HK1026506B - Continuous method of manufacturing wire wound inductors - Google Patents

Description

Continuous manufacturing method of wire-wound inductor

Technical Field

The present invention relates to a method of manufacturing a wire wound inductor, and more particularly to a method of continuously manufacturing a wire wound inductor using extruded core material and simplified terminal attachment and wire winding processes to reduce the cost of manufacturing the inductor.

Background

The inductor forms a component of a Radio Frequency (RF) circuit. As a group, inductors constitute a basic building block of about 1/3 in a circuit design.

The basic form of the inductor is a coil of wire. The coils may be freestanding (hollow) or wound around a core. Other types of inductors, such as multilayer or printed designs, are also known, but superior performance can be obtained from the coil. With the advent of surface mount technology for high speed printed circuit board manufacturing, the size of inductors has decreased significantly. Surface mount wire wound inductors are currently popular in industry standard 0805 and 0603 size packages. These inductors are constructed of molded core material (thermoset or ceramic) and wire windings and plated terminals.

The electrical measurement unit of inductance is henry. For a first approximation, the inductance value of a wire coil is L ═ 4 pi N²A/W)×10^-9Henry, where N is the number of coil turns, a is the coil cross-sectional area, and W is the coil length. All three variables (N, A and W) are independent variables that can be independently varied to achieve the desired inductance value L.

It is common to connect the wire ends of the windings while the inductors are in the winding jig, thereby manufacturing the individual inductors one at a time. This method is time consuming, thus increasing manufacturing costs and may result in out of tolerance deviations. In addition, conventional inductors do not utilize a core material that is not extruded in large quantities and therefore do not achieve the benefits of a continuous process. Furthermore, conventional core materials are difficult to machine, and as a result, it is difficult to accurately determine the cross-sectional area of the coil. Furthermore, the terminals of conventional inductors are coplanar (i.e., on the same side of the inductor), and the wire wrap starts and ends on the same side of the device (typically at the bottom). As a result, only integer multiples of the winding (N in the above equation for henry) are possible. Thus, for a given core size, this limits the number of inductance values (L in the above equation) that can be obtained. Furthermore, to secure the wire windings and to provide a smooth, uniform surface for the automated placement device, an adhesive coating (particularly Ultraviolet (UV) or heat curable plastic) needs to be added to the wire wound surface mount inductor. Since coating material may flow out of the edges of the device, the outer mold is required to provide a uniform surface.

Disclosure of Invention

The present invention is directed to overcoming the disadvantages of the prior art and providing a wire wound inductor and a method of manufacturing a wire wound inductor. It is another object of the present invention to provide a wire wound inductor wherein materials are employed that facilitate manufacturing and reduce manufacturing costs.

In an exemplary embodiment according to the present invention, there is provided a method of manufacturing a wire-wound inductor, including the steps of: (a) extruding a length of core material, (b) subsequently forming a wire staple from a bendable wire material around the core material, bending the wire staple around the core material to form wire staple terminals, (c) winding wire windings around the core material between the wire staple terminals, connecting the wire windings to the wire staple terminals.

In the above method, step (a) may be carried out by (d) extruding the thermoplastic material to form an arbitrary cross section, and (e) feeding the extruded thermoplastic material into the core reforming station. After the step (e) which is continuous with the steps (a) and (d), the core material may be processed into a desired cross section according to the required inductance. Forming a notch in the material and performing step (b) by securing the wire staple terminal in the notch. Process (b) may be performed by unwinding a length of wire coil, cutting the length of wire, shaping the wire for assembly around a core material, and bending the wire around the core material to form the inductor terminals. Step (c) may be performed by connecting the wire windings to the wire staple terminals at selected locations around the core material according to the desired inductance. Step (c) may be performed by (f) soldering the wire winding to the wire staple terminal. In this respect, it is preferable to perform the step (f) by hot staking or tack welding. The method may further include the step of (g) applying a coating material to the wire windings between the wire staple terminals. In this regard, it is preferred that step (g) be practiced by applying an Ultraviolet (UV) curable material to the wire windings between the wire staple terminals. The individual inductors so constructed are spaced from one another along the length of the core material. Next, the electrical performance of each inductor is tested and classified according to the allowable deviation.

According to another aspect of the present invention, there is provided a method of manufacturing a wire-wound inductor, comprising the steps of (a) extruding a length of core material sufficient for a plurality of inductors to be used, (b) subsequently forming a wire staple from a bendable wire material around the core material along the length of the core material and at a location corresponding to the plurality of inductors, bending the wire staple around the core material to form wire staple terminals, (c) winding wire windings around the core material between the wire staple terminals, and connecting ends of the wire windings to pairs of wire staple terminals respectively corresponding to each of the plurality of inductors.

These and other aspects and advantages of the invention will be described in detail below with reference to the accompanying drawings.

Drawings

Fig. 1 is a work position diagram of a method according to the invention.

FIG. 2 is the extruded core after it has passed through the core shaping station.

Fig. 3 is the core after passing through the core notching station.

Fig. 4 is a core assembled with wire staple terminals.

Fig. 5 is a core with wire staple terminals and wire windings.

Fig. 6 is the inductor after coating the table with the inductor.

Fig. 7 is a separated inductor for testing and sorting.

Figure 8 is an end view of an inductor according to the present invention.

Fig. 9 is another embodiment of an inductor according to the present invention.

Detailed description of the preferred embodiments

The structural components of the inductor according to the present invention will be described below in conjunction with a method of manufacturing the inductor. Fig. 1 is a work position diagram of a method according to the invention. Referring to fig. 2-7, a core material to be extruded having an arbitrary cross-section (preferably rectangular) as shown in fig. 2 is fed into the core shaping station 12. The extrusion process is well known and will not be described. Initially, a core material, such as a high temperature thermoplastic material, is extruded to a length sufficient for a plurality of inductors to be used. High temperature thermoplastics are those having a melting temperature above about 176.7 c (350F). The preferred material for the construction of the present invention is a thermoplastic material having a melting temperature above about 343 deg.C (650 deg.F). Examples of such materials are TEFLON, PEEK and PEK. Unlike prior art ceramic core materials or thermoset core materials, the thermoplastic core material can be extruded in a large number of successive runs. In addition, the core material is easy to machine to shape and notch (as described below). The cross-sectional area may vary arbitrarily, i.e. the variable a in the above formula, directly corresponding to the variation in the inductance value, i.e. the variable L in the above formula. Thus, the core material can be machined to the desired cross-section with great precision according to known machining processes. Typically, the core material is machined to an accuracy within +/-0.0127 mm (0.0005 "). A machined segment of core material is indicated at 14 in figure 2.

At the core notching station 16, notches 18 are formed in the core material where the device terminals are to be located. The notches 18 may be formed in any suitable manner, preferably by a solid carbide saw or high speed steel saw. Notches 18 are formed in the core material on all sides in order to accommodate the device terminals that are bent around the device. The depth of each notch can be set and controlled with great precision, depending on the diameter of the termination material and the desired inductor profile. For example, to minimize the inductor profile, deeper notches should be formed on the top and sides of the inductor. The notches at the bottom may be relatively shallow in contrast so that the inductor height on the printed circuit board may be controlled. A side view of the finished inductor illustrating the appearance of an inductor is shown in fig. 8. The core material segments for machining and notching are shown in figure 3.

Next, the inductor terminals 22 are provided on the core clip fitting table 24. The inductor terminals 22 are formed by wire staples formed from a coil and bent around the core material at the notches 18. The staple is formed of coiled wire such as american wire gauge 28AWG tin-copper material. In a single movement, the wire is cut at the appropriate length, shaped using a first U-shaped tool to fit around the core, and bent around the core using a second tool to form the device terminals. The second tool bends the U-shaped wire around the bottom of the core. The core material segment with wire staple terminals mounted thereon is shown in fig. 4.

Next, as shown in FIG. 5, the inductor windings 26 are placed on the core winding station 28 by winding a small diameter wire (typically an American wire gauge 44AWG) around the core material. The windings 26 are secured to the wire staple terminals 22 using any suitable method, such as heat staking, very high temperature brazing, and welding. In the hot staking method, the windings 26 are hot staked to the wire staple terminals at any desired location. The winding 26 comprises a polyurethane insulator. When the wire windings 26 are attached to the wire staple terminals, the heat and pressure melts the polyurethane insulation and melts the tin of the wire staple. The molten tin flows around the inductor wire, thereby soldering the wire windings in place. Since the tin coating on the wire staple terminals creates a bond between the winding wire and the terminal staple, no other material (e.g., solder) is required. Wire staple terminal 22 clamps around the core material so that wire winding 26 can be secured virtually anywhere along the perimeter of the inductor. As a result, the number of windings of the inductor (including the number of incomplete turns around the core) can be finely controlled, which enables intermediate inductance values to be achieved for a given core size.

Referring to fig. 6, the inductors are then passed through an inductor coating station 30 in which a coating material 32 is disposed between the two wire staple terminals 22 on top of each inductor. In addition to securing the inductor winding 26, the coating material 32 forms a smooth flat surface that is well suited for automated placement machines that are currently employed in circuit board assembly. The apparatus may be configured with any suitable coating material, several of which are known. The details of the configuration means will not be described. Typically, the coating material 32 is an Ultraviolet (UV) curable material such as a solder mask or an insulating coating or one of various epoxies. The wire staple terminals 22 are disposed slightly spaced (raised) above the top surface of the core to define channels 34 between the terminals. As a result of the grooves 34 defined by the terminals 22, no over-molding is necessary to form a uniform surface for an automated placement machine, as is typically required for conventional inductors.

The individual inductors 38 are separated at an inductor cut-off, test and sorting station 40. To allow sufficient space for the kerf operation to mechanically saw the inductor between the inductor terminals. In another configuration, the inductors may be separated using a known laser trimming process. Once separated, the inductors are placed on a test bench and tested for electrical performance using, for example, an impedance analyzer. Depending on the measured inductance values, each inductor is then sorted into bins according to the required tolerance. Each storage box is then placed into a standard tape and reel for packaging.

The process according to the invention is a continuous process. The inductors are formed sequentially on the mandrel material, starting with an extruded web. The inductors are not physically separated until the final stage of manufacture (specific to testing and sorting). This is in contrast to current methods of forming each inductor separately on individual cores, which are currently manufactured with tight tolerances and discrete winding. The continuous process according to the invention has a higher yield than the discrete process. Furthermore, extruding core materials is a less expensive process than molding using thermosets and ceramics.

By virtue of the extruded material, the process can maintain extremely tight tolerances (typically about 0.0127 mm (0.0005 "), which is unprecedented in the manufacture of wire-wound inductors. The ability to maintain this high precision in cross-sectional area enables highly controllable inductance values. The shaping process can be separated from the inductor manufacturing process so that the core material can be subjected to a roll-to-roll processing operation at high speed. The throughput can be greatly improved.

The wire winding process may also be a continuous process using a wire coil that rotates around the core material. This is in contrast to the prior art method where each inductor is rotated in the manner of a bobbin. Because the winding of the process of the present invention is continuous, manufacturing fluctuations due to start and stop actions can be avoided. In addition, less assembly time is required and more inductors can be wound in a given amount of time.

In addition to the continuous process portion, notching of the core material and forming staples on standard tin-plated wire coils are important features of the invention. In the prior art, after each mandrel material is processed, the terminal leads must be formed in a secondary process (typically by electroplating using high temperature solder paste). In addition to requiring additional manufacturing processes, existing methods require additional material handling (e.g., heating to high temperatures and depositing solder paste). Accordingly, the method of the present invention does not require an additional manufacturing process, and thus the manufacturing cost is low. Furthermore, more complex materials requiring special handling can be replaced with standard commercially available materials. Also, the staple forming process flattens the bottom of the wire coil, so making welding easier.

As shown in fig. 1, the entire process may be performed at a single manufacturing site having a single registration mark. Thus, the material delivered to each stage of the process does not have to be repositioned. But only all stages (including notching, stapling, winding, and severing) are aligned with a single registration mark. The existing methods include several separate manufacturing stages. As a result, each part (station) must be carefully repositioned in order to avoid large manufacturing variations that affect performance. As a result of a single manufacturing site, tighter manufacturing tolerances can be guaranteed, resulting in better yields. Furthermore, the manufacturing costs are lower, since no additional positioning means for repositioning are needed. Similarly, since the manufacturing process includes the configuration of the coating material, no additional manufacturing process is required, and thus the manufacturing cost is low.

To further enhance the performance level, referring to fig. 9, the core may be provided by pressing the core around a center conductor 45. Alternatively, a groove may be formed in the extrusion for pressing in the core in a subsequent process.

While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

Claims (24)

1. A method for manufacturing a wire-wound inductor comprises the following steps:

(a) extruding a length of core material;

(b) then forming a wire staple by bending a bendable wire material around the core material, the wire staple being bent around the core material to form wire staple terminals; and

(c) the wire winding is wound around the core material between the wire staple terminals and connected to the wire staple terminals.

2. A method according to claim 1, wherein step (a) is practiced by (d) extruding a thermoplastic material to form an arbitrary cross-section, and (e) feeding the extruded thermoplastic material into a core sizing station.

3. The method of claim 2, further comprising, after step (e) which is continuous with steps (a), (d), the step of machining the core material to a desired cross-section in accordance with a desired inductance.

4. The method of claim 1, further comprising, prior to step (b), the step of forming notches in the core material, and wherein step (b) is performed by securing wire staple terminals in the notches.

5. The method of claim 1, wherein step (b) is practiced by unwinding a length of wire coil, cutting the length of wire, shaping the wire for assembly around a core material, and bending the wire around the core material to form the inductor terminal.

6. The method of claim 1 wherein step (c) is practiced by connecting the wire windings to the wire staple terminals at selected locations around the periphery of the core material according to the desired inductance.

7. The method of claim 1, wherein step (c) is practiced by (f) brazing the wire winding to the wire staple terminal.

8. The method of claim 7, wherein step (f) is performed by hot-pressing staking.

9. The method of claim 7, wherein step (f) is performed by welding.

10. The method of claim 1, further comprising, (g) applying a coating material to the wire windings between the wire staple terminals.

11. The method of claim 10, wherein step (g) is practiced by applying an ultraviolet UV curable material to the wire windings between the wire staple terminals.

12. A method for manufacturing a wire-wound inductor comprises the following steps:

(a) extruding a length of core material sufficient for a plurality of inductors;

(b) then forming a wire staple from a bendable wire material around the core material at locations corresponding to the plurality of inductors along the length of the core material, and bending the wire staple around the core material to form wire staple terminals; and

(c) the wire winding is wound around the core material between wire staple terminals, and the ends of the wire winding are connected to pairs of wire staple terminals respectively corresponding to each of the plurality of inductors.

13. A method according to claim 12, wherein step (a) is practiced by (d) extruding a thermoplastic material to form an arbitrary cross-section, and (e) feeding the extruded thermoplastic material into a core sizing station.

14. The method of claim 13, further comprising, after step (e) which is continuous with steps (a), (d), the step of machining the core material to a desired cross-section in accordance with the desired inductance.

15. The method of claim 12, further comprising, prior to step (b), the step of forming notches in the core material, wherein step (b) is performed by securing wire staple terminals in the notches.

16. The method of claim 12, wherein step (b) is practiced by unwinding a length of wire coil, cutting the length of wire, shaping the wire for assembly around a core material, and bending the wire around the core material to form the inductor terminal.

17. The method of claim 12, wherein step (c) is practiced by connecting the wire windings to the wire staple terminals at selected locations around the periphery of the core material according to the desired inductance.

18. The method of claim 12, wherein step (c) is practiced by (f) soldering the wire windings to the wire staple terminals.

19. The method of claim 18, wherein step (f) is performed by hot-pressing staking.

20. The method of claim 18, wherein step (f) is performed by welding.

21. The method of claim 12, further comprising, (g) applying a coating material to the wire windings between the wire staple terminals.

22. The method of claim 21, wherein step (g) is practiced by applying an ultraviolet UV curable material to the wire windings between the wire staple terminals.

23. The method of claim 12 further including separating the inductors from one another along the length of the mandrel material.

24. The method of claim 23, further comprising testing the electrical performance of each inductor and sorting each inductor according to tolerance for variation.