time, the adhesion of the cover tape to the carrier tape is improved. In the adhesion layer there are uniformly dispersed conductive fine powders comprising tin oxide, zinc oxide, titanium oxide, carbon black or a Si-based organic compound. The surface resistance of the adhesion layer after film formation is preferably 10¹³ Ω/□ or less and is more preferably in a range of 10⁶-10⁹ Ω/□. When the surface resistance is larger than 10¹³ Ω/□, the antistatic effect is extremely poor and no desired property can be obtained. The amount of the conductive fine powders added is 10-1,000 parts by weight, advantageously 100-400 parts by weight per 100 parts by weight of the thermoplastic resin of the adhesion layer, in view of the above surface resistance preference. When the amount is less than 10 parts by weight, the antistatic effect is significantly reduced. When the amount is more than 1,000 parts by weight, the dispersibility of the conductive fine powders in the thermoplastic resin of the adhesion layer is reduced, the resulting adhesion layer has a significantly lower adhesion to the intermediate layer 4 and lower transparency, and the production cost is high, resulting in poor productivity. The antistatic material has conductivity by itself and accordingly has an antistatic effect semipermanently, and does not cause bleeding, etc. and therefore does not adversely affect the sealing property of the adhesion layer; the surface resistance of the adhesion layer is generally controlled at a level of 10¹³ Ω/□ or less and hence, in the package comprising the carrier tape 6 containing electronic parts and the cover tape 1 sealed to the carrier tape 6, very little static electricity is generated by the contact of the electronic parts with the cover tape 1 during the transportation of the package, or at the time of peeling of the cover tape 1 for pick-up of the electronic parts, whereby the electronic parts can be prevented from troubles due to static electricity. In order to enhance the antistatic effect, an antistatic layer or a conductive layer may be provided on both surfaces of the outer layer, i.e., the biaxially oriented film. The method for forming a heat-sealable adhesion layer may be a film formation method using a melt or a film formation method using a solution. The film formation method using a solution is preferable in view of the dispersibility of the conductive fine powders. The film thickness of the adhesion layer is preferably 5 µm or less, more preferably 2 µm or less. When the film thickness is larger than 5 µm it is difficult to form an adhesion layer by the method using a solution, in view of the procedures adopted by the method. In order to improve the lamination strength between the outer layer and the intermediate layer, it is possible to laminate these two layers via an adhesive layer, for example, of lacquer type. The layer may be formed by drying, solidifying and curing an isocyanate type lacquer, an imine type lacquer or the like. In the seal-peel process of the cover tape, first the cover tape 1 is continuously sealed to both sides of the carrier tape 6 in a two-rail shape with sealing width of about 1 mm on each side (Fig. 2); then, the cover tape 1 is peeled off from the carrier tape 6. In this peeling, when the adhesion strength between the adhesion layer 5 of the cover tape 1 and the sealing surface of the carrier tape 6 is smaller than the cohesive strength of the intermediate layer 4, the peel-off strength corresponds to the adhesion strength between the adhesion layer 5 of the cover tape 1 and the sealing surface of the carrier tape 6, and peeling occurs in the form of interfacial peeling which is the most common peeling mechanism currently adopted. In this case, strong sealing of the cover tape to the carrier tape makes peeling difficult, and weak sealing leads to spontaneous peeling; thus, it has been unable to satisfy both of two contradictory properties essentially required for the cover tape, i.e., high sealability to the carrier tape and easy peelability at the time of peeling. Meanwhile, when, as in the present invention, the adhesion strength between the adhesion layer 5 of the cover tape 1 and the sealing surface of the carrier tape 6 is larger than the cohesive strength of the intermediate layer 4 of the cover tape 1 only the sealed portion 7 of the adhesion layer 5 and the intermediate layer 4 remains on the carrier tape (Fig. 3) and, in the cover tape after peeling (Fig. 4), only the heat-sealed portion 7 of the adhesion layer 5 and the intermediate layer 4 is lost by cohesion peeling caused by cohesive failure. That is, the peel-off strength corresponds to the cohesive strength of the intermediate layer 4; this means that it is possible to design the cover tape and carrier tape combination so that the sealing/peeling surface can be completely separated, the sealing of the cover tape 1 to the carrier tape 6 can be effected strongly, and the peeling of the cover tape 1 can be effected very easily. In short, the peeling surfaces are designed in the cover tape 1, and the cohesive strength of the intermediate layer can be designed without reference to the material of the carrier tape 6. The sealing surface of the cover tape 1 can be strongly sealed to the carrier tape 6 by the selection of an adhesive, whereby a stable seal-peel mechanism can be obtained. In this case, a polyolefin film is selected so that the cohesive strength of the intermediate layer 4 of the cover tape 1 becomes advantageously 10-120 g, preferably 10-70 g per mm of sealing width. When the peeling strength is less than 10 g, there may occur a problem during transportation of the package where the cover tape spontaneously peels off and the electronic parts contained in the package fall out. When the peeling strength is greater than 120 g, there may occur a phenomenon where the carrier tape undergoes vibration at the time of cover tape peeling and the electronic parts jump out of the pockets of the carrier tape before mounting, i.e., jumping trouble. According to the cohesion peeling mechanism of the present invention, as compared with the conventional interfacial peeling, there can be obtained a cover tape having the intended property, i.e., peel-off strength which is only slightly affected by sealing conditions and which shows only small changes with the lapse of time when stored under various conditions. The present cover tape is advantageously constituted so as to have a visible light transmittance of 10% or more, preferably 50% or more, making it possible to identify the electronic parts contained in the carrier tape by sealing, visually or using an instrument. When the transmittance is lower than 10%, the identification of the electronic parts can become difficult. Examples of the present invention and Comparative Examples are shown hereinafter. However, the present invention is in no way restricted by these Examples. Examples 1, 2, 3, 4 and 5 and Comparative Examples 1, 2, 3, 4 and 5 On the polyolefin film side of a laminate of a biaxially oriented film to become an outer layer and a polyolefin film to become an intermediate layer, there was coated an ethyl acetate solution containing a mixture of a thermoplastic resin and conductive fine powders, using a gravure coater; and the coating was made into a film of 2 µm in thickness to form an adhesion layer; thus, various cover tapes composed of layers as shown in Tables 1 and 2 were obtained. Each of the cover tapes was slitted to a width of 5.5 mm and then heat-sealed to a PVC carrier tape of 8 mm in width, after which measurement of peeling strength was effected. There were also effected measurements of surface resistance at the adhesion layer side and visible light transmittance of each of the experimental cover tapes. The evaluation results of these properties are shown in Tables 3 and 4. It will be noted that Comparative Examples 1 and 2 are so designated because they do not describe a cover tape within claim 1, which defines the invention in compositional terms; these examples do, however, illustrate the invention as defined by the functional terms of claim 10. Examples 6, 7, 8, 9 and 10 The procedures of Example 1 were repeated except that the amount of conductive fine powder SnO₂ added in the adhesion layer was changed as follows: Amount of SnO₂ per 100 parts by weight of PVC type resin Example 6 20 parts by weight Example 7 50 parts by weight Example 8 500 parts by weight Example 9 750 parts by weight Example 10 900 parts by weight Properties of the resulting samples were evaluated similarly to the Example 1. The results thereof are shown in Table 5. As apparent from the foregoing Examples and Comparative Examples, owing to the following three features, i.e., a feature that the adhesion layer has been subjected to an antistatic treatment, and hence generation of static electricity by the contact of the electronic parts with the cover tape or at the time of cover tape peeling is reduced, and the antistatic effect is stable against the use conditions or the lapse of time and has no influence on the sealing property of the cover tape, a feature that the peel-off strength can be set at a desired level advantageously in the range of 10-120g per mm by the combination of the cohesive strength of the intermediate layer and the adhesion strength of the adhesion layer to the carrier tape, and a feature that the peel-off strength is determined by the cohesive strength of the intermediate layer within the cover tape and accordingly is not affected by the sealing conditions between the adhesion layer and the carrier tape, the cover tape of the present invention can alleviate the problems of conventional cover tapes, i.e., a problem that the peel-off strength is greatly affected by the sealing conditions, a problem that the peel-off strength changes with the lapse of time depending upon the storage conditions, and a problem that static electricity is generated by the contact of the electronic parts with the cover tape or at the time of cover tape peeling, and thereby it is possible to obtain a stable peel-off strength.

Claims: A plastic carrier tape and a cover tape for packaging of chip type electronic parts, which cover tape is heat-sealable to the plastic carrier tape which has at intervals pockets for the accommodation of chip type electronic parts, the cover tape comprising an outer layer of a biaxially oriented film consisting of a polyester, a polypropylene or a polyamide (nylon), an intermediate layer and an adhesion layer, wherein the adhesion layer consists of a dispersion of conductive fine powder in a thermoplastic resin, the conductive fine powder consisting of tin oxide, zinc oxide, titanium oxide, carbon black or a Si-based organic compound, or two or more thereof, in an amount of 10 to 1000 parts by weight per 100 parts by weight of the thermoplastic resin and the intermediate layer consists of a polyolefin film which facilitates peeling by its own cohesive failure, and the adhesion strength between the adhesion layer and the sealing surface of the carrier tape being greater than the cohesive strength of the intermediate layer of the cover tape when the cover tape has been heat-sealed to the carrier tape. A plastic carrier tape and cover tape according to claim 1, wherein the thermoplastic resin of the adhesion layer consists of polyurethane resin, acrylic resin, polyvinyl chloride resin, ethylene-vinyl acetate copolymer resin or polyester resin, or two or more thereof. A plastic carrier tape and cover tape according to claim 1 or 2, wherein the surface resistance of the adhesion layer is 10¹³ Ω/□ or less. A plastic carrier tape and cover tape according to any one of claims 1 to 3, wherein the intermediate layer is a polyolefin film comprising (a) 55 to 95% by weight of at least one ethylene polymer selected from polyethylenes having a density of 0.91 to 0.93 g/cm³ and ethylene-vinyl acetate copolymers containing 10% by weight or less of vinyl acetate, (b) 5 to 30% by weight of a polystyrene and (c) 0 to 20% by weight of a styrene-butadiene-styrene or styrene-isoprene-styrene copolymer having thermoplastic elastomeric properties. A plastic carrier tape and cover tape according to any one of claims 1 to 4, wherein the cohesive strength of the intermediate layer of the cover tape is 10 to 120 g per mm of sealing width. A plastic carrier tape and cover tape according to any one of claims 1 to 5, wherein the visible light transmittance of the cover tape is 10% or more. A plastic carrier tape and cover tape according to any one of claims 1 to 6, wherein the thickness of the outer layer is 6 to 100 µm. A plastic carrier tape and cover tape according to any one of claims 1 to 7, wherein the thickness of the adhesion layer is 5 µm or less. A plastic carrier tape and cover tape according to any one of claims 1 to 8, which comprises an adhesive layer between the outer layer and the intermediate layer. The use, as an intermediate layer in a cover tape comprising an outer layer, the intermediate layer, and an adhesive layer, of a material, preferably a polyolefin-based material, that will suffer cohesive failure when the cover tape is peeled from a substrate to which it is adhered.

Inventors: MAEDA SHIGERU, MIYAMOTO TOMOHARU, MAEDA, SHIGERU, MIYAMOTO, TOMOHARU, MIYAMOTO, TOMOHARU, SUMITOMO BAKELITE ITAMISO 302
Applicants: SUMITOMO BAKELITE CO, SUMITOMO BAKELITE COMPANY LIMITED
Application year: 1991
Main classification: C09J7
IPC codes: C09J7, H05K13