Adhesive tape for encapsulating an organic electronic arrangement

Abstract

The invention relates to a method for protecting an electronic arrangement which is disposed on a substrate and comprises organic constituents, where a cover is applied to the electronic arrangement in such a way that the electronic arrangement is at least partly covered by the cover, the cover being bonded at least over a partial area to the substrate and/or to the electronic arrangement, the adhesive bond being produced by means of at least one layer of an adhesive in an adhesive tape, characterized in that the adhesive comprises a getter material which is capable of at least one permeable substance, the getter material being present in the adhesive in a proportion of not more than 2 wt %, based on the adhesive with the getter material.

Claims

1. A method for protecting an electronic arrangement comprising organic constituents that is arranged on a substrate, said method comprising: applying a liner to the electronic arrangement in such a way that the electronic arrangement is at least partly covered by the liner, and bonding the liner at least to a partial area on the substrate and/or on the electronic arrangement, the bond being brought about by means of at least one layer of an adhesive in an adhesive tape, wherein the adhesive comprises a getter material capable of sorbing at least one permeable substance, the getter material being present in the adhesive at a fraction of not more than 2 wt %, based on the adhesive with the getter material.

2. The method as claimed in claim 1, wherein the adhesive tape is a single-layer adhesive tape comprising the layer of adhesive.

3. The method as claimed in claim 1, wherein the fraction of the getter material in the adhesive is not more than 1 wt %.

4. The method as claimed in claim 1, wherein the fraction of the getter material in the adhesive is at least 0.01 wt %.

5. The method as claimed in claim 1, wherein the getter material is in nanoscale form.

6. The method as claimed in claim 1, wherein an adhesive is used which when shaped to form a layer having a thickness of 50 m has a water vapor permeation rate of less than 50 g/m.sup.2d and/or an oxygen permeation rate of less than 5000 g/m.sup.2d bar.

7. The method as claimed in claim 1, wherein first of all the layer of pressure-sensitive adhesive, optionally as part of a double-sided adhesive tape comprising further layers, and, in a subsequent step, the liner are applied to the substrate and/or the electronic arrangement.

8. The method as claimed in claim 1, wherein the layer of pressure-sensitive adhesive and the liner are applied jointly to the substrate and/or the electronic arrangement.

9. The method as claimed in claim 1, wherein the liner completely covers the electronic arrangement.

10. The method as claimed in claim 9, wherein a region of the substrate around the electronic arrangement as well is wholly or partly covered by the liner.

11. The method as claimed in claim 1, wherein the layer of adhesive completely covers the electronic arrangement.

12. The method as claimed in claim 11, wherein a region of the substrate around the electronic arrangement as well is wholly or partly covered by the layer of adhesive.

13. An adhesive tape comprising at least one layer of an adhesive, the pressure-sensitive adhesive comprising a getter material capable of sorbing at least one permeable substance, wherein the getter material is present in the adhesive at a fraction of not more than 2 wt %, based on the adhesive with the getter material.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the drawing

(2) FIG. 1 shows an (opto)electronic arrangement according to the prior art, in a diagrammatic representation,

(3) FIG. 2 shows a first (opto)electronic arrangement of the invention, in diagrammatic representation, and

(4) FIG. 3 shows a second (opto)electronic arrangement of the invention, in diagrammatic representation.

(5) FIG. 4 shows a calcium text for determining the lifetime of an electronic construction.

(6) FIG. 1 shows a first embodiment of an organic electronic arrangement 1 according to the prior art. This arrangement 1 has a substrate 2 on which an electronic structure 3 is arranged. The substrate 2 itself is designed as a barrier for permeates, and thus forms part of the encapsulation of the electronic structure 3. Disposed above the electronic structure 3, in the present case also at a distance from it, is a further liner 4 designed as a barrier.

(7) In order to encapsulate the electronic structure 3 to the side as well, and at the same time to join the liner 4 to the electronic arrangement 1 in its remaining part, an adhesive 5 runs round adjacent to the electronic structure 3 on the substrate 2. It is unimportant here whether the adhesive has been joined first to the substrate 2 or first to the liner 4. The PSA 5 joins the liner 4 to the substrate 2. As a result of an appropriately thick embodiment, moreover, the PSA 5 allows the liner 4 to be distanced from the electronic structure 3.

(8) The adhesive 5 is a prior-art adhesive, in other words an adhesive with a high permeation barrier, which may also have been filled to a high fraction with getter material. In the present case the adhesive 5 does not just take on the function of joining the substrate 2 to the liner 4, but instead, moreover, also provides a barrier layer for permeates, in order thereby to encapsulate the electronic structure 2 from the side as well with respect to permeates such as water vapor and oxygen. If the adhesive is applied in the form of a liquid adhesive, a high fraction of getter material is generally not critical, since the fluid form ensures ready flow-on and hence effective sealing of the interface.

(9) Where, however, the adhesive is an adhesive transfer tape, which is tacky or which is put into a tacky state by means of an activation step, by means of heating, for example, there is not generally complete wetting of the surfaces of substrate and/or liner following application, in the case of a high fraction of getter material, and so the permeation barrier is disrupted at the interface. This necessitates the separate introduction of a getter pad into the gas space, in many cases, in spite of the adhesive transfer tape filled with getter material.

(10) An adhesive transfer tape would presently be provided, moreover, in the form of a diecut, which on account of its delicate geometry would be more difficult to handle than an adhesive transfer tape applied substantially over the full area.

(11) FIG. 2 shows an inventive embodiment of an (opto)electronic arrangement 1. Shown, again, is an electronic structure 3 which is disposed on a substrate 2 and is encapsulated by the substrate 2 from below. Above and to the side of the electronic structure, the inventive adhesive transfer tape 6 is now arranged over the full area. Accordingly, the electronic structure 3 is encapsulated fully from above by the adhesive transfer tape 6. A liner 4 is then applied to the adhesive transfer tape 6. The adhesive transfer tape 6 is one based on the inventive adhesive transfer tape as described above in general form and specified in more detail hereinafter in exemplary embodiments. In the version shown, the adhesive transfer tape consists only of a layer of an adhesive which is filled to a fraction of less than 2 wt %.

(12) The combination of an adhesive filled with getter material and the full-area liner, moreover, exhibits another surprising synergistic effect: the electronic arrangement does not suffer degradation over the entire area, but instead onlyslowly and increasinglyfrom the edge. As a result, a large part of the arrangement can still be utilized on initial penetration of permeates. Because of the impervious interface between adhesive transfer tape and substrate and/or liner, and also with respect to the electronic arrangement, permeates are forced to permeate through the adhesive itself, in which, surprisingly, the combination of a low fraction of getter material with a high permeation barrier is sufficient to prolong the lifetime to a degree similar to that afforded by a high fraction of getter material.

(13) This effect came about, surprisingly, only when the adhesive in accordance with the invention has only a low-fraction filling of getter material and hence when the interface between adhesive transfer tape and substrate and/or liner, and also with respect to the electronic arrangement, is impervious to permeation. Where the adhesive had a high-fraction filling of getter material, permeates were easily able to penetrate to the electronic arrangement at this disrupted interface, and also damage the arrangement on its surface. The damage was therefore obvious more quickly. The same was observed for the non-full-area arrangement according to FIG. 1, where permeates that had broken through are likewise able to damage the entire surface.

(14) In contrast to the preceding embodiment, the liner 4 is not mandatorily required to meet the high barrier requirements, since with a full-area covering of the electronic arrangement by the adhesive transfer tape, the barrier is provided by the PSA already. The liner 4 may merely take on, for example, a mechanical protection function, or alternatively it may additionally be provided as a permeation barrier.

(15) FIG. 3 shows an alternative embodiment of an (opto)electronic arrangement 1. In contrast to the preceding embodiments, there are now two adhesive transfer tapes 6a, b, which in the present case are identical in form, but which may also be different. The first adhesive transfer tape 6a is arranged on the full area of the substrate 2. The electronic structure 3 is provided on the adhesive transfer tape 6a, and is fixed by the adhesive transfer tape 6a. The assembly of adhesive transfer tape 6a and electronic structure 3 is then covered over its full area with the further adhesive transfer tape 6b, meaning that the electronic structure 3 is encapsulated from all sides by the adhesive transfer tapes 6a, b. Provided above the adhesive transfer tape 6b, in turn, is the liner 4.

(16) In this embodiment, neither the substrate 2 nor the liner 4 need therefore mandatorily have barrier properties. They may, however, nevertheless be provided, in order to further restrict the permeation of permeates to the electronic structure 3.

(17) In relation to FIGS. 2 and 3, in particular, it is noted that in the present case these are diagrammatic representations. From the representations it is in particular not apparent that the adhesive transfer tape, here and preferably and in each case, has a homogeneous layer thickness. At the transition to the electronic structure, therefore, there is not a sharp edge, as it appears in the representation, but instead the transition is fluid and it is possible instead for small unfilled or gas-filled regions to remain. If desired, however, there may also be conformation to the substrate, particularly when application is carried out under vacuum. Moreover, the adhesive is compressed to different extents locally, and so, as a result of flow processes, there may be a certain compensation of the difference in height of the edge structures. The dimensions shown are also not to scale, but instead serve rather only for more effective representation. In particular, the electronic structure itself is generally of relatively flat design (often less than 1 m thick).

(18) The thickness of the adhesive transfer tape may span all customary thicknesses, in other words, approximately, from 1 m up to 3000 m. A thickness of between 25 and 100 m is preferred, since, within this range, bond strength and handling properties are particularly positive. A further preferred range is a thickness of 3 to 25 m, since in this range the amount of substances permeating through the bondline can be minimized solely by the small cross-sectional area of the bondline in an encapsulation application.

(19) To produce an adhesive transfer tape of the invention, the carrier of the adhesive tape, or the liner, is coated or printed on one side with the getter material-comprising adhesive, from solution or dispersion or in 100% form (as a melt, for example), or the tape is produced by (co)extrusion. An alternative form of production is by transfer of a layer of adhesive of the invention by lamination to a carrier material or a liner. The layer of adhesive may be crosslinked by heat or high-energy radiation.

(20) This operation preferably takes place in an environment in which the specific permeate is present only in a low concentration or almost not at all. An example that may be given is a relative atmospheric humidity of less than 30%, preferably of less than 15%.

(21) To optimize the properties it is possible for the adhesive employed to be blended with one or more additives such as tackifiers (resins), plasticizers, fillers, pigments, UV absorbers, light stabilizers, aging inhibitors, crosslinking agents, crosslinking promoters or elastomers.

(22) The amount of a layer of adhesive is preferably 1 to 120 g/m.sup.2, preferably 10 to 100 g/m.sup.2, where amount means the amount after any removal of water or solvent that may be carried out.

(23) The present invention further provides for the use, for indicating the perfect integrity of the adhesive tape, of a change in the optical properties of the getter material. Thus, for example, calcium oxide changes color from white to transparent as the binding of water progresses. Metallic calcium as well loses its metallically opaque appearance and becomes increasingly transparent. Therefore, as long as getter material can still be recognized in the visual appearance of the unused state, this may be taken to be an indication that there has as yet been no diffusion, or at most low diffusion, of permeate to the adhesive that is to be protected.

EXAMPLES

Adhesive

(24) TABLE-US-00001 K1: Pressure-sensitive adhesive 100 parts Tuftec P 1500 SBBS with 30% by weight block polystyrene content from Asahi. 100 parts Escorez 5600 The SBBS contains about 68% by weight diblock content. hydrogenated HC resin with a softening point of 100 C., from Exxon 25 parts Ondina 917 white oil comprising paraffinic and naphthenic fractions, from Shell

(25) The solvent used was a 2:1 mixture of toluene and acetone.

(26) TABLE-US-00002 K2: Hotmelt adhesive 100 parts Kraton FG maleic anhydride-modified SEBS with 13% 1924 by weight block polystyrene content, 36% by weight diblock and 1% by weight maleic acid, from Kraton 25 parts Escorez 5600 hydrogenated HC resin (hydrocarbon resin) having a softening point of 100 C., from Exxon 1 part aluminum acetylacetonate

(27) The solvent used was a 2:1 mixture of toluene and acetone.

(28) TABLE-US-00003 K3: Radiation-activatable hotmelt adhesive 25 parts Epiclon bisphenol A and bisphenol F based epoxy resin from 835 LV DIC, Japan, molecular weight M.sub.w about 350 g/mol 25 parts Epicote bisphenol based epoxy resin from 1001 Mitsubishi Chemical Company, Japan, molecular weight M.sub.w about 900 g/mol 50 parts YP-70 bisphenol A and bisphenol F based phenoxy resin from Nippon Steel Chemical Group, Japan, molecular weight M.sub.w about 55 000 g/mol 1.5 parts Irgacure iodonium salt-based UV photoinitiator from BASF 250 (iodonium, (4-methylphenyl) [4-(2-methylpropyl) phenyl]-,hexafluorophosphate(1-))

(29) The solvent used was methyl ethyl ketone.

(30) TABLE-US-00004 K3: Heat-activatable adhesive 90 parts Ultramid 1C copolyamide 6/66/136 from BASF, having a viscosity number of 122 ml/g in 96% strength sulfuric acid in accordance with ISO 307 10 parts EPR 166 bisphenol based epoxy resin from Bakelite, epoxide number of 184 20 parts PEG 2000 polyethylene glycol with an average molar mass of 2000 20 parts Foralyn 5040 tackifier resin from Eastman

(31) The adhesive was prepared in a process as disclosed in DE102006047739 A1, using ethanol as solvent.

(32) K5: Conventional Acrylate Adhesive without Significant Permeation Barrier

(33) Pressure-sensitive acrylate adhesive containing as comonomers 30% by weight of ethylhexyl acrylate, 67% by weight of butyl acrylate, and 3% by weight of acrylic acid. For the preparation of the acrylate PSA, the individual comonomers were polymerized in a manner familiar to the skilled person, in a mixture of mineral spirit and acetone.

(34) For all of the adhesives, the water vapor (WVTR) and oxygen (OTR) permeation rates were ascertained. This was carried out, in the case of the activatable adhesives, in the activatedi.e., crosslinkedstate.

(35) The WVTR was measured at 38 C. and 90% relative atmospheric humidity in accordance with ASTM F-1249; the OTR was measured at 23 C. and 50% relative atmospheric humidity in accordance with DIN 53380part 3.

(36) The permeation rates ascertained were as follows (standardized for a thickness of 50 m):

(37) TABLE-US-00005 Adhesive WVTR [g/m.sup.2d] OTR [cm.sup.3/m.sup.2 d bar] K1 37 12 500 K2 22 5000 K3 32 400 K4 220 120 K5 (comparative example) 620 25 000

(38) All adhesive solutions were dried by addition of zeolites (4 molecular sieves from the supplier Sigma-Aldrich) before the getter material was added.

(39) Getter Materials Used:

(40) TABLE-US-00006 Identification Description Trade name Supplier G1 calcium oxide calcium oxide Sigma-Aldrich nanopowder G2 calcium sulfate CA-5 calcium United States Gypsum sulfate filler Company G3 calcium CA-CL-02-NP American Elements chloride (nanoparticles) G4 silica Aerosil 380 Evonik Degussa G5 zeolite 3A Purmol 3 STH Zeochem
Production of Adhesive Transfer Tapes:

(41) The adhesive tapes were produced in a glovebox under a nitrogen atmosphere at 23 C. with a water content of 1 ppm.

(42) For the production of adhesive transfer tapes, the various adhesives were applied from a solution to a conventional permeation-proof liner of type ALU I 38 UV1 from Mondi, comprising an aluminum foil carrier, by means of a laboratory coater, and were dried. The thickness of the layer of adhesive after drying was 25 m in each case. Drying took place in each case at 120 C. in a drying oven for 30 minutes. Immediately after drying, the layers of adhesive were also lined on the open side with the aforementioned liner. The adhesive transfer tapes of the invention produced as examples therefore consisted in each case only of a layer of an adhesive.

(43) As comparative examples, adhesive transfer tapes with amounts of getter greater than those according to the invention were produced.

(44) Immediately after their production, the getter-filled adhesive transfer tapes were welded into vacuumized pouches consisting of a permeation-proof film/foil laminate (polyester film-aluminum foil-sealing adhesive film), stored in the glovebox under a nitrogen atmosphere, and not removed until immediately prior to use.

(45) The adhesive transfer tapes produced were as follows:

(46) TABLE-US-00007 Fraction Adhesive Getter material [wt %] Example 1 K1 G1 0.2 2 K1 G1 1 3 K1 G1 2 4 K2 G5 1 5 K3 G1 1 6 K3 G2 0.2 7 K3 G2 1 8 K3 G2 2 9 K4 G4 0.2 10 K4 G4 1 11 K4 G4 2 Comparative examples C1 K1 G1 5 C2 K1 G1 20 C3 K2 G5 5 C4 K2 G5 20 C5 K3 G1 20 C6 K3 G2 5 C7 K3 G2 20 C8 K4 G4 5 C9 K4 G4 20 C10 K5 G1 1 C11 K5 G1 5 C12 K5 G1 20

(47) For examples 1-4 and for comparative examples C1-C4 and also C10-C12, the bond strengths to steel were determined in analogy to ISO 29862 (method 3) at 23 C. and 50% relative humidity, with a peeling speed of 300 mm/min and a peel angle of 180. Reinforcing film used was an etched PET film having a thickness of 50 m, of a kind available from Coveme (Italy).

(48) The measurement strip here was bonded by means of a laboratory laminator at a temperature of 60 C. Only adhesive K2 was bonded at a temperature of 120 C. The adhesive tapes were peeled 14 days after application.

(49) The examples show in each case that the bond strength, in the case of the adhesives having a getter material content within the range according to the invention, hardly decreases down to a low getter content, in accordance with the prior art, in the region of 5 wt %. Accordingly, here as well, the skilled person does not expect any substantial decrease in the permeation barrier. This, however, is surprisingly refuted by the lifetime tests.

(50) Lifetime Test:

(51) As a measure for determining the lifetime of an electronic construction, a calcium test was employed. This test is shown in FIG. 4. It involves depositing a thin layer of calcium 23, measuring 2020 mm.sup.2, under reduced pressure onto a glass plate 21, and then storing the assembly under a nitrogen atmosphere. The thickness of the calcium layer 23 is approximately 100 nm. The calcium layer 23 is encapsulated using an adhesive tape (2626 mm.sup.2) with the adhesive 22 under test and with a thin glass sheet 24 (35 m, from Schott) as carrier material. For stabilization, the thin glass sheet was laminated with a PET film 26 that was 100 m thick, using an adhesive transfer tape 25 that was 50 m thick, the tape comprising a pressure-sensitive acrylate adhesive of high optical transparency. The adhesive 22 is applied to the glass plate 21 in such a way that the adhesive 22 covers the calcium mirror 23 with a margin of 3 mm (A-A) remaining all round. Because of the impervious glass carrier 24, the permeation ascertained is only that through the PSA or along the interfaces.

(52) Application took place by means of a roll laminator at specific temperatures for each adhesive. In the case of adhesive 3, there was subsequent irradiation with UV light, using a medium-pressure mercury vapor lamp, with a UV-C dose of around 200 mJ/cm.sup.2 (determined using the UV-power puck device from EIT (USA) in the wavelength range of 250-260 nm). In the case of adhesive 4, there was a hot pressing step at a temperature of 160 C. under a pressure of around 1 MPa:

(53) TABLE-US-00008 Adhesive Laminating temperature K1 60 C. K2 120 C. K3 100 C. K4 140 C.

(54) The test is based on the reaction of calcium with water vapor and oxygen, as described by, for example, A. G. Erlat et al. in 47.sup.th Annual Technical Conference ProceedingsSociety of Vacuum Coaters, 2004, pages 654 to 659, and by M. E. Gross et al. in 46.sup.th Annual Technical Conference ProceedingsSociety of Vacuum Coaters, 2003, pages 89 to 92. The light transmittance of the calcium layer is monitored in the test, and increases as a result of the conversion to calcium hydroxide and calcium oxide. In the case of the test construction described, this increase takes place starting from the margin, and so the visible area of the calcium mirror goes down. The time taken for the absorption of light by the calcium mirror to halve is termed the lifetime. The method captures not only the degradation of the surface of the calcium mirror from the margin and on the surface, as a result of local degradation, but also the uniform reduction in the layer thickness of the calcium mirror as a result of full-area degradation.

(55) Measurement conditions selected were 60 C. and 90% relative humidity. The specimens were bonded over the full area, without bubbles, with a 25 m thickness of the PSA layer. The result (in h) was obtained as the average value from three individual measurements.

(56) The table below summarizes the results of the bond strength determinations and of the lifetime test:

(57) TABLE-US-00009 Bond strength to steel [N/cm] Lifetime [h] Example 1 7.3 239 2 7.4 388 3 7.0 591 4 5.3 572 5 915 6 305 7 562 8 763 9 78 10 93 11 125 Comparative examples C1 6.8 684 C2 5.4 64 C3 5.0 610 C4 3.4 46 C5 290 C6 726 C7 23 C8 119 C9 27 C10 5.3 19 C11 5.0 24 C12 3.1 41

(58) In the lifetime test, surprisingly, adhesive transfer tapes of the invention exhibit a lifetime with an order of magnitude similar to that of prior-art adhesive tapes (compare examples 1-3 with C1-C2, and 4 vs. C3-C4). For certain examples, indeed, adhesive tapes of the invention achieve longer lifetimes than adhesive tapes already considered in accordance with the prior art to be filled with only a low fraction of getter material (compare examples 5 vs. C5, 6-8 vs. C6-C7, 9-11 vs. C8-C9).

(59) Comparative examples C10-C12 show that the synergistic effect does not occur for adhesives which already have a high permeation rate of permeates that lead to degradation of the calcium in the lifetime test. In relation to the examples, the effect occurs only when using adhesives which already represent a high permeation barrier, more particularly which have, for a thickness of 50 m, a water vapor permeation rate of less than 50 g/m.sup.2d and/or an oxygen permeation rate of less than 5000 g/m.sup.2d bar.