JP2013168545A - Method for joining conductive members - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for joining conductive members capable of achieving both adhesiveness and conductivity with a simple configuration.SOLUTION: A metallic porous member 1 having voids 2 is prepared and conductive members A1, A2 are joined to each other by curing a resin-made adhesive 3 impregnated into the voids 2 of the porous member 1 interposed between the conductive members A1, A2. Here, the metallic porous member 1 is interposed between the conductive members A1, A2 and the resin-made adhesive 3 is cured by impregnating the resin-made adhesive 3 into the voids 2 of the metallic porous member 1. Moreover, the resin-made adhesive 3 is impregnated into the voids 2 of the metallic porous member 1, and the metallic porous member 1 is interposed between the conductive members A1, A2, thereby curing the resin-made adhesive 3.

Description

  The present invention relates to a method for joining conductive members, for example, a method for joining elements constituting a power module and an electrode plate.

  Conventionally, a conductive adhesive has been used as a bonding material for bonding members constituting a power module.

  Examples of the conductive adhesive include a solder mainly composed of tin and lead, a filler sintered adhesive including a filler made of inorganic or organic fine particles, and a filler dispersion adhesive.

  Among the conductive adhesives described above, solder mainly composed of tin and lead has an advantage of excellent conductivity. On the other hand, due to the composition change accompanying the recent lead-free compatibility, it is generally a joint material with high rigidity and a large linear expansion coefficient, and thermal expansion between the structural members due to temperature changes when the structural members are joined together There is a problem that the thermal stress caused by the difference becomes relatively high.

  In addition, the filler-sintered conductive adhesive has an advantage that it is excellent in conductivity because the fillers themselves melt and fuse together. On the other hand, when the adhesion area is large, there is a problem that the amount of shrinkage during sintering becomes relatively large, and for example, there is a possibility that the adhesive peels off and the adhesive force is reduced.

  Further, since the filler-dispersed conductive adhesive contains a relatively large amount of the resin component, it can alleviate the thermal stress caused by the difference in thermal expansion between the constituent members and suppress the decrease in adhesiveness. Has advantages. On the other hand, there is a problem that the filler is dispersed inside the adhesive, the conduction resistance is increased and the conductivity is lowered, and the production cost is increased when the filler filling amount is increased. .

  In particular, the recent power modules have been downsized, and the heat generated by the elements has increased with the downsizing of the power modules, and the amount of heat per unit area has increased. As a result, the thermal diffusion area of the component members has decreased, and the cooling performance by the cooler is naturally limited. It is an urgent issue to develop a joining method that can alleviate the problem and ensure the conduction between the constituent members.

  In order to solve such a problem, Patent Document 1 discloses various methods for joining constituent members by interposing a porous body between constituent members and impregnating and curing an adhesive in the voids of the porous body. -4.

  In the method for manufacturing a power module disclosed in Patent Document 1, a conductive porous body having a predetermined porosity distribution is interposed between members having different linear expansion coefficients, and the voids of the conductive porous body are impregnated with solder. This is a method of joining members together.

  In addition, the bonding method disclosed in Patent Document 2 uses a bonding material having a composite structure of a low-melting-point metal material made of solder or brazing and a porous metal body, for example, a porous metal body and a low-melting-point metal sheet, In this method, impregnation and joining are performed simultaneously.

  In addition, in the bonding method disclosed in Patent Document 3, a porous metal layer having voids inside is interposed between metal layers, and an organic bonding material containing metal is installed between the metal layer and the porous metal layer. And heating and sintering the organic bonding material to bond the two members.

  Further, in the method for producing a metal member assembly disclosed in Patent Document 4, a paste-like metal particle composition comprising heat-sinterable metal particles and a volatile dispersion medium is interposed between a plurality of metal members. In this method, the volatile dispersion medium is volatilized by heating, the metal particles are sintered together, impregnated with a curable liquid resin composition, and cured to join metal members together. .

JP 2009-277856 A JP 2000-349100 A JP 2006-202944 A JP 2010-065277 A

  According to the power module manufacturing method disclosed in Patent Document 1, the linear expansion coefficient and Young's modulus inside the bonding material are linearly changed by linearly changing the porosity of the porous body-solder composite material. It is possible to reduce the thermal stress by suppressing the stress concentration inside the bonding material or at the bonding interface. Moreover, electroconductivity and thermal conductivity can be improved by impregnating the voids of the conductive porous body with solder.

  Moreover, according to the joining method disclosed in Patent Document 2, it is possible to suppress the outflow due to leakage of the low melting point metal material by the porous metal body, and to dispose the members to be joined precisely apart. In addition, the conductivity and thermal conductivity can be increased.

  Moreover, according to the joining method disclosed in Patent Document 3, by using the inside of the porous metal layer as an organic matter volatilization path, the organic matter can be volatilized even near the center of the joining surface, and pressure is applied during joining. Two members can be joined.

  In addition, according to the method for manufacturing a metal member assembly disclosed in Patent Document 4, metal members can be firmly bonded to each other by a sintered product of heat-sinterable metal particles, By impregnating the curable liquid resin composition into the voids of the binder and curing, it is possible to prevent the liquid from being sucked into the voids of the sintered product and ensure the hardness and strength of the sintered product.

  However, in the method for manufacturing the power module disclosed in Patent Document 1 and the joining method disclosed in Patent Document 2, the voids of the conductive porous body are impregnated with a low melting point metal material made of solder or solder. Therefore, there is a problem that the rigidity of the bonding material is still high and the linear expansion coefficient may be increased. In particular, in the method for manufacturing a power module disclosed in Patent Document 1, there is a problem that a process for manufacturing a conductive porous body having a predetermined porosity distribution becomes complicated and the manufacturing cost increases.

  In addition, in the joining method disclosed in Patent Document 3, for example, Ag nanopaste is impregnated in the voids of the porous metal layer instead of solder, but an organic joining material containing a large amount of metal is used. However, the problem that the rigidity of the bonding material is still high and the linear expansion coefficient may be increased cannot be solved.

  Furthermore, in the joining method disclosed in Patent Document 3 and the metal member joined body disclosed in Patent Document 4, two organic bonding materials and heat-sinterable metal particles are sintered. Since the members are joined, when the adhesion area is large, the amount of shrinkage during sintering becomes large, and the problem that the joining material may peel off and the adhesive force may be reduced cannot be solved.

  As described above, in the joining methods disclosed in Patent Documents 1 to 4, the problems caused by the conductive adhesive described above can be solved individually, but a joining method capable of achieving both adhesiveness and conductivity is constructed. It has not been done.

  The present invention has been made in view of the above-described problems, and an object thereof is to provide a method for joining conductive members that can achieve both adhesiveness and conductivity with a simple configuration.

  In order to achieve the above object, a conductive member joining method according to the present invention provides a metal porous body having voids, and the voids of the metal porous body interposed between the conductive members are impregnated. In this method, the conductive adhesive is cured by curing the resin adhesive.

  Here, the metal porous body used in the bonding method of the conductive member of the present invention is preferably a foam metal, and as the forming material of the metal porous body, for example, aluminum (Al), copper (Cu), nickel (Ni), iron (Fe), gold (Au), silver (Ag), palladium (Pd), and alloys thereof. In addition, examples of the shape of the metal porous body include a rectangular shape, a disk shape, and a sheet shape.

  Examples of the resin adhesive include thermosetting resins such as epoxy resins, silicone resins, polyimide resins, polyamide resins, urethane resins, and phenol resins.

  According to the bonding method described above, by interposing the metal porous body between the conductive members, a conductive path can be formed between the conductive members to ensure excellent conductivity, and the metal porous body can be secured. In the case where the material has a predetermined rigidity, the thickness of the bonding material can be ensured and the conductive members can be precisely spaced apart. Also, by curing the resin adhesive impregnated in the voids of the metal porous body and bonding the conductive members together, the rigidity of the entire bonding material can be reduced, and the conductivity caused by temperature changes Thermal stress that can occur in the bonding material due to the difference in thermal expansion between the members can be reduced. In addition, by using a resin adhesive, it is possible to relieve the thermal stress that can occur in the resin adhesive due to the difference in thermal expansion between the metal porous body and the resin adhesive contained in the voids inside the metal porous body. Therefore, the adhesiveness can be remarkably enhanced. Furthermore, by interposing a metal porous body prepared in advance between the conductive members, it is possible to suppress the occurrence of peeling of the bonding material due to sintering and the like, while simplifying the arrangement process of the metal porous body The adhesive force can be further increased.

  In the joining method described above, the metal porous body may be interposed between the conductive members, and the resin adhesive may be impregnated in the voids of the metal porous body to cure the resin adhesive. Alternatively, the resin adhesive may be impregnated in the voids of the metal porous body, and the resin adhesive may be cured by interposing the metal porous body between the conductive members.

  For example, when a metal porous body is interposed between conductive members and the resin porous adhesive is impregnated into the voids of the metal porous body, the arrangement process of the metal porous body should be simplified. Can do. Also, for example, when the metal porous body is impregnated between the conductive members after impregnating the void in the metal porous body with the resin adhesive, the resin adhesive impregnation step is simplified. be able to.

  Further, the porosity of the metallic porous body can be appropriately set according to the required characteristics, but the metallic porous body preferably has a porosity of 20 to 60%, particularly 40 to 60%. It is desirable to have a porosity of When the porosity of the metal porous body exceeds 60%, the bonding strength between the conductive members is increased, but the volume resistivity of the entire bonding material is also increased. Further, when the porosity of the metal porous body is lower than 20%, although the volume resistivity of the whole bonding material is reduced, the adhesive strength between the conductive members is also reduced. That is, when the metal porous body has a porosity of 40 to 60%, both adhesion and conductivity can be improved more effectively.

  As can be understood from the above description, according to the conductive member bonding method of the present invention, the resin adhesive impregnated in the voids of the metal porous body interposed between the conductive members is cured. By an extremely simple improvement method, it is possible to effectively improve the adhesion and conductivity between the conductive members.

It is the flowchart explaining Embodiment 1 of the joining method of the electroconductive member of this invention. It is the longitudinal cross-sectional view which demonstrated typically each process in the joining method of Embodiment 1 shown in FIG. 1, (a) is a process which prepares a metal porous body, (b) is between electroconductive members. (C) is a step of impregnating a metal porous body with a resin adhesive, and (d) is a diagram illustrating a step of curing the resin adhesive. It is. It is the flowchart explaining Embodiment 2 of the joining method of the electroconductive member of this invention. It is the perspective view which showed the sample of the Example typically. It is the figure which demonstrated typically the measuring method of the volume resistivity in the sample for a test | inspection. It is the figure which showed the measurement result of the volume resistivity in the sample of an Example and Comparative Examples 1 and 2. FIG. It is the figure which demonstrated typically the measuring method of the adhesive strength in the test sample. It is the figure which showed the measurement result of the adhesive strength in the sample of an Example and Comparative Examples 1 and 2. FIG. It is the figure which showed the relationship between the porosity in the sample of an Example, adhesive strength, and volume resistivity.

  Embodiments of the present invention will be described below with reference to the drawings.

[Embodiment 1]
FIG. 1 is a flowchart for explaining the first embodiment of the method for joining conductive members of the present invention, and FIG. 2 schematically explains each step in the joining method of the first embodiment shown in FIG. 2A is a longitudinal sectional view, FIG. 2A is a step of preparing a metal porous body, FIG. 2B is a step of interposing a metal porous body between conductive members, and FIG. 2C. FIG. 2D is a diagram illustrating a step of impregnating a resinous adhesive into the voids of the metal porous body, and FIG. 2D is a diagram illustrating a step of curing the resinous adhesive.

  As shown in FIG. 1, in the joining method of the first embodiment, first, a metal porous body having a void inside is prepared in advance (S11). Next, the metallic porous body is interposed between the conductive members (S12). Then, the resin adhesive is impregnated in the voids of the metal porous body by a predetermined method (S13), and the resin adhesive impregnated in the voids of the metal porous body is cured by heating or the like (S14).

  Specifically, as shown in FIG. 2 (a), first, a rectangular and sheet-like copper porous body 1 in a plan view is prepared.

  Next, as shown in FIG. 2B, the copper porous body 1 is made up of a first conductive member (for example, a semiconductor element for a power module) A1 and a second conductive member (for example, a copper electrode plate) A2. Intervene between.

  Next, as shown in FIG. 2C, the void 2 of the copper porous body 1 is impregnated with a paste-like epoxy resin adhesive 3 by a predetermined method. Here, the voids 2 formed in the copper porous body 1 have a configuration in which they communicate with each other, and a part of the impregnated resin adhesive 3 is used as the first conductive member A1 or the second conductive member A1. It penetrates into the adhesive surfaces 4 and 5 with the conductive member A2.

  And as shown in FIG.2 (d), the epoxy resin adhesive 3 impregnated in the space | gap 2 of the copper porous body 1 is hardened by heating etc., and 1st electroconductive member A1 and 2nd electroconductivity are carried out. The member A2 is bonded via the bonding material 10 made of the epoxy resin adhesive 3 and the copper porous body 1. When the epoxy resin adhesive 3 is cured by heating or the like, it is necessary to press the first conductive member A1 and the second conductive member A2 in consideration of the thermal expansion of the adhesive 3. In addition, the copper porous body 1 can be used as a structural member, and the first conductive member A1 and the second conductive member A2 can be easily separated from each other at precise positions.

  According to the joining method of the first embodiment, it is possible to form a conduction path between conductive members using a metal porous body, and to ensure conductivity between the conductive members. In addition, by joining the conductive members through the resin adhesive, the thermal stress that can occur in the resin adhesive due to the difference in thermal expansion between the conductive members can be reduced, and the conductive members can be bonded to each other. Strength can be increased. In addition, by interposing a metal porous body prepared in advance between the conductive members, the bonding strength of the metal porous body can be further enhanced while simplifying the arrangement process of the metal porous body. Furthermore, according to the joining method of the first embodiment, there is an advantage that the amount of the resin adhesive to be used can be suppressed.

[Embodiment 2]
FIG. 3 is a flowchart illustrating Embodiment 2 of the method for joining conductive members of the present invention. The bonding method according to the second embodiment is different from the bonding method according to the first embodiment in that a metal porous body is interposed between the conductive members, and a void in the metal porous body is impregnated with a resin adhesive. The order of the steps is changed.

  In the joining method of the second embodiment, first, a metallic porous body having a void inside is prepared in advance (S21). Next, a resin adhesive is impregnated in the voids of the metal porous body by a predetermined method (S22). Then, the metallic porous body is interposed between the conductive members (S23), and the resin adhesive impregnated in the voids of the metallic porous body by heating or the like is cured (S24).

  Thus, the resin adhesive impregnation step is performed by changing the order of the step of interposing the metal porous body between the conductive members and the step of impregnating the metal porous body with the resin adhesive. Can be simplified.

  In addition, as a forming material of the conductive member joined by the joining method of the first and second embodiments described above, for example, aluminum (Al), copper (Cu), nickel (Ni), gold (Au), silver (Ag ), Palladium (Pd), platinum (Pt) and alloys thereof. Specifically, examples of the conductive member include a metal substrate such as a gold-plated substrate, a silver substrate, a silver-plated metal substrate, a copper substrate, an aluminum substrate, a nickel-plated substrate, and a tin-plated metal substrate, and a semiconductor placed on the substrate. An element, a lead frame, a heat sink, etc. can be mentioned. In other words, the above-described joining method can be applied to the fields of electronic components, electronic devices, electrical components, electrical devices and the like having a metal substrate or a metal part, such as a power module.

[Experiment and result of measuring volume resistivity and adhesive strength of bonding material with test sample]
The present inventors produce a test sample (Example) in which copper plates are bonded to each other using the bonding method according to Embodiment 1 described above, and volume is measured using the four-terminal method and a tensile shear test on the sample. Resistivity measurement and adhesive strength measurement were performed.

[Example]
First, an outline of the method for preparing the test sample of the example is as follows. As shown in FIG. 4, two copper plates (conductivity) having a longitudinal length of 100 mm, a lateral length of 25 mm, and a thickness of 3.0 mm. Member) and arrange the two copper plates approximately parallel to the position where the opposite ends of the copper plate in the longitudinal direction overlap by 12.5 mm. Next, a copper porous body having a thickness of 500 μm and a porosity of about 55% is interposed between the two copper plates, and an adhesive made of an epoxy resin applied to the copper porous body is placed in a vacuum environment. The voids of the copper porous body were impregnated and the adhesive was cured by heating to join the two copper plates. In addition, the joining material which consists of a copper porous body and an adhesive agent was formed over the whole longitudinal direction of a copper plate.

[Comparative Examples 1 and 2]
In addition, the present inventors produced inspection samples (Comparative Examples 1 and 2) in which copper plates for comparing the volume resistivity and adhesive strength with the inspection samples of the above-described examples were joined. The inspection sample of Comparative Example 1 used a filler sintered conductive adhesive as the bonding material, and the inspection sample of Comparative Example 2 used a filler dispersed conductive adhesive as the bonding material. .

  An outline of the method for preparing the test sample of Comparative Example 1 is as follows. Like the example, two copper plates (conductive members) having a longitudinal length of 100 mm, a lateral length of 25 mm, and a thickness of 3.0 mm. Is prepared, and is arranged substantially parallel to the position where the opposite ends of the copper plates in the longitudinal direction overlap each other by 12.5 mm. Next, a filler-sintered conductive adhesive containing silver powder as a filler and an epoxy resin as a base resin is interposed between the two copper plates so that the thickness of the bonding material after curing is 200 μm. The adhesive was cured by heating, and the two copper plates were joined.

  The outline of the method for preparing the test sample of Comparative Example 2 is as follows. As in the case of the example, two copper plates having a longitudinal length of 100 mm, a lateral length of 25 mm, and a thickness of 3.0 mm (conductive Member) and arrange the two copper plates approximately parallel to the position where the opposite ends of the copper plate in the longitudinal direction overlap by 12.5 mm. Next, 80% by mass of spherical silver powder having an average particle size of 5.0 μm as a filler and 20% by mass of epoxy resin as a base resin between the two copper plates so that the thickness of the bonded material after curing is 200 μm. % Filler-dispersed conductive adhesive was interposed, and the adhesive was cured by heating to join two copper plates.

[Experiments and results of measuring volume resistivity]
The inventors of the present invention performed volume resistivity measurement on the test samples (Examples, Comparative Examples 1 and 2) prepared by the above-described manufacturing method using a four-terminal method.

  To outline the volume resistivity measurement method, as shown in FIG. 5, two copper plates are connected with a current type A and a voltmeter V, and a current of 100 mA is used at an ambient temperature of 25 ° C. using the current type A. The resistance value between two copper plates and the resistance value for one copper plate are measured using a voltmeter V. And the resistance value of the joining material was computed based on the following formula | equation (1), and also the volume resistivity of the joining material was computed based on the dimension of the joining material.

FIG. 6 is a diagram showing the measurement results of volume resistivity in the samples of Example and Comparative Examples 1 and 2. As shown in the figure, the volume resistivity of the test sample of the example is 6.0 × 10 ⁻⁴ Ω · cm, and the volume resistivity of the test sample of the comparative example 1 is 2.9 × 10 ⁻⁴ Ω · cm. The volume resistivity of the test sample was 9.4 × 10 ⁸ Ω · cm. In addition, the volume resistivity of copper at 20 ° C is 1.68 × 10 ^-8 Ω · cm, and the volume resistivity of silver is 1.59 × 10 ^-8 Ω · cm. It is considered extremely small.

  From this experimental result, the test sample of the example has the same conductivity as the test sample of Comparative Example 1 using the filler sintered conductive adhesive, and the filler dispersed conductive adhesive is used. It was proved that the conductivity was much better than the test sample of Comparative Example 2 used.

[Experiment and results of measuring adhesive strength]
Next, the present inventors performed an adhesive strength measurement on the test samples (Examples, Comparative Examples 1 and 2) produced by the production method described above using a tensile shear test.

  As shown in Fig. 7, the method of measuring the adhesive strength is outlined. The opposite side in the longitudinal direction of two copper plates in the shape of a lap joint is chucked at a chuck distance of 100 mm, and the tensile speed is 5.0 at 25 ° C ambient temperature. It was pulled in the direction opposite to the longitudinal direction at mm / min, and the tensile load at the time of fracture of the bonding material was measured.

  FIG. 8 is a diagram showing the measurement results of the adhesive strength in the samples of Examples and Comparative Examples 1 and 2. As shown in the figure, the bonding strength of the test sample of the example was 12 MPa, and the bonding strength of the test sample of the comparative example 2 was 19 MPa. In the test sample of Comparative Example 1, the bonding material was broken by the stress generated when chucking the two copper plates, and the adhesive strength could not be measured.

  From this experimental result, it was demonstrated that the test sample of the example has excellent adhesiveness although the adhesive strength is lower than that of the test sample of Comparative Example 2 using the filler-dispersed conductive adhesive. It was.

  Thus, the test sample of the example has conductivity equivalent to that of the test sample of Comparative Example 1 using the filler sintered conductive adhesive, and the filler sintered conductive adhesive is used. It was confirmed that the adhesive strength was higher than the test sample of Comparative Example 1 used, and the decrease in the adhesive strength was suppressed with respect to the test sample of Comparative Example 2 using a filler-dispersed conductive adhesive. It was.

  Therefore, the inspection sample of the example uses the filler dispersion type conductive adhesive excellent in adhesiveness and the inspection sample of Comparative Example 1 using the filler sintered conductive adhesive excellent in conductivity. The characteristics of both of the test samples of Comparative Example 2 were demonstrated, and it was demonstrated that both adhesiveness and conductivity can be achieved.

[Experiment and results of measuring changes in bond strength and volume resistivity of test specimens due to changes in porosity]
The present inventors made seven types of test samples having different porosity of the copper porous body for the test samples of the above-described examples, and measured the bonding strength and volume resistance of the bonding material for each sample. Rate measurements were performed. In addition, the measuring method of adhesive strength and volume resistivity is the same as the measuring method mentioned above.

  FIG. 9 is a diagram showing the relationship between the porosity, the adhesive strength, and the volume resistivity in the sample of the example. In addition, in FIG. 9, the result of having implemented the adhesive strength measurement and volume resistivity measurement about the copper porous body which has a porosity of about 20%, about 42%, about 55%, about 69%, and about 79%. In addition, for comparison, the results of adhesion strength measurement and volume resistivity measurement for a copper porous body having porosity of 0% and about 100% are shown.

  As shown in the figure, as a result of performing adhesive strength measurement and volume resistivity measurement on the copper porous body having the above porosity, the adhesive strength of the sample of the example increases substantially linearly according to the change in porosity. This was confirmed (solid line in the figure). In addition, it was confirmed that the volume expansion rate of the sample of the example was relatively low until the porosity was about 55%, and was relatively high when the porosity was about 69% or more (in the figure, a one-dot chain line). ). From the results of the volume expansion coefficient with a porosity of approximately 55% and the volume expansion coefficient with a porosity of approximately 69%, it was considered that the increase rate of the volume expansion coefficient was increased when the porosity was approximately 60%.

  From this experimental result, although the test sample of the example can achieve both adhesion and conductivity, the predetermined porous strength can be obtained by setting the porosity of the copper porous body to 20%, more preferably 40% or more. It was proved that the volume resistivity of the bonding material can be reduced by setting the porosity of the copper porous body to 60% or less. That is, by setting the porosity of the copper porous body to 40 to 60%, it is possible to suppress an increase in volume low efficiency while ensuring a predetermined adhesive strength, and to further improve both adhesiveness and conductivity. It has been demonstrated that

  The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and there are design changes and the like without departing from the gist of the present invention. They are also included in the present invention.

1 ... Copper porous body (metal porous body)
2 ... Gap 3 ... Epoxy resin adhesive (resin adhesive)
4, 5 ... Adhesive surface 10 ... Joining material A1 ... First conductive member A2 ... Second conductive member

Claims (5)

A method of joining conductive members together,
Conductivity for preparing a metal porous body having voids and curing the resin adhesive impregnated in the voids of the metal porous body interposed between the conductive members to join the conductive members together Member joining method.   The conductive material according to claim 1, wherein the metallic porous body is interposed between the conductive members, and the resin adhesive is cured by impregnating the resinous adhesive in the voids of the metallic porous body. Member joining method.   2. The conductive material according to claim 1, wherein the resin adhesive is impregnated in the voids of the metal porous body, and the resin adhesive is cured by interposing the metal porous body between the conductive members. Member joining method.   The method for joining conductive members according to any one of claims 1 to 3, wherein the metal porous body has a porosity of 40 to 60%. The said conductive member is a member which comprises a power module, The joining method of the conductive member as described in any one of Claims 1-4.

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