HK1076193A - Face mount coil member and a manufacturing process thereof - Google Patents

Description

Surface mount coil component and method for manufacturing the same

Technical Field

The present invention relates to a surface-mounted coil component such as a step-up/step-down coil suitable for a DC/DC power supply of a portable electronic device.

Background

As a current-matching coil (choke coil or the like) for DC/DC power supply use of portable electronic devices such as portable telephones and digital still color cameras, a surface-mounted coil component having a small external dimension while securing desired inductance coil characteristics is particularly required.

Since these portable electronic devices are often carried and used by ordinary users and the temperature environment of use is changed drastically, a 10-cycle thermal cycle test is performed at-25 to +85 ℃ or a 10-cycle thermal cycle test is performed under more severe conditions, that is, at-40 to +85 ℃, as surface-mount coil components to be mounted on component mounting boards accommodated in these portable electronic devices.

A major structure of a surface mount coil component that has been used in the conventional portable electronic device is to cover a sleeve core around the outer periphery of a ferrite core of drum (ドラム) type in which a wire is wound around a winding core portion connecting an upper flange and a lower flange, to fix a terminal electrode made of a metal frame to the sleeve core with an adhesive, to bind and fix both ends of the wire to the terminal electrode, and to solder the terminal electrode. (not shown).

Further, as another conventional surface mount coil component, there is a surface mount coil component having a structure in which a winding is wound around a winding core and both ends of the winding are conductively connected to a flat external electrode directly formed on the core, or a structure in which a sealing resin is filled between two flanges of the drum ferrite core so as to cover the outer periphery of the winding.

As a structure of the conventional surface-mount coil component, a structure of a coil component using a drum-shaped ferrite core as shown in a perspective view seen from below in fig. 6 is described as a conventional technique in japanese patent document 1, japanese unexamined patent publication No. 7-115023.

That is, the coil component 10 is configured to have: a drum-shaped ferrite core 8 composed of a winding core 1 with a vertical winding shaft and an upper flange 4 and a lower flange 2 respectively extended from the upper and lower ends of the winding core 1; two pairs of external electrodes 3a, 3b, 3c, 3d provided on the lower flange 2 of the drum-shaped ferrite core 8; and windings 5 and 6 wound around the core 1 of the drum-shaped ferrite core 8 and having both ends 5a and 5b and ends 6a and 6b conductively connected to the external electrodes 3a, 3b, 3c and 3d, respectively, by soldering or thermocompression bonding.

Disclosure of Invention

In the surface mount coil component using the conventional drum ferrite core, when the height is reduced, the drum ferrite core and the sleeve core are used, and the sleeve core is arranged adjacent to the peripheral surfaces of both flanges of the drum ferrite core, so that the surface mount coil component looks close to the closed magnetic circuit structure. Therefore, although the coil is advantageous in terms of characteristics (particularly L: inductance value) of the coil, the number of parts is large, which is disadvantageous in terms of cost and is not suitable for downsizing and height.

On the other hand, in the conventional surface-mount coil component 10 shown in fig. 6, if a current-carrying coil having a small height and desired inductance characteristics is to be obtained, in order to secure a necessary winding volume of the winding and form a high-efficiency magnetic path around the winding, it is necessary to cover the outer periphery of the winding wound around the winding core between the flanges with a sealing resin having a magnetic powder content of 60 to 90% by weight.

In order to produce a surface mount coil component having a small external dimension such as a height dimension of 1.2mm or less, for example, using such a single drum-type ferrite core, it has been conventionally employed to set the linear expansion coefficient of the drum-type ferrite core and the linear expansion coefficient of the magnetic powder-containing sealing resin to values close to each other.

However, in the surface mount coil component manufactured by the above conventional method, the thickness of the flange of the drum-shaped ferrite core is not more than 0.35mm, and the value of the ratio L2/L1 of the external dimension L2 to the upper flange of the core diameter L1 of the drum-shaped ferrite core is not less than 1.9 (in the case of the surface mount coil component corresponding to the present, the maximum overhang dimension of the upper flange of the drum-shaped ferrite core in the radial direction from the outer circumferential direction of the core exceeds 1.0mm), the flange strength of the drum-shaped ferrite core cannot resist the stress generated by the difference between the linear expansion coefficient of the drum-shaped ferrite core and the linear expansion coefficient of the magnetic powder-containing sealing resin in the thermal cycle test (25 ℃ C. -85 ℃ C., 10 cycles; or 40 ℃ C. -85 ℃ C., 10 cycles) generally required for the component for the portable electronic device, and a problem that cracks (crick) may be inevitably generated in the flange.

In addition, in the manufacturing process, there is a case where a crack is generated in the flange due to curing shrinkage of the magnetic powder-containing sealing resin when the magnetic powder-containing sealing resin is filled and cured in the outer periphery of the winding core wound around the winding core between the flanges of the drum-shaped ferrite core.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a surface-mounted coil component that achieves both low cost and small height and durability required for a thermal cycle test.

In order to solve the above problems, the present invention,

(1) a surface mount coil component is provided, which comprises a core having a winding shaft arranged perpendicularly to a mounting surface and a drum-shaped ferrite core having an upper flange and a lower flange formed integrally with the core at upper and lower ends of the core; and at least one pair of external electrodes formed directly on the core and formed on the lower surface of the lower flange of the drum-type ferrite core; and a winding wire wound around the core of the drum-shaped ferrite core and having both ends conductively connected to the external electrode, wherein the surface mount coil component further comprises a magnetic powder-containing sealing resin which covers the winding wire between the upper flange and the lower flange of the drum-shaped ferrite core and fills a space between the upper flange and the lower flange, and the magnetic powder-containing sealing resin has a glass transition temperature of less than or equal to-20 ℃ in a transition from a glassy state to a rubbery state in a change of a rigidity ratio with respect to a temperature as a physical property at the time of curing.

(2) There is provided the surface-mount coil component as set forth in the above (1), characterized by comprising a magnetic powder-containing sealing resin which covers the winding wire between the upper flange and the lower flange of the drum-shaped ferrite core and is filled in the space between the flange and the lower flange, wherein a glass transition temperature in a transition from a glass state to a rubber state in a change of a rigidity ratio with respect to a temperature is lower than or equal to-50 ℃ as a physical property at the time of curing.

(3) The surface mount coil component according to the above (1), wherein the thickness of the upper flange of the drum ferrite core is not more than 0.35mm, and the value of the ratio L2/L1 of the outer dimension L2 of the upper flange of the drum ferrite core to the core diameter L1 of the drum ferrite core is not less than 1.9.

(4) A method for manufacturing a surface mount coil component includes a preparation step, an external electrode forming step, a conductive connection step, a filling step, and a curing step.

The preparation step is a step of preparing a drum-shaped ferrite core integrally having a core, an upper flange disposed at one end of the core and having a thickness of 0.35mm or less and a value of a ratio L2/L1 of an outer dimension L2 to a core diameter L1 of the drum-shaped ferrite core of 1.9 or more, and a lower flange disposed at the other end of the core so as to face the upper flange;

the external electrode forming step is a step of forming an external electrode directly formed on the core on the lower surface of the lower flange.

The conductive connection step is a step of winding a winding wire around the core of the drum-shaped ferrite core and conductively connecting both ends thereof to the external electrodes;

the filling step is a step of filling a magnetic powder-containing potting resin coating material in a space region between an upper flange wound around the outer periphery of the winding core of the drum-shaped ferrite core and having a thickness of 0.35mm or less and a value of a ratio L2/L1 of an outer dimension L2 to a core diameter L1 of the drum-shaped ferrite core of 1.9 or more and a lower flange disposed to face the upper flange,

the curing step is a step of curing the magnetic powder-containing resin coating,

the step of filling the magnetic powder-containing encapsulating resin coating uses a magnetic powder-containing encapsulating resin coating having a glass transition temperature of less than or equal to-20 ℃ in a transition from a glassy state to a rubbery state in a change of a rigidity ratio with respect to temperature, as physical properties at the time of curing;

(5) there is provided the method for manufacturing a surface-mount coil component according to item (4), wherein the step of filling the magnetic powder-containing encapsulating resin coating is performed using a magnetic powder-containing encapsulating resin coating having a glass transition temperature of-50 ℃ or lower in a transition from a glassy state to a rubbery state in a change in rigidity ratio with respect to temperature as a physical property at the time of curing.

The surface mount coil component and the method for manufacturing the same according to the present invention are configured as described above, and therefore,

(1) a current-corresponding coil having a small height and desired inductance characteristics can be obtained at low cost.

(2) A surface-mount coil which is suitable for use on a component-mounting board housed in a portable electronic device in which a change in the temperature environment during transition from a glass state to a rubber state is prevented from cracking in a thermal cycle test and which has a sealing resin containing magnetic powder filled in the outer periphery of a winding wound around a winding core and sandwiched between an upper flange and a lower flange, the sealing resin having a glass transition temperature of less than or equal to-20 ℃, preferably less than or equal to-50 ℃ in the transition from the glass state to the rubber state as a physical property at the time of curing, and which is suitable for mounting on the component-mounting board housed in the interior of the portable electronic device in which the change in the temperature environment of use is drastic.

(3) The process comprises filling a magnetic powder-containing encapsulating resin coating material into a space region between an upper flange having a thickness of 0.35mm or less and a ratio L2/L1 of an outer dimension L2 to a core diameter L1 of a drum-shaped ferrite core of 1.9 or more and a lower flange disposed opposite to the upper flange, and a step of curing the magnetic powder-containing encapsulating resin coating, wherein the step of filling the magnetic powder-containing encapsulating resin coating is used as a physical property at the time of curing, an encapsulating resin coating containing a magnetic powder having a glass transition temperature of less than or equal to-20 ℃ in a transition from a glassy state to a rubbery state in a change of a rigidity ratio with respect to temperature, therefore, thermal stress due to expansion and contraction actions of the resin generated during curing heating after coating the resin in the manufacturing process is reduced, thereby preventing breakage of the flange of the drum-type ferrite core. As a result, the surface-mount coil component having high reliability against a change in the use temperature environment can be produced with high yield.

Drawings

Fig. 1 is a perspective view showing a typical surface mount choke coil structure as a surface mount coil component of the present invention, as viewed from above.

Fig. 2 is a perspective view showing a structure of a surface-mount choke coil according to the present invention, as viewed from below.

Fig. 3 is a front view of the surface mount choke coil of the present invention.

Fig. 4 is a longitudinal sectional view of the surface mount choke coil of the present invention.

Fig. 5 is a process flow chart for explaining a method of manufacturing the surface mount choke coil according to the present invention.

Fig. 6 is a perspective view of a known surface-mounted coil component viewed from below.

Detailed Description

Embodiments of the surface-mount coil component according to the present invention will be described below with reference to the drawings.

Fig. 1 is a perspective view showing a typical surface mount choke coil structure as a surface mount coil component of the present invention viewed from above, and fig. 2 is a perspective view of the surface mount choke coil of the present invention viewed from below. Fig. 3 is a front view of the surface mount choke coil of the present invention. Fig. 4 is a longitudinal sectional view thereof.

In fig. 1 to 4, a surface mount choke coil 20 of the present invention is a surface mount coil component including: a drum-shaped ferrite core 14 including a winding core 11 having a winding shaft arranged perpendicularly to an actual mounting surface, and an upper flange 12 and a lower flange 13 formed integrally with the winding core 11 at upper and lower ends of the winding core 11; and at least one pair of external electrodes 15a, 15b formed directly on the lower surface of the lower flange 13 of the drum-shaped ferrite core 14; and a winding wire 17 wound around the winding core 11 of the drum-shaped ferrite core 14 and having both ends conductively connected to the external electrodes 15a and 15b by soldering, thermocompression bonding, or the like, and particularly, a magnetic powder-containing sealing resin 18 for covering the winding wire 17 between the upper flange 12 and the lower flange 13 of the drum-shaped ferrite core 14 and filling the space between the upper flange 12 and the lower flange 13, wherein the magnetic powder-containing sealing resin has physical properties when cured such that a glass transition temperature Tg in a transition from a glass transition state to a rubber state in a change in a rigidity ratio with respect to temperature is lower than or equal to-20 ℃, more preferably lower than or equal to-50 ℃.

In addition, in the above configuration, the thickness d of the upper flange 12 of the drum-shaped ferrite core 14 is not more than 0.35mm, and the value of the ratio L2/L1 of the outer dimension L2 of the upper flange (the diameter of the upper flange when the upper flange is circular; the dimension of the one side that is longer and longer in the vertical and horizontal directions when the upper flange is rectangular) to the core diameter L1 of the drum-shaped ferrite core 14 is not less than 1.9 (this ratio corresponds to the maximum dimension t of the upper flange 12 in the radial direction from the outer periphery of the core 11 (the dimension from the outer periphery of the core to the maximum outer diameter of the upper flange) in the current smallest drum-shaped ferrite core being not less than 1.0 mm).

The requirement for the thickness d of the upper flange 12 is indispensable for reducing the height of the surface mount coil component (the height dimension H in fig. 3 is not more than 1.6mm), the requirement for the ratio L2/L1 between the outer dimension L2 of the upper flange and the core diameter L1 is not less than 1.9, the requirement for the maximum extension dimension t of the upper flange 12 from the outer periphery of the core 11 in the radial direction of the existing small drum-type ferrite core, and the requirement for the winding volume required for obtaining the choke characteristic for the single drum-type ferrite core 14 in the height dimension H. In addition, the lower limit of the thickness d of the upper flange 12 should be made small by the progress of the processing technique and sintering manufacturing technique of the ferrite core material.

The physical properties of the magnetic powder-containing sealing resin 18 at the time of curing are required to have a glass transition temperature Tg of not more than-20 ℃ in the transition from the glass state to the rubber state in the change of the rigidity ratio with respect to temperature, and are required to obtain an effect of preventing cracking of the upper flange 12, which is found by the present inventors in a careful study based on an actual measurement value of a crack defect occurrence state of the upper flange 12 in a thermal cycle test result of 50 cycles of-25 to +85 ℃ of the surface mount choke coil 20. The requirement of not more than-50 ℃ is a requirement for obtaining an effect of preventing cracks in the upper flange 12, which is obtained from an actual measurement value of the occurrence of crack defects in the upper flange 12 in the results of a 50-cycle thermal cycle test at-40 ℃ to +85 ℃ of the surface mount choke coil 20.

A method for manufacturing the surface mount choke coil 20, which is a typical surface mount coil component of the present invention, includes the steps of steps 1 to 5, as shown in a flowchart for explaining the process flow of fig. 5. Hereinafter, each step will be described while describing specific examples of the members used.

Step 1: step 1 is a preparation step of preparing a drum-shaped ferrite core 14 in which a core 11, an upper flange 12 having a thickness d of 0.35mm or less and a ratio L2/L1 of an outer dimension L2 to a core diameter L1 of the drum-shaped ferrite core 14 is formed integrally with a lower flange 13 disposed at the other end of the core 11 so as to face the upper flange 12 are provided integrally with the core 11. As a specific example, there is a method of spray-drying a suspension containing a nickel zinc ferrite material powder, a binder and a solvent, granulating the resultant powder, and integrally molding the resultant powder into a drum-shaped ferrite core shape by a dry molding press, or a method of obtaining a flat ferrite molding by the same method as described above, then subjecting the flat ferrite molding to grinding to form a drum-shaped ferrite core shape, and further calcining the molding obtained by these methods at 105 ℃ for 2 hours to obtain a drum-shaped sintered ferrite core 14. The magnitude of the value of the ratio L2/L1 between the external dimension L2 of the drum-shaped ferrite core 14 and the core diameter L1 is closely related to the occurrence of cracks.

Step 2: step 2 is a step of forming the external electrodes 15a and 15b, and is a step of forming the external electrodes 15a and 15b directly formed on the core in the region including the winding guide groove 19 of the lower surface 13a of the lower flange 13. As a specific example, the drum-type ferrite core 14 is held on a printing table by a screen printing method using a screen mask (スクリ - ンマスク) having a desired opening pattern, and then an Ag electrode material paste containing Ag conductive powder, glass frit and a color spreader (Vehide) is coated on the printing table and sintered at 650 ℃ for 30 minutes. If necessary, nickel plating, tin plating, copper plating, or the like is performed on the surface of the electrode made of sintered Ag.

And step 3: the method is a step of winding a winding wire 17 around the winding core 11 of the drum-shaped ferrite core 14 and connecting both ends of the winding wire to the external electrodes 15a and 15b so as to be conductive. Specifically, a winding wire 17 of a polyurethane resin coated copper wire having a wire diameter of 100 μm is wound around the outer periphery of the core 11 of the drum-shaped ferrite core 14 by 10 turns, and both ends thereof are bent along the outer electrodes 15a and 15b on the winding guide grooves 19, respectively. Then, in order to cover the ends of the wire 17, a solder paste containing a flux component is printed on the surface of the external electrodes 15a and 15b through an orifice plate, and after drying, a hot plate heated to 30 ℃ is brought into contact with the solder surface and then held for 30 seconds, whereby the solder paste is melted, and the urethane resin coating layer is decomposed and removed, and the ends of the copper wires and the external electrodes 15a and 15b are soldered. Further, the step of soldering may be performed before and after the winding wire, or the winding wire and the soldering may be performed as separate steps.

And 4, step 4: is a filling process. That is, the coating material of the magnetic powder-containing encapsulating resin 18 is filled in a space region which is provided around the outer periphery of the winding 17 wound around the core 11 of the drum-type ferrite core 14 and is sandwiched by the upper flange 12 having the thickness d of 0.35mm or less and the ratio L2/L1 of the outer dimension L2 to the core diameter L1 of 1.9 or more and the lower flange 13 disposed to face the upper flange 12, and the coating material of the magnetic powder-containing encapsulating resin 18 has a glass transition temperature Tg of-20 ℃ or less or equal to-50 ℃ in the transition from the glass state to the rubber state in the change of the rigidity against the temperature as physical properties at the time of curing. Specifically, the space region sandwiched between the upper flange 12 and the lower flange 13 and around the periphery of the winding is filled with the encapsulating resin paint containing the magnetic powder by a dispenser, and left to stand at room temperature for 30 minutes to dry the coating.

As the encapsulating resin 18 containing the magnetic powder, for example, a coating material in which an epoxy resin and a carboxyl group-modified propylene glycol are mixed in a composition shown in (compounding ratio 3) to (compounding ratio 7) as a coating material of the encapsulating resin 18 containing the magnetic powder having a glass transition temperature Tg of not more than-20 ℃ in a table of the encapsulating resin coating material containing the magnetic powder and the physical properties (1) after curing, and a coating material in which a composition shown in (compounding ratio 6) or (compounding ratio 7) as a coating material having a glass transition temperature Tg of not more than-50 ℃ are mixed in a composition shown in (compounding ratio 6) or (compounding ratio 7) are used. For reference, a composition (1) of a magnetic powder-containing encapsulating resin 18 mainly composed of only an epoxy resin, which is generally used in a conventional surface-mount coil component, and a composition (2) of an epoxy resin and a carboxyl-modified propylene glycol at a ratio of 7: 3 are disclosed. As is clear from Table 1, the higher the ratio of the carboxyl group-modified propylene glycol to the epoxy resin, the lower the glass transition temperature Tg becomes to-20 ℃ or lower. Further, it is understood from (formulation 3) to (formulation 7) that when the glass temperature Tg is not more than-20 ℃ (particularly not more than-50 ℃), the longitudinal elastic modulus of the magnetic powder-containing encapsulating resin 18 after curing at room temperature (20 ℃) is significantly lower than that of (formulation 1) or (formulation 2), and the resin has the property of a soft resin rich in cushioning properties.

TABLE 1 coating of encapsulating resin containing magnetic powder and physical properties after curing (1)

	Ratio 1	Ratio 2	Ratio 3	Ratio 4	Ratio 5	Ratio 6	Ratio 7
								Carboxyl modified propylene glycol epoxy resin ferrite magnetic powder silica curing agent solvent	01001111515	30701111515	40601111515	50501111515	55451111515	60401111515	70301111515
Sum of	232	232	232	232	232	232	232
								Tg(℃)	120	-10	-20	-34	-40	-50	-53
Longitudinal modulus of elasticity (MPa) at 20 DEG C	10000	3800	1500	320	155	37	17

As another preferred example of the magnetic powder-containing encapsulating resin 18, an example (formulation 8) in which the same weight part of ferrite magnetic powder was added to silicone resin TSE325-B manufactured by GE toshiba シリコ - ン (ltd.) is shown in the magnetic powder-containing encapsulating resin coating material and the physical properties after curing (2) in table 2 below.

Further, as the physical properties of the magnetic powder-containing sealing resin 18 at the time of curing, a magnetic powder-containing resin containing 10 to 90% by weight of ferrite magnetic powder is preferable for improving the inductance characteristics, as long as the glass transition temperature Tg in the transition from the glassy state to the rubbery state with respect to the change in the rigidity ratio with respect to temperature is not more than-20 ℃, more preferably not more than-50 ℃.

TABLE 2 coating of magnetic powder-containing encapsulating resin and physical properties after curing (2)

	Mixing 8
		Silicon resin TSE325-B ferrite magnetic powder silica curing agent solvent	100100000
Sum of	200
		Tg(℃)	-60
Longitudinal modulus of elasticity (MPa) at 20 DEG C	0.2

And 5: the step is to heat and cure the resin 18 containing the magnetic powder. Specifically, the heat treatment was carried out in a heating furnace at 150 ℃ for 10 minutes.

Using the magnetic powder-containing encapsulating resin paint produced by the production method described above and using the above (formulation 1) to (formulation 8), the upper flange 12 was square with an outer dimension of 4mm, the ratio L2/L1 of the outer dimension L2 to the core diameter L1 thereof was 2.1, the gap dimension y between the upper and lower flanges was 0.5mm, the upper flange thickness d was 0.25mm, 0.30mm, 0.35mm, and 0.40mm, samples of the surface-mounted choke coil (the number of samples n under each condition was 3), first held at-40 ℃ for 30 minutes in a thermal cycle test cell, then held at +85 ℃ for 30 minutes, and then cooled at-40 ℃ to repeat a 50-cycle thermal cycle test. Table 3 below shows the visually observed occurrence of cracks in the upper flange 12 of each sample after the test.

Table 3 thermal cycling test (-40-85 ℃ 50 cycles) · o: seamless ●: with a gap

Flange thickness (mm)	Ratio 1	Ratio 2	Ratio 3	Ratio 4	Ratio 5	Ratio 6	Ratio 7	Ratio 8
									0.25	● ●●	● ●●	● ●●	● ●●	○ ●●	○ ○●	○ ○○	○ ○○
0.30	● ●●	● ●●	● ●●	● ●●	○ ○●	○ ○○	○ ○○	○ ○○
									0.35	● ●●	● ●●	● ●●	● ●●	○ ○○	○ ○○	○ ○○	○ ○○
0.40	○ ●●	○ ○●	○ ○○	○ ○○	○ ○○	○ ○○	○ ○○	○ ○○
									Outer diameter size 4mm square outer diameter size/axial center diameter 2.1

In addition, for each of the samples (formulation 1) to (formulation 8) similar to those in table 3, the thermal cycle test was performed for 50 cycles by repeating the operation of first holding at-25 ℃ for 30 minutes, then holding at +85 ℃ for 30 minutes, and then cooling at-25 ℃ in the thermal cycle test chamber, and the occurrence of cracks in the upper flange 12 of each sample after the test was performed, which was visually observed, is shown in table 4 below.

Table 4 thermal cycling test (-40-85 ℃ 50 cycles) · o: seamless ●: with a gap

Flange thickness (mm)	Ratio 1	Ratio 2	Ratio 3	Ratio 4	Ratio 5	Ratio 6	Ratio 7	Ratio 8
									0.25	●●●	● ●●	○ ○○	○ ○○	○ ○○	○ ○○	○ ○○	○ ○○
0.30	●●●	○ ●●	○ ○○	○ ○○	○ ○○	○ ○○	○ ○○	○ ○○
									0.35	○●●	○ ○○	○ ○○	○ ○○	○ ○○	○ ○○	○ ○○	○ ○○
0.40	○○●	○ ○○	○ ○○	○ ○○	○ ○○	○ ○○	○ ○○	○ ○○
									Outer diameter of 4mm square 2.1 (outer diameter/axial diameter)

Next, the crack occurrence state of the upper flange 12 in each of the samples (formulation 1) to (formulation 8) after the thermal cycle test of 50 cycles at-40 to +85 ℃ was visually observed in table 5, where the thickness d of the upper flange 12 was 0.35mm, the pitch dimension y between the upper and lower flanges was 0.5mm, and the ratio L2/L1 of the outer dimension L2 of the upper flange 12 to the core diameter L1 was 4.00 (corresponding to the upper flange maximum protrusion dimension of 1.5 mm), 2.50 (corresponding to the upper flange maximum protrusion dimension of 1.2 mm), 1.90 (corresponding to the upper flange maximum protrusion dimension of 1.0mm), and 1.30 (corresponding to the upper flange maximum protrusion dimension of 0.5 mm).

Table 5 thermal cycling test (-40 to +85 ℃ 50 cycles) · o: seamless ●: with a gap

Physical dimension/core diameter	Ratio 1	Ratio 2	Ratio 3	Ratio 4	Ratio 5	Ratio 6	Ratio 7	Ratio 8
									4.00	● ●●	● ●●	● ●●	● ●●	● ●●	○ ●●	○ ○○	○ ○○
2.50	● ●●	● ●●	● ●●	● ●●	○ ●●	○ ○○	○ ○○	○ ○○
									1.90	● ●●	● ●●	● ●●	● ●●	○ ○○	○ ○○	○ ○○	○ ○○
1.30	○ ○○	○ ○○	○ ○○	○ ○○	○ ○○	○ ○○	○ ○○	○ ○○
									The thickness of a square flange with the outer diameter of 4mm is 0.35mm

The results of visual observation of the occurrence of cracks in the upper flange 12 of each sample after the 50-cycle thermal cycle test at-25 to +85 ℃ were carried out on each of the above samples (ratio 1) to (ratio 8) similar to those in table 5 are shown in table 6 below.

Table 6 thermal cycling test (-25 to +85 ℃ 50 cycles) · o: seamless ●: with a gap

Physical dimension/core diameter	Mixing 1	Mixing 2	Mixing 3	Mixing 4	Mixing 5	Mixing 6	Mixing 7	Mixing 8
									4.00	● ●●	● ●●	○ ○○	○ ○○	○ ○○	○ ○○	○ ○○	○ ○○
2.50	● ●●	● ●●	○ ○○	○ ○○	○ ○○	○ ○○	○ ○○	○ ○○
									1.90	○ ●●	○ ○○	○ ○○	○ ○○	○ ○○	○ ○○	○ ○○	○ ○○
1.30	○ ○○	○ ○○	○ ○○	○ ○○	○ ○○	○ ○○	○ ○○	○ ○○
									The thickness of a square flange with the outer diameter of 4mm is 0.35mm

As is clear from Table 4, in the heat cycle test of-25 to +85 ℃ and 50 cycles, no cracks occurred in the samples of (ratio 3) to (ratio 8) having a glass transition temperature Tg of-20 ℃ or lower, and in particular, in the samples of (ratio 6) to (ratio 8) having a glass transition temperature Tg of-50 ℃ or lower, it is clear from Table 3 that cracks hardly occurred in the heat cycle test of-40 to 85 ℃ and 50 cycles. In addition, from the values of the ratio L2/L1 with respect to the outer dimension L2 of the upper flange 12 of the drum-type ferrite core 14 and the core diameter L1, it is clear from Table 6 that, in the samples having a value of the ratio L2/L1 of not less than 1.9, cracks are not generated in the samples of (formula 3) to (formula 8) having a glass transition temperature Tg of not more than-20 ℃ in the heat cycle test of-25 to +85 ℃ and 50 cycles, and in particular, in the samples having a glass transition temperature Tg of not more than-50 ℃ (formula 6) to (formula 8), cracks are hardly generated in the heat cycle test of-40 to +85 ℃ and 50 cycles in Table 5.

In the surface mount choke coil 20 having the above-described structure, as seen from the results of tables 1 to 6, the magnetic powder-containing sealing resin 18 is filled in the space region sandwiched between the outer periphery of the winding wire 17 wound around the winding core 11, the corners of the upper surface of the lower flange 13, and the corners of the lower surface of the upper flange 12, and therefore, the magnetic powder-containing sealing resin 18 does not hold the upper flange 12 and the lower flange 13 with a relatively large rigidity under the use temperature condition, and can be said to have a function of alleviating deformation occurring in the core as a buffer material. As a result, the upper flange 12 can be prevented from cracking in the thermal cycle test.

Further, the above-mentioned (ratio 3) to (ratio 8), particularly (ratio 6) to (ratio 8), have a relatively long pot life after mixing, so that the stability of the process conditions is excellent in mass production of the surface mount coil component, and as another modification of the coating material containing the magnetic powder encapsulating resin in which the glass transition temperature in the transition from the glass state to the rubber state is less than or equal to-50 ℃ in the change of the rigidity ratio with respect to the temperature, table 7 below shows a two-liquid modification.

TABLE 7 Low Tg blend examples (two-fluid type)

	Proportioning
		ジエフア-ミンD-2000(1)Ferrite powder solvent of epoxy resin (bisphenol A type)	703010020

サンテクノミカル Kabushiki Kaisha

Specifically, 70 parts by weight of ジエフア - ミン D-2000 (manufactured by サンテクノミカル K.K.), 30 parts by weight of an epoxy resin (bisphenol A), 100 parts by weight of ferrite magnetic powder, and 20 parts by weight of a solvent can be used. The glass transition temperature Tg of the cured magnetic powder-containing sealing resin was-50 ℃ but, because it was a two-liquid type, the applicable time for coating after mixing was about 1 hour, and it was possible to use it in small-volume production of various products.

It is preferable that the area of the upper surface of the upper flange 12 is equal to the area of the lower flange 13 disposed opposite thereto, or at least 85% or more of the area of the lower flange 13, but slightly smaller than the area of the lower flange 13.

The height dimension H of the surface mount choke coil 20 of the present invention having the above-described structure can be reduced to 1.2mm or less, and further 1.0mm or less, and can be made smaller than the height of the conventional surface mount coil component (about 1.6mm or more).

The drum-shaped ferrite core 14 may have a cylindrical or substantially quadrangular prism shape as the winding core 11, and the upper flange 12 and the lower flange 13 may have a disk-like or square or rectangular plate shape. At least one pair or two pairs of external electrodes 15a and 15b may be arranged on the lower surface 13a of the lower flange 13, and the position and shape thereof are not limited.

Claims (18)

1. A surface mount coil component comprising:

a core constituted by a winding core and flanges formed respectively on both end portions of the winding core;

an external electrode formed on a main surface of any one of the flanges;

and a winding wound around the core of the core and having both ends conductively connected to the external electrode,

characterized in that the ferrite core further comprises a magnetic powder-containing sealing resin which covers a winding between the upper flange and the lower flange of the drum-shaped ferrite core and fills a space between the upper flange and the lower flange,

the physical properties of the magnetic powder-containing encapsulating resin upon curing are such that the glass transition temperature in the transition from the glassy state to the rubbery state in the change of the rigidity ratio with respect to temperature is less than or equal to-20 ℃.

2. The surface-mount coil component according to claim 1, wherein an encapsulating resin containing magnetic powder is provided, the encapsulating resin containing magnetic powder covers the winding wire between the upper flange and the lower flange of the drum-type ferrite core and is filled in the space between the flange and the lower flange, and the physical properties of the encapsulating resin containing magnetic powder at the time of curing are such that a glass transition temperature in a transition from a glass state to a rubber state in a change of a rigidity ratio with respect to temperature is less than or equal to-50 ℃.

3. The surface-mount coil component as claimed in claim 1, wherein the thickness of the upper flange of the drum-shaped ferrite core is not more than 0.35mm, and the value of the ratio L2/L1 of the outer dimension L2 of the upper flange of the drum-shaped ferrite core to the core diameter L1 is not less than 1.9.

4. A method for manufacturing a surface-mount coil component, comprising a preparation step, an external electrode forming step, a conductive connection step, a filling step, and a curing step,

the preparation step is a step of preparing a drum-shaped ferrite core in which a core, an upper flange disposed at one end of the core and having a thickness of 0.35mm or less and a value of a ratio L2/L1 of an outer dimension L2 to a core diameter L1 of the drum-shaped ferrite core of 1.9 or more, and a lower flange disposed at the other end of the core so as to face the upper flange are integrated with each other;

the upper external electrode forming step is a step of forming an external electrode directly formed on the core on the lower surface of the lower flange;

the conductive connection step is a step of winding a winding around a core of the drum-shaped ferrite core and conductively connecting both ends thereof to the external electrodes, respectively;

the filling step is a step of filling a magnetic powder-containing sealing resin coating material in a space region sandwiched by an upper flange having a thickness of 0.35mm or less and a ratio L2/L1 of an outer dimension L2 to a core diameter L1 of the drum-shaped ferrite core of 1.9 or more and a lower flange disposed to face the upper flange, the outer periphery of a winding wound around the core of the drum-shaped ferrite core,

the curing step is a step of curing the magnetic powder-containing encapsulating resin coating,

the step of filling the magnetic powder-containing encapsulating resin coating uses an encapsulating resin coating containing magnetic powder whose physical properties at the time of curing are such that the glass transition temperature in the transition from the glassy state to the rubbery state in the change of the rigidity ratio with respect to temperature is less than or equal to-20 ℃;

5. the method for manufacturing a surface-mount coil component according to claim 4, wherein the step of filling the magnetic powder-containing sealing resin coating is performed using a magnetic powder-containing sealing resin coating in which a glass transition temperature in a transition from a glassy state to a rubbery state in a change in a rigidity ratio with respect to a temperature is less than or equal to-50 ℃ as a physical property at the time of curing.

6. The surface-mount coil component according to claim 2, wherein the magnetic powder-containing sealing resin is a sealing resin obtained by curing a paint containing a magnetic powder, an epoxy resin and a carboxyl-modified propylene glycol.

7. The surface-mount coil component according to claim 2, wherein the magnetic powder-containing sealing resin is a resin obtained by curing a paint containing magnetic powder and silicone resin.

8. The surface-mount coil component according to claim 2, wherein the magnetic powder-containing sealing resin is a resin obtained by curing a paint containing magnetic powder, polyetheramine, and an epoxy resin.

9. The surface mount coil component as claimed in claim 3, wherein the drum type ferrite core has an upper flange whose maximum protrusion dimension in a radial direction from an outer peripheral direction of the core exceeds 1.0 mm.

10. The surface-mount coil component according to claim 3, wherein the drum-shaped ferrite core is formed by integrally molding the core in a dry molding press and then firing the core.

11. The surface-mount coil component according to claim 3, wherein the drum-shaped ferrite core is obtained by grinding and baking a flat ferrite molding.

12. The surface mount coil component as claimed in claim 3, wherein the drum type ferrite core has a guide groove of a winding end portion on a lower face of a lower flange thereof.

13. The surface-mount coil component according to claim 3, wherein at least one or two pairs of the external electrodes are provided on the lower surface of the lower flange.

14. The surface-mount coil component according to claim 13, wherein the external electrode is formed by applying and sintering an Ag electrode material paste.

15. The surface-mount coil component according to claim 13, wherein the external electrode is formed by plating nickel, tin or copper on a surface of the Ag sintered electrode.

16. The method for manufacturing a surface-mount coil component according to claim 5, wherein the magnetic powder-containing sealing resin coating material contains magnetic powder, epoxy resin, and carboxyl-modified propylene glycol.

17. The method for manufacturing a surface-mount coil component according to claim 5, wherein the magnetic powder-containing potting resin coating material contains a magnetic powder and a silicone resin.

18. The method for manufacturing a surface-mount coil component according to claim 5, wherein the magnetic powder-containing encapsulating resin paint contains magnetic powder, polyetheramine and epoxy resin.