Resin-molded unit including an electronic circuit component

BACKGROUND OF THE INVENTION

This invention relates to a resin-molded unit comprising an electronic circuit component, such as a semiconductor chip, sealed in a resin mold. In the present specification, the term “resin-molded unit” is used in a broad sense including a resin case and a resin housing also.

In recent years, highly integrated semiconductor devices operable at a high speed are remarkably wide spread and more and more increasingly used. As active devices using the semiconductor devices, there are known a random access memory (RAM), a read only memory (ROM), a microprocessor (MPU), a central processing unit (CPU), an image processor arithmetic logic unit (IPALU), and so on. The above-mentioned active devices are improved every minute so that an operation speed and/or a signal processing speed is rapidly increased. Under the circumstances, an electric signal propagated at a high speed is accompanied with drastic changes in electric voltage or electric current. Such changes constitute a main factor in generation of a high-frequency noise.

On the other hand, the reduction in weight, thickness, and size of electronic components or electronic apparatuses is endlessly making a rapid progress. This results in a remarkable increase in degree of integration of the semiconductor devices and in density of mounting the electronic components to a printed wiring board. In this event, electronic devices and signal lines densely integrated or mounted are very close to one another. Such high-density arrangement, in combination with the increase in signal processing speed mentioned above, will cause the high-frequency noise to be readily induced.

As one example of the electronic components or the electronic apparatuses, there is known a resin-molded unit comprising an electronic circuit component, such as a semiconductor chip, sealed in a resin mold. It is pointed out that such resin-molded unit has a problem of undesired radiation produced from a power supply line. In order to avoid the problem, various countermeasures have been taken. For example, a lumped constant component such as a decoupling capacitor is inserted into the power supply line.

However, in the resin-molded unit including the electronic circuit component operable at a high speed, the noise generated as mentioned above will contain a harmonic component. In this event, a signal path exhibits the behavior as a distributed constant circuit. Therefore, the conventional technique of preventing the noise is not effective because such technique assumes a lumped constant circuit.

SUMMARY OF THE INVENTION

It is therefore an object of this invention to provide a resin-molded unit capable of effectively reducing undesired radiation produced from an electronic circuit component operable at a high speed.

Other objects of the present invention will become clear as the description proceeds.

According to an aspect of the present invention, there is provided a resin-molded unit comprising an electronic circuit component, a resin molding the electronic circuit component therein, and a high-frequency current suppressor covering at least one part of the resin, the high-frequency current suppressor being made of a magnetic loss film.

According to another aspect of the present invention, there is provided a resin-molded unit comprising an electronic circuit component, a resin molding the electronic circuit component therein, and a high-frequency current suppressor covering at least one part of the resin, the high-frequency current suppressor being made of a magnetic loss film which serves to attenuate a high-frequency current flowing through the electronic circuit component and having a frequency within a frequency band between several tens MHz and several GHz.

According to still another aspect of the present invention, there is provided a resin-molded unit comprising an electronic circuit component, a resin molding the electronic circuit component therein, and a high-frequency current suppressor covering at least one part of the resin, the high-frequency current suppressor being made of a magnetic loss film which is made of a magnetic substance of a magnetic composition comprising M, X and Y, where M is a metallic magnetic material consisting of Fe, Co, and/or Ni, X being element or elements other than M and Y, and Y being F, N, and/or O, the M-X-Y magnetic composition having a concentration of M in the composition so that the M-X-Y magnetic composition has a saturation magnetization of 35-80% of that of the metallic bulk of magnetic material comprising M alone, the magnetic composition having the maximum value μ″

max

of an imaginary part μ″ of relative permeability in a frequency range of 0.1-10 gigahertz (GHz).

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1

is a schematic sectional view of a resin-molded unit according to one embodiment of this invention;

FIG. 2

is a schematic view showing a granular structure of M-X-Y magnetic composition;

FIG. 3A

is a schematic sectional view showing a structure of a sputtering apparatus which was used in examples;

FIG. 3B

is a schematic sectional view showing a structure of a vapor deposition apparatus which was used in examples;

FIG. 4

is a graphical view showing a permeability frequency response of film sample 1 in Example 1;

FIG. 5

is a graphical view showing a permeability frequency response of film sample 2 in Example 2;

FIG. 6

is a graphical view showing a permeability frequency response of comparable sample 1 in Comparable Example 1;

FIG. 7

is a schematic and perspective view of a test apparatus for testing an noise suppressing effect of magnetic samples;

FIG. 8A

is a graphic view showing a transmission characteristic of film sample 1;

FIG. 8B

is a graphic view showing a transmission characteristic of comparable sample of composite magnetic material sheet;

FIG. 9A

is a distribution constant circuit with a length l showing a magnetic material as a noise suppressor;

FIG. 9B

is an equivalent circuit with a unit length Δl of the distribution constant circuit of

FIG. 9A

;

FIG. 9C

is an equivalent circuit with a length l of the distribution constant circuit of

FIG. 9A

;

FIG. 10A

is a graphic view showing a frequency response of an equivalent resistance R of film sample 1 in Example 1; and

FIG. 10B

is a graphic view showing a frequency response of an equivalent resistance R of comparative sample of a composite magnetic material sheet.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to

FIG. 1

, description will be made of a resin-molded unit according to one embodiment of this invention.

The resin-molded unit is depicted by a reference numeral

1

and contains a semiconductor bear chip

2

arranged inside and sealed in an epoxy resin mold

3

. From the semiconductor bear chip

2

, a plurality of lead frames

4

are extracted through the epoxy resin mold

3

to the outside.

Furthermore, the epoxy resin mold

3

is entirely covered with a high-frequency current suppressor

5

. The high-frequency current suppressor

5

is a thin film magnetic substance formed in the form of a film by sputtering or vapor deposition known in the art, having a thickness between 0.3 μm and 20 μm, and exhibiting the conductivity in a frequency band lower than several tens MHz. The high-frequency current suppressor

5

serves to attenuate a high-frequency current flowing through a circuit portion inside the epoxy resin mold

3

and having a frequency within a frequency band between several tens MHz and several GHz.

Upon forming the high-frequency current suppressor

5

, use may be made of chemical vapor deposition (CVD), ion beam deposition, gas deposition, and pattern transfer in addition to the sputtering or the vapor deposition mentioned above.

As a material for each of the high-frequency current suppressors

4

a,

4

b,

and

5

, use may be made of a narrow-band magnetic loss material which has an M-X-Y composition as a mixture of components or elements M (M being at least one of Fe, Co, and Ni), Y (Y being at least one of F, N, and O), and X (X being at least one element other than those contained in M and Y) and which has a permeability characteristic, given as a relationship between a frequency and an imaginary part μ″ with respect to a real part μ′ of relative permeability, such that the maximum value μ″

max

of the imaginary part μ″ (which may be called a magnetic loss term) is present within a frequency range between 100 MHz and 10 GHz and that a relative bandwidth bwr is not greater than 200% where the relative bandwidth bwr is obtained by extracting a frequency bandwidth between two frequencies at which the value of μ″ is 50% of the maximum μ″

max

and normalizing the frequency bandwidth at the center frequency thereof. It is assumed here that the narrow-band magnetic loss material has saturation magnetization between 80% and 60% of that of a metal magnetic material comprising the component M alone and a d.c. electric resistance between 100 μΩ•cm and 700 μΩ•cm.

As the material for each of the high-frequency current suppressors

4

a,

4

b,

and

5

, use may also be made of a wide-band magnetic loss material which has an M-X-Y composition as a mixture of components M (M being at least one of Fe, Co, and Ni), Y (Y being at least one of F, N, and O), and X (X being at least one element other than those contained in M and Y) and which has a permeability characteristic, given as a relationship between a frequency and an imaginary part μ″ with respect to a real part μ′ of relative permeability, such that the maximum value μ″

max

of the imaginary part μ″ is present within a frequency range between 100 MHz and 10 GHz and that a relative bandwidth bwr is not smaller than 150% where the relative bandwidth bwr is obtained by extracting a frequency bandwidth between two frequencies at which the value of μ″ is 50% of the maximum μ″

max

and normalizing the frequency bandwidth at the center frequency thereof. It is assumed here that the wide-band magnetic loss material has saturation magnetization between 60% and 35% of that of a metal magnetic material comprising the component M alone and a d.c. electric resistance greater than 500 μΩ•cm.

In each of the narrow-band magnetic loss material and the wide-band magnetic loss material used as the high-frequency current suppressors

4

a,

4

b,

and

5

, the component X is at least one of C, B, Si, Al, Mg, Ti, Zn, Hf, Sr, Nb, Ta, and rare earth elements. The component M is present in a granular structure where particles or grains of the component M are dispersed in a matrix of a compound of the components X and Y The particles have an average particle size between 1 nm and 40 nm. The narrow-band or the wide-band magnetic loss material has an anisotropic magnetic field of 47400 A/m or less. Preferably, the M-X-Y composition of the wide-band or the narrow-band magnetic loss material is an Fe—Al—O composition or an Fe—Si—O composition.

The resin-molded unit

1

is similar in appearance to that of the conventional product but is superior in effect. Specifically, even in occurrence of a harmonic current as an undesired harmonic having a frequency ranging from several tens MHz to several GHz, such high-frequency can be sufficiently attenuated by the high-frequency current suppressor

5

. As a result, production of a high-frequency noise can be prevented so as to remove an adverse affect by the high-frequency noise.

As the high-frequency current suppressor

5

, use is made of a thin-film magnetic substance which is small in volume and therefore requires less space and which is a magnetic loss material having a large imaginary part (i.e., a “magnetic loss term”) μ″ of relative permeability so as to provide effective protection against undesired radiation. As a magnetic substance which shows large magnetic loss, a granular magnetic material is known. Specifically, in case where the concentration of magnetic metal particles in the granular magnetic material falls within a particular range, excellent magnetic loss characteristic can be obtained in a high-frequency region.

Next, description will be made as to granular structure and production methods of M-X-Y magnetic composition.

Referring to

FIG. 2

in which schematically shows the granular structure of M-X-Y magnetic composition, particles

11

of metallic magnetic material M are uniformly or evenly distributed in a matrix

12

consisting of X and Y.

Referring to

FIG. 3A

, a sputtering apparatus shown therein was used for producing samples in the following examples and comparative examples. The sputtering apparatus has a conventional structure and comprises a vacuum container

20

, a shutter

21

, an atmospheric gas source

22

, a substrate or a glass plate

23

, chips

24

(X or X-Y), a target

25

(M), an RF power source, and a vacuum pump

27

. The atmospheric gas source

22

and the vacuum pump

27

are connected to the vacuum container

20

. The substrate

23

confronts to the target

25

on which chips

24

are disposed. The shutter

21

is disposed in front of the substrate

21

. The RF power source

26

is connected to the target

25

.

Referring to

FIG. 3B

, a vapor deposition apparatus shown therein was also used another apparatus for producing samples in the following examples and comparative examples. The vapor deposition apparatus has a conventional structure and has vacuum container

20

, atmospheric gas source

22

, and vacuum pump

27

similar to the sputtering apparatus but has a crucible

28

including materials (X-Y) in place of chips

24

, target

25

and RF power source

26

.

EXAMPLE 1

A thin film of M-X-Y magnetic composition was made on a glass plate by use of the sputtering apparatus shown in

FIG. 3A

at a sputtering condition shown in Table 1.

TABLE 1

Vacuum degree before sputtering

<1 × 10

−6

Torr

Atmosphere

Ar gas

Electric Power

RF

Targets

Fe (diameter of 100 mm) and

Al

2

O

3

chip (120 pieces)

(chip size: 5 mm × 5 mm × 2 mm)

The film sample 1 produced was analyzed by a fluorescent X-ray spectroscopy and confirmed as a film of a composition Fe

72

Al

11

O

17

. The film sample 1 had 2.0 micrometer (μm) in thickness, 530 micro ohm centimeters (μΩ•cm) in DC specific resistance, 18 Oe in anisotropy field (Hk), and 16,800 Gauss in saturation magnetization (Ms).

A percent ratio of the saturation magnetization of the film sample 1 and that of the metallic material M itself {Ms(M-X-Y)/Ms(M)}×100 was 72.2%.

In order to measure a permeability frequency response, the film sample 1 was formed in a ribbon like form and inserted in a coil. Under application of a bias magnetic field, an impedance variation of the coil was measured in response to frequency change of AC current applied to the coil. The measurement was several times for different values of the bias magnetic field. From the measured impedance variation in response to frequency variation, the permeability frequency response (μ″-f response) was calculated and is shown in FIG.

4

. It will be noted from

FIG. 4

that the imaginary part of relative permeability has a high peak or the maximum value (μ″

max

) and rapidly falls either side of the peak. The natural resonance frequency (f(μ″

max

)) showing the maximum value (μ″

max

) is about 700 MHz. From the μ″-f response, a relative bandwidth bwr was determined as a percentage ratio of bandwidth between two frequency points which shows the imaginary part of relative permeability as a half value μ″

50

of the maximum value μ″

max

, to center frequency of said bandwidth. The relative bandwidth bwr was 148%.

EXAMPLE 2

In a condition similar to that in Example 1 but using of 150 Al

2

O

3

chips, a film sample 2 was formed on a glass plate.

The film sample 2 produced was analyzed by a fluorescent X-ray spectroscopy and confirmed as a film of a composition Fe

44

Al

22

O

34

. The film sample 2 had 1.2 micrometer (μm) in thickness, 2400 micro ohm centimeters (μΩ•cm) in DC specific resistance, 120 Oe in anisotropy field (Hk), and 9600 Gauss in saturation magnetization (Ms). It will be noted that film sample 2 is higher than film sample 1 in the specific resistance.

A percent ratio of the saturation magnetization of the film sample 2 and that of the metallic material M itself {Ms(M-X-Y)/Ms(M)}×100 was 44.5%.

The μ″-f response of film sample 2 was also obtained in the similar manner as in Example 1 and shows in FIG.

5

. It is noted that the peak has also a high value similar to that in film sample 1. However, the frequency point at the peak, or the natural resonance frequency is about 1 GHz and the imaginary part of relative permeability gradually falls either side of the peak so that the μ″-f response has a broadband characteristic.

A relative bandwidth bwr of film sample 2 was also confirmed as 181% by the similar way as in Example 1.

COMPARATIVE EXAMPLE 1

In a condition similar to that in Example 1 but using of 90 Al

2

O

3

chips, a comparative sample 1 was formed on a glass plate.

The comparative sample 1 produced was analyzed by a fluorescent X-ray spectroscopy and confirmed as a film of a composition Fe

86

Al

6

O

8

. The comparative sample 1 had 1.2 micrometer (μm) in thickness, 74 micro ohm centimeters (μΩ•cm) in DC specific resistance, 22 Oe in anisotropy field (Hk), 18,800 Gauss in saturation magnetization (Ms), and 85.7% in a percent ratio of the saturation magnetization of the comparative sample 1 and that of the metallic material M itself {Ms(M-X-Y)/Ms(M)}×100, and was 44.5%.

The μ″-f response of comparative sample 1 was also obtained in the similar manner as in Example 1, and is shown in FIG.

6

. It will be noted from

FIG. 6

that the imaginary part μ″ of relative permeability of the comparative sample 1 has a high peak at a frequency about 10 MHz but rapidly reduces at the higher frequency range than 10 MHz. It can be supposed that this reduction is caused by generation of eddy current due to the lower specific resistance.

COMPARATIVE EXAMPLE 2

In a condition similar to that in Example 1 but using of 200 Al

2

O

3

chips, a comparative sample 2 was formed on a glass plate.

The comparative sample 2 produced was analyzed by a fluorescent X-ray spectroscopy and confirmed as a film of a composition Fe

19

Al

34

O

47

. The comparative sample 2 had 1.3 micrometer (μm) in thickness, 10,500 micro ohm centimeters (μΩ•cm) in DC specific resistance.

The magnetic characteristic of comparative sample 1 exhibited superparamagnetism.

EXAMPLE 4

A thin film of M-X-Y magnetic composition was made on a glass plate by the reactive sputtering method using the sputtering apparatus shown in

FIG. 3A

at a sputtering condition shown in Table 2. The partial pressure ratio of N

2

was 20%. The thin film was heat-treated at a temperature of 300° C. for two hours in vacuum under magnetic field and obtained a film sample 4.

TABLE 2

Vacuum degree before sputtering

<1 × 10

−6

Torr

Atmosphere

Ar + N

2

gas

Electric Power

RF

Targets

Fe (diameter of 100 mm) and

Al chip (150 pieces)

(chip size: 5 mm × 5 mm × 2 mm)

The properties of film sample 4 are show in Table 3.

TABLE 3

Film thickness

1.5 μm

{Ms(M-X-Y)/Ms(M)} × 100

51.9%

μ″

max

520

f(μ″

max

)

830 MHz

bwr

175%

EXAMPLE 5

A thin film of M-X-Y magnetic composition was made on a glass plate by using the sputtering apparatus shown in

FIG. 3A

at a sputtering condition shown in Table 4. The thin film was heat-treated at a temperature of 300° C. for two hours in vacuum under magnetic field and obtained a film sample 5.

TABLE 4

Vacuum degree before sputtering

<1 × 10

−6

Torr

Atmosphere

Ar gas

Electric Power

RF

Targets

Co (diameter of 100 mm) and

Al

2

O

3

chip (130 pieces)

(chip size: 5 mm × 5 mm × 2 mm)

The properties of film sample 5 are show in Table 5.

TABLE 5

Film thickness

1.1 μm

{Ms(M-X-Y)/Ms(M)} × 100

64.7%

μ″

max

850

f(μ″

max

)

800 MHz

bwr

157%

EXAMPLE 6

A thin film of M-X-Y magnetic composition was made on a glass plate by the reactive sputtering method using the sputtering apparatus shown in

FIG. 3A

at a sputtering condition shown in Table 6. The partial pressure ratio of N

2

was 10%. The thin film was heat-treated at a temperature of 300° C. for two hours in vacuum under magnetic field and obtained a film sample 6.

TABLE 6

Vacuum degree before sputtering

<1 × 10

−6

Torr

Atmosphere

Ar + N

2

gas

Electric Power

RF

Targets

Co (diameter of 100 mm) and

Al chip (170 pieces)

(chip size: 5 mm × 5 mm × 2 mm)

The properties of film sample 6 are show in Table 7.

TABLE 7

Film thickness

1.2 μm

{Ms(M-X-Y)/Ms(M)} × 100

32.7%

μ″

max

350

f(μ″

max

)

1 GHz

bwr

191%

EXAMPLE 7

A thin film of M-X-Y magnetic composition was made on a glass plate by using the sputtering apparatus shown in

FIG. 3A

at a sputtering condition shown in Table 8. The thin film was heat-treated at a temperature of 300° C. for two hours in vacuum under magnetic field and obtained a film sample 7.

TABLE 8

Vacuum degree before sputtering

<1 × 10

−6

Torr

Atmosphere

Ar gas

Electric Power

RF

Targets

Ni (diameter of 100 mm) and

Al

2

O

3

chip (140 pieces)

(chip size: 5 mm × 5 mm × 2 mm)

The properties of film sample 4 are show in Table 9.

TABLE 9

Film thickness

1.7 μm

{MS(M-X-Y)/Ms(M)} × 100

58.2%

μ″

max

280

f(μ″

max

)

240 MHz

bwr

169%

EXAMPLE 8

A thin film of M-X-Y magnetic composition was made on a glass plate by the reactive sputtering method using the sputtering apparatus shown in

FIG. 3A

at a sputtering condition shown in Table 10. The partial pressure ratio of N

2

was 10%. The thin film was heat-treated at a temperature of 300° C. for two hours in vacuum under magnetic field and obtained a film sample 8.

TABLE 10

Vacuum degree before sputtering

<1 × 10

−6

Torr

Atmosphere

Ar + N

2

gas

Electric Power

RF

Targets

Ni (diameter of 100 mm) and

Al chip (100 pieces)

(chip size: 5 mm × 5 mm × 2 mm)

The properties of film sample 10 are show in Table 11.

TABLE 11

Film thickness

1.3 μm

{Ms(M-X-Y)/Ms(M)} × 100

76.2%

μ″

max

410

f(μ″

max

)

170 MHz

bwr

158%

EXAMPLE 9

A thin film of M-X-Y magnetic composition was made on a glass plate by using the sputtering apparatus shown in

FIG. 3A

at a sputtering condition shown in Table 12. The thin film was heat-treated at a temperature of 300° C. for two hours in vacuum under magnetic field and obtained a film sample 9.

TABLE 12

Vacuum degree before sputtering

<1 × 10

−6

Torr

Atmosphere

Ar gas

Electric Power

RF

Targets

Fe (diameter of 100 mm) and

TiO

2

chip (150 pieces)

(chip size: 5 mm × 5 mm × 2 mm)

The properties of film sample 9 are show in Table 13.

TABLE 13

Film thickness

1.4 μm

{Ms(M-X-Y)/Ms(M)} × 100

43.6%

μ″

max

920

f(μ″

max

)

1.5 GHz

bwr

188%

EXAMPLE 10

A thin film of M-X-Y magnetic composition was made on a glass plate by the reactive sputtering method using the sputtering apparatus shown in

FIG. 3A

at a sputtering condition shown in Table 14. The partial pressure ratio of O

2

was 15%. The thin film was heat-treated at a temperature of 300° C. for two hours in vacuum under magnetic field and obtained a film sample 10.

TABLE 14

Vacuum degree before sputtering

<1 × 10

−6

Torr

Atmosphere

Ar + O

2

gas

Electric Power

RF

Targets

Fe (diameter of 100 mm) and

Si chip (130 pieces)

(chip size: 5 mm × 5 mm × 2 mm)

The properties of film sample 10 are show in Table 15.

TABLE 15

Film thickness

1.5 μm

{Ms(M-X-Y)/Ms(M)} × 100

55.2%

μ″

max

920

f(μ″

max

)

1.2 GHz

bwr

182%

EXAMPLE 11

A thin film of M-X-Y magnetic composition was made on a glass plate by using the sputtering apparatus shown in

FIG. 3A

at a sputtering condition shown in Table 16. The thin film was heat-treated at a temperature of 300° C. for two hours in vacuum under magnetic field and obtained a film sample 11.

TABLE 16

Vacuum degree before sputtering

<1 × 10

−6

Torr

Atmosphere

Ar gas

Electric Power

RF

Targets

Fe (diameter of 100 mm) and

HfO

3

chip (100 pieces)

(chip size: 5 mm × 5 mm × 2 mm)

The properties of film sample 11 are show in Table 17.

TABLE 17

Film thickness

1.8 μm

{Ms(M-X-Y)/Ms(M)} × 100

77.4%

μ″

max

1800

f(μ″

max

)

450 MHz

bwr

171%

EXAMPLE 12

A thin film of M-X-Y magnetic composition was made on a glass plate by using the sputtering apparatus shown in

FIG. 3A

at a sputtering condition shown in Table 18. The thin film was heat-treated at a temperature of 300° C. for two hours in vacuum under magnetic field and obtained a film sample 12.

TABLE 18

Vacuum degree before sputtering

<1 × 10

−6

Torr

Atmosphere

Ar gas

Electric Power

RF

Targets

Fe (diameter of 100 mm) and

BN chip (130 pieces)

(chip size: 5 mm × 5 mm × 2 mm)

The properties of film sample 12 are show in Table 19.

TABLE 19

Film thickness

1.9 μm

{Ms(M-X-Y)/Ms(M)} × 100

59.3%

μ″

max

950

f(μ″

max

)

680 MHz

bwr

185%

EXAMPLE 13

A thin film of M-X-Y magnetic composition was made on a glass plate by using the sputtering apparatus shown in

FIG. 3A

at a sputtering condition shown in Table 20. The thin film was heat-treated at a temperature of 300° C. for two hours in vacuum under magnetic field and obtained a film sample 13.

TABLE 20

Vacuum degree before sputtering

<1 × 10

−6

Torr

Atmosphere

Ar gas

Electric Power

RF

Targets

Fe

50

Co

50

(diameter of 100 mm) and

Al

2

O

3

chip (130 pieces)

(chip size: 5 mm × 5 mm × 2 mm)

The properties of film sample 13 are show in Table 21.

TABLE 21

Film thickness

1.6 μm

{Ms(M-X-Y)/Ms(M)} × 100

59.3%

μ″

max

720

f(μ″

max

)

1.1 GHz

bwr

180%

EXAMPLE 14

A thin film of M-X-Y magnetic composition was made on a glass plate by using the vapor deposition apparatus shown in

FIG. 3B

at a condition shown in Table 22. The thin film was heat-treated at a temperature of 300° C. for two hours in vacuum under magnetic field and obtained a film sample 14.

TABLE 22

Vacuum degree before sputtering

<1 × 10

−6

Torr

Atmosphere flowing rate

O

2

at 3.0 sccm

Elements in crucible 28 and 29

Fe and Al

The properties of film sample 14 are show in Table 23.

TABLE 23

Film thickness

1.1 μm

{Ms(M-X-Y)/Ms(M)} × 100

41.8%

μ″

max

590

f(μ″

max

)

520 MHz

bwr

190%

Now, description will be made as to tests relating to noise suppressing effect of sample films and comparative samples, using a test apparatus shown in FIG.

7

.

A test piece was film sample 1 with dimensions of 20 mm×20 mm×2.0 μm. For a comparison, a sheet of known composite magnetic material having dimensions of 20 mm×20 mm×1.0 mm. The composite magnetic material comprising polymer and flat magnetic metal powder dispersed in the polymer. The magnetic metal powder comprises Fe, Al and Si. The composite magnetic material has a permeability distribution in quasi-microwave range and has the maximum value of the imaginary part of relative permeability at a frequency about 700 MHz. Table 24 shows magnetic properties of both of the test piece and comparative test piece.

TABLE 24

Film sample 1

Comparative test piece

μ″/700 MHz

about 1800

about 3.0

bwr

148

196

As seen from Table 24, the film sample 1 is about 600 times more than comparative test piece in the maximum value of imaginary part of relative permeability. Since the noise suppressing effect is generally evaluated from a value of a product (μ″

max

×δ) of the maximum value μ″

max

of the imaginary part of relative permeability and thickness of the piece δ, the thickness of the comparative test piece of the composite magnetic material sheet was selected 1 mm so that the both of test pieces have the similar values of (μ″

max

×δ).

Referring to

FIG. 7

, the test apparatus comprises a micro-strip line

61

having two ports, coaxial cables

62

connected to the two ports, and a network analyzer (not shown) connected across the two ports. The micro-strip line

61

has a line length of 75 mm and a characteristic impedance of 50 ohms. The test piece

63

was disposed at a region

64

on the micro-strip line

61

and the transmission characteristic S

21

was measured. The frequency response of S

21

are shown in

FIGS. 8A and 8B

for film sample 1 and the comparative sample, respectively.

With respect to use of film sample 1, it will be noted from

FIG. 8A

that S

21

reduces above 100 MHz, becomes to the minimum of −10 dB at a frequency of 2 GHz and then increases above 2 GHz. On the other hand, with respect to use of comparative sample, it will be noted from

FIG. 8B

that S

21

gradually reduces and becomes to the minimum of −10 dB at a frequency of 3 GHz.

The results demonstrate that S

21

is dependent on the frequency distribution of the permeability and that the noise suppressing effect is dependent on the product of (μ″

max

×δ).

Now, providing that the magnetic sample forms a distribution constant circuit having a length of l as shown in

FIG. 9A

, an equivalent circuit was calculated for a unit length of Δl from transmission characteristics S

11

and S

21

, as shown in FIG.

9

B. Then, the equivalent circuit for the length l was obtained from the equivalent circuit for the unit length Δl , as shown in FIG.

9

C. The equivalent circuit of the magnetic sample comprises series inductance L and resistance R and parallel capacitance C and conductance G, as shown in FIG.

9

C. From this, it will be understood that the change of transmission characteristic of the micro-strip line caused due to disposition of the magnetic substance on the micro-strip line is mainly determined by the equivalent resistance R added in series.

In view of the above, a frequency response of the equivalent resistance R was measured. The measured data were shown in

FIGS. 10A and 10B

for the film sample 1 and the comparative sample, respectively. It will be noted from these figures that the equivalent resistance R gradually reduces in the quasi-microwave range and is about 60 ohms at about 3 GHz. It is seen that the frequency dependency of the equivalent resistance R is different from that of the imaginary part of relative permeability which has the maximum value at about 1 GHz. It will be supposed that this difference will be based on the gradual increase of a ratio of the product and the sample length to the wavelength.

Resin-molded unit including an electronic circuit component

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