KR100286214B1 - Thermistor elements with bumps for surface mounting - Google Patents

Abstract

The thermistor element has a pair of electrodes formed opposite to each other on the lower surface of the thermistor element. For example, bumps made of metal materials such as Au, Sn, and alloys thereof are first formed on these electrodes, so that the thermistor element is formed. Can be easily surface mounted on a printed circuit board by bump bonding. The third electrode may be formed on the upper surface of the thermistor element to reduce the resistance between the pair of electrodes. The insulating resin layer is provided on the upper and lower surfaces, and improves moisture resistance and temperature characteristics, and can prevent a short circuit between the electrode pairs.

Description

Thermistor elements with bumps for surface mounting}

The present invention relates to thermistor elements used for temperature detection and temperature compensation of circuits. In particular, the present invention relates to thermistor elements having an external electrode structure suitable for surface mounting.

Since high density mounting of electronic components is required, thermistor elements are required to be surface mounted on a printed circuit board or the like. An example of a surface mountable thermistor element is described in Japanese Patent Laid-Open No. 7-29704, denoted by reference numeral 65 in Fig. 17, and facing each other at predetermined intervals on the lower surface 66a of the thermistor element 66 having a parallelepiped shape. The first electrode 67 and the second electrode 68 formed are provided. If the thermistor element is miniaturized and the spacing between electrodes 67 and 68 is reduced, the risk of short circuits will increase due to the occurrence of solder bridges when soldered for mounting. In order to prevent the occurrence of such a situation, in thermistor element 65, a pair of external electrodes 69 and 70 formed on the first and second electrodes 67 and 68, respectively, may be spaced between the first electrode 67 and the second electrode. It is made larger than the gap between the electrodes 68. In addition, the short-circuit-proof insulating layer 71 made of an inorganic material is provided over the portion between the external electrodes 69 and 70, and the lower surface 66a of the thermistor element 66 is coated.

In addition to the first and second electrodes 67 and 68, the thermistor element 65 may have external electrodes 69 and 70 formed only on the bottom surface 66a of the thermistor element 66 and not on any other surface of the thermistor element 66. do. When the thermistor element 65 is provided on the printed circuit board, the lower surface 66a of the thermistor element 66 is arranged to contact the printed circuit board. Then, solder is used as the reflow mounting method or the flow mounting method. Since the first and second electrodes 67 and 68 and their external electrodes 69 and 70 are formed only on the bottom surface 66a of the thermistor element 66, the thermistor element 65 does not require a large area for mounting. That is, these thermistor elements can be mounted at high density.

The thermistor element 65 of FIG. 17, however, was originally conceived to use a reflow mounting method using solder paste or a flow mounting method using molten solder. It is very difficult to achieve for the following reasons:

(1) If solder lands to be formed (such as printed circuit boards) are not performed with high accuracy by the printing method, high density mounting is impossible, but the accuracy of the solder lands has been limited.

(2) When the solder material is melted, the thermistor element tends to deviate from the solder land of the base board.

(3) It was difficult to control the thickness of the solder layer, and therefore, it was difficult to control the mounting position of the thermistor element in the height direction.

Recently, a new mounting method called bump mounting as an improved mounting method capable of high-density mounting is more popular than the reflow or flow mounting method. In the bump mounting method, a cylindrical or circumferential bump, usually made of bumps containing Au or Sn-Pb, is inserted between a chip part and a base board, and the bump, the board and the chip part are joined together. It is a technique characterized by joining by thermocompression bonding or eutectic alloy formation.

By this method, bumps can be formed on the chip component or on the substrate with high accuracy, and the chip components can be accurately bonded onto the substrate as long as the bumps can be formed accurately. Another effect of this method is that there is no problem of fillets.

The conventional thermistor element 65 described above having base layers for electrodes made of conductive paste is not suitable for bump mounting because it is mounted as described above using a solder material. That is, in order to obtain the base layers, the first and second electrodes 67 and 68 described above are formed by applying a conductive paste made of Ag to the lower surface 66a of the thermistor element 66 and firing it.

Therefore, when the external electrode layers for external connection are formed by plating Ni or Sn-Pb on the electrodes formed by applying the conductive paste and then firing as described above, the base layers are thick and uneven, The surfaces of the external electrodes thereon are not necessarily even.

When the thermistor element is mounted on the substrate by the bump mounting method, the bumps and the electrodes of the thermistor element are surely in contact with each other. Therefore, when the thermistor element has external electrodes having a very uneven surface with large indentations and protrusions, reliable contact cannot be expected by the bump bonding method.

In the case where the conventional thermistor element is mounted by a bump bonding method on a printed circuit board or lead frame as indicated by the reference numeral 65 above, however, the method includes an annoying operation as described below with reference to FIG.

FIG. 18 schematically illustrates a bonding process between a conventional thermistor element 65 and a lead frame 72 by a bump bonding method. In this process, the bump 73 is disposed on the electrode 70 of the thermistor element 65, and heat is applied while the bump 73 is inserted between the electrode 70 and the lead frame 72. That is, the following cumbersome series of operations are performed: (1) the bump 73 and lead frame 72 are manufactured; (2) the electrode 70 and lead frame 72 and bump 73 are properly positioned; (3) the bump 73 is inserted between the electrode 70 and the lead frame 72; (4) Apply heat while keeping bump 73 inserted. If thermistor element 65 is mounted on a printed circuit board, a similar cumbersome series of work will be performed.

As an alternative to the method described above, the bumps are first attached to the lead frame or to the electrodes of the thermistor element and heat is applied to the attached bumps while contacting the lead frame or the electrodes. By this method, a series of necessary tasks will be complicated since the bumps are first transferred to the thermistor element or to the lead frame.

Therefore, it is an object of the present invention to provide a thermistor element suitable for reliable surface mounting.

1A and 1B are side and bottom views, respectively, of a thermistor element according to a first embodiment of the present invention.

2A and 2B are side and bottom views, respectively, of a thermistor element according to a second embodiment of the present invention.

3A and 3B are side and bottom views, respectively, of a thermistor element according to a third embodiment of the present invention.

4A and 4B are side and bottom views, respectively, of another thermistor element according to a variation of the third embodiment of the invention.

5 and 6 are bottom views of thermistor elements with one or more bumps formed on each electrode.

7A and 7B are cross-sectional views of thermistor elements showing preferred and undesirable dimensional relationships between bumps and lead frames.

8A and 8B are perspective views of bumps having other shapes.

9 is a side view of the thermistor element in which the thermistor element of FIG. 1 shows a state in which a lead frame is joined.

FIG. 10 is a side view of the thermistor element of FIG. 1 illustrating a state in which the thermistor element of FIG. 1 is surface mounted on a printed circuit board.

11A, 11B and 11C (referred together as FIG. 11) are side, top, and bottom views of a thermistor element according to another variation of the invention.

12A, 12B and 12C (referred together as FIG. 12) are side, top, and bottom views, respectively, of a thermistor element according to another variation of the present invention.

13A, 13B and 13C (referred together as FIG. 13) are side, top, and bottom views of a thermistor element according to another variant of the invention.

14A, 14B and 14C (referred to together as FIG. 14) each show a side view, a cross sectional view and a bottom view of a thermistor element according to another variant of the invention, respectively.

15A, 15B, and 15C (referred to together as FIG. 15) are cross-sectional, side, and bottom views, respectively, of a side surface of a thermistor element according to another variation of the present invention.

16A, 16B, and 16C (referred to together as FIG. 16) are cross-sectional views, side cross-sectional views, and bottom views, respectively, of a thermistor element according to another variation of the present invention.

17 is a side view of a conventional thermistor element.

18 is a side view of the conventional thermistor of FIG. 17 in which a lead frame is joined by a bump bonding method.

(Explanation of symbols for the main parts of the drawing)

1, 11, 21, 31, 41, 43, 44, 46, 48, 50: thermistor element

2, 12: thermistor body

2a, 12a:

2d: thermistor element face

3, 4: first and second electrodes

3a, 4a, 13a, 14a: contact layer

3b and 4b: external electrode layer

13, 14: first and second electrodes

13b and 14b: electrode layer

13c and 14c: bonding layer

15, 16: bump

17: insulating resin layer

18: second insulating resin layer

42, 42A, 45a, 45b: third electrode

47, 49a, 49b, 51: internal electrode

Thermistor element embodying the present invention and capable of realizing the above and other objects includes: a thermistor element; A pair of first and second electrodes facing each other on the bottom surface of the thermistor element; And bumps formed on the first and second electrodes. In such a thermistor element, the surface on which the first and second electrodes are formed may be surface mounted on a printed circuit board or the like. Since the bumps are formed in the first and second electrodes in advance, the thermistor element can be easily attached to the lead frame or the printed circuit board by a bump bonding method.

In addition to the first and second electrodes, a third electrode may be formed on the surface of the thermistor element opposite to the surface on which the first and second electrodes are formed. Similarly, internal electrodes can be formed inside the thermistor element.

Conductive materials may be used as the bump material, but preferred materials for the bump include Au, Sn, and alloys thereof. Since bumps comprising Au, Sn, and alloys thereof are known, bump junctions of conventional methods can be used for the purposes of the present invention.

According to a preferred embodiment of the present invention, an insulating resin material is provided at least in the lower surface portion of the thermistor element in which the first and second electrodes are not formed, so that moisture resistance can be improved. This insulating resin layer also prevents the formation of solder bridges when reflow or flow mounting is used for mounting the thermistor elements, and also prevents the formation of solder bridges even when the first and second electrodes are small in intervals. It works by preventing short circuits between them. The insulating resin layer may be formed to apply a part of the first and second electrodes, or may be formed to apply other surfaces or surfaces other than the surface of the thermistor element on which the first and second electrodes are formed.

The second insulating resin layer is further provided on the upper surface of the thermistor element, which can further improve the moisture resistance and temperature characteristics of the thermistor element. These insulating resin layers may preferably include polyimide, epoxy-based resin or fluorine-containing resin.

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention in conjunction with the description, and serve to explain the principles of the invention.

1A and 1B illustrate a thermistor element 1 according to a first embodiment of the present invention, the thermistor element 1 having a resistance having a negative temperature coefficient (NTC) composed of a plurality of transition metal oxides. It has the thermistor element 2 containing a sintered compact. The thermistor element 2 has a parallel hexahedron, which includes a first electrode 3 and a second electrode 4 formed on the lower surface 2a thereof. According to the present embodiment, the first electrode 3 extends toward the center of the lower surface 2a from the edge portion of one end face 2b of the thermistor element, and the second electrode 4 is formed from the edge portion of the opposite end surface 2c toward the center of the lower surface 2a. And extend so that the first electrode 3 and the second electrode 4 oppose each other on the lower surface 2a of the thermistor element 2.

Each of the first electrode 3 and the second electrode 4 includes a contact layer 3a or 4a and external electrode layers 3b or 4b formed on a corresponding one of the contact layers 3a and 4a. The contact layers 3a, 4a are, for example, Cr; Ni; Cu; And materials capable of ohmic contact with thermistor element 2, such as alloys thereof including Ni-Cu and Ni-Cr alloys. The contact layers 3a and 4a may be formed by thin film formation such as vapor deposition, sputtering, electroless plating, and electrolytic plating. According to this embodiment, as shown in detail below, the contact layers 3a and 4a are formed by attaching the Ni-Cr alloy to the thermistor element 2 by vacuum deposition. The contact layers 3a and 4a thus formed by the thin film formation method are characterized by less surface protrusion and surface indentation than thick film electrodes formed by applying and firing conductive paste.

The external electrode layers 3b and 4b are provided to increase the reliability of the electrical connection with the outside. According to the examples described above, these include Ag films formed by vacuum deposition, but examples of materials that can be used to form the external electrode layers 3b and 4b include Au; Pd; And alloys containing them, such as, for example, Ag-Pd, Au-Sn, Au-Si, and Au-Ge.

According to the examples described above, each of the first and second electrodes 3, 4 comprises a contact layer 3a or 4a comprising a Ni—Cr alloy, and an external electrode layer 3b or 4b comprising an Ag film, such a material The choice of does not limit the scope of the invention. Although forming them into a plurality of layers using different metal materials is preferable in view of durability over time, each of the first electrode layer 3 and the second electrode layer 4 may be formed as a single layer.

When each of the first and second electrodes 3 and 4 is formed as a single layer structure, for example, Cr, Ni, Ag, Pd, Pt, Ti, Al, Au, Cu and an alloy containing one of them Metallic materials such as may be used. In the case where the first and second electrodes 3, 4 are each formed in a two-layer structure, many mixing of materials is possible within the scope of the present invention. For example, one of the layers may comprise Ni, Cr, Cu or an alloy containing any of these, and the other of the layers contains Cr, Ni, Ag, Pd, Pt, Ti or any of these. It may include an alloy.

The external electrode layers 3b and 4b are provided with bumps 5 and 6 including Au, respectively. As described below, after the external electrode layers 3b and 4b are formed, the bumps 5 and 6 are formed by photolithography. As described above, the bumps 5 and 6 have a cylindrical shape. The preferred thickness of the bumps depends on the size of the contact area, but in order to prevent falling and deformation, the thickness of the bumps 5 and 6 is usually 5 µm or more and less than 100 µm.

Since the bumps 5 and 6 are pre-installed in the thermistor element 1 according to the present invention, the thermistor element 1 can be directly bump mounted on a printed circuit board or a lead frame. Since the first and second electrodes 3 and 4 are located opposite to each other on the lower surface 2a of the thermistor element 2, the thermistor element 1 may be easily surface mounted on the printed circuit board by the bumps 5 and 6. . In addition, since the contact layers 3a and 4a are provided by the thin film formation method, there is little protruding and indentation of their surfaces and therefore the external electrode layers 3b and 4b formed by the vacuum deposition method on them are also smooth. Therefore, the bumps 5 and 6 formed by photolithography are firmly attached to the external electrode layers 3b and 4b, which acts to increase the adhesion strength between the bumps 5 and 6 and the external electrode layers 3b and 4b. do.

Hereinafter, the manufacturing method of the thermistor element 1 mentioned above is demonstrated, for example.

Oxides of Mn, Ni, and Co were mixed and kneaded together with a binder to obtain a slurry, which was formed into a sheet by a doctor blade method. The sheet having the predetermined thickness thus obtained was cut into a size of 65 × 65 mm to obtain a plurality of green sheets. Then, these green sheets were laminated, pressed together in the thickness direction, and then fired at about 1300 ° C. for 1 hour to obtain a thermistor body wafer having a dimension of 50 × 50 × 0.5 mm.

Then, a Ni-Cr alloy film having a thickness of 0.2 µm was formed on the thermistor body wafer by applying a vacuum evaporation method, and a 0.2 µm Au film was similarly formed thereafter to prepare a laminated metal film. On this metal film, a photoresist film was formed by spin coating method so as to have a thickness of 20 mu m. After the photo-mask was placed over the photoresist, it was exposed to light, and then the photoresist was developed using a dissolving reagent.

Then, a portion of the metal film not applied by the photoresist was etched by acid. In other words, the Au layer of the metal film was etched with acid and then the Ni-Cr layer was etched with acid, leaving only a part of the laminated metal film applied by the photoresist. The photoresist was then peeled off to obtain a laminated metal film patterned on the thermistor body wafer.

Then, a photoresist was applied to the surface of the thermistor element wafer to a thickness of 20 mu m by spin coating, and a photo mask was disposed thereon so as to expose a portion of the laminated metal film on which bumps are to be formed, and then it was exposed to light. The photoresist was then developed, whereby bumps were formed by electroplating on the portion of the laminated metal film that was not applied by the photoresist. Finally, the thermistor elementary wafer was cut and diced into respective pieces having a planar shape of 1.6 mm x 0.8 mm to obtain a plurality of thermistor elements 1 shown in FIG.

The thermistor body wafer is, for example, by lapping process, thereby further increasing the smoothness of the surface of the thermistor element. For example, the surface roughness is less than Ra 0.46 μm. In this method, the protrusion and indentation of the contact layer and the bumps formed thereon are further reduced, so that the strength of surface bonding to a printed circuit board or the like can be further improved by the bump bonding method.

2A and 2B show another thermistor element 11 according to a second embodiment of the present invention, the thermistor element 11 having a thermistor element 12 structurally similar to thermistor element 2 of the first embodiment described above. The first electrode 13 and the second electrode 14 are formed on the lower surface 12a of the thermistor element 12, each of the contact layers 13a or 14a; Electrode layer 13b or 14b; And bonding layer 13c or 14c. The contact layers 13a, 14a, and the electrode layers 13b, 14b are formed in the same manner as the contact layers 3a, 4a and the external electrode layers 3b, 4b of the first embodiment described above, respectively, and extend to the cross sections 12b, 12c. It is arranged not to be. In short, the only difference between the first and second embodiments is the presence of bonding layers 13c and 14c.

Bonding layers 13c and 14c according to this embodiment are formed by vacuum deposition of Ti, but they are Cr; Ni; Ag; Pt; Pd; Al; Or an alloy of Ti; Or by using an alloy of any of these metals. Since the purpose of these bonding layers 13c, 14c is to increase the bonding strength with the bumps 15, 16, the material for the bonding layers 13c, 14c can be appropriately selected depending on the material of the bumps 15, 16. . According to the examples, the bumps 15, 16 comprise Au as in the first embodiment, and the bumps 15, 16 and the bonding layers 13c, 14c are all likewise formed by photolithography. .

Since the bumps 15 and 16 are formed in advance on the surface, the thermistor element 11 according to the embodiment of the present invention can also be easily surface mounted on the printed circuit board or the lead frame by the bump bonding method. Since the bumps 15 and 16 contain Au and the bonding layers 13c and 14c are additionally provided, the bumps 15 and 16 and the bonding layers 13c and 14c together form an alloy at the time of bump bonding, Bonding strength between them is effectively improved.

3a and 3b show yet another thermistor element 21 according to a third embodiment of the invention, first that the electrode layers 13b, 14b comprise Al instead of Ag, and secondly, the insulating resin layer 17 comprises thermistor element 12. Is identical to the thermistor element 11 according to the second embodiment described above, except that it is installed at the bottom surface 12a. Accordingly, components of FIGS. 3A and 3B that are the same as those of FIGS. 2A and 2B are denoted by the same reference numerals and will not be described repeatedly below.

Electrode layers 13b and 14b containing Al of thermistor element 21 are also formed by a method such as vacuum deposition for thin film formation. Thus, these Al electrode layers 13b, 14b have a smooth surface, and if the bonding layers 13c, 14c and the bumps 15, 16 are also similarly formed by thin film formation, bumps 15, 16 and The bonding strength between the first and second electrodes 13 and 14 may be increased. According to this example, the insulating resin layer 17 includes polyimide, but it may be formed of other kinds of insulating resin materials such as epoxy resins and fluorine-containing resins.

The thermistor element 21 according to the third embodiment of the present invention is advantageous in that the insulating resin layer 17 including polyimide is formed on the lower surface 12a of the thermistor element 12, so that the moisture resistance and the temperature characteristic stability are improved. Furthermore, since the insulating resin layer 17 is formed so as to apply at least the lower surface 12a of the thermistor element 12 in addition to the portion where the first and second electrodes 13 and 14 are formed, an unwanted short circuit between the first electrode 13 and the second electrode 14. (short circuiting) can be effectively prevented. As shown in FIGS. 3A and 3B, the insulating resin layer 17 may be formed to partially apply a portion of the first electrode 13 and the second electrode 14.

4A and 4B show another thermistor element 31, which is a modification of the thermistor element 21 described above, and is substantially the same in structure except that the second insulating resin layer 18 is provided on the top surface 12d of the thermistor element 12. FIG. According to this example, the second insulating resin layer 18 similar to the (first) insulating resin layer 17 comprises a polyimide, but this may be composed of another insulating resin material having moisture resistance and heat resistance such as epoxy resin and fluorine-containing resin. Can be. By the insulating resin layers 17 and 18 in which the upper and lower surfaces 12a and 12d of the thermistor element 12 are applied in this way, the moisture resistance of the thermistor element 31 is improved and its temperature characteristic is further stabilized.

In all the examples described above, each of the electrodes 13, 14 described above had only one bumps 15 or 16 formed, but this does not limit the scope of the present invention. As shown in FIG. 5, for example, a plurality of bumps 15, 16 can be formed in the first and second electrodes 13, 14, each of which a plurality of bumps 15 or 16 being the first and the first. The two electrodes 13 and 14 are separated in the vertical direction and in the separated direction. The thermistor element having such distributed bumps, for example, when bump-bonded to a lead frame, even when the position of the lead frame deviates in the width direction from the center (as indicated by dashed line 32), It is advantageous because it can be joined by one of the bumps 16. More specifically, if the electrode 14 has only one bump indicated by the broken line A, if the lead frame 32 deviates too much in the width direction thereof from the center of the thermistor element 31, the lead frame 32 may be bump mounted. Will fail. If the two bumps 15 and 16 are each formed on the first electrode 13 and the second electrode 14, respectively, as shown in FIG. 5, the lead frame 32 can be reliably bump-bonded to the thermistor element 31.

As shown in FIG. 6, the plurality of bumps 15 and 16 of the first and second electrodes 13 and 14 are separated in the longitudinal direction in the same manner as the first and second electrodes 13 and 14 are separated from each other. Can be reliably bump-bonded even when the lead frame is arranged in the longitudinal direction. Similarly, a plurality of bumps may be formed in both the longitudinal direction and the width direction at each of the distributed electrodes 13 and 14.

Since the size of the bumps 15 and 16 to be formed depends on the size of the electrode land on the lead frame or printed circuit board to be bonded, the present invention does not limit this. When bonded to the lead frame, as shown in Fig. 5, when the width of the lead frame is b and the dimension of the transverse direction (i.e., the width direction) of the bumps 15 and 16 is a, preferably, shown in Fig. 7A. As described above, since bump 15 is easily deformed by heat so that bump between lead frame 32 and electrode 13 can be reliably achieved, a is preferably b or less. On the other hand, as shown in FIG. 7B, when a is larger than b, bump 15 'is too long to be easily deformed by heat, and thus bump bonding between lead frame 32 and electrode 13 may be difficult.

The present invention is not particularly limited according to the shape of the bumps integrally formed in the thermistor element. FIG. 8A shows a bump 33 shaped like a mushroom with a stem-cylindrical top and a hemispherical top. 8B shows a spherical bump 34 with portions removed by the plane. The bumps according to the invention can be shaped differently, such as in the shape of columns and prisms.

Hereinafter, the method of surface-mounting the thermistor element of this invention is demonstrated below with reference to FIG. 9 and FIG. FIG. 9 is the thermistor element 1 of FIG. 1 disposed upside down, and the lead frame 32 is bonded to the first and second electrodes 13 and 14 by contacting and applying heat to the lead frame 32 to the bumps 15 and 16. . FIG. 10 shows thermistor element 1 of FIG. 1, wherein bumps 15, 16 are in contact with electrode lands 37a, 37b of a printed circuit board 37 and heated, so that thermistor element 1 is placed on the bottom surface 2a of thermistor element 2. Surface mounted. 9 and 10 clearly show that the thermistor elements according to the present invention can be joined more easily than conventional thermistor elements, since the bumps are pre-formed in the thermistor element and the cumbersome positioning process can be eliminated. .

According to the present invention, a third electrode may be formed on the surface of a thermistor element facing the surface on which the first electrode and the second electrode facing each other are formed. Such thermistor elements are shown in Figs.

11A, 11B, and 11C (referred to together as FIG. 11) show a thermistor element 41 similar to thermistor element 1 of FIGS. 1A and 1B, but the entirety of the opposing top surface of the lower surface 2a of thermistor element 2 is applied. It differs from that in that the 3rd electrode 42 is formed. The third electrode 42 acts to reduce the resistance between the first electrode 3 and the second electrode 4 and may comprise a suitable metal material, such as a Ni—Cr alloy.

12A, 12B, and 12C (referred to together as FIG. 12) show another thermistor element 43 similar to thermistor element 41 shown in FIG. 11, but with the third electrode 42a covering the top surface of thermistor element 2 as a whole. Rather, it exposes its periphery or does not reach the outer edges of the top surface. The third electrode 42a thus configured also serves to reduce the resistance of the thermistor element 43. The advantage of forming the third electrode 42A only at the center portion of the upper surface of thermistor element 2 is that the variation of the resistance due to nonuniformity can be reduced when each thermistor element is cut from the mother element and thus has a desired resistance value. Thermistor elements can be obtained more reliably.

13A, 13B, and 13C (referred to together as FIG. 13) show another thermistor element 44 similar to thermistor element 43 shown in FIG. 12, but with the third electrode extending to the edges of thermistor element 2. In the other state, it is different in that it has two separate parts 45a, 45b formed opposite each other on the upper surface 2d.

14 to 16 illustrate thermistor elements 46, 48, and 50 according to another modification, wherein the thermistor elements have at least one internal electrode inside the thermistor element. Thermistor elements 46, 48, and 50 are each constructed similarly to thermistor element 1 of FIG. 1, except that one or more internal electrodes are included. Therefore, the same elements as in Fig. 1 to Fig. 14 to 16 are denoted by the same reference numerals and will not be described repeatedly.

The thermistor element 46 shown in Figs. 14A, 14B and 14C (referred to as Fig. 14) has an internal electrode 47 formed in the thermistor element 2 at a predetermined height (i.e., at a predetermined position in the thickness direction). And extend to outer peripheral surfaces of thermistor element 2. The internal electrode 47 serves to reduce the resistance between the first electrode 3 and the second electrode 4, and also to reduce the variation of the resistance of the products.

The thermistor element 48 shown in Figs. 15A and 15B and 15C (referred to together as Fig. 15) includes a plurality of opposing pairs of internal electrodes 49a and 49b formed at predetermined heights inside the thermistor element 2. It is characterized in that they are not extended to the outer peripheral surface of the thermistor element. Internal electrodes 49a and 49b also serve to reduce the resistance between the first and second electrodes 3 and 4. Since the internal electrodes 49a and 49b do not extend to the outer circumferential surfaces of the thermistor element 2, the resistance value will not change due to the variation caused when the thermistor element 48 is cut from the parent element.

The thermistor element 50 shown in Figs. 16A, 16B and 16C (referred to together as Fig. 16) has a plurality of internal electrodes 51 formed at predetermined heights inside the thermistor element 2, and the plurality of internal electrodes. Fields 51 were successively stacked so as to be alternately drawn out in cross sections 2b, 2c of thermistor element 2. These internal electrodes 51 also serve to reduce the resistance between the first electrode 3 and the second electrode 4.

Although not described separately, the internal electrodes 47, 49a, 49b, and 51 shown in FIGS. 14 to 16 are combined with any of the third electrodes 42, 42a, 45a, and 45b shown in FIGS. 11 to 13. These thermistor elements may further include the first and second insulating resin layers described above. In summary, the conclusion is interpreted broadly.

Thermistor element embodying the present invention and capable of realizing the above and other objects includes: a thermistor element; A pair of first and second electrodes facing each other on the bottom surface of the thermistor element; And bumps formed on the first and second electrodes. In such a thermistor element, the surface on which the first and second electrodes are formed may be surface mounted on a printed circuit board or the like. Since the bumps are formed in the first and second electrodes in advance, the thermistor element can be easily attached to the lead frame or the printed circuit board by a bump bonding method.

In addition to the first and second electrodes, a third electrode may be formed on the surface of the thermistor element opposite to the surface on which the first and second electrodes are formed. Similarly, internal electrodes can be formed inside the thermistor element.

Conductive materials may be used as the bump material, but preferred materials for the bump include Au, Sn, and alloys thereof. Since bumps comprising Au, Sn, and alloys thereof are known, bump junctions of conventional methods can be used for the purposes of the present invention.

According to a preferred embodiment of the present invention, an insulating resin material is provided at least in the lower surface portion of the thermistor element in which the first and second electrodes are not formed, so that moisture resistance can be improved. This insulating resin layer also prevents the formation of solder bridges when reflow or flow mounting is used for mounting the thermistor elements, and also prevents the formation of solder bridges even when the first and second electrodes are small in intervals. It works by preventing short circuits between them. The insulating resin layer may be formed to apply a part of the first and second electrodes, or may be formed to apply other surfaces or surfaces other than the surface of the thermistor element on which the first and second electrodes are formed.

The second insulating resin layer is further provided on the upper surface of the thermistor element, which can further improve the moisture resistance and temperature characteristics of the thermistor element. These insulating resin layers may preferably include polyimide, epoxy-based resin or fluorine-containing resin.

Claims (12)

Thermistor body having a lower surface; First and second electrodes formed to face each other on the lower surface of the thermistor element; And Bumps composed of a metal material selected from the group consisting of Au, Sn, and alloys containing Au or Sn, and firmly attached to a portion of the first electrode and the second electrode; Thermistor element having a bump for surface mounting comprising a. The surface mount of claim 1, wherein the thermistor element has an upper surface opposite to the lower surface, and the thermistor element further comprises a third electrode on the upper surface of the thermistor element. Thermistor element with bumps. The thermistor element as claimed in claim 1, further comprising internal electrodes formed inside the thermistor element. The thermistor element as claimed in claim 2, further comprising internal electrodes formed inside the thermistor element. The thermistor element with a bump for surface mounting according to claim 1, further comprising an insulating resin layer for applying at least the above lower surface portion on which neither the first electrode nor the second electrode is formed. 6. The thermistor element according to claim 5, wherein another insulating resin layer is further formed on the upper surface of the thermistor element. 6. The surface according to claim 5, wherein the insulating resin layer is made of a resin material selected from the group consisting of polyimide, epoxy resins and fluorine-containing resins. Thermistor element with mounting bumps. 7. The resin material according to claim 6, wherein the insulating resin layer and the other insulating resin layer are selected from the group consisting of polyimide, epoxy resins and fluorine-containing resins. Thermistor element provided with the bump for surface chambers characterized by the above-mentioned. The electrode layer of claim 1, wherein each of the first electrode and the second electrode is made of a metal selected from the group consisting of Cr, Ni, Ag, Pd, Pt, Ti, Al, Au, Cu, and alloys thereof. And the bumps are made of a metal selected from the group consisting of Au, Sn, and alloys thereof. The electrode layer of claim 2, wherein each of the first electrode and the second electrode is made of a metal selected from the group consisting of Cr, Ni, Ag, Pd, Pt, Ti, Al, Au, Cu, and alloys thereof. And the bumps are made of a metal selected from the group consisting of Au, Sn, and alloys thereof. The electrode layer of claim 3, wherein each of the first electrode and the second electrode is made of a metal selected from the group consisting of Cr, Ni, Ag, Pd, Pt, Ti, Al, Au, Cu, and alloys thereof. And the bumps are made of a metal selected from the group consisting of Au, Sn, and alloys thereof. The electrode layer of claim 4, wherein each of the first electrode and the second electrode is made of a metal selected from the group consisting of Cr, Ni, Ag, Pd, Pt, Ti, Al, Au, Cu, and alloys thereof. And the bumps are made of a metal selected from the group consisting of Au, Sn, and alloys thereof.