JPH11251157A - Flat type magnetic induction part and ultra-small power converter using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ultra-small power converter device by allowing magnetic induction parts such as a coil, a transformer, etc., to be flat and small, for improved mounting method on a semiconductor substrate where a semiconductor device is built. SOLUTION: Related to a flat coil 20 comprising a pair of magnetic thin films 24a and 24b with a coil conductor 27 formed into coil shape through insulation films 23a and 23b in between on a silicon wafer 21, a solder bump which is to be a terminal of the coil conductor 27 is provided. A bump electrode 29 is matched and mounted on an electrode 2 of a semiconductor chip 1 where semiconductor devices are integrated, and the solder bump 29 is melted and jointed on the semiconductor chip 1 to form an ultra-small power converter device. It may be a flat coil whose surface is covered with a polyimide resin, and may be mounted by thermocompression bonding at such low temperature as 200 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic induction component such as an inductor and a transformer used in a power converter such as a DC-DC converter, and a power converter using the same.

[0002]

2. Description of the Related Art In recent years, electronic information devices, especially various types of portable electronic information devices, have become remarkably widespread. Many of these electronic information devices use a battery as a power source, and incorporate a power conversion device such as a DC-DC converter. Usually, the power converter is a hybrid power converter in which active components such as switching elements, rectifiers, and control ICs and individual components such as coils, transformers, capacitors, and resistors are mounted on a ceramic substrate. It is configured as a device.

[0003]

With the demand for miniaturization and weight reduction of various electronic information devices including portable devices, there is a strong demand for miniaturization of a built-in power converter. The miniaturization of the hybrid power supply module has been advanced by technologies such as MCM (multi-chip module). In addition, as technological advances in control ICs, switching elements, rectifiers, etc. used therein are remarkable, there is a problem of the volume occupied by passive elements such as coils, transformers, capacitors, etc. used in these power converters. It has been embossed. In particular, magnetic induction components such as inductors and transformers are very large in volume compared to integrated circuits, and are the biggest bottleneck in miniaturizing electronic devices.

The future direction of miniaturization of these magnetic induction components is to make them as small as chip components without limit.
There are two directions: a direction in which the entire power supply is reduced by surface mounting, and a direction in which a thin film is formed on a silicon substrate. recent years,
In response to the demand for miniaturization of magnetic induction components, there has been reported an example in which magnetic induction components are mounted on a semiconductor substrate by applying semiconductor technology. The colleague of the inventor also filed Japanese Patent Application No. 8-14962.
6, such a planar magnetic induction component was devised.

FIG. 9 is a partial sectional view of a micro power converter integrated on a semiconductor chip. A planar coil 10 in which a coil conductor 17 is sandwiched between magnetic thin films 14a and 14b is formed on a surface of a semiconductor chip 1 in which a semiconductor device such as a switching element and a control circuit is fabricated by a thin film technique. The coil conductor 17 and the electrode 2 of the semiconductor device are connected by a connection conductor 18. 13a and 13b are upper and lower insulating films for insulating the magnetic thin films 14a and 14b.

However, for example, the connection conductor 18 connecting the electrode 2 of the semiconductor chip 1 and the coil conductor 17 is usually formed by a plating method.
There is a problem of corrosion of the insulating film 13 to prevent the problem.
A device such as tapering the end of “a” is employed.
In addition, after the semiconductor device is built, the semiconductor chip 1
In order to form a planar magnetic induction component using thin film technology,
There are problems that the process becomes complicated and the process becomes long. An object of the present invention is to facilitate the miniaturization of a power conversion device,
An object of the present invention is to provide a planar magnetic induction component such as a transformer and a micro power conversion device using the same.

[0007]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention relates to a planar magnetic induction component having a structure in which a coil conductor formed in a coil shape is sandwiched between a pair of magnetic thin films via an insulating film. And a bump electrode as a terminal. By doing so, it is easy to join the bump electrode to an electrode of a semiconductor substrate, for example, and it is possible to mount the bump electrode on the semiconductor substrate. In particular, by manufacturing the planar magnetic induction component as a separate chip, the number of steps can be reduced, and adverse effects on the electrode portion and the like of the semiconductor device can be avoided.

The bump may be a hemispherical solder bump or a stud bump formed by wire ball bonding of a solder wire or a gold wire. In the latter case, a bump having a height higher than the diameter can be formed. The formation of the conductor can be omitted. If a coil conductor is formed on a silicon wafer, the thermal characteristics are the same as those of other silicon semiconductor substrates, and matching is good. In addition, if the coil conductor is formed on the high-molecular polymer film, a flat magnetic induction component having a small thickness can be obtained.

In particular, if the surface is covered with a polyimide resin, it can be easily bonded by thermocompression bonding without using an adhesive when mounting on a semiconductor substrate. As a mounting method of the above-described planar magnetic induction component, a bump electrode is aligned with an electrode of a semiconductor substrate on which a semiconductor device is integrated, and the semiconductor device is mounted on the semiconductor substrate.

By mounting the semiconductor device on a semiconductor substrate in such a manner, a large area conventionally required for mounting a magnetic induction component is not required, and the size can be reduced. In particular, it is assumed that the bumps whose surfaces are covered with the polyimide resin are aligned with the electrodes of the semiconductor substrate on which the semiconductor device is integrated, and mounted on the semiconductor substrate by thermocompression bonding. If you do that,
Bonding on a semiconductor substrate can be performed only by heating at a low temperature.

[0011] A terminal pad provided in contact with the coil conductor and an electrode of the semiconductor device may be connected by wire bonding. This eliminates the need for a connection conductor that connects the coil conductor, the terminal, and the electrode of the semiconductor device, and can omit a process for forming a through-hole for connection and a process for forming the connection conductor.

In particular, when a silicon chip having a planar magnetic induction component formed thereon is mounted on a semiconductor substrate on which a semiconductor device is integrated, the planar magnetic induction component can be formed on a separate substrate from the semiconductor device, thereby shortening the process. it can.

[0013]

Embodiments of the present invention will be described below in detail with reference to examples. Embodiment 1 FIG. 1A is a partial cross-sectional view of a planar coil according to a first embodiment of the present invention (hereinafter, referred to as Embodiment 1).

The planar coil 20 is made of a silicon wafer 21
A magnetic thin film 24a of CoHfTaPd is laminated thereon with an oxide film 22 interposed therebetween, and a coil is formed on an insulating film 23a made of polyimide which covers the magnetic thin film 24a. In the figure, a coil conductor 27 having a cross section of the coil,
A cross section of the polyimide intermediate insulating film 26 therebetween is shown. On the coil conductor 27 and the intermediate insulating film 26, a CoHfTaPd magnetic thin film 24b is laminated via a polyimide insulating film 23b, and the polyimide insulating film 23b further covers the magnetic thin film 24b. 28 is a coil conductor 27
, And a solder bump 29 is formed on the surface of the connection conductor. The size of the solder bump 29 is about 50 μm in radius and 30 μm in height.

FIGS. 3A to 3E and FIG. 4A
FIGS. 3D to 3D are partial cross-sectional views illustrating a method of manufacturing the planar coil 20 according to the first embodiment in the order of manufacturing steps. Hereinafter, the manufacturing method will be described in the order of steps.

Oxide film 2 of 1 μm thickness on Si wafer 21
2 [FIG. 3 (a)]. A 3 μm-thick CoHfTaPd magnetic thin film 24a is formed by a sputtering method, and a pattern is formed by photolithography (FIG. 2B). As an etchant for the magnetic thin film 24a, for example, aqua regia is used.

A polyimide is applied as an interlayer insulating film 23a and cured. The polyimide film thickness is 3 μm. Platinum (Pt) serving as a nucleus for electroless plating on the insulating film 23a
The nuclei 25 are formed in an island shape with a thickness of 0.4 nm by sputtering [FIG.

A photosensitive polyimide for forming the intermediate insulating film 26 is applied, exposed using a photomask, developed, and a coil pattern serving as a plating mold is formed and cured [FIG. The polyimide film thickness is 4 before cure.
0 μm, 25 μm after cure. The dimensions of the plating mold are, for example, an inner dimension of 80 μm and an interval of 70 μm.

Electroless copper plating is performed to deposit 0.2 μm of copper on the bottom of the plating mold to form a conductive layer for electrolytic plating, and then electrolytic copper plating is performed to form a coil conductor 27 [FIG. )]. The thickness of the coil conductor 27 is 25 μm as in the case of the intermediate insulating film 26.

After polyimide is applied as an interlayer insulating film 23b and cured, a magnetic thin film 24b of CoHfTaPd is formed to a thickness of 3 μm by sputtering, a positive photoresist is applied to form a pattern, and the photoresist is used as a mask. Etching is performed with aqua regia to form a pattern of the magnetic thin film 24b. Thereafter, the photoresist is removed by immersion in acetone [FIG. 4 (a)].

A silicon oxide film (thickness: 3 μm) is formed by sputtering.
m) is deposited and patterned to form a polyimide etching mask. Next, using the silicon oxide film mask, a through hole reaching the coil conductor 27 as the base is formed, and then the silicon oxide film is removed with hydrofluoric acid [FIG.

9 μm of copper is applied to the through hole by electrolytic plating.
Embedding m, to form a connection conductor 28 [FIG. A nickel layer and a bump metal 29a for a solder bump are formed on the connection conductor 28 by electrolytic plating [FIG.

If necessary, unnecessary portions of the bump metal 29a are removed by a photo-etching process, a flux process is performed, and a process called a wet back is performed by heating and melting in a tunnel furnace. Solder bumps 29 are used (FIG. 1A). Thereafter, the silicon wafer is cut into chips by dicing.
FIG. 1B is a partial cross-sectional view illustrating a state in which the planar coil according to the first embodiment is mounted on a semiconductor substrate on which a semiconductor device is integrated.

The semiconductor chip 1 has integrated therein a power semiconductor element for flowing an output current and a control circuit for controlling the power semiconductor element. The state where the solder bumps 29 of the planar coil 20 of the present invention are melted and connected to the electrodes 2 of the semiconductor chip 1 is shown. Reference numeral 3 denotes a protection film such as a nitride film or a polyimide film covering the semiconductor surface. If the adhesive strength is insufficient with only the solder bump 29, an adhesive such as an epoxy resin may be used.

As shown in FIG. 1B, a planar coil was mounted on a semiconductor integrated circuit, and a 1 W class DC-DC converter module was prototyped. The dimensions of the flat coil are about 4 ×
4 mm, which can greatly reduce the space required for mounting a planar coil on a module substrate, which was required conventionally, and the size of the module is 10 × 10 × 2 (mm), which is about １ ／ of the conventional volume. Could be reduced to

If the semiconductor device is directly mounted on the semiconductor substrate by using bump electrodes, no wiring is required, and there is no problem of extra inductance of the wiring or noise induction. In addition, since the planar coil is formed as a single chip, there is no problem in forming the conventional connection conductor, the manufacture is easy, and the process can be shortened. The insulation between the silicon wafer 21 and the magnetic thin film 24a does not necessarily have to be the oxide film 22, but may be an insulating film such as a polyimide film.

[Second Embodiment] FIG. 2 is a partial sectional view of a small power converter in which the planar coil of the second embodiment is mounted on a semiconductor substrate on which a semiconductor device is integrated.

100 μm thick polyimide film 31
A planar coil 30 is formed on the upper side (the lower side in the figure) in the same manner as in the first embodiment. Then, the planar coil 30 is opposed to the electrode 2 of the semiconductor chip 1 on which the semiconductor device in a wafer state is integrated so that the solder bumps 39 of the planar coil 30 are aligned, and a polyimide film covering the surface is coated with the polyimide film of the semiconductor chip 1. It is made into a chip by dicing after being closely adhered to the protective film 3 by thermocompression bonding.

According to this method, bonding can be performed at a low temperature of about 200 ° C. without using an adhesive, and mounting can be performed at a time on a wafer basis, and peeling at a chip interface due to stress deformation due to adhesion of polyimide can be prevented. There is an advantage that it is unlikely to occur.

Third Embodiment FIG. 5A is a partial sectional view of a flat coil 40 according to a third embodiment of the present invention. The difference from the flat coil of the first embodiment is that the connection conductor and the hemispherical solder bump are not formed, and a stud bump 49 of a low-temperature solder wire is provided instead.

As the manufacturing method, FIG.
Then, after forming the nickel film 6 by plating, the tip of the solder wire of, for example, lead-60% tin may be melted and wire ball bonded. The size of the stud bump 49 is, for example, a radius of 35 μm and a height of 70 μm. 41
Is a silicon wafer, 47 is a coil conductor, 44a, 44b
Is a magnetic thin film.

FIG. 5B is a partial sectional view of a small power converter in which the planar coil of the third embodiment is mounted on a semiconductor chip 1 on which a semiconductor device is integrated by solder reflow at 200 ° C.

A power device and a control circuit are integrated in the semiconductor chip 1. Electrode 2 of the semiconductor chip 1
5 shows a state in which the stud bumps 49 of the planar coil 40 of the present invention are connected as molten bumps 49a. Reference numeral 4 denotes nickel-copper-titanium (each having a thickness of 0.5 μm, 1
μm, 0.5 μm) layer.

The stud bumps 49 formed by wire ball bonding can be made higher within the opening on the coil conductor 47 since the height can be increased in proportion to the diameter as compared with a normal hemispherical bump or the like. The formation of the connection conductor becomes unnecessary. Then, if the stud bumps 49 are joined together on the electrodes 2 of the semiconductor chip 1, no wiring is required, and no extra inductance of the wiring and no problem of noise induction occur. In addition, since the flat coil is formed as a single chip, the process is short and the manufacture is easy. Again,
The same space reduction effect as in the first embodiment was obtained.

Fourth Embodiment FIG. 6A is a partial cross-sectional view of a flat coil 50 according to a fourth embodiment of the present invention. In this example, gold wire stud bumps 59 are provided.

As a manufacturing method, as in the first embodiment, after FIG. 4B, for example, the tip of a gold wire may be melted and wire ball bonded. Stud bump 59
Has a radius of about 75 μm and a height of about 100 μm. 51 is a silicon wafer, 57 is a coil conductor, 54
a and 54b are magnetic thin films. In the case of a gold wire, it is not necessary to form a nickel film on the coil conductor 57 as in the third embodiment.

FIG. 6B shows a planar coil 5 according to the fourth embodiment.
FIG. 1 is a partial cross-sectional view of a small power conversion device in which a semiconductor device 0 is mounted on a semiconductor substrate on which a semiconductor device is integrated with an adhesive. As the insulating adhesive, for example, a polyimide resin, an epoxy resin, or the like can be used.

A power device and a control circuit are integrated in the semiconductor chip 1. Electrode 2 of the semiconductor chip 1
7 shows a state where the stud bumps 59 of the planar coil 50 of the present invention are in contact with each other.

Also in this case, since the semiconductor device is directly mounted on the semiconductor substrate by the bump electrodes, no wiring is required, and there is no problem of extra inductance of the wiring or noise induction. In addition, since the flat coil is manufactured separately as a chip, the process is short and the manufacture is easy.

[Embodiment 5] FIG. 7 is a partial sectional view of a small power converter in which a planar coil according to Embodiment 5 of the present invention is mounted on a semiconductor chip 1 on which a semiconductor device is integrated.

In this example, the planar coil 60 is mounted as a chip on the semiconductor chip 1 on which the semiconductor device is integrated, as in the previous examples. It is different from the previous examples in that it is not directed toward one side but is provided above.

An aluminum electrode pad 69 is provided in conductive contact with the opening of the coil conductor 67, and the electrode pad 69 and the electrode 2 on the semiconductor substrate are connected by the wire 5. 61 is a silicon wafer, 67
Is a coil conductor, and 64a and 64b are magnetic thin films.

As a manufacturing method, after FIG. 4B, after depositing an Al film (thickness: 2 μm) by, for example, a sputtering method, an electrode pad 69 is formed by photolithography and wet etching. The planar coil 60
Is bonded on the protective film 3 of the semiconductor chip 1 with an insulating adhesive or the like, and then the electrode pads 69 of the planar coil 60 and the electrodes 2 of the semiconductor chip 1 are wire-bonded. It should be noted that if the thickness of the silicon wafer 61 is large, the overall height will be high. Therefore, after forming the planar coil 60, it is preferable to grind the back surface of the silicon wafer 61 and reduce the thickness to about 200 μm before joining.

Also in this case, a planar coil is used as a chip.
Since it is made independently, there is no problem when forming the conventional connection conductor,
Also, the process is short and the production is easy. Wire connection can be performed at the same time as wire bonding of the semiconductor chip 1.

[Embodiment 6] FIG. 8 is a partial sectional view of a small-sized power converter according to Embodiment 6 of the present invention. In this example, unlike the previous examples, the planar coil is not mounted as a chip, and a thin-film laminated type planar coil is laminated via a polyimide insulating film 71 on a semiconductor chip 1 in which a semiconductor device is built. It is.

However, the coil conductor 77 of the planar coil 70
This terminal is different from the conventional small power converter shown in FIG. 9 in that the terminals are not directed toward the semiconductor chip 1 but are provided above. 74a and 74b are magnetic thin films.

An aluminum electrode pad 79 is provided in conductive contact with the opening of the coil conductor 77, and the electrode pad 79 and the electrode 2 on the semiconductor substrate are connected by the wire 5. Wire connection can be performed at the same time as wire bonding of the semiconductor chip 1.

The manufacturing method may be the same as that of the fifth embodiment. In this example, since the planar coil 70 is laminated on the semiconductor chip 1 in which the semiconductor device is integrated, the process is not much shortened as compared with the conventional micro power converter of FIG. Can be shortened, and there is an advantage that there is no problem in forming the connection conductor.

[0049]

As described above, according to the present invention, a pair of magnetic thin films sandwiching a coil conductor formed in a coil shape via an insulating film on a silicon wafer or a polymer film, By forming a thin-film laminated type planar magnetic induction component having a bump electrode as a terminal, through-hole formation is not required, so that the manufacturing process is shortened, and mounting on a semiconductor chip or the like is facilitated. Moreover, miniaturization has become possible.

The bump electrodes are aligned with the electrodes of the semiconductor chip on which the semiconductor device is integrated, and mounted on a semiconductor substrate. For example, as shown in the embodiment, a 1 W class DC
-In the DC converter, the volume of the module is reduced to almost 1/4.
Was reduced to

In particular, it has been shown that mounting can be carried out by low-temperature thermocompression bonding at about 200 ° C. by covering the surface with a polyimide resin.

[Brief description of the drawings]

FIG. 1A is a cross-sectional view of a planar coil according to a first embodiment of the present invention, and FIG. 1B is a partial cross-sectional view of a microminiature power converter in which the planar coil is mounted on a semiconductor chip.

FIG. 2 is a cross-sectional view of a micro power converter in which a planar coil according to a second embodiment of the present invention is mounted on a semiconductor chip.

3 (a) to 3 (e) are cross-sectional views in a process order for explaining a method of manufacturing the flat coil of FIG. 1;

4A to 4D are cross-sectional views of the planar coil of FIG. 1 in the order of steps following FIG. 3E;

FIG. 5A is a cross-sectional view of a planar coil according to a third embodiment of the present invention, and FIG. 5B is a partial cross-sectional view of a microminiature power converter in which the planar coil is mounted on a semiconductor chip.

FIG. 6A is a cross-sectional view of a planar coil according to a fourth embodiment of the present invention, and FIG. 6B is a partial cross-sectional view of a microminiature power converter in which the planar coil is mounted on a semiconductor chip.

FIG. 7 is a partial sectional view of a micro power converter according to a fifth embodiment of the present invention.

FIG. 8 is a partial sectional view of a micro power converter according to a sixth embodiment of the present invention.

FIG. 9 is a partial cross-sectional view of a conventional micro power converter.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Semiconductor chip 2 Electrode 3 Protective film 4 Ni / Cu / Ti film 5 Wire 6 Ni film 10, 20, 30, 40, 50, 60, 70 Planar coil 13a, 13b, 23a, 23b Insulating film 14a, 14b, 24a , 24b, 44a, 44b, 5
4a, 54b, 64a, 64b, 74a, 74b Magnetic thin film 17, 27, 37, 47, 57, 67, 77 Coil conductor 18, 28 Connection conductor 21, 41, 51, 61 Silicon wafer 22 Oxide film 25 Platinum nucleus 26 Intermediate Insulating film 29, 39 Solder bump 29a Bump metal 31 Polyimide film 49, 59 Stud bump 49a Fused bump 69, 79 Electrode pad 71 Polyimide insulating film

Claims (12)

[Claims] In a flat type magnetic induction component for a micro power converter having a structure in which a coil conductor formed in a coil shape is sandwiched between a pair of magnetic thin films via an insulating film, a bump electrode serving as a terminal of the coil conductor is provided. A planar magnetic induction component, comprising: 2. The planar magnetic induction component according to claim 1, further comprising a hemispherical solder bump. 3. The flat magnetic induction component according to claim 1, further comprising a stud bump formed by wire ball bonding. 4. The planar magnetic induction component according to claim 3, further comprising a stud bump formed by wire ball bonding of the solder wire. 5. The planar magnetic induction component according to claim 3, further comprising a stud bump formed by wire ball bonding of a gold wire. 6. The planar magnetic induction component according to claim 1, wherein a coil conductor is formed on a silicon wafer. 7. The planar magnetic induction component according to claim 1, wherein a coil conductor is formed on the polymer film. 8. The planar magnetic induction component according to claim 1, wherein a surface other than the bump electrode portion is covered with a polyimide resin. 9. An ultra-compact power converter comprising the planar magnetic induction component according to claim 1, wherein bump electrodes are aligned with electrodes of a semiconductor substrate on which a semiconductor device is integrated. apparatus. 10. A planar magnetic induction component according to claim 8, wherein the bump electrode is aligned with the electrode of the semiconductor substrate on which the semiconductor device is integrated, and the polyimide resin is thermocompression-bonded to the semiconductor substrate. Micro power converter. 11. A micro power converter in which a planar magnetic induction component having a structure in which a coil conductor formed in a coil shape is sandwiched between a pair of magnetic thin films via an insulating film is mounted on a semiconductor substrate on which a semiconductor device is integrated. 3. The ultra-compact power conversion device according to claim 1, wherein a terminal of the coil conductor and an electrode of the semiconductor device are connected by wire bonding. 12. The microminiature power converter according to claim 11, wherein the chip on which the planar magnetic induction component is formed is mounted on a semiconductor substrate on which a semiconductor device is integrated.