JP3148026B2 - Thermistor and manufacturing method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermistor used as a temperature sensor in which a lead wire is bonded to a terminal electrode, or used as a thermistor for temperature compensation of an electronic device by being surface-mounted on a printed circuit board and a method of manufacturing the same. It is.

[0002]

2. Description of the Related Art Conventionally, in this type of thermistor, electrodes mainly composed of Ag-Pd are baked at both ends of a thermistor body. The reason for containing Pd in addition to Ag in the electrode component is to prevent Ag from eluting and disappearing in the solder when soldering the thermistor to the substrate, and to obtain solder heat resistance of the electrode. However, when the content of Pd is increased, the solder adhesion of the electrode is reduced, and the fixing force of the thermistor to the substrate is weakened. Therefore, the content of Pd has a certain limit. For this reason, when the electrodes are soldered at a high temperature for a long time, the conventional thermistor still has insufficient solder heat resistance. In order to improve solder heat resistance and solder adhesion, it is conceivable to provide a plating layer on the surface of the base electrode, which is a baked electrode, as in the case of chip type capacitors. Therefore, if plating is performed while exposing the thermistor body, plating will adhere to the surface of the body and the resistance value of the thermistor will differ from the expected value, and the thermistor body will be eroded by the plating solution and the thermistor body will be eroded. Problems such as a decrease in the reliability of the device.

In order to improve this point, the present applicant filed a patent application for a thermistor in which the surface of the thermistor body other than the portion where the baked electrode layer contacts is covered with a glass layer and a plating layer is formed on the surface of the baked electrode layer. (Japanese Unexamined Patent Publication No. 3-25060)
3). This thermistor is manufactured by the following method.
First, an insulating glass layer is formed by printing and firing glass paste on both sides of a ceramic sintered sheet for a thermistor body. Next, after cutting the sintered sheet having both surfaces covered with the glass layer into a strip shape, a glass paste is printed and fired on the cut surfaces on both sides in the same manner as described above to form a glass layer. Next, the strip is finely cut in a direction perpendicular to the cut surface to produce a chip. A conductive paste is applied to both ends of the chip so as to cover the cut surface of the chip, and the paste is baked to form a baked electrode layer. Further, a plating layer is formed on the surface of the baked electrode layer as a base electrode layer to obtain a thermistor having a terminal electrode composed of the baked electrode layer and the plated layer.

Further, there is disclosed a thermistor element in which a solder layer is formed on an electrode having a two-layer structure so that Ag electrodes provided on both side surfaces facing each other do not elute (Ag is eroded) when soldering. (JP-A-3-136204).
This thermistor element is manufactured by the following method. First, the cylindrical thermistor is cut into a wafer using a slicing saw, and then 60-80% Ag, 3.5-3.5%.
A paste containing 7.0% glass frit component is screen-printed and baked on both sides of the wafer to form an electrode lower layer. Next, 75-
An electrode upper layer is formed by screen-printing and baking a paste containing 85% Ag and 0 to 1% glass frit component. Further, the thermistor wafer having the electrode of the two-layer structure is immersed in a solder solution in a solder bath to form a solder layer on the electrode upper layer, and then cut into chips by a dicing saw to obtain a thermistor element. This thermistor element improves the solder adhesion by forming a solder layer, prevents the electrode from peeling when cut with a dicing saw by adding a large amount of a glass frit component to the electrode lower layer, and forms an Ag upper layer on the electrode. By including a large amount of components, the electrode remains even if Ag is eroded.

[0005]

However, Japanese Patent Application Laid-Open No.
In the method of manufacturing a thermistor disclosed in JP-A-250603, it is necessary to coat the glass layer in two parts, and after forming a chip, a conductive paste is applied to both ends of the chip, or a plating layer is formed. Or must be formed.
For this reason, great care must be taken in handling the chips. For these reasons, there has been a problem that the manufacturing process is complicated and the manufacturing cost is necessarily high.
The method of manufacturing a thermistor element disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 3-136204 has an advantage that no special processing is required after forming a chip. However, since the solder layer is formed by dipping in a solder liquid, the method is uniform. There is a disadvantage that the layer is difficult to be formed, and since the Ag electrode needs to be baked twice, the energy amount for the baking is large and the Ag electrode is
Since no countermeasures are taken to prevent erosion, the amount of Ag used per chip increases, which raises the problem of increasing costs.

SUMMARY OF THE INVENTION It is an object of the present invention to provide excellent heat resistance and solder adhesion, no change in resistance due to plating of electrodes, and a more reliable electrical connection between the thermistor body and the substrate mounting body.
The object is to provide a highly connected thermistor with high reliability. Another object of the invention is to solder to a circuit board.
Board mounting body to relieve thermal stress when
Thermal durability and soldering to the board
It is to provide an easy thermistor. Another object of the present invention is to provide a method for manufacturing a thermistor that uniformly forms a layer having solder heat resistance and solder adhesion on the surface of a base electrode layer. Still another object of the present invention is to provide a method for manufacturing a thermistor which can manufacture the excellent thermistor relatively easily and at low cost.

[0007]

[Means for solving the problem] FIGS. 1 , 7 to 11,
As shown in FIGS. 14 and 15, the outgoing <br/> bright according to the present gun claim 1, a pair of terminal electrodes 12, 12 on both side surfaces facing each other of the chip-thermistor element 11 consisting of hexahedron It is an improvement of the formed thermistor. Its characteristic configuration is laminated to the terminal electrode 12 is formed of a plating layer 17. formed on the surface of the underlying electrode layer 16 this underlying electrode layer 16 containing a noble metal
Electrodes, and four side surfaces of the laminated electrode are a pair of terminals.
The other four of the thermistor body where the electrodes 12, 12 are not formed
Is the same plane as the surface and is a lead frame or block
A pair of conductive board mounting bodies 31, 32 or 3
4 is a pair of terminal electrodes made of high-temperature cream solder
12 are joined to each main surface . In addition, FIG.
As shown in FIG. 13 and FIG.
One configuration is such that the terminal electrode 12 is a base electrode layer 1 containing a noble metal.
6 and the plating layer 1 formed on the surface of the base electrode layer 16
7 and four of the laminated electrodes
Thermistors whose side surfaces do not have a pair of terminal electrodes 12
It is the same surface as the other four surfaces of the star element body, and
Of the conductive board mounting body 33 made of a metal frame.
The surface is made of a pair of terminal electrodes 12, 1 made of high-temperature cream solder.
2 on both sides of the thermistor body 11 including
It is in. The Ni plating layer 17a in which the plating layer 17 is formed on the surface of the base electrode layer 16 and the Ni plating layer 1
Sn or Sn / Pb plating layer 1 formed on the surface of 7a
7b, and the board mounting bodies 31, 32, 3
3, 34 are conductive metal body 30a and the surface
With the formed Sn or Sn / Pb plating layer 30b
Is preferred.

Further, a method for manufacturing a thermistor according to the present invention comprises:
The base electrode layers 16, 16 are formed on both surfaces of the ceramic sintered sheet 21 for thermistor body shown in FIG.
And FIG. 4 ), the Ni plating layer 17a and the Sn or Sn / Pb plating layer 1 are formed on the respective surfaces of the base electrode layers 16, 16.
7b are formed in this order (FIGS. 1 and 5 ), and the sintered sheet 21 on which both surfaces of the electrode composed of the base electrode layer 16 and the plating layer 17 are formed is cut into chips by a dicing saw to form a chip thermistor body. After a pair of terminal electrodes 12 and 12 are provided on both opposite side surfaces of the pair 11 (FIG. 6), a pair of terminal electrodes 12 and 12 are provided.
A lead frame or a block is provided on each main surface of the
, A pair of conductive board mounting bodies 31, 32,
34 are joined by high-temperature cream solder.
7 to 11, 11, 14 and 15) .

Hereinafter, the present invention will be described in detail. (a) Preparation of Ceramic Sintered Sheet As shown in FIG. 2 , a ceramic sintered sheet 21 for thermistor body is prepared. This sintered sheet 21 is made by the following method. First, Mn, Fe, Co, Ni, Cu, A
One or more metal oxide powders such as 1 are mixed.
When mixing two or more, each metal oxide is weighed so as to have a predetermined metal atomic ratio. The mixture is calcined and pulverized, an organic binder is added and mixed to form a rectangular parallelepiped, and then fired to produce a ceramic sintered block (not shown). Next, this block is cut into a wafer using a band saw, and a sintered sheet 21 shown in FIG. 2 is obtained. After calcination and pulverization of the mixture of metal oxides, an organic binder and a solvent were added and kneaded to prepare a slurry, and the slurry was formed into a film by a doctor blade method and dried to form a green sheet. May be fired to obtain a sintered sheet 21.

(B) Formation of Underlying Electrode Layer Next, as shown in FIG. 3 , a conductive paste containing a noble metal powder and an inorganic binder is applied to both surfaces of the sintered sheet 21. Figure 4 is an F part enlarged view of FIG. This coating is preferably performed by a printing method for uniformly printing the conductive paste. Examples of noble metal powders include Ag, Au, Pd, and Pt.
And a powder obtained by mixing these.
By this baking, the base electrode layer 16 is formed on both surfaces of the sintered sheet 21. In addition to applying a conductive paste by a printing method and baking the conductive paste to form a base electrode layer of a baked electrode layer, a base electrode layer may be formed on both surfaces of the sintered sheet 21 by a thermal spraying method.

(C) Formation of Plating Layer As shown in FIGS. 1 and 5 , a plating layer 17 is provided on each surface of the base electrode layers 16, 16, and an electrode is formed by the base electrode layer 16 and the plating layer 17. . As the plating layer 17, a Ni plating layer 17a and a Sn or Sn / Pb plating layer 17b are formed in this order. These plating layers are formed by electrolytic plating. Known plating baths are used for Ni, Sn and Sn / Pb. The reason why the plating layer has a double structure is to improve the solder heat resistance by the Ni plating layer 17a and prevent the electrode of the base electrode layer from being eroded by solder, and the terminal electrode 12 is formed by the Sn or Sn / Pb plating layer 17b. This is for the purpose of improving the solder adhesion.

(D) Formation of a pair of terminal electrodes As shown in FIGS. 5 and 6 , a base electrode layer 16 and a plating layer 17 are laminated at a position indicated by an arrow M using a dicing saw such as a cutting machine with a diamond blade. The sintered sheet 21 thus cut is cut along a broken line to form a strip-shaped thermistor body. Next, this thermistor body was cut along the broken line at the point of arrow N, and a large number of chip-like thermistor bodies 1 were cut.
A pair of terminal electrodes 12, 12 are formed on both opposite side surfaces of the pair.
To achieve. If the thermistor 10 is rotated 90 degrees so that the upper and lower terminal electrodes 12, 12 shown in FIG.
Chip of FIG. 1 thermistor ing.

[0013] (e) bonding FIGS. 7 11 of the substrate mounting member, as shown in FIGS. 14 and 15, each main surface of the pair of terminal electrodes 12, 12 of the thermistor 10, Li
The main surfaces of a pair of conductive substrate mounting members 31 , 32 and 34 each formed of a card frame or a block are made of a high-temperature cream.
It is joined by the reason. The substrate mounting body is a metal element 30a.
Sn or Sn / Pb formed on the surface of the element body 30a
It is preferable to include the plating layer 30b. Here, the metal element 30a is not particularly limited as long as it is a material that can be plated with Sn or Sn / Pb. Also shown in FIG. 12 and FIG.
Made of square tubular lead frame made of conductive
The inner surfaces of the board mounting body 33 are paired with high-temperature cream solder.
Sides of the thermistor body 11 including the terminal electrodes 12
Joined to the part. With this configuration, Sir
The mist body and the board mount are more securely connected electrically.
In addition to obtaining a highly reliable thermistor, when the thermistor receives a thermal stress, the board mounting members 31 to
34 alleviates this and increases the durability of the thermistor. In addition, soldering to the substrate becomes easy. 7 to 9 show an example in which a lead frame having an L-shaped cross section is used as the board attachment body 31. FIG. The main surface extending in the vertical direction of the substrate mounting body 31 is joined to the main surface of the terminal electrode 12 by high-temperature cream solder. FIG.
0 and FIG. 11 show an example in which a lead frame having a U-shaped cross section is used as the substrate mounting body 32. The bending interval of the board mounting body 32 is determined according to the thickness of the thermistor body 11 . Also in this example, the main surface of the board mounting body 32 extending in the vertical direction is the terminal electrode 1.
2 is joined to the main surface by high-temperature cream solder. FIG.
And FIG. 13 shows a case where the rectangular cylindrical lead frame is
Here is an example of setting the number to 3. The substrate mounting body 33 is a thermistor body 1
The internal dimensions are determined so that they just fit into one . The inner surface of the cylinder includes a pair of terminal electrodes 12 with high-temperature cream solder.
On both sides of the thermistor body 11 . FIG. 14 and
FIG. 15 shows an example in which a rectangular parallelepiped block is used as the board mounting body 34. The main surface of the hand of the board mounting member 34 is joined to the main surface of the terminal electrode 12 of the thermistor element 11 by a high temperature solder.

[0014]

When the thermistor is soldered, the terminal electrode 12
The Ni plating layer 17a improves the solder heat resistance, prevents the underlying electrode layer 16 from being eroded by solder, and
The solder adhesion of the terminal electrode 12 is improved by the n or Sn / Pb plating layer 17b. In addition, the other four surfaces of the thermistor body where the terminal electrodes are not formed are not exposed before cutting the sintered sheet. Therefore, these four surfaces are not eroded by the plating solution due to the plating treatment, and the resistance value of the thermistor is expected. Does not change with respect to the value of. Furthermore, a lead is connected to the main surface of the terminal electrode 12.
Board mounting bodies 31 , 32 composed of frames or blocks ,
Runode be joined 34 main surface of the high-temperature solder paste,
Alternatively, a substrate mounting body 3 formed of a square cylindrical lead frame
3 is high-temperature cream solder on both sides of the thermistor body 11
So that the thermistor body and the substrate mounting body
A more reliable thermistor that is more securely connected electrically
Together is obtained, the thermal resistance of the thermistor Ri higher <br/> Well, and soldered to the substrate is facilitated.

[0015]

As described above, the conventional Japanese Patent Laid-Open Publication No.
In the method of manufacturing a thermistor disclosed in Japanese Patent No. 50603, the number of steps is large and complicated.
In the method of manufacturing a thermistor element disclosed in Japanese Patent Application Laid-Open No. 6204, the amount of energy for baking is large, and the amount of use of a noble metal per chip is increased, thereby increasing the cost. An ultra-small thermistor can be manufactured relatively easily in a small number of steps without consuming a large amount of energy and without increasing the amount of noble metal used. For this reason, the manufacturing method of the present invention is suitable for mass production and the manufacturing cost is reduced. In particular, by precisely cutting the thermistor body after forming the base electrode layer and the plating layer, the dimensions of the element, the electrode area, etc. can be strictly controlled,
A thermistor that does not require any special processing after forming a chip and has high resistance value accuracy can be obtained. Further , by forming a plating layer on the surface of the base electrode layer, the solder heat resistance and the solder adhesion are excellent, and the electrode is not eroded by the solder . In addition, connect the lead frame or
The Rukoto provided electrically conductive certain substrate mounting member made of locking
The electrical connection between the thermistor body and the substrate
If a thermistor that is actually connected and highly reliable can be obtained
Moni, Ri thermal resistance of the thermistor is more Takama, and the substrate
It becomes easy to solder to.

[0016]

EXAMPLES Next, the present invention will be described based on examples to show specific embodiments of the present invention. The embodiments described below do not limit the technical scope of the present invention. <Example> The thermistor shown in FIG. 1 was produced by the following method. First, commercially available manganese carbonate, nickel carbonate, and cobalt carbonate were used as starting materials, and these were weighed at a metal atomic ratio of 3: 1: 2 in terms of MnO ₂ : NiO: CoO.
The weighed product was uniformly mixed by a ball mill for 16 hours and then dehydrated and dried. Next, the mixture was calcined at 900 ° C. for 2 hours, and the calcined product was again pulverized by a ball mill and dehydrated and dried. After adding an organic binder to the pulverized material and mixing uniformly, the mixture was compression-molded into a rectangular parallelepiped. This compression molded product was fired at 1200 ° C. for 4 hours under atmospheric pressure to produce a ceramic sintered block (not shown) having a length of about 35 mm, a width of about 50 mm, and a thickness of about 10 mm. Next, this block was cut into a wafer by a band saw to obtain a sintered sheet 21 having a length of about 35 mm, a width of about 50 mm, and a thickness of about 0.5 mm shown in FIG .

Next, as shown in FIG. 3 and FIG. 4 , a conductive paste containing a noble metal powder and an inorganic binder was applied to both surfaces of the sintered sheet 21 by a printing method. The conductive paste is a commercially available Ag paste (JPN-117 manufactured by DuPont).
6) wherein Ag powder, SiO ₂ , TiO ₂ , B
_{It is} composed of glass fine particles composed of ₂ O ₃ , Na ₂ O and K ₂ O, and an organic vehicle. After the thermistor body coated with the conductive paste is dried under atmospheric pressure, the temperature is increased to 820 ° C. at a rate of 30 ° C./min, and held there for 10 minutes.
The temperature was lowered to room temperature at a rate of / min to obtain the underlying electrode layers 16 and 16 of the baked electrode layer made of Ag.

As shown in FIG . 5 , a Ni plating layer 17a having a thickness of 1 to 2 μm is formed on each surface of the base electrode layers 16 and 16 by electrolytic plating, and then a Ni plating layer 17 having a thickness of 3 μm is formed thereon.
A Sn plating layer 17b of about 6 μm was formed (FIG. 1). Subsequently, the sintered sheet 21 is cut at the position indicated by the arrow M by using the above-described cutting machine.
Is cut into strips using the same cutting machine, and cut into chips in the direction perpendicular to the cut surface of the strip-shaped thermistor body at the location of arrow N, as shown in FIG. 0.5m
m, a length L = about 1.0 mm, and a thickness T = about 0.5 mm were obtained .

Comparative Example A conductive electrode containing 80% of Ag and 20% of Pd was baked at 850 ° C. without providing a Ni plating layer and a Sn plating layer to form a terminal electrode only with a baked electrode layer made of Ag-Pd. . Otherwise, a thermistor was manufactured in the same manner as in the above-described example.

<Comparative Test and Results> Solder Adhesiveness The thermistor of the example and the thermistor of the comparative example were prepared in a quantity of 20 each, and were placed in an Ag-containing eutectic solder (H60-A) bath melted at 230 ° C. Sandwich the sample with tweezers
After immersion for 2 seconds, the solder adhesion area of the terminal electrode was examined with an optical microscope. Table 1 shows the results. Solder Heat Resistance Twenty pieces each of the thermistor of the example and the thermistor of the comparative example were prepared.
After immersion for 0 second, the disappearance of the terminal electrode was examined with an optical microscope. Table 1 shows the results.

[0021]

[Table 1]

[Brief description of the drawings]

FIG. 1 is an external perspective view of a thermistor of the present invention.

FIG. 2 is an external perspective view of a ceramic sintered sheet as a thermistor body of the thermistor of the present invention.

FIG. 3 is a perspective view in which a base electrode layer is formed on both sides of the sintered sheet.

FIG. 4 is an enlarged perspective view of a portion F in FIG. 3 ;

FIG. 5 is a perspective view in which a plating layer is formed on each surface of a base electrode layer on both surfaces of the sintered sheet of FIG. 4 ;

FIG. 6 is a perspective view of the sintered sheet of FIG. 5 cut into chips.

FIG. 7 is a perspective view of a substrate mounting body of the thermistor of the present invention.

FIG. 8 is a perspective view of a thermistor to which the substrate mounting body of FIG. 7 is joined.

FIG. 9 is a perspective view of a thermistor to which the substrate mounting body of FIG. 7 is joined by another method.

FIG. 10 is a perspective view of another substrate mounting body of the thermistor of the present invention.

FIG. 11 is a perspective view of a thermistor to which the substrate mounting body of FIG. 10 is joined.

FIG. 12 is a perspective view of another substrate mounting body of the thermistor of the present invention.

FIG. 13 is a perspective view of a thermistor to which the substrate mounting body of FIG. 12 is joined.

FIG. 14 is a perspective view of still another substrate mounting body of the thermistor of the present invention.

FIG. 15 is a perspective view of a thermistor to which the substrate mounting body of FIG. 14 is joined.

[Description of Signs] 10 Thermistor 11 Thermistor element 12 Terminal electrode 16 Base electrode layer 17 Plating layer 17a Ni plating layer 17b Sn or Sn / Pb plating layer 21 Ceramic sintered sheet 30a Metal element 30b Sn or Sn / Pb plating layer 31, 32, 33, 34 Board mounting body

Claims (8)

(57) [Claims] 1. A chip-shaped thermistor element comprising a hexahedron
(11) In the thermistor having a pair of terminal electrodes (12, 12) formed on opposite side surfaces thereof, the terminal electrode (12) includes a base electrode layer (16) containing a noble metal and the base electrode layer (16). And a plating layer (17) formed on the surface of the laminated electrode, wherein the four side surfaces of the laminated electrode and the other four surfaces of the thermistor element body on which the pair of terminal electrodes (12, 12) are not formed. name the same plane, and the lead frame or
A pair of conductive board mounts consisting of blocks (31, 3
Each main surface of (2,34) is made up of a pair
A thermistor characterized by being joined to each main surface of a terminal electrode (12) . (2) Lead frame with L-shaped cross section
2. The thermistor according to claim 1, wherein the thermistor is a system. (3) Lead frame with U-shaped cross section
(32), the bending interval of the lead frame (32)
2 corresponds to the thickness of the thermistor body (11).
Thermistor. (4) The board mounting body is a rectangular parallelepiped block (34)
The thermistor according to claim 1. (5) Chip-shaped thermistor body consisting of hexahedron
A pair of terminal electrodes (12, 12) are formed on opposite side surfaces of (11).
In the formed thermistor, The terminal electrode (12) is a base electrode layer (16) containing a noble metal and the
With the plating layer (17) formed on the surface of the base electrode layer (16)
Wherein the four side surfaces of the laminated electrode are located on the front.
Thermistor element where the pair of terminal electrodes (12, 12) are not formed
A rectangular tube-shaped lead frame that is flush with the other four surfaces of the body
Of a pair of conductive board mounting bodies (33)
The surface of the pair of terminal electrodes (12,
12) is joined to both sides of the thermistor body (11) including
A thermistor. 6. A Ni plating layer (17a) having a plating layer (17) formed on the surface of a base electrode layer (16), and a Ni plating layer (17).
a) Sn or Sn / Pb plating layer (17)
The thermistor according to any one of claims 1 to 5 , comprising: b). 7. If the board mount (31, 32, 33, 34) is conductive
Metal body (30a) and Sn or
And a Sn / Pb plating layer (30b).
6. The thermistor according to any one of 6. 8. A ceramic sintered sheet for a thermistor body
Forming a base electrode layer (16, 16) on both surfaces of the (21); and forming a Ni plating layer (17a) and a Sn or Sn / Pb plating layer (17b) on each surface of the base electrode layer (16, 16). ) In this order, and a sintered sheet (21) formed on both sides of a laminated electrode comprising the base electrode layer (16) and the plating layer (17) is cut into a chip shape by a dicing saw to form a chip shape. A step of providing a pair of terminal electrodes (12, 12) on opposite side surfaces of the thermistor body (11)
And a lead frame or on each main surface of the pair of terminal electrodes (12).
A pair of conductive board mounts consisting of blocks (31, 3
(2, 34) bonding each main surface with high-temperature cream solder
And a method for manufacturing a thermistor.