JP3201529B2 - Thermal shock resistant ferrite material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ferrite material having thermal shock resistance.

[0002]

2. Description of the Related Art Among ferrite cores to be coiled and used as inductors, ferrite cores are provided with a lead pin for connecting a terminal of the coil, and the terminal of the coil is entangled with this lead pin and soldered. Is widely used.

In the case of such an inductor, as a method of soldering a terminal of a coil to a lead pin, a method of inserting a core into a high-temperature solder bath with the terminal of the coil tangled to the lead pin and soldering is used. ing. In this case, there is a problem that the core undergoes a rapid temperature change, and the core is cracked by the thermal shock.

[0004] On the other hand, in the conventional ferrite, the porosity of the material is increased to 5% or more so that the thermal stress is dispersed.

[0005]

In the conventional method, that is, the method of increasing the porosity of the material, the strength, saturation magnetic flux density, magnetic permeability, etc. of the ferrite material become relatively small, and a practical problem arises. In order to solve this problem, it is necessary to reduce the porosity, and it is not possible to obtain a ferrite material that is excellent in thermal shock resistance and that satisfies strength, saturation magnetic flux density, magnetic permeability, and the like. Was eagerly awaited.

On the other hand, the present inventors have disclosed in
No. 03953, Ni—Zn
It is invented that the thermal shock resistance can be improved by adding a predetermined amount of Bi2O3 and PbO to the ferrite of the system. The present inventors have conducted intensive studies on these ferrite materials.As a result, when the grain boundary of the crystal structure has a characteristic thickness, the ferrite material has low porosity, high electromagnetic properties and strength, and thermal shock resistance. It has been found that a ferrite material having excellent properties can be obtained.

[0007]

According to the present invention, Fe2O3 is 40 to 50 mol%, ZnO is 10 to 35 mol%, C
This ferrite material is obtained by adding 0.03 to 2% by weight of Bi2O3 or PbO to a ferrite composed of 3 to 10 mol% of uO and the balance of NiO, and after firing, controlling grain boundaries between crystals to a thickness of 2 to 50 nm. This makes it possible to obtain a ferrite material having excellent thermal shock resistance and high strength, high saturation magnetic flux density and high magnetic permeability.

Further, the ferrite material of the present invention is made of NiO
At most 1/2 or less of MgO and / or (1/4)
The same effect can be obtained by substituting (Li2O + Fe2O3) and / or Mn oxide. Also, the same effect can be obtained by adding 0 to 1 wt% of SiO2.

[0009]

EXAMPLE Each sample was weighed and mixed at the composition ratio shown in Table 1 and mixed with 85
After calcining at 0 ° C. for 2 hours, the mixture was pulverized with a vibration mill.
A 5 μm ferrite powder was prepared. A predetermined amount of Bi2O3, PbO, SiO2 is added to this ferrite powder in a mortar, mixed, granulated, formed into a round rod-shaped core, dried, and grooved with a diamond grinder to form a drum-shaped core. The sample was fired at 1100 ° C for 2 hours to prepare a sample. Approximately half of the total length of the sample was immersed in a solder bath at 450 ° C., the breakage rate of the core was counted, and the thermal shock resistance was evaluated. The porosity, thickness of grain boundaries, strength, magnetic permeability, and saturation magnetic flux density of this sample were measured. (A transmission electron microscope was used to measure the thickness of the grain boundary.)

[0010]

[Table 1]

Table 2 shows the characteristic values of the fracture rate, porosity, grain boundary thickness, transverse rupture strength, μi, and Bm of each sample. In Table 2, Samples 1 to 10 have no additives and Samples 11 and 2
0 is 0.3 wt.% Of Bi2O3 in samples 1 to 10, respectively.
%, Sample 21 was prepared by adding granules of 300 μm to 50 μm.
0 μm to increase the porosity of the fired body.

[0012]

[Table 2]

As can be seen from this sample 21, when the porosity is increased, the destruction rate can be reduced.
It can be seen that the method of controlling the thickness of the grain boundary to 2 to 50 nm by adding Bi2O3 is advantageous, since the bending strength, μi, and Bm are largely reduced.

Next, 0.3 wt% of Bi2O3 was added to the sample 3.
0.3 wt% of PbO, 0.3 wt% of Bi 2 O 3 and 0.1 w of SiO 2
Table 3 shows the fracture ratio, porosity, thickness of the grain boundary, and magnetic permeability at the time when the thickness of the grain boundary was changed between the case where t% was added and the case where no t% was added. FIG. 1 shows a change in the fracture rate depending on the thickness of the grain boundary, and FIG. 2 shows a change in the change in the magnetic permeability depending on the thickness of the grain boundary. As is clear from Table 3 and FIG. 1, when the grain boundary is 2 to 50 nm, it has an excellent thermal shock resistance. As shown in FIG. 2, when the grain boundary has a thickness of 60 nm or more, the magnetic permeability is reduced by 30%. Therefore, the thickness of the grain boundary is preferably 2 to 50 nm.

[0015]

[Table 3]

Table 4 shows the breaking ratio, porosity, and grain boundary thickness when the firing temperature was 1100 ° C. and the amount of the additive (Bi2O3, PbO, Bi2O3 + SiO2) was changed. Even when the additive is changed, the thickness of the grain boundary is 2 to 50 n.
If it is m, it is understood that it has excellent thermal shock resistance.

[0017]

[Table 4]

[0018]

According to the present invention, there is provided a ferrite material having excellent thermal shock resistance, and excellent strength and electromagnetic properties. Therefore, it is extremely useful as a ferrite material for a drum core with a lead pin electrode, a chip inductor, and the like that directly receives heat from a solder tank, a soldering iron, and the like, and can cope with miniaturization and SMD of these components. It is also possible to apply to a ferrite board with a circuit pattern printed on a ferrite plate. Improve the production yield of each product,
Cost can be reduced.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the thickness of a grain boundary and the destruction rate due to thermal shock.

FIG. 2 is a graph showing the relationship between the thickness of a grain boundary and magnetic permeability.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) C04B 35/26-35/40

Claims (3)

(57) [Claims] 1. The method according to claim 1, wherein the content of Fe2O3 is 40 to 50 mol%,
O is 10 to 35 mol%, CuO is 3 to 10 mol%,
Bi2O3, P
A ferrite material containing at least one kind of bO in an amount of 0.03 to 2 wt%, wherein the grain boundary of the crystal structure is Bi2O.
3. A thermal shock resistant ferrite material formed of an amorphous layer comprising PbO and impurities, and having a grain boundary thickness of 2 to 50 nm. 2. The method according to claim 1, wherein the NiO
At most 1/2 of MgO and / or (1/4) (L
A thermal shock-resistant ferrite material characterized by being substituted by i2O + Fe2O3) and / or Mn oxide. 3. The method according to claim 1, wherein
2. A thermal shock resistant ferrite material, wherein 0 to 1 wt% of 2 is added.