JPH0734034B2 - Magnetoresistive sensor and its manufacturing method - Google Patents

Description

The present invention relates to an MR (magnetoresistive) sensor composed of a ferromagnetic thin film used in a magnetic encoder, a VTR or the like, and a manufacturing method thereof.

[Prior Art] In recent years, it is made of a ferromagnetic thin film for the purpose of precisely controlling a magnetic encoder or a capstan motor for a VTR.
MR sensor is used, and this sensor is becoming indispensable for precise control of motors.

FIG. 12 shows a cross-sectional view of an example of a VTR capstan motor using this MR sensor. In the case of this example, reference numeral 15 in the drawing indicates a rotor yoke, reference numeral 16 indicates a rotor magnet, and reference numeral 13 'indicates an FG magnet in which a fine pitch N pole and S pole are alternately magnetized, and these are rotors. Make up part.

Reference numeral 17 denotes a motor driving stator coil, and 18 denotes a case. Reference numeral 14 is an MR sensor fixed to a resin holder 14H, and is arranged so that its magnetic detection portion faces the FG magnet 13 '. The rotation control of the motor is performed by using the output signal of the MR sensor. 14
M is a mold part in which the lead bonding part of the MR sensor is reinforced with resin, and reference numeral 7 is the MR sensor and the circuit board 19
The lead portion for electrically connecting and is shown.

FG magnets are usually magnetized at a fine pitch, and their magnetic field strength is also small. Therefore, in order to obtain the output signal necessary for controlling the rotation of the motor, the MR sensor 14
It is necessary to properly maintain the gap between the magnetic detection part and the FG magnet 13 ', that is, about 80 to 120 μm. If the gap is too large, the magnetic field strength will be weakened and the required output cannot be obtained. On the other hand, the reinforcement of the terminal portion by the mold requires a thickness of at least about 300 μm. Therefore, as shown in FIG. 13, the magnetic sensor 14 of the MR sensor
Even if S is made to face the FG magnet 13 together with the mold portion 14M, the desired output cannot be obtained, so normally, as shown in FIG. 14, avoid the mold portion 14M from the FG magnet 13,
The MR sensor is arranged so that the magnetic detection part 14S and the FG magnet can maintain an appropriate gap.

FIG. 15 (A) shows a front view of a conventional MR sensor before being attached to a resin holder, and FIG. 15 (B) shows a sectional view thereof. In the figure, 1 is a glass substrate, 14S is a magnetic detection part of the MR sensor 14, 14W is a wiring part, 14T is a terminal part, 14SB is a bonding part by soldering, 14M is a mold reinforcing part of the bonding part, and 7 is a lead. Is shown.
Further, 14P indicates a protective film made of an inorganic material. Bonding with solder is difficult to automate, which makes it difficult to rationalize the bonding process as compared with the wire bonding method, which is easy to automate. In addition, since the required bonding pad area is large, it is difficult to reduce the size of the device.

Further, when the bonding portion is exposed, an electrical short circuit is likely to occur and the lead is peeled off from the connection portion. Therefore, the bonding portion is mold-reinforced for the purpose of eliminating such a problem. In the case of solder bonding, since its melting point is low, it is not possible to apply the transfer molding method, which has high heat resistance, excellent shape stability during molding, and low molding cost when reinforcing the mold. Therefore, the bonding portion is reinforced by applying or potting a resin such as epoxy. The potting mold has poor shape stability and reproducibility. That is, in this method, when the molding resin is cured, there is a problem that the resin flows toward the upper surface of the terminal portion, that is, toward the sensor portion. Therefore, conventionally, the space between the lower end of the sensor part and the upper end of the mold part needs to be large considering the margin. Therefore, the MR sensor including the sensor pellet could not be downsized.

Therefore, the assembly of an element based on solder bonding has major problems in terms of automation of bonding and molding, stability of shape, and miniaturization of the element. Also,
Further, the connection by solder has a problem that reliability is poor in a high temperature heat load test such as a "solder heat resistance test". Also, when it is mounted on a circuit board, it cannot withstand the “reflow process” of heating the entire atmosphere of the board and surroundings to 200 ° C. or higher. Therefore, there is also a problem that it is not possible to “rationalize the rotating substrate assembly” by introducing the “reflow process”.

FIG. 15 shows a cross-sectional structure of another conventional element in which the lead is connected to the terminal portion on the pellet by a wire.

In this device, a protective film 50 is formed on a pellet magnetic detection portion having a magnetic detection portion 2 ', a wiring portion 3', and a terminal electrode 4'on a flat substrate 1 ', and the pellet and the lead 7 are connected by a wire 6. ′, And the resin is molded with a thermosetting resin 9 ″ so that the resin is covered with a constant thickness on the magnetic detection part. Normally, this molding is performed automatically by transfer molding. Also, compared with the previous example, it is labor-saving and can keep the assembly cost low.By adopting such a wire bonding structure, reliability in high temperature heat load test such as "solder heat resistance test" is high. It is possible to increase the sex.

However, with such a structure, it is very difficult to control the thickness of the resin covering the surface of the magnetic detection unit to a constant thickness when transfer molding is performed. Because MR
When manufacturing a sensor, many pellets are formed on a wafer such as silicon or glass at the same time. Although the wafer usually has a small thickness tolerance within the same wafer, the absolute value between the wafers is about 40 to 100 μm. Has a tolerance. That is, even in the case of individually separating the pellets, even if there is little variation in thickness within the same pellet, variation in thickness between pellets is about the same. Therefore, when the pellet-attached leads that have undergone wire bonding are set in a mold for transfer molding, the upper surface of the pellet, that is, the gap between the molded surface of the pellet and the mold cannot always be made constant. Therefore, it becomes impossible to make the thickness of the resin covering the surface of the magnetic detection unit constant.

Therefore, as described above, such an element is used, for example, in the state shown in FIG. 11 or FIG.
Since the thickness of the mold resin covering the upper surface of the magnetic detection unit is not constant, there is a problem that it is difficult to properly maintain the gap between the magnetic detection unit and the magnetic signal source. Therefore, the required output could not be stably obtained.

Further, for the purpose of eliminating the above-mentioned problems, it is possible to reduce variations in the thickness of pellets by selecting or polishing the wafer. However, even if it does, it is impossible to completely eliminate the variation in thickness. In reality, the absolute value is about 40 μm, so the variation in the gap between the magnetic detector and the magnetic signal source becomes larger in consideration of the assembling accuracy, and the output is not stable. There is also a problem that the cost is very high when the wafer is selected or polished.

[Problems to be Solved by the Invention] An object of the present invention is to solve the conventional problems described above and to provide an MR sensor with a high magnetic resistance and an exposed magnetic detection section.

Also, it is intended to provide a method for manufacturing an MR sensor that absorbs variations in the thickness of pellets, can easily and stably expose the magnetic detection unit, and can efficiently assemble the MR sensor, and that has excellent mass productivity. It is in.

[Means for Solving the Problems] In order to achieve such an object, an MR sensor according to the present invention is a resin-molded magnetoresistive sensor in which a magnetic detection part made of a ferromagnetic thin film is not covered with a molding resin. An element pellet having a magnetic sensing portion and a terminal electrode portion on the surface is bonded to one surface of the lead island on at least a part of the back surface thereof,
The terminal electrode and the lead are connected by a wire, and a thin resin layer having elasticity is formed on the other surface of the lead island.

Here, the thickness of the resin thin layer is preferably 50 μm or more and 300 μm or less.

The manufacturing method of the present invention comprises a step of adhering the MR sensor pellet on the lead island on at least a part of the back surface of the pellet, a step of electrically connecting the pellet and the lead by wire bonding, and at least a back surface of the lead island. The step of applying or adhering a resin having elasticity to a part of the pellet, by pressing the surface of the resin with a pin provided in the lower mold so that the magnetic detection portion forming surface of the pellet adheres to the upper mold. The method is characterized by including a step of pressing the pellets into an upper mold, and a step of injecting a resin into the mold and performing resin molding.

Here, the surface roughness of the die surface against which the upper surface of the pellet is pressed is preferably 1 μm or less.

[Operation] In the present invention, since the magnetic detection portion is exposed without being covered with the mold resin, it is easy and stable to arrange the MR sensor at a proper gap with respect to the magnetic signal source. You can do it.

Further, since the MR sensor according to the present invention can be manufactured by an automated process such as wire bonding and resin molding, it is possible to manufacture an MR sensor with high heat resistance at low cost and with good reproducibility. In particular, because the elastic resin is formed on the back surface of the lead island,
Good controllability of the molding process.

[Examples] Hereinafter, the present invention will be described with reference to the drawings.

FIG. 1 shows a structural example of an MR sensor using a glass substrate as an example of the MR sensor of the present invention. FIG. 1A is a front view and FIG. 1B is a sectional view. In the figure, 1 is a glass substrate,
2 is a ferromagnetic thin film, 2S is a magnetic sensing part made of a ferromagnetic thin film,
Reference numeral 3 is a wiring portion made of a conductive material, 4 is a terminal electrode, and 5 is a protective film made of an inorganic material. Also,
The resin 8 having elasticity is adhered to the opposite surface of the lead island to which the MR sensor pellets made of a glass substrate are adhered and fixed, and the magnetic detection portion 2S has a structure in which the resin is not covered. . Further, the thermosetting mold resin 9 mold-reinforces the terminal portion on the pellet, the wire 6 and the lead portion 7.

Next, a method for manufacturing the MR sensor of the present invention will be described. First, as shown in the front view of FIG. 2A and the sectional view of FIG.
1, that is, magnetic detection unit 2S, inorganic protective film 5, terminal electrode 4
The formed pellets are bonded onto the lead island 7I. The adhesive is not particularly limited, but Ag paste or the like is generally used. Note that the description of the adhesive layer is omitted in all the drawings. Next, as shown in the front view of FIG. 3 (A) and the sectional view of FIG.
Make electrical connection between the sensor pellet and the lead. Then, as shown in the front view of FIG. 4 (A) and the sectional view of FIG. 4 (B), the resin 8 having elasticity is adhered to the opposite surface of the island to which the pellets are adhered. Next, the lead with pellets is set in a mold. At that time, the resin portion 8 shown in FIG. 4 is pressed by a pin provided on the lower mold so that the magnetic detection portion forming surface and a part of the upper mold are in close contact with each other. Next, resin molding is performed to complete the MR sensor shown in FIG. The resin 8 can be formed by application instead of adhesion.

As described above, according to the present invention, since the magnetic detection portion is pressed against the upper die through the elastic resin layer 8 adhered or applied to a part of the lead island, the magnetic detection portion forming surface is not damaged. Can be molded. Further, by utilizing the elasticity of the resin layer 8, it is possible to absorb the thickness tolerance of the pellet and stably press the magnetic detection portion on the pellet against the upper mold. For example, even if the thickness variation of the pellet is 50 μm in absolute value, if the metal mold is designed so as to crush the resin layer 8 adhered to the lead island by 50 μm or more, the surface on which the magnetic detection section is formed is always made to be the upper metal. It can be pressed against the mold. In practice, the wafer thickness tolerance is generally 50 μm or more in absolute value. Therefore, the thickness of the resin layer 8 is also preferably 50 μm or more. In addition, the upper limit of the thickness is preferably 300 μm or less in consideration of the mold thickness on the back surface of the lead island. Any material having elasticity may be used as the material of the resin layer 8, but a material having high heat resistance is preferable since the mold temperature during molding is high. In that respect,
Silicone-based resins are preferred. In addition, there is no problem even with a modified acrylate resin.

Furthermore, in order to obtain the same effect as applying a silicon-based resin or the like, it is equally possible to bond an elastic rubber or the like through an adhesive.

It should be noted that, in order to prevent the magnetic detection portion surface from being damaged when the magnetic detection portion forming surface is pressed against the upper die, an organic material, that is, polyimide, is formed on the protective film 5 made of an inorganic material. Alternatively, a resin such as a solder resist may be further applied.

The resin for transfer molding has a very good flow, and the resin enters even in a small gap. Therefore, even when the surface of the pellet on which the magnetic sensing portion is formed is pressed against the upper mold during molding, if the upper mold has irregularities at that portion, the mold resin will flow and adhere to the surface of the pellet.
Practically, there is no problem even if the resin adheres to the surface of the pellet by about 10 μm, but it is more preferable that the surface has no resin. Table 1 shows the surface roughness of the upper die and the resin thickness flowing into the pellet surface after molding. When the surface roughness is 1 μm or less, the resin does not flow in. Therefore, the surface roughness of the upper mold is preferably 1 μm or less.

Further, as the resin for molding, a thermoplastic resin can be used as well as a thermosetting resin represented by an epoxy resin used at the time of transfer molding. However,
Regarding the heat resistance of the solder, it is disadvantageous as compared with the thermosetting resin used in transfer molding because the resin is thermoplastic, but there is no problem if a resin with high heat resistance such as PPS and PBT is used.

Furthermore, after molding with a mold such as transfer molding, there is no problem even if the resin 9'is applied and molded on the opposite surface side of the lead island to which the pellets are bonded as shown in FIG. By applying and molding the resin 9 ', the surface of the MR sensor can be made flat, and water can be prevented from penetrating from that portion, thus improving reliability. As the material of the resin 9 ',
Although not particularly limited, materials such as epoxy resin, silicon resin, and polyimide having high reliability such as moisture resistance are preferable.

The pellet structure applicable to the present invention includes structures other than those described above. FIG. 6 shows an example of such a pellet structure, FIG. 6 (A) is a front view, and FIG. 6 (B) is a sectional view. The pellet shown in FIG. 6 is obtained by glazeing the glass layer 9 on the upper surface of the stepped ceramic 1 '. Further, even if this glaze layer is formed on the entire substrate, there is no problem.

7 (A) and 7 (B) show another example of the pellet structure to which the present invention can be applied. In this example, the glass glaze layer is provided on the flat ceramic substrate 1 ″ only in the magnetic sensing portion forming portion. In order to maximize the magnetic characteristics of the element, the surface of the magnetic sensing portion forming portion should be flat. Since it is desirable, a glass glaze film is preferable to be formed on the magnetic sensing portion as shown in FIG. 6 or 7 rather than forming the magnetic sensing portion directly on the ceramic.

In addition to ceramics, substrates having such steps can be manufactured by machining glass or etching Si wafers, and these substrates can also be used in the present invention. You can

Example 1 As a first example of the present invention, an MR sensor having the sectional structure shown in FIG. 5 will be described. First, the manufacturing procedure of this MR sensor will be described below with reference to FIG. The magnetic detection part 2 and the wiring part 3 made of a ferromagnetic material were formed on the glass substrate 1. Then, the terminal portion 4 was formed. Next, a protective film 5 made of SiO ₂ was adhered and formed in a desired shape, and a solder resist 5'was applied and cured on the protective film 5 '. Since the steps up to this point are performed in a wafer state, a large number of MR sensor pellets are actually formed on the same wafer at the same time. The wafer was then diced into individual pieces on pellets.

Next, the pellet was die-bonded to a lead island to be fixed by adhesion. Next, the terminal portion of the pellet and the lead were connected with the wire 6, and then the silicon-based resin 8 was applied to the opposite surface of the lead island. Then, a lead frame with pellets was set in a mold for molding. At that time, the mold structure is such that the magnetic detection portion is pressed against the upper mold via the silicon-based resin 8 by the fixing pin in the lower mold. After the mold was set, the epoxy thermosetting resin 9 was injected, that is, transfer molding was performed, and then the epoxy resin 9'was potted on the recessed portion of the fixing pin to flatten the back surface of the MR sensor. In this way, the first example was manufactured.

Table 2 shows a comparison of the characteristic variation values in the solder reflow test between the MR sensor by the conventional solder bonding and this example. The characteristics of the sensor of this embodiment are much smaller than those of the conventional sensor.

Embodiment 2 FIG. 8 shows a cross section of another embodiment of the present invention. In this embodiment, instead of applying the silicon-based resin 8 in the first embodiment, a silicone rubber 8'is bonded with an epoxy-based resin 8 ". Other manufacturing steps are the same as in the first embodiment. By pressing the silicone rubber 8'with the pin of the above and pressing it against the upper mold and injecting the molding resin, an element in which the sensor surface is not molded is manufactured.

Example 3 FIG. 9 shows the cross-sectional structure of an MR sensor manufactured using pellets as shown in FIG. The manufacturing method is the same as in Example 1. This pellet has a step between the magnetic sensing portion and the terminal portion. Therefore, as shown in FIG. 9, it is possible to perform molding so that the magnetic sensing portion forming surface and the molding surface are substantially flush with each other. It can be said that the element having such a cross-sectional structure is advantageous when facing the magnetic signal source (FG magnet) 13 as shown in FIG. That is, the gap between the magnetic signal source and the surface on which the magnetic detection portion is formed can be set arbitrarily.

Embodiment 4 FIG. 11 shows an MR sensor pellet manufactured by using an MR sensor pellet in which a protective film 5 ″ made of polyimide is further applied on the surface of the pellet on which the magnetic sensing portion is formed as shown in FIG.
The cross-sectional structure of the sensor is shown. The manufacturing method is the same as in Example 1 above.
Alternatively, the procedure is the same as that of 3, but the thermoplastic resin PPS (12) was used as a material during resin molding.

In this embodiment, as in the case of the third embodiment, the molding is performed so that the molding surface on the terminal electrode is formed at a lower position than the magnetic detection forming surface during molding. Further, in this embodiment, the back surface of the lead island is molded with epoxy resin 9 '. In this way, by reinforcing the back surface of the lead island with the mold, it is possible to prevent the occurrence of problems such as electrical short-circuiting and water intrusion mediated by the lead island.

[Advantages of the Invention] As described above, according to the present invention, when the upper surface of the magnetic sensing portion is pressed against the upper mold, the elastic resin side is adhered or applied to the back surface of the lead island on which the sensor pellets are mounted. Since the resin is pressed by the pins in the lower mold, the thickness unevenness of the pellet is absorbed by the resin, and it is possible to manufacture an MR sensor in which the magnetic detection part is stably exposed.

Furthermore, since wire bonding is used, it is possible to manufacture MR sensors with high heat resistance. Also,
Since the assembly is performed by wire bonding and resin molding, automation of the assembly process is easy and rationalization can be achieved, so that the assembly cost can be reduced.

[Brief description of drawings]

1 (A) and 1 (B) are a front view and a sectional view showing the structure of the MR sensor of the present invention, FIGS. 2 (A), (B), 3 (A), (B) and 4 respectively. (A) and (B) are a front view and a sectional view showing a process for manufacturing the MR sensor of FIG. 1, FIG. 5 is a sectional view of the first embodiment, and FIGS. B) and FIGS. 7 (A) and 7 (B) are front views and sectional views of pellets before the completion of the sensor, which can be used in the sensor of the present invention, FIG. 8 is a sectional view of the second embodiment, and FIG. 9 is Sectional drawing of 3rd Example, FIG. 10 is a figure which shows schematic sectional form at the time of making the MR sensor of 3rd Example face a motor, FIG. 11 is sectional drawing of 4th Example, FIG. 12 is a sectional view showing a state in which a conventional sensor is arranged in a VTR motor to which the MR sensor of the present invention can be applied, and FIGS. 13 and 14 are conventional MR sensors of FIG. FIG. 15 (A) and FIG. 15 (B) are front views and cross-sectional views of a conventional element, and FIG. 16 is a cross-sectional view of another conventional MR sensor. 1 ... Glass substrate, 2 ... Ferromagnetic thin film, 2S ... Magnetic sensing part, 3 ... Wiring part, 4 ... Terminal part, 5 ... Protective film made of inorganic material, 6 ... Wire, 7 ... Lead portion, 8 ... resin layer having elasticity, 8 '... silicon rubber, 9 ... mold resin, 10,11 ... glass glaze layer, 12 ... thermoplastic resin, 13 ... FG magnet, 14 ... Conventional MR sensor, 15 …… rotor yoke, 16 …… rotor magnet, 17 …… motor drive stator coil, 18 …… case.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-62-128578 (JP, A) JP-A-62-131589 (JP, A) JP-A-2-62988 (JP, A) JP-A-2- 162279 (JP, A) JP-A-1-262488 (JP, A) Actual flat 2-24390 (JP, U)

Claims (7)

[Claims] 1. In a resin-molded mold type magnetoresistive sensor in which a magnetic detection part made of a ferromagnetic thin film is not covered with a molding resin, an element pellet having a magnetic detection part and a terminal electrode part on the surface has at least one of its back surface. Part of the lead island is bonded to one surface of the lead island, the terminal electrode and the lead are connected by a wire, and the other surface of the lead island is formed with a thin resin layer having elasticity. Is a magnetoresistive sensor. 2. The resin thin layer has a thickness of 50 μm or more and 300.
The magnetoresistive sensor according to claim 1, wherein the magnetoresistive sensor has a thickness of μm or less. 3. The magnetoresistive sensor according to claim 1, wherein the resin thin layer having elasticity is embedded with another resin. 4. The magnetism detecting portion is formed on the same surface as the upper surface of the mold on the terminal electrode or on a surface protruding from the upper surface. Or the described magnetoresistive sensor. 5. A step of adhering the MR sensor pellet on a lead island on at least a part of the back surface of the pellet, a step of electrically connecting the pellet and the lead by wire bonding, and at least one of the back surface of the lead island. The step of applying or adhering a resin having elasticity to the portion, the pellet is provided by pressing the surface of the resin with a pin provided on the lower die so that the magnetic detection portion forming surface of the pellet adheres to the upper die. A method of manufacturing a magnetoresistive sensor, comprising: a step of pressing the upper mold against an upper mold; and a step of injecting a resin into the mold and performing resin molding. 6. The surface roughness of the mold surface is at least 1 μm at least at a portion where the magnetic detection portion forming surface is pressed.
The method for manufacturing a magnetoresistive sensor according to claim 5, wherein: 7. The magnetoresistive sensor according to claim 5, further comprising a step of filling a resin on the opposite surface of the lead island to which the pellets are adhered after the resin molding step. Manufacturing method.