Patent Description:
For example, a thermoelectric module undergoes a difference in temperature between one principal surface and the other principal surface with the supply of electric power to thermoelectric elements. Moreover, for example, a thermoelectric module produces electric power via thermoelectric elements upon a difference in temperature between one principal surface of the module and the other principal surface. Thermoelectric modules having such useful characteristics are used for temperature control purposes or thermoelectric power generation purposes, for example.

An example of such thermoelectric modules includes: a pair of support substrates including mutually opposed regions; wiring conductors disposed on opposed one principal surfaces of the pair of support substrate, respectively; a plurality of thermoelectric elements disposed between the one principal surfaces of the pair of support substrates; and a lead member joined to the wiring conductor located on one support substrate of the pair of support substrates.

Patent Literature <NUM>: <CIT>
Moreover, <CIT> discloses a thermoelectric generation module comprising a plurality of thermoelectric elements, a pair of flexible boards holding the thermoelectric elements therebetween, a plurality of interelement electrodes, a lead wire, and a reinforcing pattern interposed between the flexible boards.

The present invention provides a thermoelectric module according to claim <NUM>. Preferred embodiments are described in the dependent claims.

In a conventional thermoelectric module with a lead member soldered to a wiring conductor located on a low-temperature-side support substrate of the pair of support substrates which has a relatively low temperature, the lead member is positioned in parallel with the principal surface of the support substrate.

In the thermoelectric module so constructed, transmission of heat from the lead member to the wiring conductor and the support substrate leads to poor cooling performance, and, the lead member may become detached from the wiring conductor under external forces, for example.

The disclosure addresses the problems discussed above, and aims to provide a thermoelectric module that achieves reduction in cooling performance degradation, and reduction in separation of a lead member from a wiring conductor.

A thermoelectric module in accordance with an embodiment of the invention will now be described with reference to drawings.

A thermoelectric module <NUM> shown in <FIG> includes: a pair of support substrates <NUM> and <NUM> including mutually opposed regions; wiring conductors <NUM> and <NUM> disposed on opposed one principal surfaces of the support substrates <NUM> and <NUM>, respectively; a plurality of thermoelectric elements <NUM> and <NUM> disposed between the one principal surfaces of the support substrates <NUM> and <NUM>; a lead member <NUM> joined to the wiring conductor <NUM> located on one support substrate <NUM> of the pair of support substrates; and an electrically conductive joining material <NUM> for joining the wiring conductor <NUM> and the lead member <NUM> together.

The pair of support substrates <NUM> and <NUM> constituting the thermoelectric module <NUM> include mutually opposed regions of, for example, a rectangular shape, for holding and supporting the plurality of thermoelectric elements <NUM> therebetween in sandwich style. For example, dimensions of each of the mutually opposed rectangular regions can be set to <NUM> to <NUM> in longitudinal length, <NUM> to <NUM> in transverse length, and <NUM> to <NUM> in thickness in plan configuration.

An upper surface of the support substrate <NUM> is placed so as to serve as one principal surface facing the support substrate <NUM>, and, a lower surface of the support substrate <NUM> is placed so as to serve as one principal surface facing the support substrate <NUM>. For example, the support substrate <NUM> serves as a low-temperature-side support substrate which has a relatively low temperature, whereas the support substrate <NUM> serves as a high-temperature-side support substrate which has a relatively high temperature.

The support substrate <NUM> bears the wiring conductor <NUM> on its upper surface serving as one principal surface facing the support substrate <NUM>, and, the support substrate <NUM> bears the wiring conductor <NUM> on its lower surface serving as one principal surface facing the support substrate <NUM>. Thus, the upper-surface side of the support substrate <NUM> and the lower-surface side of the support substrate <NUM> are each made of an insulating material. For example, the pair of support substrates <NUM> and <NUM> are each constructed of a <NUM> to <NUM>-thick substrate body made of alumina filler-added epoxy resin, with a <NUM> to <NUM>-thick copper sheet bonded to the outward principal surface of the substrate body. Alternatively, the pair of support substrates <NUM> and <NUM> may each be constructed of a substrate body made of a ceramic material such as alumina or aluminum nitride, with a metal sheet such as a copper sheet bonded to the outward principal surface of the substrate body. In another alternative, each support substrate may be constructed of a substrate body made of a conductive material such as copper, silver, or a silver-palladium material, with an insulating layer made of, for example, epoxy resin, polyimide resin, alumina, or aluminum nitride formed on the inward principal surface of the substrate body.

The wiring conductors <NUM> and <NUM> are disposed on the opposed inward one principal surfaces of the support substrates <NUM> and <NUM>, respectively. For example, the wiring conductors <NUM> and <NUM> are obtained by laminating a copper sheet to each of the opposed inward principal surfaces of the support substrates <NUM> and <NUM>, with a mask placed on each of a part of the copper sheet which constitutes the wiring conductor <NUM> and a part of the copper sheet which constitutes the wiring conductor <NUM>, and removing mask-free areas of each copper sheet by etching. Alternatively, it is possible to use copper sheets die-cut in the form of the wiring conductors <NUM> and <NUM>. The material of construction of the wiring conductors <NUM> and <NUM> is not limited to copper. For example, silver or a silver-palladium material may be used instead.

Between the opposed inward one principal surfaces of the support substrates <NUM> and <NUM>, there are provided the plurality of thermoelectric elements <NUM> electrically connected to one another via the wiring conductors <NUM> and <NUM>. The plurality of thermoelectric elements <NUM> include p-type thermoelectric elements <NUM> and n-type thermoelectric elements <NUM>. The thermoelectric elements <NUM> are members for temperature control utilizing the Peltier effect, or members for power generation utilizing the Seebeck effect. For example, the plurality of thermoelectric elements <NUM> are arranged in a matrix of rows and columns with spacing which equals <NUM> to <NUM> times the diameter of each thermoelectric element <NUM>. The thermoelectric elements <NUM> are soldered to the wiring conductors <NUM> and <NUM>. More specifically, the p-type thermoelectric elements <NUM> and the n-type thermoelectric elements <NUM> are alternately disposed adjacent each other, while being electrically connected in series via the wiring conductors <NUM> and <NUM> and solder. That is, all the thermoelectric elements <NUM> are connected in series.

The body of each of the plurality of thermoelectric elements <NUM> is formed of a thermoelectric material made of A<NUM>B<NUM> crystal (A refers to Bi and/or Sb, and B refers to Te and/or Se), or preferably formed of a Bi (bismuth) and Te (tellurium)-based thermoelectric material. More specifically, the p-type thermoelectric element <NUM> is formed of, for example, a thermoelectric material made of a solid solution of Bi<NUM>Te<NUM> (bismuth telluride) and Sb<NUM>Te<NUM> (antimony telluride). On the other hand, the n-type thermoelectric element <NUM> is formed of, for example, a thermoelectric material made of a solid solution of Bi<NUM>Te<NUM> (bismuth telluride) and Bi<NUM>Se<NUM> (bismuth selenide).

For example, the thermoelectric element <NUM> may be shaped in a circular cylinder or a polygonal prism such as a quadrangular prism. The thermoelectric element <NUM> of circular cylinder shape, in particular, is less influenced by thermal stress caused therein under heat cycles during use. For example, dimensions of the circular cylinder-shaped thermoelectric element <NUM> are set to <NUM> to <NUM> in diameter and <NUM> to <NUM> in height.

For example, the thermoelectric material constituting the p-type thermoelectric element <NUM> is formed as a rod-like body having a circular sectional profile of <NUM> to <NUM> in diameter from a p-type thermoelectric material made of Bi, Sb, and Te, which has undergone one melting-and-solidification process, through unidirectional solidification using Bridgman method. Moreover, the thermoelectric material constituting the n-type thermoelectric element <NUM> is formed as a rod-like body having a circular sectional profile of <NUM> to <NUM> in diameter from an n-type thermoelectric material made of Bi, Te, and Se, which has undergone one melting-and-solidification process, through unidirectional solidification using Bridgman method.

After being coated on its side surface with a resist to prevent adhesion of plating as required, each thermoelectric material is cut in a length (thickness) of, for example, <NUM> to <NUM> with a wire saw. Subsequently, on an as needed basis, a Ni layer is formed only on the cut surface of the material by electrolytic plating, for example, and then a Sn layer is formed on the Ni layer. Thus, the p-type thermoelectric elements <NUM> and the n-type thermoelectric elements <NUM> are obtained.

A sealing material made of, for example, resin such as silicone resin or epoxy resin may be provided as required around the plurality of thermoelectric elements <NUM> disposed between the support substrate <NUM> and the support substrate <NUM>. Although the outer periphery of the construction becomes deformed greatly due to a difference in temperature between the pair of support substrates <NUM> and <NUM>, the sealing material for filling the gaps among a plurality of outer periphery-side thermoelectric elements <NUM> disposed between the one principal surface of the support substrate <NUM> and the one principal surface of the support substrate <NUM> serves as a reinforcing material, thereby restraining the thermoelectric elements <NUM> from separating from the wiring conductors <NUM> and <NUM>.

One support substrate <NUM> of the pair of support substrates <NUM> and <NUM> is provided with an extended portion <NUM> as required. The extended portion <NUM> is a part of the support substrate <NUM> which lies outside the part thereof opposed to the support substrate <NUM> as seen in a plan view, or equivalently, a part of the support substrate <NUM> which lies to the left of the chain double-dashed line in <FIG>.

For example, extending amount (extending length) of the extended portion <NUM> are set to <NUM> to <NUM>, and a width along the entire length of a short side of the support substrate <NUM> is set to <NUM> to <NUM>.

The wiring conductor <NUM> disposed on the one principal surface of the support substrate <NUM> lies also on the extended portion <NUM>, and an end of the lead member <NUM> is joined, with the electrically conductive joining material <NUM> such as solder, to the wiring conductor <NUM> disposed on one principal surface of the extended portion <NUM>. The wiring conductor <NUM> and the lead member <NUM> may be joined together by laser beam welding rather than soldering.

The lead member <NUM> is intended for electrical connection between the thermoelectric module <NUM> and an external circuit, and provides electric power to the thermoelectric element <NUM> or extracts electric power produced by the thermoelectric element <NUM>. The lead member <NUM> includes a core <NUM> and a covering layer <NUM>. The front end of the lead member <NUM>, which is joined to the wiring conductor <NUM>, is made as a bared portion of the core <NUM>. Moreover, the lead member <NUM> includes the covering layer <NUM> with which the core <NUM> is covered on the side located close to the rear end of the lead member <NUM> rather than on the side located close to the front end thereof. Expressed differently, the covering layer <NUM> is disposed about the periphery of the core <NUM>, except at least for the front end of the core <NUM> which is electrically connected to the wiring conductor <NUM>.

The front end of the lead member <NUM> refers to an end of the lead member <NUM> which is joined to the wiring conductor <NUM> located on the support substrate <NUM>. The front end of the lead member <NUM> in the form of the bared portion of the core <NUM> refers to a part of the core <NUM> which extends beyond an edge of the covering layer <NUM> located close to the front end for electrical connection of the lead member <NUM> to the wiring conductor <NUM>. For connection between the lead member <NUM> and an external circuit, the rear end of the lead member <NUM> may also be made as a bared portion of the core <NUM>, or the rear end of the lead member <NUM> may be provided with a connector.

For example, the core <NUM> is formed of a bundle of a plurality of metallic wires such as copper wires, for example, a bundle of <NUM> to <NUM> copper wires, each having a diameter of <NUM> to <NUM>. For example, the covering layer <NUM> is formed of a <NUM> to <NUM>-thick sheet made of polyvinyl chloride or polyethylene.

As shown in <FIG>, the bonding interface between the electrically conductive joining material <NUM> and the wiring conductor <NUM> is smaller in width on the side of the bonding interface which is close to the thermoelectric element <NUM> than on the side of the bonding interface which is away from the thermoelectric element <NUM>, as viewed in a section in a direction perpendicular to an axial direction of the lead member <NUM>. This reduces the contact area on the side close to the thermoelectric element <NUM> where wide temperature variations are encountered. Thus, for the support substrate <NUM> serving as a low-temperature-side support substrate which has a relatively low temperature, transmission of heat from the lead member <NUM> to the wiring conductor <NUM> is reduced, and consequently the thermoelectric module <NUM> delivers a higher level of cooling performance. Moreover, the contact area is large on the side away from the thermoelectric element <NUM> enough to restrain the lead member <NUM> from separating from the wiring conductor <NUM>, and consequently the thermoelectric module <NUM> becomes more durable against external force.

Let it be assumed that a junction between the electrically conductive joining material <NUM> and the wiring conductor <NUM> is divided lengthwise into two portions, namely a portion located farther away from the thermoelectric element <NUM> than the lengthwise midpoint of the junction, and a portion located nearer to the thermoelectric element <NUM> than the lengthwise midpoint of the junction. When viewed in a section in a width direction perpendicular to the length direction of the lead member <NUM>, given that the width of the junction on the side close to the thermoelectric element <NUM> is <NUM> to <NUM>, then the junction on the side away from the thermoelectric element <NUM> has a width two to three times the width of the junction on the side close to the thermoelectric element <NUM>.

As shown in <FIG> and <FIG>, in the thermoelectric module <NUM>, the lead member <NUM> is inclined relative to a direction parallel to the one principal surface, as viewed in a section in a direction perpendicular to the one principal surface of the support substrate <NUM>, as well as along the axial direction of the lead member <NUM>. This reduces clearance between the support substrate <NUM> and the lead member <NUM>, and thus can reduce ingress of moisture into the wiring conductor <NUM>. Moreover, for the support substrate <NUM> serving as a high-temperature-side support substrate which has a relatively high temperature, on the occurrence of downwardly-curved convex warpage in the module which is in operation as a product due to the thermal expansion of the support substrate <NUM> and the thermal shrinkage of the support substrate <NUM>, the lead member <NUM> takes a nearly horizontal position within a housing case accommodating the thermoelectric module <NUM>. Thus, the module becomes more durable during the passage of current therethrough.

For example, the angle of inclination of the lead member <NUM> with respect to the one principal surface of the support substrate <NUM> falls in the range of <NUM> degree to <NUM> degrees.

Moreover, as shown in <FIG>, a resin material <NUM> may be provided to cover the electrically conductive joining material <NUM> and at least part of the core <NUM>. This achieves greater mechanical strength with which the support substrate <NUM> becomes resistant to deformation under the application of external force to the lead member <NUM>. Thus, the lead member <NUM> can be restrained from separating from the wiring conductor <NUM>, and consequently the thermoelectric module <NUM> becomes more durable against external force.

Moreover, as shown in <FIG>, a void <NUM> may be provided in a part of the boundary of the electrically conductive joining material <NUM> and the resin material <NUM>. This reduces distortion resulting from a difference in thermal expansion between the electrically conductive joining material <NUM> and the resin material <NUM>, and thus can restrain the resin material <NUM> from separating from the electrically conductive joining material <NUM>.

Moreover, as shown in <FIG>, the core <NUM> may be configured to extend through and beyond the electrically conductive joining material <NUM>, so that the front end of the core <NUM> is bare of the electrically conductive joining material <NUM>. This increases the surface area of the joined portion of the lead member <NUM>, and thus achieves greater heat-dissipating capability with which Joule heat generated in the joined portion can be dissipated efficiently. Dissipation of heat from the lead member <NUM> can minimize cooling performance degradation.

As the first step, p-type and n-type thermoelectric materials made of Bi, Sb, Te, and Se were melted and solidified by Bridgman method to prepare rod-like materials each having a circular sectional profile of <NUM> in diameter. More specifically, the p-type thermoelectric material was formed from a solid solution of Bi<NUM>Te<NUM> (bismuth telluride) and Sb<NUM>Te<NUM> (antimony telluride), and the n-type thermoelectric material was formed from a solid solution of Bi<NUM>Te<NUM> (bismuth telluride) and Bi<NUM>Se<NUM> (bismuth selenide). The surfaces of the p-type thermoelectric material and the n-type thermoelectric material each in rod-like form were roughened by etching using nitric acid.

Next, the rod-like p-type thermoelectric material and the rod-like n-type thermoelectric material were cut into <NUM> in height, or <NUM> in thickness with a wire saw to obtain a p-type thermoelectric element and an n-type thermoelectric element. A nickel layer was formed on each of the cut surfaces of the obtained p-type thermoelectric element and n-type thermoelectric element by electrolytic plating.

Next, a substrate clad on both principal surfaces with copper, which is prepared by bonding a <NUM>-thick copper sheet to both sides of alumina filler-added epoxy resin under pressure, was printed with a solder paste by screen printing.

On the solder paste, <NUM> p-type thermoelectric elements and <NUM> n-type thermoelectric elements were arranged electrically in series with a mounter. The arrangement of the p-type thermoelectric elements and the n-type thermoelectric elements was sandwiched between a pair of support substrates. The construction so obtained was heated in a reflow furnace, with its upper and lower surfaces subjected to pressure, and, the thermoelectric elements were soldered to corresponding wiring conductors.

Next, a silicone-made sealing material was applied to between the pair of support substrates with an air dispenser.

To permit the passage of electric current through the obtained thermoelectric module, two lead members were joined to the construction with a solder-made conductive joining material. At this time, samples in which, by carrying out adjustments of the amount of solder supply and the angle at which the lead member was joined, the area of contact between the conductive joining material and the wiring conductor (a width of a bonding interface between the conductive joining material and the wiring conductor) was adjusted, as shown in <FIG>, were prepared (Sample No. <NUM> and Sample No. <NUM>). Table <NUM> shows a list of bonding interface widths as viewed in a section in the width direction of the lead member.

Moreover, samples in which, by applying thermosetting epoxy resin so as to cover the joined portion of the lead member (an electrically conductive joining material), with an air dispenser, and thereafter curing the epoxy resin under heat in a dryer, the electrically conductive joining material and at least part of the core were covered with the resin material, as shown in <FIG>, were prepared (Sample No. <NUM> to Sample No. <NUM>). At this time, samples in which a void was provided in the boundary of solder and epoxy resin, as shown in <FIG>, were prepared (Sample No. <NUM> and Sample No. <NUM>).

In addition, sample in which a core length of a lead member was changed and the core of the lead member extended beyond the surface of the joined portion (the electrically conductive joining material) to provide a bared core portion, as shown in <FIG>, was prepared (Sample No. <NUM>).

Each sample was manufactured by <NUM> pieces (n = <NUM>), and measurement results described later were an average of values of <NUM> pieces.

For each of the samples thus prepared, a horizontal force was applied to the lead member using a tensile strength tester, and the strength (before the endurance test) when the lead member was separated was measured. Table <NUM> shows the results.

Next, a thermal conductive grease was applied to a surface of the pair of support substrates of the obtained thermoelectric module, the thermoelectric module was set on a heat sink whose temperature was controlled at <NUM>, and <NUM> W of power was supplied to the thermoelectric module to generate a temperature difference. A temperature difference at the maximum voltage was defined as the cooling performance. Thereafter, an endurance test in which the energization direction was reversed every <NUM> seconds was carried out for <NUM> cycles.

Then, for the samples after the endurance test, a horizontal force was applied to the lead member using the tensile strength tester, the strength when the lead member was separated was measured, and a change rate of the lead member tensile strength before and after the endurance test was calculated. Table <NUM> shows the results.

As seen from Table <NUM>, Sample No. <NUM> in which the area of contact between the electrically conductive joining material and the wiring conductor (the width of the bonding interface) is smaller on the side close to the thermoelectric elements than on the side away from the thermoelectric elements, is higher in cooling performance level and smaller in the change rate in lead member tensile strength than Sample No. <NUM> in which the area of contact on the side close to the thermoelectric elements is substantially equal to the area of contact on the side away from the thermoelectric elements.

Sample No. <NUM> in which the joined portion of the lead member is coated with the resin material is smaller in the change rate in lead member tensile strength and is thus more satisfactory than Sample No. <NUM>.

Sample No. <NUM> in which the void is provided in the boundary of solder and epoxy resin is smaller in the change rate in lead member tensile strength and is thus more satisfactory than Sample No. <NUM>.

Claim 1:
A thermoelectric module (<NUM>), comprising:
a pair of support substrates (<NUM>,<NUM>) comprising mutually opposed regions;
wiring conductors (<NUM>,<NUM>) disposed on one principal surface of one support substrate of the pair of support substrates (<NUM>,<NUM>) and one principal surface of another support substrate of the pair of support substrates (<NUM>,<NUM>), respectively, the one principal surface of the one support substrate (<NUM>) and the one principal surface of the other support substrate (<NUM>) being opposed to each other;
a plurality of thermoelectric elements (<NUM>) disposed between the one principal surface of the one support substrate (<NUM>) of the pair of support substrates (<NUM>,<NUM>) and the one principal surface of the other support substrate (<NUM>) of the pair of support substrates (<NUM>,<NUM>);
a lead member (<NUM>) joined to one wiring conductor of the wiring conductors (<NUM>,<NUM>), the one wiring conductor located on either the one support substrate (<NUM>) or the other support substrate (<NUM>) of the pair of support substrates (<NUM>,<NUM>), the lead member (<NUM>) comprising a core (<NUM>), and a covering layer (<NUM>) which covers a rear end-side part of the core (<NUM>), and which does not cover a front end-side part of the core (<NUM>); and
an electrically conductive joining material (<NUM>) which joins the one wiring conductor (<NUM>) and the lead member together (<NUM>),
wherein a bonding interface between the electrically conductive joining material (<NUM>) and the one wiring conductor (<NUM>) is smaller in width on a side of the bonding interface which is close to the thermoelectric elements (<NUM>) than on a side of the bonding interface which is away from the thermoelectric elements (<NUM>), as viewed in a respective section in a direction perpendicular to an axial direction of the lead member (<NUM>), and
wherein the lead member (<NUM>) is inclined relative to a direction parallel to the pair of support substrates (<NUM>,<NUM>), so that a front end of the lead member (<NUM>) is directed away from the one wiring conductor (<NUM>) in a direction from the rear end-side part of the core (<NUM>) to the front end-side part of the core (<NUM>), as viewed in a section of the thermoelectric module perpendicular to the pair of support substrates (<NUM>,<NUM>) and along the axial direction of the lead member (<NUM>).