GB2251732A - Electromagnetic bead core filter manufacture - Google Patents

Abstract

An EMI bead core filter to suppress noise has an impedance which increases with frequency, and comprises a ferrite core 3, a wire 7 and an epoxy powder coating layer P. The layer is deposited on the upper portion of the core 3 and on a bend portion 8 of the wire to adhere the core and the wire. The filter is produced by bending the wire 7 and then inserting it into the core 3 to form a prefilter 1' which is supported on a tape 11, 13. The portion 8 of the prefilter 1' is then heated and coated with epoxy powder from a chamber 27. The filter is then packaged and hardened. The coating is accomplished by heating at 380 DEG C initially, and then at 335 DEG C to 340 DEG C for three more times. <IMAGE>

Description

-, -, 1 EMI BEAD CORE FILTER, PROCESS AND APPARATUS THEREOF

FIELD OF INVENTION

This invention relates to an EMI (electro magnetic interference) bead core filter, especially to an EMI bead core filter which is constructed to suppress or reduce a noise by utilizing the characteristics of increasing the impedance in high-frequency, a process for the preparation and an apparatus for the preparation of such noise filter.

BACKGROUND OF INVENTION

Recently, digital electronic instruments are rapidly progressed in various field together with the development of the semiconductor Industrials, especially digital electronic instruments for OA (office automation), FA(factory automation), cars, CD(compact disk), DAT (digital audio tape) and video tape are more rapidly progressed.

In general, these digital electronic instruments are commonly generated an electronic noise, and the noise may cause an electro magnetic Interference (EMI, it is simply called as "noise" by any person) and the EM! may make mulfunctions or effects of reducing the S/N ratio of other hearby electronic equipment or appliance through the supply line or electrical radiation.

Therefore, the like noise is recently become a social problem and 2 it is proceeding to restrict the diffusion of the noise under the legal in the world. For examples, to restrict the noise, under the FCC(federal communication commission) of the United States of America Docket No.20780 was issued on October, 1979 and also administerred under the CSA in Canada and the VDE in Germany. - A filter is utilized as an electronic part to protect or reduce such noise and the generally characteristics of the filter are illustrated in Figs.l(A), l(B) and i(C), wherein Fig.l(A) shows to the one of a simple or coil filter, Fig.l(B) shows to the one of a L-type filter and Fig.l(C) shows to the one of 7--type or T-type filter.

Hitherto, the three-terminal capacitor is usually used to protec or reduce a noise in low-frequency and the two-terminal capacitor or coil is often used to protect or reduce a noise in high-frequency. However they have shown many problems such as, for examples, occuring the residual inductance based on the lead wire and electrode structure, enlarging the -suspended capacity inter wire wound, appearing the resonance point from several MHz to several tens MHz, and rapidly decreasing the effect of reducing the noise in high-frequency. Additionally, a lead through capacitor which does not occur the residual inductance in high-frequency may be applied, however it has the complexity in preparing them and increased the unit cost of production thereof. Accordingly, a lead through capacitor can be only applied to use restrictively [Refs.:E.P.Pat. PubIn. Nos.275093 and 276684, U.S.Pat. 4370698 and K.R.Pat. PubIn. No. 90-2514 etc.] Recently, it does not described in the literatures but a filter is practically made of combination of ferrite core and lead wire. Bead cores are often used as a component for a counter-noise for preventing 3 EMI (electro magnetic interference). in the cases, ferrite cores having a small eddy current loss and a high magmetic permeability are also used, because ferrite cores are very cheap and it can be made a noise filter having a relatively structure and-few side effects such as, distorted signals and extraordinary oscillation. These known filters consisted of ferrite core and lead wire are illustrated in Figs. 2(A) to 2(D). A filter illustrated In Fig.2(A) is an axial type one and filters illustrated in Figs. 2(B),2(C) and 2(D) are radial type one. As shown in Figs.3(A) and 3(B), to bond a ferrite core (201) and a lead wire (202), liquid bonding agent (203) such as liquid poste or liquid starch is used t the top of the hole (204) or all the hole (204) of the core (201). However, the filter illustrated in Fig.3(A) has a characteristic of a high impedance (IZJ) along with a weak mechanical strength, z.,n the contrary, the filter illustrated in Fig.3(B) has a characteristic of a low impedance along with a strong mechamical strength. Therefore, it desires to develop a new filter having a high impedance as well as a strong mechanical strength, by a simple process.

SUMMARY OF THE INVENTION

The EMI bead core filter of this invention consists of a ferrite core, a lead wire and a coating layer of an epoxy powder, and is prepared by bending a lead wire and inserting a bending lead wire into the hole of the ferrite core a;.id then heating, melting and coating with epoxy powder four timc-s at. about 340" to 38OrC.

4 An object of this invention is to provide a new EMI bead core filter having a high impedance as well as an excellant mechanical strength and having a relatively small size filter applicable automatically to the PCB(printed circuit board) by an auto-mounting 5 machine.

Further objects of this invention is to provide a suitable process to be workable on a large scale in preparing and a coating apparatus thereof.

BRIF DESCRIPTION OF THE DRAWINGS

Figs. 1(A) to 1(C) illustrate the generally characteristics of the conventional filter.

Figs. 2(A) to 2(D) are front views of the variety embodiments of the EMI bead core filter of the prior art.

Figs. 3(A) and 3(B) are enlarged sectional views of the variety enbodiments of the EMI bead core filter of the prior art.

Fig. 4 is a sectional view of the EMI'bead core filter of this invention.

Figs. 5 To 8 illustrate the embodiments in each step of the process of this invention; Fig.5 is a front view of prefilter before coating with epoxy powder, Fig.6 is a-front view of the prefilter and an auto-coating apparatus in coating with epoxy powder, Fig.7 is a plan view of a heating apparatus and Fig.8 is an enlarged front view of the prefilter to explain in detail the coating process shown in Fig.6.

Figs.9 and 10 are schematic views to explain the coating conditions in coating process of this invention.

DETAILED DESCRIPTION OF THE INVENTION

This Invention relates to an EMI bead core filter, especially to an EMI bead core filter which is constructed to suppress or reduce a noise by utilizing the characteristics of increasing the impedance in 10 highfrequency, a process for the preparation and an equipment for the pneparation of such noise filter.

The EMI bead core filter (hereinafter referred to as "filter") of this invention comprising a ferrite core, a lead wire and a coating layer of an epoxy powder, further details and advantages of this is invention may be learned from the following detailed description in connection with the accompanying drawings.

The filter(l) of this invention was shown in Fig.4 and the filter comorising a ferrite core (3) having a hole (5) at the canter, a lead wire (7) bent by a fixed type ahd a coated layer with an epoxy powder resin (P; hereinafter referred to as "powder") to adhere between the core (3) with the wire (7).

The said powder (P) is used to fix and seal tightly up the upper side and the upper hole of the core (3) and the bending portion of the wire (7). The ingredients of the powder (P) consist of about 47 weight % of Aluminium (A1), 48 weight % of Silicon (Si) and 5 weight % of Cl, Ag, Sb, Ti, Fa and Co.

The coating process in carrying out this invention is a very 6 important process belonging to a high and elaborate technology in this industrial field. The impedance of the filter depends on the coating process, it generally shown a 25% to 35% reduction of the value of the standard for the impedance (M) according to the general bonding process. Though, the value of the standard obtains in case of having no any certain obstruction in the hole of the core (3), however it is necessary to fix the core and the wire in order to insert in the auto-mounting machine and to prevent of moving the core. Accordingly, a bonding agent such as a liquid paste or starch has been unavoidably applied in shortening the impedance (IZI). A bonding agent such as liquid epoxy consisted aluminium oxide (A120: as an ingredient may be also applied, but the impedance (IZI) is also decreased by increasing up the magnetic resistance on the reason.of the mass of Aluminium.

A process for the preparation of the filter in this invention is described in detail in the following example.

Example

The 1st step (forming and inserting):

This step is to insert a lead wire (7) into the hole (5) of the ferrite core (3). The step is carried out by an EMI filter auto-machine and included a series of the forming and inserting stage. The operations in these stages are almost and simultaneously carried 25 out on the whole.

The lead wire (7) was cutted by a regular length and bent by the type of " U "' substantial.ly, then inserted into the hole (5) of the 7 core (3) to obtain a prefilter (not adhered between lead wire and core).

The afore-mentioned EMI filter auto-machine comprises a cylindric and vertical drum for moving the core (3) in a regular intervals, an air cylinder device for inserting in sequence the core (3) into the vertical drum, a forming device for bending to form U - shaped wire and a vibration feeder for suppling the core (3).

The 2nd step (tapping and punching):

The obtained prefilter which was simply inserted the wire (7) into the core (3), was tapped on the tape and punched to make a sproket hole in order to be applicable by an auto-mounting machine. That is, the prefilter (1') was tapped on a paper tape (11) and a thermal tape (13) as shown in Fig.5. The adhesive portion (9) of the end of the wire (7) %as fixed by the paper tape (11) and thermal tape (13). After carried out this invention, the adhesive portion (9) may become a soldering region in case of inserting actually to a PCB(printed circuit board). A tack adhesive was applied in the inner part of the thermal tape (13) and the wire (7) was adhered by complexing with the heating by a thermal adhesive machine which is able to control at about 400"C of the heating temperature. It is desirable that the thermal tape (13)has an adhesive effect at least at 2500C up of the temperature.

8 I 1he 3rd step (coating) The prefilter which tapped and punched according to the 2nd step was coated with an epoxy powder (P). As shown in Fig.6, the coating of the bending portion (8) of the wire (7) was carried out by the coating apparatus (21) during moving in the direction of the arrow, under condition of the style of standing on head of the prefilter(l').

The coating apparatus (21) comprises a vacuum fan (23) operating by a motor (M) at the top of the-apparatus, a series of vacuum device having a vacant column (25) connected with a powder chamber (27), an electro control box 30) and a heater having a hot wire (33). A body of rotation (28) was constructed in the inner of the powder chamber (27). In proceeding of the coating by the coating apparatus, because of the coating was carried out under condition of the style of standing on head of tapped and punched prefilter, the core (3) automa:ically moved round the bottom of the bending partion (8) of the wire (7) upon the weight of core (3) itself. The embodiment of the heater (31) whicn applied to heat the prefilter (1') is shown in Fig.7. In Fig.7 the mark H represents an air hose-connected with an air blower (not shown) and the mark W represents a conducting wire which supplied an electric power to the hot wire (33).

The coating- in this invention is accomplished by carrying repeatedly out four (4) times. A paper tape (11) which adhered the prefilter (1'), was:assed through a space between two heaters (31) and (31) in order to heat the core (3). The prefilter was preheated at about 380 C of the first heating temperature and dipped into the epoxy powder (P), next heated at about 335 to 340 C of the second, third and fourth heating temperature to melt and coated with expoxy 9 powder (P). After heated from the hot wire (33) of the heater (31) the temperature for the preheating was controlled by the hot wind of the air. Two heaters (31),(31) have the same figure and function each other, but it is more desirable that the one of the two heaters is an 5 opening and shutting heater.

The ingredients of the epoxy powder (P) in this invention consist of 47 weight % of Al, 48 weight % of Si and the residuals of Cl, Ag, Sb, Ti, Fe and Co and the coating process more explained as the followings accompanying with the Figs. 7 and 8. The body of rotation '(28) in the inner of the powder. chamber (27) was rotated on the direction of the arrow because of connecting with the axis of rotation (29) by a motor (not shown), that is, on the same direction of the moving paper tape (11).

A powder feeder (27a) and a powder out-let (27b) which connected with a.vacuum hose (27C) are constructed in the rear of the powder chamber (27). The va:ant column (25) is led to the inner part of the powder chamber (27) and the powder can be refluxed under vacuum in the column (25) and powder chamber (27). The heaters (31) are constructed in the number of corresponding with the number of powder chamber at the frount of the powder chamber (27), that is to say, the heaters are located at the front portion of the body of rotation (28) on setting a standand of the direction of the moving paper tape (11). The head portion of the prafilter (I') was preheated by the heater (31). The prefilter itself was heated at a lower temperature the preheating temperature because the paper tape (11) was moved into the direction of the arrow and the head of the prefilter and the ferrite core (3) were preheated by the heater (31). The heated prefilter (1') was contacted with the epoxy powder (P) on the top position of the body of rotation (28), and the head of the filter-was dipped into the powder (P), then the powder (P) was melted and the head of the prefilter was coated. The afore-mentioned coating process was repeatedly carried out four (4) times by the coating appaeatus to completely adhere the core (3) and the wire (7).

Fig.9 is a schematic view to explain the amounts of the powder (P) for the coating. The length (L) from the center of the axis of rotation (29) in the body of rotation (28) to the end of the head of the prefilter becomes shorter in proportion to the repeated times of the coating. According to this invention the coating was carried out four times on the head of the prefilter (1') to obtain the filter (1) having a uniform coating layer, The degree of an angle ((3) of the body of rotation (28) was illustrated in Fig.10. The body of rotation (28) was constructed so as to have a slant on the center Iine (CL) of the paper tape (11).

The afore-mentimed length (L) and angle ( G) may b e changed according to the model of the filter.

The 4th step (packaging):

After coated_according to the coating step the filter (1) was taped and reel packaged to be able to apply to the auto-mounting machine. The packaging was carried out by reeling the paper tape (11) round a body of winding (not shown in Figs.) The Sth step (hardening):

The packaged filter was hardened at 1500C for 45 to 50 minutes in 11 oven to increase the strength of the filter.

The characteristics of the filter (1) obtained according to this invention were measured by an impedance analyzer (Hewlett packard Co., U. S.A.) and the results are descrbed in table 1.

In addition, the characteristics of the filter obtained according to the comparative example were measured - by the afore-mentioned analyzer and the results are described in table 2.

Table 1 (The invention) No.of test IZI M) I.R.M2) Terminal strength(Kg) 1 109.23 3 X 104 3.1 2 109.58 200 X 104 4.4 3 109.70 40 X 104 5.3 4 108.58 800 X 104 5.3 109.64 30 X 104 3.4 6 107.80 7c) X 104 3.6 ? 108.42 50 X 104 4.1 8 109.22 160 X 104 3.6 9 107.90 20 X 104 3.2 107.23 15 X 104 3.0 1-1 107.66 30 X 104 3.1 12 107.18 30 X 104. 3.5 13 108.40 60 X 104 3.7 14 105.31 17 X 104 4.1 12 (continued) No.of test IZI( Q) I.R.(M92) Terminal strength(Kg) is 107.58 7 X 104 3.0 16 108.58 30 X 104 3.9 17 105.34 26 X 104 4.2 18 105.34 80 X 104 3.1 19 107.43 180 X 104 3.8 108.89 400 X 104 3.7 X 107.97 111.23 X 104 3.85 S 1.33 188.56 X 104 0.80 min. 105.34 26 X 104 3.0 max. 109.70 800 X 104 5.7 Remarks:

- Use the epoxy powder as an adhesive agent.

- The powder: 47 weight % of Al, 48 weight % of SI and 5 weigh % of Cl, Ag, Sb, Ti, Fe and Co.

- Analyzing: 10OHzV20C The appearance and soldering of the filter are excellent.

13 Table 2 (The comparative) No.of test 1 Z1 (Q) I.R. (MQ). Terminal 1 102.86 50 X 104 2 98.62 16 X 104 2.0 3 85.29 500 X 104 2.0 4 85.39 3,000 X 104 2.6 86.81 90 X 104 2.4 6 84.08 90 X 104 2.7 7 106.50 300 X 104 5.9 8 92.70 O X 104 5.4 9 88.28 200 X 104 5.5 87.60 400 X 104 3.2 11 87.79 20 X 104 4.8 12 96.08 300 X 104 2.6 13 87.74 2 X 104 2.4 14 98.13 11 X 104 2.4 84.70 200 X 104 2.3 is 100.10 400 X 104 2.7 17 88.35 11 X 104 3.4 18 101.42 300 X 104 3.9 19 86.55 6 X 104 2.5 102.27 200 X 104 2.4 X 92.56 308.30 X 104 3.25 S 7.15 635.74 X 104 1.18 min. 84.08 2 X 104 2.0 max. 106.50 3,000 X 104 5.9 strength(Kg) 2.9 14 Remarks: - Use the liquid epoxy as an adhesive agent The liquid: 80 weight % of Al, 8 weight % of Si and 12 weight % of Cl, Aq, Sb, Ti, Fe and Co.

- Analyzing: 10OHz/20 C The appearance-and soldering of the filter are excellent.

- The process for the preparation of the comparative example is the same with that of this invention.

As shown from the analytic datadescribed in tables 1 and 2, IZI values of the filter (1) prepared by the process described in Example of this invention measured in 105.34 (min.) and 109.70 (max.), whereas those of the comparative example measured in 84.08 (min.) and 106.50 (max.). As the results of analyzing, it was confirmed that the filter of this invention has a higher impedance.

jzJ - f values of the filter according to this invention as well as those of the comparative example were measured by an impedance analyzer (H.P. co., Model 4194 Impedance Analyzer) and the results accompanying with the standard value are descrbied in table 3.

is Table 3

No.of test The Invention The comparative Standard 1 104 83 106 2 106 88 107 3 104 83 108 4 105 85 108 105 83 106 6 105 81 106 7 106 81 105 8 105 87 106 9 106 97 107 105 89 106 11 105 84 106 12 105 83 106 13 104 93 106 14 104 97 106 103 85 107 16 105 97 106 17 105 84 107 18 105 93 105 19 104 85 106 104 97 104 X 104.8 87.8 106.3 S 0.76.5.6 0.79 min. 103 81 105 max. 106 97 108 16 As shown from the analytic data described in table 3, IZI f values of this invention and the comparative measured in 104.8 and 87.8, respectively, and the standard value of the filter which does not coated meased in 106.3. The differences of the standard deviation of this invention and the comparative are remarkable. Accordingly, as the results of analyzing, it was more concretely confirmed that the filter of this invention has a higher impedance. As shown in table 3, the mean deviations of this invention, the comparative and the standard also measured in 0.76, 5.6 and 0.79, respectively.

Accordingly, it was also confirmed that the filter of this invention has a high quality.

This invention provides the filter having a high impedance and a small size. When the filter according to this invention was applied to the printed circuit board, it is of great advantages to decrease the number of the filter, to take a small area for the unit area per filter, to be realized by an unmanned automatization in preparing, to be workable for the mass production, to have quite sufficient the competitive power and, to reproduce the prefilter by collecting the in ferior goods and removing the coating layer by- treating with a chemical agent and thR like.

Claims (20)

1. A filter comprising a hollow ferrite core and a wire extending through and being affixed to said core, wherein the wire has been affixed to said core by an epoxy resin.

2. An EMI bead core filter comprising a ferrite core having a hole, a lead wire having a bending portion and a coating layer deposited on the upper portion of said core and the bending portion of said wire to adhere between said core and said wire by coating with an epoxy resin.

3. A filter as claimed in Claim 1 or 2, wherein said epoxy resin is a powder and comprises Aluminium (A1) and Silicon (Si).

4. A filter as claimed in Claim 3, wherein said epoxy p6wder comprises 47% by weight of Al, 48% by weight of Si and 5% by weight % of Cl, Ag, Sb, Ti, Fe and/or Co.

5. A process of making a filter comprising the steps of:

(a) inserting a wire into a bore in a ferrite core to obtain a prefilter, (b) preheating at least part of the wire of said prefilter and coating at least said part of said wire with an epoxy resin to adhere said wire to said core, and (c) hardening the epoxy resin.

6. A process for the preparation of an EMI bead core filter comprising the steps of:

(a) bending a lead wire and inserting said wire into a hole of a ferrite core to obtain a prefilter, (b) tapping said prefilter on a paper tape with a thermal tape and punching to make a sprocket hole, (c) preheating the bending portion.of said prefilter and coating the upper portion of said wire with an epoxy resin to adhere between said core and said wire, (d) packaging by reeling a coated prefilter, and (e) hardening to obtain said filter.

7. A process as claimed in Claim 6, wherein said thermal tape has an adhesive effect at least up to 2500C.

8. A process as claimed in any of Claims 5 to 7, wherein said preheating is carried out at the temperature of 3800C for a first time, and at 3350 to 3400C for the second to fourth times.

9. A process as claimed in any of Claims 5 to 8, wherein'said coating is carried out under condition of the style of standing on head of said prefilter.

10. A coating apparatus for use in preparing a filter comprising a vacuum device having a vacuum fan operable by a motor, and arranged to apply suction to a vacuum column in communication with a chamber for epoxy resin, and heaters arranged in advance of said chamber.

11. An apparatus for coating in preparing an EMI bead core filter comprising the devices of:

(a) a vacuum device having a vacuum fan be operating by a motor, a vacant column and a vacuum hose, (b) a powder chamber connected with a vacant column and a body of rotation, and (c) two heaters each having a hot wire and an inlet of an air hose.

12. An apparatus as claimed in Claim 10 or 11, wherein each said heater has an air hose for the control of the heating temperature, whereby air can be blown through said air hose from an air blower.

13. An apparatus as claimed in any of Claims 10 to 12, wherein at least the one of said heaters is an opening and shutting heater.

14. An apparatus as claimed in any of Claims 10 to 13, wherein a rotatable body is mounted in said chamber and is arranged at an angle to a plane between the chamber and the vacuum device.

15. An apparatus as claimed in Claim 11, wherein said body of rotation is constructed so as to have a slant by the degree of an angle on the center line of a paper tape.

16. An apparatus as claimed in any of Claims 10 to 15, wherein the number of said heaters corresponds to the number of chambers.

17. A filter when made by an apparatus as claimed in any of Claims 10 to 16.

18. A filter substantially as hereinbefore described with reference to the accompanying drawings.

19. A process of making a filter substantially as hereinbefore described with reference to the accompanying drawings.

20. A coating apparatus for use in preparing a filter substantially as hereinbefore described with reference to the accompanying drawings.