Adhesive tape for encapsulating electronic constructions

Abstract

The aim is to provide an adhesive tape that effectively protects an electronic construction from permeants, especially water, and that at the same time has good gap-filling qualities. To solve this problem an adhesive tape is proposed that has in the following order:—a carrier layer without barrier effect at least towards water and with a WVTR of at least 1 g/(m.sup.2*d) (38° C., 90% relative humidity, 50 μm layer thickness); —a layer comprising at least one getter material capable of sorbing at least water; —a water barrier ply; and—a layer of pressure-sensitive adhesive, where the carrier layer bears an outward-facing release layer and/or the layer of pressure-sensitive adhesive is lined with a release liner which has a release layer lying on the layer of pressure-sensitive adhesive.

Claims

1. An adhesive tape for encapsulating electronic structures, comprising in the following order: a carrier layer without a barrier effect at least against water having a WVTR of at least 1 g/(m.sup.2*d) (38° C., 90% relative humidity, 50 μm layer thickness); a layer containing at least one getter material capable of sorption at least of water; a layer having a barrier effect against water; a pressure-sensitive adhesive layer; wherein an outward-facing release layer lies on the carrier layer and/or the pressure-sensitive adhesive layer is covered with a release liner that has a release layer lying on the pressure-sensitive adhesive layer.

2. The adhesive tape as claimed in claim 1, wherein the carrier layer without a barrier effect at least against water is a film comprising a material selected from the group consisting of ethylene vinyl acetate, polyurethanes, cellulose acetate, polymethyl methacrylate, polyvinyl alcohols and paper or is a microperforated polyethylene film.

3. The adhesive tape as claimed in claim 1, wherein the getter material is selected from the group consisting of absorbent and adsorbent materials.

4. The adhesive tape as claimed in claim 1, wherein the getter material is selected from the group composed of calcium chloride, calcium oxide, boron trioxide, sodium sulfate, potassium carbonate, copper sulfate, magnesium perchlorate, magnesium sulfate, zeolites and mixtures of two or more of the above-mentioned substances.

5. The adhesive tape as claimed in claim 1, wherein the getter material is in the form of a dispersed phase.

6. The adhesive tape as claimed in claim 5, wherein the getter material is in the form of a dispersed phase in an adhesive.

7. The adhesive tape as claimed in claim 1, wherein the pressure-sensitive adhesive layer comprises a polymer base selected from the group consisting of styrene block copolymers, polyolefins and epoxy resins, and mixtures of two or more of these polymers.

8. The adhesive tape as claimed in claim 1, wherein the pressure-sensitive adhesive layer is covered with the release liner that has a release layer lying on the pressure-sensitive adhesive layer, wherein this release layer is a silicone, fluorinated silicone, silicone-copolymer, fluoropolymer, polycarbamate or polyolefin release layer.

9. The adhesive tape as claimed in claim 1, wherein the outward-facing release layer lies on the carrier layer and this release layer is a silicone release coating.

10. The adhesive tape as claimed in claim 1, wherein the layer having a barrier effect against water is selected from the group consisting of: (A) a composite of (i) a film selected from the group consisting of polyurethane, polypropylene, polyethylene, polyvinyl chloride, polyvinylidene chloride, polyethylene-2,6-naphthalate, polyacrylonitrile, polyethylene terephthalate, ethylene-vinyl alcohol copolymer, polyacrylate, and poly-ε-caprolactam films and (ii) at least one permeation-inhibiting layer arranged between said film (i) and the pressure-sensitive adhesive layer; (B) a metallic film; and (C) a glass film.

11. A method comprising encapsulating an electronic structure with the adhesive tape as claimed in claim 1.

Description

EXAMPLES

Test Methods

(1) Unless otherwise indicated, all measurements are conducted at 23° C. and 50% relative humidity.

(2) Adhesive Force

(3) The adhesive forces on steel were determined analogously to ISO 29862 (Method 3) at 23° C. and 50% relative humidity with a peeling rate of 300 mm/min and a peeling angle of 180°. An etched PET film with a thickness of 50 μm, such as that available e.g. from the firm Coveme (Italy), was used as a reinforcing film. The measuring strip was adhesively bonded using a winding machine at a temperature of 23° C. The adhesive tapes were peeled off immediately after application. The measured value (in N/cm) was taken as the average of three individual measurements. The test was carried out on uncrosslinked samples.

(4) Liner Release

(5) The liner release forces were determined at 23° C. and 50% relative humidity with a peeling rate of 300 mm/min and a peeling angle of 180°. The measuring strip was adhesively bonded to a steel plate using a winding machine at a temperature of 23° C. The adhesive tapes were peeled off immediately after application. The measured value (in cN/cm) was taken as the average of three individual measurements. The test was carried out on uncrosslinked samples.

(6) Water Vapor Transmission Rate (WVTR)

(7) The water vapor transmission rate (WVTR) was determined according to DIN 53380 Part 3 or ASTM F-1249. For this purpose, the pressure-sensitive adhesive was applied to a permeable membrane with a layer thickness of 50 μm. The water vapor transmission rate was determined at 38° C. and a relative humidity of 90%. The test was carried out on crosslinked samples.

(8) Adhesive Resin Softening Temperature

(9) The adhesive resin softening temperature is measured according to the relevant method, which is known as the ring and ball method and is standardized according to ASTM E28.

(10) The ring and ball unit HRB 754 from the firm Herzog was used to determine the adhesive resin softening temperature of the resins. The resin samples were first finely ground in a mortar. The resulting powder was placed in a brass cylinder with a bottom opening (inner diameter at the upper part of the cylinder 20 mm, diameter of the bottom opening of the cylinder 16 mm, cylinder height 6 mm) and melted on a hot table. The filling amount was selected so that the resin completely filled the cylinder after melting in a level manner.

(11) The resulting test piece was placed together with the cylinder in the sample holder of the HRB 754. Glycerol was used to fill the heating bath in cases where the adhesive resin softening temperature was between 50° C. and 150° C. It was also possible to use a water bath at lower adhesive resin softening temperatures. The test balls had a diameter of 9.5 mm and weighed 3.5 g. In accordance with the HRB 754 procedure, the ball was arranged above the test piece in the heating bath and deposited on the test piece. A target plate was positioned 25 mm below the cylinder bottom, with a light barrier located 2 mm above the latter. During the measurement process, the temperature was increased at a rate of 5° C. per min. In the range of the adhesive resin softening temperature, the ball began to move through the bottom opening of the cylinder, finally coming to rest on the target plate. In this position, it was detected by the light barrier, and the temperature of the heating bath was recorded at this time. Double determination was carried out. The adhesive resin softening temperature is the average of the two individual measurements.

(12) MMAP

(13) MMAP, the mixed methylcyclohexane aniline cloud point, was determined using a modification of the ASTM C 611 method. Methylcyclohexane was used instead of the heptane used in the standard test method. The method uses resin/aniline/methylcyclohexane in a ratio of 1/2/1 (5 g/10 ml/5 ml); the cloud point is determined by cooling a heated, clear mixture of the three components until the point at which complete cloudiness occurs.

(14) DACP

(15) DACP, the diacetone cloud point, is determined by cooling a heated solution of 5 g of resin, 5 g of xylene and 5 g of diacetone alcohol until the point at which the solution becomes cloudy.

(16) Water Content Measurement

(17) The water content was determined according to DIN 53715 (Karl Fischer titration). Measurement was carried out on a Karl Fischer Coulometer 851 in combination with an oven sampler (oven temperature 140° C.). In each case, with an initial weight of approx. 0.3 g, triple determination was carried out. The arithmetic average of the measurements is taken as the water content. Initial weighing was carried out in determination of the starting values of raw materials (higher measurement values) in an air-conditioned room at 23° C. and 50% rH. Initial weighing of the dried adhesive tapes in the measuring vials was carried out in a protective nitrogen atmosphere (“glove box”), in which a constant humidity of less than 3 ppm was maintained. In order to minimize the effect of the dry environment as much as possible, after opening the aluminum bag with the dried adhesive tapes, the measuring vial was filled with the sample amount and sealed within 2 min. In order to allow evaluation of both the dried pressure-sensitive adhesive and the remaining layer structure, the pressure-sensitive adhesive was peeled off the layer having a barrier effect.

EXAMPLES

(18) Production of the adhesive tapes according to the invention was carried out in the laboratory in three steps.

(19) Product Structure A (Without an Additional Release Liner)

(20) 1) Production of a Layer Having a Barrier Effect/Getter-Material-Containing Layer/Carrier Layer Laminate

(21) As an example of the group of layers with a barrier effect, a laminate composed of an aluminum film (d=20 μm) and a PET film (23 μm) from the firm Novelis was selected. 40 μm of the getter-material-containing layer was applied from solution with a doctor blade to the PET side (see composition in Table 1). The solvent was removed for 10 min at room temperature followed by 10 min at 110° C. The getter-material-containing layer was laminated together with the carrier layer (one-side siliconized 50 μm PET film from the firm SKC) in such a way that it did not come into contact with the non-siliconized side.

(22) 2) Application of the Pressure-Sensitive Adhesive Layer

(23) A pressure-sensitive adhesive was applied from solution with a doctor blade to the non-siliconized side (side with barrier effect) of the laminate of step 1) (see composition in Table 2). The solvent was removed for 10 min at room temperature followed by 10 min at 110° C. The layer thickness of the pressure-sensitive adhesive was 50 μm.

(24) 3) Storage for Determination of Drying Efficiency

(25) In order to simulate an adhesive tape roll, two DIN A4 samples produced according to steps 1-2 were laminated together in such a way that the pressure-sensitive adhesive of the one structure came into contact with the siliconized side of the other structure. This two-layer structure was heat-sealed in an aluminum bag and stored for 7 days.

(26) After 7 days, the residual humidity of the product structure located on the siliconized side of the other product structure was determined. The residual humidity was less than 20 ppm in all cases.

(27) Product Structure B (With Additional Release Liner)

(28) 1) Production of a Layer Having a Barrier Effect/Getter-Material-Containing Layer/Carrier Layer Laminate

(29) As an example of the group of layers with a barrier effect, a laminate composed of an aluminum film (d=20 μm) and a PET film (23 μm) from the firm Novelis was selected. 40 μm of the getter-material-containing layer was applied from solution with a doctor blade to the PET side (see composition in Table 1). The solvent was removed for 10 min at room temperature followed by 10 min at 110° C. The getter-material-containing layer was laminated together with the carrier layer (50 μm PET film from the firm Laufenberg).

(30) 2) Application of the Pressure-Sensitive Adhesive Layer

(31) A pressure-sensitive adhesive was applied from solution with a doctor blade to the aluminum side of the laminate of step 1) (see composition in Table 2). The solvent was removed for 10 min at room temperature followed by 10 min at 110° C. The layer thickness of the pressure-sensitive adhesive was 50 μm. The open adhesive layer was laminated with a 50 μm siliconized PET release liner from the firm SKC onto the siliconized side to form the adhesive composition.

(32) 3) Storage for Determination of Drying Efficiency

(33) In order to simulate an adhesive tape roll, two DIN A4 samples produced according to steps 1-2 were laid over one another in such a way that the release liner of the one structure came into contact with the carrier layer of the other structure. The two-layer structure was heat-sealed in an aluminum bag, pressed together with a DIN A4 plate and a 2-kg weight in order to simulate the winding tension, and stored for 7 days.

(34) After 7 days, the residual humidity of the product structure that had come into contact with the second structure on the carrier side was determined.

(35) TABLE-US-00001 TABLE 1 Composition of getter-material-containing layer 100 parts Tuftec P 1500 SBBS with 30 wt % block polystyrene from the firm Asahi. The SBBS contains approx. 68 wt % diblock. 100 parts Escorez 5600 Hydrogenated hydrocarbon resin with a softening point of 100° C. from the firm Exxon 25 parts Ondina 917 White mineral oil from paraffinic and naphthenic fractions from the firm Shell 40 parts Calcium oxide Absorbent getter material from the firm Sigma-Aldrich. CAS: 1305-78-8

(36) A mixture of toluene and acetone in a ratio of 2:1 was used as a solvent. The solid content was 45% before addition of the getter. Calcium oxide was incorporated into the adhesive while vigorously stirring only shortly before coating.

(37) TABLE-US-00002 TABLE 2 Pressure-sensitive adhesive 40 parts Kraton G 1657 SEBS with 13 wt % block polystyrene from the firm Kraton. The SEBS contains 36 wt % diblock. 40 parts Regalite 1100 Fully hydrogenated hydrocarbon resin from the firm Eastman (ring and ball 100° C., DACP = 45, MMAP = 82). 20 parts Uvacure 1500 Cycloaliphatic diepoxide from the firm Dow. 1 part Triarylsulfonium Cationic photoinitiator from the firm hexafluoroanti- Sigma-Aldrich. The photoinitiator has monate an absorption maximum in the range of 320 nm to 360 nm and was present in propylene carbonate as a 50 wt % solution.

(38) A mixture of toluene and benzine in a ratio of 3:7 was used as a solvent. The solid content was 50%.

(39) TABLE-US-00003 TABLE 3 Results Getter-material- Pressure- containing layer sensitive adhesive Carrier layer Adhesive force/N 3.2 2.6 — cm.sup.−1 WVTR/g m.sup.−2 d.sup.−1 — 31 14 Initial moisture/ppm — 843 2348 Moisture after 7- — <20 ppm <20 ppm day storage in composite/ppm (structure A) Moisture after 7- <20 ppm <20 ppm day storage in composite/ppm (structure B)

Comparative Example with Getter-Containing Layer in the Removable Liner

(40) Here, the layer sequence was modified using a liner that was comparable to structure B but contained the getter-containing layer. For this purpose, the getter-material-containing layer described in Table 1 was applied from solution using a doctor blade to the carrier layer (50 μm PET film from the firm Laufenberg), dried, and laminated together with the non-siliconized side of the liner used in structure B (50 μm siliconized PET release liner from the firm SKC). In a second step, the pressure-sensitive adhesive of Table 2 was applied in a layer thickness of 50 μm to the siliconized side, which was now facing outward, and, after drying, laminated together with a layer having a barrier effect. A laminate of an aluminum film (d=20 μm) and a PET film (23 μm) from the firm Novelis was selected. Lamination was carried out with the aluminum side to form the pressure-sensitive adhesive.

(41) TABLE-US-00004 TABLE 4 Results for release Comparative Structure A Structure B example Layer thickness — 50 μm 150 μm liner/μm Liner release/cN No liner used, but 5 13 cm.sup.−1 adhesive tape unrolled without problems