Source: http://www.google.com/patents/US6552642?ie=ISO-8859-1&dq=7,104,347
Timestamp: 2014-08-23 02:33:34
Document Index: 338411733

Matched Legal Cases: ['art 32', 'arts 32', 'art 32', 'arts 32', 'art 32', 'arts 32', 'art 32']

Patent US6552642 - Electronic device having electric wires and method of producing same - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Sign in<nobr>Advanced Patent Search</nobr>PatentsAn electronic device such as a chip coil including an electric wire firmly connected to electrodes in a highly reliable fashion is constructed to be mounted on a printed circuit board or substrate in a stable and reliable manner. At both ends of a core of the chip coil, there are provided electrodes...http://www.google.com/patents/US6552642?utm_source=gb-gplus-sharePatent US6552642 - Electronic device having electric wires and method of producing sameAdvanced Patent SearchPublication numberUS6552642 B1Publication typeGrantApplication numberUS 09/317,665Publication dateApr 22, 2003Filing dateMay 24, 1999Priority dateMay 14, 1997Fee statusPaidAlso published asCN1098618C, CN1208322A, US6027008Publication number09317665, 317665, US 6552642 B1, US 6552642B1, US-B1-6552642, US6552642 B1, US6552642B1InventorsTakaomi Toi, Tetsuya Morinaga, Masahiro Bando, Tetsuo Hatakenaka, Kazuo Kasahara, Koki Sasaki, Takayuki HirotsujiOriginal AssigneeMurata Manufacturing Co., Ltd.Export CitationBiBTeX, EndNote, RefManPatent Citations (16), Referenced by (5), Classifications (16), Legal Events (2) External Links: USPTO, USPTO Assignment, EspacenetElectronic device having electric wires and method of producing sameUS 6552642 B1Abstract An electronic device such as a chip coil including an electric wire firmly connected to electrodes in a highly reliable fashion is constructed to be mounted on a printed circuit board or substrate in a stable and reliable manner. At both ends of a core of the chip coil, there are provided electrodes having a multilayer structure including a high-conductivity layer made of Ag, Ag�Pd, or a similar material; a solder barrier layer made of Ni; and an easy-soldering layer made of Sn or solder. End portions of the electric wire are embedded in the easy-soldering layer so that the resultant electrode structure has a substantially flat surface. A thermo-compression process is performed so that the end portions of the electric wire are connected to the solder barrier layer via solid welding and to the easy-soldering layer via brazing.
a base having a central core and raised portions disposed at opposite ends of said base, each of said raised portions including a surface which defines a mounting surface for said electronic component; at least one electrode located on the mounting surface of each of said raised portions of said base; an electric wire located on said central core of said base and respective ends of said electric wire being connected to said at least one electrode located on the mounting surface of each of said raised portions of said base; wherein said at least one electrode located on the mounting surface of each of said raised portions of said base includes at least a solder barrier layer made of a material having a high melting point and an easy-soldering layer made of a material having a low melting point compared to said high melting point; and a portion of said electric wire is embedded in said easy-soldering layer such that said portion of said electric wire and said easy-soldering layer of said at least one electrode located on the mounting surface of each of said raised portions of said base are substantially flush and no part of said portion of said electric wire embedded in said easy-soldering layer extends above said easy-soldering layer of said at least one electrode located on the mounting surface of each of said raised portions of said base, and said portion of said electric wire located on a mounting surface side is flattened and exposed. 2. An electronic component according to claim 1, wherein said electric wire embedded in said easy-soldering layer is substantially flush with a surface of said easy-soldering layer.
3. An electronic component according to claim 1, wherein said electronic component comprises one of a chip coil and a wire wound inductor.
4. An electronic component according to claim 1, wherein only one end portion of said electric wire is embedded in said easy soldering layer.
5. An electronic device according to claim 1, wherein the at least one electrode has a two layer structure.
6. An electronic component according to claim 1, wherein said at least one electrode includes two electrodes mounted on said base and each including said solder barrier layer and said easy-soldering layer, and opposite ends of said electric wire being embedded in said easy-soldering layer.
7. An electronic component according to claim 6, wherein a remaining portion of said electric wire other than said opposite ends is wound around said base.
8. An electronic component according to claim 1, wherein said electric wire embedded in said easy-soldering layer is connected to said easy-soldering layer at three separate regions thereof.
9. An electronic component according to claim 1, wherein the at least one electrode further includes a high conductivity layer located between said base and said solder barrier layer.
10. An electronic component according to claim 1, wherein said embedded portion of said electric wire has a width which is greater than the diameter of the wire.
This is a Divisional of U.S. patent application Ser. No. 09/076,549 now U.S. Pat. No.6,027,008 filed on May 12, 1998.
FIG. 5 illustrates a conventional chip coil made up of an electric wire 5 wound around a core 1 made of a magnetic material, wherein ends 5 a of the wire 5 are connected, via thermo-compression bonding such as a wire bonding process, to respective electrodes 2 located on the core 1. The electrodes 2 are made of a material such as Ag or Ag�Pd. When the ends 5 a of the wire are connected to the respective electrodes 2, the resultant connecting portions of the wire 5 have raised portions bulging from the surface of the electrodes 2. The bulging shape of the connecting portions causes the chip coil to become unstable when it is mounted on a printed circuit board. That is, the chip coil is mounted unevenly in a slanted orientation or topples over and is separated from the printed circuit board in the worst case. Another problem with the chip coil of this type is that the ends 5 a of the wire 5 are exposed directly to air and thus, the ends of the wire are oxidized. This makes it difficult to solder the ends of the wire during the process of mounting the chip coil.
One possible technique of improving the stability of the mounted position is to form recesses 3 as seen in FIG. 6 in both end portions of the core 1 so that the ends 5 a of the wire can be placed inside the recesses 3. However, the shape of the core 1 becomes complicated and difficult processes are required to produce such a complicated structure including the recesses 3.
A pressing tip 56 heated at about 500� C. is moved down so that the insulated electric wire 53 is pressed against the electrode 52. The electric wire 53 a is flattened by the pressure and the electric wire 53 a is connected to the electrode 52 via thermo-compression bonding.
In this connection technique, if the electrode 52 is made of metal having a high melting point such as Ag, Cu, or Ni, the insulating coating 53 b melts at a temperature lower than the melting point of the electrode 52, and the electric wire 53 a and the electrode 52 are directly connected to each other. Another feature of this technique is that the electric wire 53 a is flattened by the pressure.
However, although the electric wire 53 a on the electrode 52 is flattened, there is still a processing step required on the surface of the electrode 52 and the electric wire 53 a. When the coil device is mounted on a printed circuit board such that the surface of the electrode 52 and attached electric wire 53 a comes into contact with the printed circuit board, the above-described step can cause the coil device to become unstable or cause the soldered connection to become unreliable.
In many cases, the surface of the electrodes 52 of the coil device is plated with metal having a low melting point such as Sn or solder so that a low-melting-point electrode layer is formed on the electrode 52 thereby ensuring that the electrode can be easily soldered. For example, as shown in FIG. 12, the electrode 52 is produced by coating a silver-filled paste on the surface of the core 51 and baking it so as to form a base layer 52 a, then plating the surface of the base layer 52 a with Ni thereby forming a Ni-plated layer 52 b for protecting the base layer 52 a from being eroded by solder, and finally forming an electrode layer 52 c of low-melting-point metal which allows the electrode 52 to be easily soldered.
In the case of the coil device having the above structure, when connection is performed with the pressing tip 54 heated at about 500� C., the electrode layer 52 c is heated by the pressing tip 54 to a temperature higher than the melting point of the low-melting-point metal. In the connecting process, the electrically conductive wire 53 a is pressed by a pressure high enough to compress the electrically conductive wire 53 a. As a result, the insulating coating 53 b and the electrode layer 52 c made of the low-melting-point metal at the top layer are both melted into liquid states, and the electrically conductive wire 53 a is compressed into a flattened shape.
As a result, in the pressing process using the pressing tip 54, the low-melting-point metal in the liquid state is pushed aside by the insulating coating 53 b in the liquid state toward the sides of the electrically conductive wire 53 a. In the above process, after the low-melting-point metal is pushed aside by the melted insulating coating 53 b, if the melted insulating coating 53 b sticks to the pressing tip 54 and is removed when the pressing tip 54 is moved up to its original position, the Ni-plated layer 52 b is sometimes exposed in an area A at a side of the conductive wire 53 a. If the Ni-plated layer 52 b is partially exposed, when the coil device is mounted on a printed circuit board via soldering, a connection failure can occur because the Ni-plated layer 52 b has poor solder wettability.
Even in the case where the Ni-plated layer 52 b does not become exposed in the area A in FIG. 12 after the low-melting-point metal is pushed aside by the melted insulating coating 53 b, if the melted insulating coating 53 b sticks to the pressing tip 54 and is removed when the pressing tip 54 is moved up to its original position, a crater 52 d is produced in an area on the surface of the electrode 52 where the insulating coating 53 b of the electrically conductive wire 53 a was present. If such a crater is produced, it becomes difficult to make a good connection in the soldering process.
FIG. 1C is a cross-sectional view taken along line C�C in FIG. 1B;
As shown in FIG. 1C, each electrode 13 is preferably formed as follows. First, a high-conductivity material such as Ag or Ag�Pd is coated on the core 10 and baking is performed thereby forming a high-conductivity layer 13 a. The surface of the high-conductivity layer 13 a is electroplated with Ni so as to form a solder barrier layer 13 b. Furthermore, the surface of the solder barrier layer 13 b is electroplated with Sn or solder so as to form an easy-soldering layer 13 c. The wire 15 is preferably made of a conductor of Cu with a diameter of about 20 to about 60 μm and is preferably covered with an insulating material such as polyesterimide. The end portions 16 of the wire 15 are connected, preferably via thermo-compression, to the respective electrodes 13 in an embedded arrangement as seen in FIG. 1C.
As shown in FIG. 2A, the end portions 16 of the wire are placed on the respective electrodes 13 and pressed from above by a heater 20 so that the end portions 16 are heated by the heater 20. The pressing and heating are preferably performed at the same time for both end portions 16 of the wire. In a short period of time, for example, less than about 1 sec, the temperature of the heater 20 is increased to a value higher than the melting point of the easy-soldering layer 13 c (the melting point of Sn is 231� C. and that of solder is 183� C.) and lower than the melting point of the solder barrier layer 13 b (the melting point of Ni is 1455� C.), and more preferably, to a temperature higher than 500� C. The temperature is maintained at this value for about 1 sec or for a shorter time period. The temperature of the heater 20 is decreased quickly in a short period of time, preferably less than about 1 sec to a value lower than the melting point of the easy-soldering layer 13 c. Then the heater 20 is moved away from end portions 16 of the wire. For example, a pulse heating heater may be used as the heater 20. With this type of heater, heating can be performed by supplying a pulse current while precisely controlling the heating and pressing conditions. The melting points of Cu and Ag are 1083� C. and 960.5� C., respectively.
In the connecting process described above, the insulating coating of the end portions 16 of the wire is melted/vaporized by heat. The surface of the end portions 16 of the wire melts and becomes soft. The easy-soldering layer 13 c also melts. The end portions 16 of the wire are flattened by the pressure and sink into the easy-soldering layer 13 c (see to FIG. 1C). In this state, the end portions 16 of the wire and the solder barrier layer 13 b are connected to each other at a contact plane 17 a via solid-phase welding, and the end portions 16 of the wire and the easy-soldering layer 13 c are connected to each other at a contact plane 17 b via brazing.
After completion of the connecting process, the electrode has a structure in which the end portion 16 of the electric wire and the easy-soldering layer 13 c become substantially flush and thus, there is no raised portion of the wire extending up from the electrode 13. This structure makes it possible to mount the chip coil on a printed circuit board in a stable fashion without the chip coil being slanted or being prone to topple over or to be removed from the printed circuit board. Furthermore, because the end portions 16 of the electric wire are connected to the electrodes 13 via solid welding and brazing, the connections are highly reliable. Furthermore, the insulating coating of the end portions 16 of the electric wire are removed during the heating process and no additional process or step for removing the coating is necessary. The heating is performed for a very short time so that the insulating coating of the electric wire 15 in the winding part is not damaged.
In some cases, as shown in FIG. 1C, the melted easy-soldering layer 13 c flows toward the end portions 16 of the electric wire and thus, the end portions 16 of the electric wire are covered by the easy-soldering layer 13 c. This results in a further improvement in the flatness of the surface of the electrode 13 and also prevents the end portions 16 of the electric wire from being oxidized. In particular, after completion of the above connecting process, if another easy-soldering layer 13 d of Sn or solder is formed via plating or other suitable process on the surface of the electrode 13 as shown in FIG. 3, then the flatness is further improved and the end portions 16 of the electric wire are prevented from being oxidized in a more reliable fashion. In the case where the easy-soldering layer 13 d is formed via plating, the size of the end portions 16 of the electric wire are reduced by the plating bath. As a result, the solderability is further improved by the synergistic effects of the presence of the easy-soldering layer 13 d and the reduction of the end portions 16 of the wire.
FIG. 4 illustrates a second preferred embodiment of a chip coil according to the present invention. The second preferred embodiment differs from the first preferred embodiment described above in that the electrode 13′ disposed on the core 10 has a two-layer structure including of a solder barrier layer 13 b made of Ni and an easy-soldering layer 13 c made of Sn or solder. The end portions 16 of the electric wire are connected preferably via a thermo-compression bonding process similar to that used in the first preferred embodiment so that the end portions 16 of the electric wire and the solder barrier layer 13 b are connected to each other at a connecting plane 17 a via solid welding, and the end portions 16 of the electric wire and the easy-soldering layer 13 c are connected to each other at a connecting plane 17 b via brazing Furthermore, as in the first preferred embodiment, the end portions 16 of the electric wire are connected to the electrodes in an embedded arrangement so that the resultant structure has a flat surface. After completion of the connecting process described above, the surface of the resultant electrode structure may be covered with another easy-soldering layer made of Sn or solder.
The chip type coil device 31 includes a core 32 made of a dielectric material, magnetic material, or an insulating material such as insulating ceramic or plastic. The core 32 includes a winding part 32 a around which an insulated electric wire 33 is wound and electrode parts 32 b located at both ends of the winding part 32 a wherein the electrode parts 32 b have a greater thickness than the winding part 32 a. First and second electrodes 34 and 35 are disposed on the upper surface of the electrode portions 32 b and 32 c, respectively, so that electrical connections to external components can be achieved via the first and second electrodes 34 and 35.
The method of producing a coil device, such as the chip type coil device 31 described above, according to the present preferred embodiment of the invention includes a novel process of connecting the insulating wire 33 to the first and second electrodes 34 and 35. The other processes may be accomplished by known techniques. That is, the process of forming the winding part by winding the insulated electric wire 33 around the outer surface of the core 32 and the process of forming the electrodes 34 and 35 on the upper surface of the electrode parts 32 b and 32 c of the core 32 may be performed using known techniques.
First, as shown in FIG. 7a, the insulated electric wire 33 is placed on the first electrode 34 located on the upper surface of the electrode part 32 b of the core 32 of the coil device. The first electrode 34 preferably has a multilayer structure including of a base layer 34 a, a Ni-plated layer 34 b, and a Sn-plated layer 34 c. The base layer 34 a is formed by coating, for example, a silver-filled conductive paste and then baking. Alternatively, the base layer 34 a may also be formed via evaporation, plating, sputtering, or other suitable techniques.
The Ni-plated layer 34 b disposed on the base layer 34 a functions as a solder barrier layer for protecting the base layer 34 a from being eroded by solder. Instead of Ni, Cu or Fe may also be used for the same purpose.
The Sn-plated layer 34 c disposed on the outer surface of the Ni-plated layer 34 b functions as an easy-soldering layer which makes it easy to perform soldering when the coil device is mounted. Instead of Sn, solder or other materials which can be easily soldered may also be used to form the plated layer functioning as the easy-soldering layer.
In the present preferred embodiment, the insulated electric wire 33 includes an electrically conductive wire 33 a made of Cu covered with an insulating coating 33 b. The insulating coating 33 b may be formed using polyesterimide or similar material. When polyesterimide is used to form the insulating coating 33 b, it can be melted at a temperature equal to or higher than 330� C.
When the insulated electric wire 33 is connected to the first electrode 34, the insulated electric wire 33 is first placed on the first electrode 34 and a pressing tip 36 is moved down to the wire 33, wherein the pressing tip 36 is heated at a temperature high enough to melt the insulating coating 33 b on the electric wire. In this specific preferred embodiment, the tip 36 is preferably heated at about 500� C. or a higher temperature. In the above process, the pressing tip 36 is moved down so that the insulated electric wire 33 is pressed against the first electrode 34 by a relatively low pressure. The optimum pressure in this pressing process depends on the diameter and material of the insulated electric wire 33. In an example in which the insulated electric wire is made of Cu and has a diameter of about 40 μm, the pressure is preferably set to a value within the range of about 30 to about 50 gF. Thus, in the preferred embodiments of the present invention, the low-pressure pressing process is preferably performed in the manner described above.
In the low-pressure pressing process, the insulating coating 33 b melts because the pressing tip 36 is heated at a temperature high enough to melt the insulating coating. As a result, as shown in FIG. 7b, the melted insulating coating 33 b on the first electrode 34 moves to both sides of the electrically conductive wire 33 a, and thus the lower side of the electrically conductive wire 33 a comes into direct contact with the Sn-plated layer 34 c which is the top layer of the electrode 34.
In the above low-pressure pressing process, as shown in FIG. 7b, substantially no deformation occurs in the electrically conductive wire 33 a because the pressure applied by the pressing tip 36 is low enough. That is, the low-pressure pressing process is performed at a low pressure at which the electrically conductive wire 33 a does not become flat.
Furthermore, in the low-pressure pressing process, because the Sn-plated layer 34 c is not in direct contact with the pressing tip 36 and because the pressure applied by the pressing tip 36 is low, and because the pressing process is performed in a rather short period of time as shown in FIG. 9, the Sn-plated layer 34 c is not melted although the insulating coating 33 b is melted. In other words, the pressure and the pressing time are selected so that the insulating coating 33 b is melted but the Sn-plated layer 34 c is not melted.
Following the low-pressure pressing process, a high-pressure pressing process is performed at a relatively high pressure. In this high-pressure pressing process, the electrically conductive wire 33 a is pressed against the first electrode 34 by a high enough pressure so that the electrically conductive wire 33 a is flattened and embedded into the first electrode 34. The high-pressure pressing process is described in further detail below with reference to FIGS. 7c and 7 d. In the high-pressure pressing process, as shown in FIG. 7c, the pressure applied to the pressing tip 36 in a downward direction is increased so that the electrically conductive wire 33 a is made flattened. That is, in the high-pressure pressing process, the pressure applied by the pressing tip 36 to the electrically conductive wire 33 a is selected so that the electrically conductive wire 33 a becomes flat and so that the flattened wire 33 a is embedded into the first electrode 34.
Thus, in the above high-pressure pressing process, the electric wire 33 a is made flat and embedded into the first electrode 34 as shown in FIG. 7d. Preferably, the temperature in the high-pressure pressing process is set to a value lower than the melting point of the top layer of the first and second electrodes, and more specifically, lower than the melting point of the Sn-plated layer 34 c, and higher than the freezing point of the Sn-plated layer 34 c. In this specific preferred embodiment, the temperature is set to about 230� C. If the temperature in the high-pressure pressing process is selected within the above range, it becomes possible to make the Sn-plated layer 34 c of the first electrode 34 soft enough so that the electrically conductive wire 33 a is embedded into the first electrode 34.
If the temperature in the high-pressure pressing process is set to a value higher than the melting point of the Sn-plated layer 34 c, then the Sn-plated layer 34 c is melted during the high-pressure pressing process and melted tin is pushed aside by the insulating coating 33 b. As a result, there is a possibility that some portion of the Ni-plated layer 34 b is exposed or a crater is produced after the insulating coating 33 b is removed.
The optimum pressure in the high-pressure pressing process depends on the diameter and the material of the electrically conductive wire 33 a. In an example in which the electrically conductive wire is made of Cu and has a diameter of about 40 μm, the pressure is preferably set to about 300 gF.
After completion of the high-pressure pressing process, the pressing tip 36 is moved upward. As a result, the insulating coating 33 b sticking to the lower surface 36 a of the pressing tip 36 is removed from the first electrode. As shown in FIG. 7d, after the insulating coating 33 b is removed, the electrode 34 has a flat surface having no craters.
According to the production method of the present preferred embodiment, as described above, the electric wire 33 a becomes flat and the flattened wire 33 a is embedded into the first electrode 34. As a result, the first electrode 34 has a flat surface after the insulated electric wire 33 is connected to the first electrode 34. Therefore, the coil device can be mounted on a printed circuit board or the like in such a manner that the electrodes are connected via solder or the like to the printed circuit board in a highly reliable manner.
Furthermore, because the Sn-plated layer 34 c is exposed at the area outside the electrically conductive wire 33 a, excellent solderability can be achieved.
Although in the above described preferred embodiment, the high-pressure pressing process is performed at a temperature lower than the temperature used in the low-pressure pressing process, the temperature in the high-pressure pressing process may be higher than that in the low-pressure pressing process. For example, in the case where the insulating coating 33 b is made of a urethane resin, the urethane resin melts at about 280� C. however the Sn-plated layer does not become soft at such a temperature. In this case, the urethane resin insulating coating is melted in the low-pressure pressing process, and the Sn-plated layer is made soft in the high-pressure pressing process by using a higher temperature in the high-pressure pressing process than the temperature in the low-pressure pressing process thereby ensuring that the electrically conductive wire is embedded into the Sn-plated layer of the first electrode, as in the preferred embodiment described above.
Although in the third preferred embodiment described above the first and second electrodes are incorporated into the multilayer structure including the base layer 34 a made of the silver-filled conductive paste, the Ni-plated layer 34 b, and the Sn-plated layer 34 c, the first and second electrodes may also be formed to have a single layer structure.
That is, the first and second electrodes may be formed of a single metal material and the insulated electric wire may be connected to the first and second electrodes by performing the low-pressure pressing process and the high-pressure pressing process. Also in this case, as in the case of the third preferred embodiment described above, in the low-pressure pressing process performed first, the electrically conductive wire does not become flat and the insulating coating is melted and pushed aside. Then in the high-pressure pressing process, a relatively high pressure is applied by the pressing tip 36 to the electrically conductive wire 33 a so that the wire 33 a is embedded into the electrode 24, as shown in FIG. 10. To ensure that the wire 33 a can be embedded, it is preferable that the temperature in the high-pressure pressing process is higher than the temperature at which the first electrode 24 made of the single material becomes soft, that is, the freezing temperature, and should be lower than the melting point of the first electrode 24.
The insulating coating 33 b melts and moves to the sides of the wire 33 a if the low-pressure pressing process is performed first. When the pressing tip 36 is moved up after completion of the high-pressure pressing process performed after the low-pressure pressing process, the insulating coating 33 b is removed because the insulating coating 33 b sticks to the lower surface 36 a of the pressing tip 36. Therefore, as shown on the right side of FIG. 10, after the completion of the high-pressure pressing process, the first electrode 24 has a structure in which the wire 33 a is connected to the first electrode 24 in such a manner that the surface of the connecting part becomes flat.
Although in the above-described preferred embodiment the temperature in the low-pressure pressing process is preferably set to a value at which the insulating coating 33 b melts but the Sn-plated layer 34 c or the low-melting-point metal layer hardly melts at all, the temperature in the low-pressure pressing process may also be set to a value at which the low-melting-point metal layer 34 c melts. In the case where the temperature in the low-pressure pressing process is set to a value at which the low-melting-point metal layer 34 c melts, the low-melting-point metal layer 34 c may be cooled, in the following process, to a temperature higher than its freezing point so that the low-melting-point metal layer 34 c is in a soft state thereby ensuring that the wire 33 a is embedded into the electrode in the high-pressure pressing process, as in the above-described preferred embodiment. The cooling may be performed either during or prior to the high-pressure pressing process.
The electric wire 33 a may also be made of metal other than copper. For example, Ni or Ag may be used for this purpose. Furthermore, the insulating material of the insulating coating 33 b is not limited to polyesterimide or urethane resins, but other proper synthetic resins may also be used.
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