JP3152350B2 - Manufacturing method of small choke coil - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a small choke coil mounted on a printed circuit board of a digital device and used for preventing unnecessary radiation noise in an electronic device.

[Conventional technology]

Conventionally, as shown in FIG. 6, this type of small choke coil has an external terminal 61 made of a ferrite bead core (hereinafter referred to as a bead core) 21 having a through hole 22 and a metal plate and subjected to a surface treatment such as solder plating. And the outer periphery thereof is sealed and molded with an exterior molding resin 62 made of an electrically insulating resin such as an epoxy resin, thereby positioning the bead core 21. The structure is such that small coils can be collectively obtained.

[Problems to be solved by the invention]

Conventionally, in such a small choke coil, there is a problem that a bead core is mechanically strained by sealing and molding.

That is, at the time of this sealing molding, as shown by the curve C in FIG. 5, the bead core originally has due to the mold distortion due to the curing shrinkage of the mold resin and the distortion due to the difference in the thermal expansion coefficient between the bead core and the mold resin. There has been a problem that the magnetic characteristics are greatly impaired, the impedance value is degraded, the characteristics are degraded, and the characteristics of the product are widely dispersed.

Conventionally, it has been reported that the application of a silicon resin has an effect of alleviating the deterioration of magnetic characteristics. However, by applying the silicon resin after inserting the lead frame into the bead core, the lead caused by resin dripping can be obtained. Outflow and adhesion to the terminal pieces easily occur, the coating thickness varies, and the effect of alleviating the deterioration of the magnetic characteristics varies. Conventionally, due to variations in the mold thickness of the exterior molding resin, when a small choke coil is mounted on a printed circuit board of a digital device and soldered, cracks are generated in the exterior molding resin due to applied heat and stress.

An object of the present invention is to provide a method for manufacturing a small choke coil in which characteristics are not deteriorated and variations in characteristics are extremely small.

B. Configuration of the Invention [Means for Solving the Problems] The present invention provides a metal thin strip-shaped lead terminal piece having a penetrating signal line, an arrowhead-shaped insertion portion at the tip thereof, and a base portion of a reinforcing frame. Are formed on the lead frame at regular intervals, and a bead core is preliminarily coated with a silicon-based resin by vacuum impregnation, etc. The outer mold resin added to the bead cores by holding at intervals, collectively penetrating the lead terminal pieces into a number of bead cores, integrally sealing and molding with an outer mold resin made of an electrically insulating resin A small choke coil which reduces the mechanical distortion caused by the mold and solves the above-mentioned problem.

That is, the present invention relates to a method for manufacturing a small choke coil having a large number of signal circuits, wherein a large number of Ni-Zn-based ferrite materials, each of which is provided with a protective film layer having a predetermined thickness by vacuum impregnation with a silicon-based resin, are used. The through-hole of the small diameter ferrite bead core passes through a large number of lead terminal pieces with small core positioning projections that are provided on the metal thin strip-shaped lead frame to form the external terminals. And cutting the lead terminal pieces.

[Action]

Before the ferrite bead core is inserted into the lead terminal piece, a protective film of a certain thickness is applied to the surface by vacuum impregnation with an elastic resin such as silicon resin, so it is sealed with an exterior molding resin. Even so, the strain applied to the ferrite bead core is reduced, and even with the same core dimensions, deterioration of the impedance particularly in a low frequency range can be prevented.

〔Example〕

 An embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a perspective view of a completed small choke coil according to the present invention, FIG. 2 is a perspective view of a bead core used in the present invention, FIG. 3 is an enlarged perspective view of a lead frame part used in the present invention, and FIG. FIG. 5 is a schematic diagram of the manufacturing process, and FIG. 5 is a characteristic diagram in which a change in impedance due to mechanical strain applied to a bead core when sealing molding is performed with a resin is measured in accordance with a frequency.

The bead core 21 is made of Ni-Zn as shown in FIG.
It is made of a ferrite material and usually has an outer diameter of 1 mm to 7 mm, a through hole of 0.3 mm to 6 mm, and a length of about 1 mm to 10 mm. The bead core 21 was entirely coated with a coating 23 having a thickness of 10 μm or more by vacuum impregnation with an electrically insulating resin having a rubber hardness of about 60 such as a silicone resin.

As shown in FIG. 3, the signal line is made of a non-magnetic metal plate such as stainless steel, copper-iron alloy, phosphor bronze,
It consists of a lead terminal piece 24 that has been subjected to a surface treatment such as solder plating, and has a terminal width of about 0.2 mm to 2 mm and a terminal thickness of about 0.1 mm to 0.3 mm.

The lead terminal piece 24 has an arrowhead-shaped insertion part 25 at the tip by precision sheet metal processing or photo etching processing,
A small core positioning projection 26 is provided in the vicinity of the base, and the base is connected by a reinforcing frame 27, and a plurality of the bases are provided at regular intervals to form a part of the lead frame 29. Further, the reinforcing frame 27 has a positioning hole 28.

Next, the assembly of the small choke coil will be described with reference to the schematic diagram of the manufacturing process shown in FIG.

First, a plurality of bead cores 21 indicated by an arrow A are arranged and held at a predetermined arrangement pitch by using a dedicated jig having a cross section of a V-shaped groove. By inserting the lead terminals, it is possible to easily and simultaneously insert the lead terminal pieces into a large number of bead cores simultaneously.

Furthermore, after inserting until the small core positioning projection 26 of the lead terminal piece shown by the arrow C contacts the bead core 21, it is removed from the dedicated jig.

Next, as shown by an arrow D, the entire lead frame 29 is mounted on a sealing mold and molded integrally with an epoxy-based, PPS-based, or polyester-based resin.

Next, as shown by the arrow E, the lead terminal piece 24 is cut, lead forming is performed, and electrical characteristics inspection and the like are performed to complete a small choke coil having a large number of signal circuits as shown in FIG. As shown in FIG. 5, it can be seen that the small choke coil of the present invention (curve B) has almost the same characteristics as before the sealing molding (curve A).

Therefore, in the small choke coil of the present invention as described above, a predetermined coating film can be applied to the entire surface of the bead core by vacuum impregnation or the like with the silicone resin in advance on the bead core. It is possible to provide a small-sized choke coil excellent in mass productivity with little variation in the relaxation effect.

C. Effects of the Invention [Effects of the Invention] As described above, according to the present invention, a predetermined coating is applied to the entire surface of the bead core in advance by vacuum impregnation or the like with an elastic resin such as a silicone resin on the bead core, and the through-hole of the bead core is formed. The lead terminal pieces to be passed are precisely formed in a predetermined shape and arrangement pitch in advance from a single metal plate by precision sheet metal processing, photo-etching, etc., and are integrally formed on the lead frame. By using a dedicated jig with a simple structure, a large number of beads can be easily arranged, and by moving the lead terminals along the lead terminal piece guide groove, the lead terminals can be easily batched into many bead cores at the same time. A small choke coil can be obtained by inserting a piece and performing sealing molding as it is.

Therefore, since the assembling work can be performed with a special jig having a relatively simple structure, expensive equipment is not required as in the past, and a certain coating film is previously formed on the bead core with a silicone resin or the like over the entire bead core. By applying it, there is almost no deterioration in properties, resin sealing is possible, there is little variation in the effect of alleviating the deterioration in magnetic properties, there is no deterioration due to the exterior molding resin due to heating during soldering, and it is inexpensive and stable in quality It has become possible to provide a small choke coil with excellent mass productivity.

[Brief description of the drawings]

FIG. 1 is a perspective view showing one embodiment of a small choke coil according to the present invention. FIG. 2 is a perspective view of a bead core used in the present invention. FIG. 3 is a perspective view showing a partially enlarged view of a lead frame of the small choke coil used in the present invention. 4A and 4B are plan views showing a manufacturing process of a small choke coil according to the present invention, wherein FIG. 4A shows a bead core and a lead terminal piece arranged in a dedicated jig, and FIG. (C) shows a state in which the bead core is inserted to the position of the core positioning small protrusion of the lead terminal piece, and (e) shows a state in which the external terminal has been cut off from the lead frame. FIG. 4 is a plan view showing a manufacturing process of the small choke coil according to the present invention. FIG. 5 is a characteristic diagram showing an influence on impedance with respect to frequency by sealing molding of a conventional small choke coil;
A: characteristics before sealing molding, B: characteristics of the small choke coil according to the present invention, C: characteristics after sealing molding (conventional small choke coil). FIG. 6 is a perspective view of a conventional small choke coil. twenty one……
(Ferrite) Bead core, 22: Through hole, 23: Coating film, 24: Lead terminal piece, 25: Insertion part, 26: Small projection for core positioning, 27: Reinforcement frame part, 28: Positioning Hole, 29 ... Lead frame, 30 ... Silicon resin,
61 ... external terminals, 62 ... exterior molding resin.

Claims (1)

(57) [Claims] 1. A method of manufacturing a small choke coil having a large number of signal circuits, comprising a plurality of small-diameter ferrite materials made of a Ni-Zn-based ferrite material on which a protective film layer having a predetermined thickness is previously applied by vacuum impregnation of a silicon-based resin. In the through hole of the ferrite bead core,
A large number of lead terminal pieces having small core positioning projections forming external terminals provided on a metal ribbon-shaped lead frame are collectively penetrated and molded integrally with an electrically insulating resin, and the lead is formed. A method for manufacturing a small choke coil, characterized by cutting terminal pieces.