JPH0438486A - Magnetic resistance sensor and manufacture thereof - Google Patents

Abstract

PURPOSE:To stably manufacture an MR sensor whose magnetic detection part is exposed by absorbing the thickness irregularity of pellets by a resin by pressing the same by the pin in a lower mold. CONSTITUTION:A magnetic detection part 2 composed of a ferromagnetic material, a wiring part 3 and a terminal part 4 are formed to a glass substrate 1. Next, a protective film 5 composed of SiO2 is bonded and formed to the substrate in a required shape and a solder resist 5' is further applied thereon in a required shape to be cured. Subsequently, the wafer thereof is diced to be individually separated on pellets and, next, the pellets are bonded and fixed to lead islands by die bonding. Subsequently, the terminal parts of the pellets and leads are connected by wires 6 and a silicone resin 8 is applied to the opposite surface of the lead islands and molded to set a lead frame fitted with pellets to a mold.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application 1] The present invention relates to an MR (magnetoresistive) sensor made of a ferromagnetic thin film used in a magnetic encoder, a VTR, etc., and a method for manufacturing the same.

[Conventional technology 1] In recent years, MR sensors made of ferromagnetic thin films have been used for the purpose of precisely controlling magnetic encoders or capstan motors for VTRs, and these sensors have become indispensable for precisely controlling motors. It's coming.

FIG. 12 shows a sectional view of an example of a VTR cab drive motor using this MR sensor.

In the case of this example, the reference numeral 15 in the drawing indicates the rotor yoke, the reference numeral 16 indicates the rotor magnet, and the reference numeral 13° indicates the FG magnet whose north and south poles are alternately viewed at a minute pitch. It forms the child part.

Also, reference numeral 17 is a stator coil for driving the motor, and 18
indicates the case. Reference numeral 14 is a resin holder 1
It is an MR sensor fixed to 4H, and is arranged so that its magnetic detection part faces 13 degrees of the FG magnet.

The rotation of the motor is controlled using the output signal of the MR sensor. 14M is a molded part in which the lead bonding part of the MR sensor is reinforced with resin, and the code 7 is M.
A lead portion for electrically connecting the R sensor and the circuit board 19 is shown.

FG magnets are usually magnetized with a fine pitch,
The magnetic field strength is also small. Therefore, in order to obtain the output signal necessary to control the rotation of the motor, it is necessary to maintain the gap between the magnetic detection part of the MR sensor 14 and the FG magnet 13° appropriately, that is, about 80 to 120 μm. If the gap is too large, the magnetic field strength will weaken, making it impossible to obtain the required output. On the other hand, reinforcing the terminal portion by molding requires a thickness of at least about 300 μm. Therefore, as shown in FIG. 13, the magnetic detection part 14S of the MR sensor is F
Since the desired output cannot be obtained even if the G magnet 13 is opposed to the G magnet 13, normally the mold part 1 is
Avoid 4M from FG magnet 13, magnetic detection part 1
The MR sensor is arranged so that a proper gap can be maintained between the 4S and the FG magnet.

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 cross-sectional view thereof. In the figure, 1 is the glass substrate, 14s is the magnetic detection part of the MR sensor 14, 14W is the wiring part, 14T is the terminal part, 143B is the solder bonding part, 14M is the mold reinforcement part of the bonding part, 7
indicates a lead. Further, 14P indicates a protective film made of an inorganic material. Solder bonding is difficult to automate, and therefore it is difficult to streamline the bonding process compared to wire bonding, which is easier to automate. Furthermore, since the required area of the bonding pad is large, it is difficult to downsize the device.

Furthermore, when the bonding part is exposed, electrical shorts are likely to occur and leads may peel off from the connection part, so the bonding part is reinforced by molding in order to eliminate such problems. In the case of solder bonding, since its melting point is low, when reinforcing the mold, transfer molding, which has high heat resistance, excellent shape stability during molding, and low mold cost, cannot be applied. Therefore, the bonding portion has been reinforced by coating or botting with a resin such as epoxy. The mold produced by this botting has poor shape stability and reproducibility. That is, in this method, when the molding resin is cured, a problem arises in that the resin flows from the terminal portion toward the upper surface, that is, toward a part of the sensor. Therefore, in the past, it was necessary to provide a large space between the lower end of the sensor part and the upper end of the mold part, taking into account the margin. Therefore, it has not been possible to reduce the size of the MR sensor, including the sensor pellet.

Therefore, device assembly based on solder bonding has had major problems in terms of automation of bonding and molding, shape stability, and miniaturization of the device. Also,
Furthermore, connections using solder have a problem of poor reliability in high-temperature heat load tests such as "solder heat resistance tests." In addition, when attaching to a circuit board, the "reflow process" heats the board and the entire surrounding atmosphere to over 200 degrees Celsius.
I can't stand it. Therefore, the "reflow process"
There was also the problem that it was not possible to rationalize circuit board assembly by introducing this method.

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

This element has a magnetic sensing part 2 degrees above a flat substrate 1 degree.

A protective film 50 is formed on the magnetic sensing part of the pellet, which has a wiring part 3' and a terminal electrode 4°, and is connected to the pellet lead 7 with a wire 6°. It is molded with thermosetting resin 9" so that it is covered. Normally, this molding is done automatically by transfer molding. Therefore, compared to the previous example, assembly is labor-saving and assembly cost is reduced. In addition, by adopting such a wire bonding structure, reliability in high-temperature heat load tests such as "solder heat resistance tests" can be increased.

However, in such a structure, when transfer molding is performed, it is very difficult to control the thickness of the resin covering the surface of the magnetic sensing portion to a constant thickness. Because, M
When manufacturing the R sensor, many pellets are simultaneously formed on a wafer of silicon or glass, and the wafer usually has a small thickness tolerance within the same uniform bar, but the absolute value between wafers is about 40 to 100 μm. It has a tolerance of In other words, even if the pellets are separated into individual pellets, the variation in thickness between the pellets will be the same even if the variation in thickness within the same pellet is small. Therefore, when a lead with a pellet after wire bonding is set in a mold for transfer molding, the gap between the upper surface of the pellet, that is, the surface to be molded of the pellet, and the mold cannot always be kept constant. Therefore, it becomes impossible to maintain a constant thickness of the resin covering the surface of the magnetic sensing portion.

Therefore, as mentioned earlier, such an element is used in the state shown in FIG. 11 or FIG. There was a problem in that it was difficult to maintain an appropriate gap between the detection section and the magnetic signal source. Therefore, it was not possible to stably obtain the necessary output.

Further, in order to eliminate the above-mentioned problems, it is possible to reduce variations in the thickness of the pellets by sorting or polishing the wafers. However, even if this is done, it is impossible to completely eliminate the variation in thickness.Actually, the absolute limit is about 40 μm, so the variation in the gap between the magnetic sensing part and the magnetic signal source is The assembly becomes even larger when precision is taken into account, and the output is not stable.There is also the problem that the cost of sorting or polishing wafers is extremely high.

[Problem to be Solved by the Invention 1] An object of the present invention is to solve the conventional problems as explained above, and to provide a highly heat-resistant MR sensor in which the magnetic detection section is exposed.

Further, it is an object of the present invention to provide a manufacturing method for an MR sensor that can absorb variations in the thickness of pellets, easily and stably expose a magnetic detection part, and can efficiently assemble the MR sensor, and is excellent in mass production. It is in.

[Means for Solving the Problems 1] In order to achieve such an object, the MR sensor according to the present invention is a resin molded magnetoresistive sensor in which a magnetic sensing portion 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 its surface is adhered to one surface of a lead island (at least in part) on its back surface, and the connection between the terminal electrode and the lead is made by a wire. , and a thin elastic resin layer is formed on the other surface of the lead island.

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

The manufacturing method of the present invention includes a step of bonding an MR sensor pellet onto a lead island at least in part on the back surface of the pellet, a step of electrically connecting the pellet and the lead by wire bonding, and a step of bonding the MR sensor pellet onto a lead island at least in part on the back surface of the lead island. a step of applying or adhering an elastic resin to at least a portion of the pellet, and pressing the surface of the resin with a pin provided in the lower mold so that the magnetic sensing portion forming surface of the pellet comes into close contact with the stopper mold. The method is characterized in that it includes a step of pressing the pellet against an upper mold, and a step of injecting a resin into the mold and performing resin molding.

Here, it is preferable that the surface roughness of the mold surface against which the upper surface of the pellet is pressed is 1 μm or less.

[Function] In the present invention, since the magnetic detection part is exposed without being covered with molded resin, it is easy and stable to arrange the MR sensor with an appropriate gap relative to the magnetic signal source. I can do it.

Furthermore, since the MR sensor according to the present invention can be manufactured using automated processes such as wire bonding and resin molding, it is possible to manufacture highly heat-resistant MR sensors at low cost and with high reproducibility. Since an elastic resin is formed on the back surface, the controllability of the molding process is good.

[Example 1 The present invention will be described below with reference to the drawings.

FIG. 1 shows an example of the structure of an MR sensor using a glass substrate as an example of the MR sensor of the present invention.

FIG. 1(A) is a front view, and FIG. 1(B) is a sectional view. 1 in the diagram
2 is a glass substrate, 2 is a ferromagnetic thin film, 2s is a magnetic sensing part made of a ferromagnetic thin film, 3 is a wiring part made of a conductive material, 4 is a terminal electrode, and 5 is a protective film made of an inorganic material. . In addition, an elastic resin 8 is bonded to the opposite surface of the lead island to which the MR sensor pellet made of a glass substrate is bonded and fixed, and the magnetic sensing portion 2
The structure is that S is not covered with resin. Further, the thermosetting mold resin 9 molds and reinforces the terminal portions, wires 6, and lead portions 7 on the pellet.

Next, a method for manufacturing the MR sensor of the present invention will be described. First, as shown in the front view in FIG.
1, that is, the pellet on which the magnetic sensing portion 2S, the inorganic protective film 5, and the terminal electrode 4 are formed is adhered 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 this adhesive layer is omitted in all the figures. Next, Figure 3 (A
) is a front view, and (B) is a cross-sectional view of the wire 6.
Electrical connection between the MR sensor pellet and the lead is established. Next, as shown in FIG. 4(A) as a front view and as shown in FIG. 4(B) as a sectional view, the pellets are bonded and an elastic resin 8 is bonded to the opposite surface of the island. Next, the lead with pellets is set in a mold. At this time, the resin portion 8 shown in FIG. 4 is pressed by a pin provided on the lower mold so that the magnetic sensing portion forming surface and a part of the upper mold come into close contact. Next, the MR sensor shown in FIG. 1 is completed by resin molding. Note that the resin 8 can be formed not only by adhesion but also by coating.

In this way, in the present invention, the magnetic sensing part is pressed against the upper mold via the elastic resin N8 that is adhered or applied to a part of the lead island, so the mold can be molded without damaging the surface on which the magnetic sensing part is formed. can do. Furthermore, by utilizing the elasticity of the resin layer 8, the thickness tolerance of the pellet can be absorbed, and the magnetic sensing portion on the pellet can be stably pressed against the upper mold. For example, even if the absolute value of the variation in pellet thickness is 50 μm, if the mold is designed to compress the resin layer 8 bonded to the lead island by 50 μm or more, the surface on which the magnetic sensing portion will be formed will always be on the upper mold. It can be pressed into a 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. Further, the upper limit of the thickness is preferably 300 μm or less, taking into account the mold thickness on the back surface of the lead island. The resin layer 8 may be made of any material as long as it has elasticity, but since the mold temperature during molding is high, a material with high heat resistance is preferred. From this point of view, silicon-based resins are preferable. Also,
There is no problem with modified acrylate resin.

Further, in order to obtain the same effect as applying a silicone resin or the like, it is equally possible to adhere elastic rubber or the like through an adhesive.

In order to prevent the magnetic sensing part surface from being damaged when the magnetic sensing part forming surface is pressed against the upper mold, an organic material such as polyimide is further applied on the protective film 5 made of an inorganic material. Alternatively, a resin such as solder resist may be further applied.

Resin for transfer molding has a very smooth flow (
, resin can get into even the slightest gap. Therefore, even if the magnetic sensing portion forming surface of the pellet is pressed against the upper mold during molding, if the upper mold has irregularities in that area, the molding resin will flow in and adhere to the surface of the pellet. In practical terms, there is no problem even if a resin of about 10 μm is attached to the pellet surface, but it is more preferable that the surface is free of resin. Table 1 shows the surface roughness of the upper mold and the thickness of the resin that flowed onto the pellet surface after molding.

If the surface roughness is 1 μm or less, the resin will not flow in, so it is preferable that the surface roughness of the upper mold is 1 μm or less.

Table 1 Also, as the resin for molding, thermoplastic resins can be used as well as thermosetting resins, typically epoxy resins, used in transfer molding. however,
Regarding solder heat resistance, since the resin is thermoplastic, it is disadvantageous compared to the thermosetting resin used in transfer molding, but there is no problem if a resin with high heat resistance such as PPS or PBT is used.

Furthermore, after molding with a metal mold such as a transfer mold, there will be no problem even if a 9° resin is applied and molded on the opposite side of the lead island to which the pellet is bonded, as shown in FIG. By applying and molding the 9° resin, the back surface of the MR sensor can be made flat, and moisture can be prevented from entering from that part, improving reliability. The material for the resin 9° is not particularly limited, but materials such as epoxy resin, silicone, and polyimide, which have high reliability such as moisture resistance, are preferable.

Pellet structures applicable to the present invention include structures other than those described so far. FIG. 6 shows an example of such a pellet structure, with FIG. 6(A) being a front view and FIG. 6(B) being a sectional view. The pellet shown in FIG. 6 is made by glazing a glass layer 9 on the top surface of a ceramic layer with steps. Furthermore, there is no problem even if this glaze layer is formed over the entire substrate.

FIGS. 7(A) and 7(B) show other examples of the vine pellet structure to which the present invention is applied. In this example, a glass glaze layer is provided on a 1" flat ceramic substrate only in the area where the magnetic sensing part is formed. In order to maximize the magnetic properties of the element, the surface of the magnetic sensing part is flat. Therefore, it is more preferable to have a glass glaze film at the area where the magnetic sensing portion is formed, 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 also be manufactured by machining glass or etching Si wafers, and these substrates can also be used in the present invention. I can do it.

As a first embodiment of the present invention, an MR sensor having a cross-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. A magnetic detection section 2 and a wiring section 3 made of a ferromagnetic material were formed on a glass substrate 1. Then, the terminal portion 4 was formed. Next, a protective film 5 made of Sing was adhered and formed in a desired shape, and a solder resist 5° was further applied thereon in a desired shape and cured. Since the steps up to this point are performed on a wafer, a large number of MR sensor pellets are actually formed simultaneously on the same unibar. The wafer was then individually separated into pellets by dicing.

Next, the pellet was adhesively fixed to the lead island by bonding. Next, the terminal portion of the pellet and the lead were connected with a wire 6, and then a silicone resin 8 was applied to the opposite surface of the lead island. Next, the lead frame with pellets was set in a mold for molding. At this time, the mold structure is such that the magnetic detection section is pressed against the upper mold via the silicone resin 8 by a fixing pin in the lower mold. After setting the mold, an epoxy-based thermosetting resin 9 was injected, ie, transfer molding was performed, and then 9° of epoxy resin was potted in the area where the fixing pin recess was, to make the back surface of the MR sensor flat. In this way, the first example was manufactured.

Table 2 shows a comparison of the values of characteristic fluctuations in the solder reflow test between the conventional MR sensor using solder boarding and the present example. The sensor of this embodiment has very small characteristic fluctuations compared to the conventional example.

Table 2 * Solder reflow test results (conditions: 260° C. atmosphere, 60 SEC) Figure 8 shows a cross section of another example of the present invention. In this example, instead of applying silicone resin 8 in Example 1, silicone rubber 8° is bonded with epoxy resin 8''.Other manufacturing steps are the same as in Example 1.Lower mold An element whose sensor surface is not molded is manufactured by pressing the silicone rubber 8' against the upper mold with pins and injecting molding resin.

Figure 9 shows the cross-sectional structure of an MR sensor manufactured using the pellet shown in Figure 6. The manufacturing method is the same as in Example 1. This pellet has a step between the magnetic sensing part and the terminal part. Therefore, as shown in FIG. 9, it is possible to mold the magnetic sensing portion forming surface and the molding surface so that they are substantially on the same plane. It can be said that an element having such a cross-sectional structure has an advantageous structure when it is opposed to a magnetic signal source (FG magnet) 13, as shown in FIG. 1O. That is, the gap between the magnetic signal source and the magnetic sensing portion formation surface can be set arbitrarily.

Uri U Figure 11 shows an MR sensor manufactured using an MR sensor pellet with a protective film 5'' made of polyimide further coated on the magnetic sensing portion forming surface of the pellet as shown in Figure 7. The cross-sectional structure is shown.The manufacturing method was the same as in Example 1 or 3, except that thermoplastic resin PP5 (12) was used as the material for resin molding.

In this example, as in the previous example 3, molding is performed so that the mold surface on the terminal electrode is formed at a lower position than the magnetic detection forming surface. Further, in this embodiment, the back surface of the lead island is molded with epoxy resin at 9 degrees. In this way, by reinforcing the back surface of the lead island by molding, it is possible to prevent problems such as electrical short-circuits and moisture infiltration caused by the lead island.

[Effects of the Invention] As described above, in the present invention, when pressing the upper surface of the magnetic sensing part against the upper mold, the elastic resin side adhered or applied to the back surface of the lead island on which the sensor pellet is placed is pressed. Since the pellet is pressed by a pin in the lower mold, the uneven thickness of the pellet is absorbed by the resin, making it possible to stably manufacture an MR sensor in which the magnetic detection part is exposed.

Furthermore, since wire bonding is used, it is also possible to produce an MR sensor with high heat resistance. Furthermore, since assembly is performed using wire bonding and resin molding, the assembly process can be easily automated and streamlined, thereby reducing assembly costs.

[Brief Description of the Drawings] Figures 1 (A) and (B) are a front view and a cross-sectional view showing the structure of the MR sensor of the present invention, respectively, Figures 2 (A), (B), and Figure 3 (A) , (B) and FIGS. 4(A) and CB) are a front view and a cross-sectional view showing the process for manufacturing the MR sensor of FIG. 1, FIG. 5 is a cross-sectional view of the first embodiment, and FIG. Figures (A) and (B) and Figures 7 (A) and (B) are front views and cross-sectional views of the vine used in the sensor of the present invention and the pellet before the sensor is completed. Figure 8 is a cross-section of the second embodiment. Figure 9 is a cross-sectional view of the third embodiment, Figure 10 is a diagram showing a schematic cross-sectional form when the MR sensor of the third embodiment is opposed to the motor, and Figure 11 is a cross-sectional view of the fourth embodiment.
12 is a sectional view showing a conventional sensor arranged in a VTR motor to which the MR sensor of the present invention is applied; FIGS. 13 and 14 are the conventional MR sensor of FIG. 12. 15(A) and (B) are a front view and a sectional view of a conventional element, and FIG. 16 is a sectional view of another conventional MR sensor. . 1...Glass substrate, 2...Ferromagnetic thin film, 2S...Magnetic detection section, 3...Wiring section, 4...Terminal section, 5...Protective film made of inorganic material, 6. ...Wire 7...Lead part, 8...Resin layer having elasticity, 8°...Silicon rubber, 9...Mold resin, 10.11...Glass glaze layer, 12...Heat Plastic resin, 13... FG magnet, 14... Conventional MR sensor 15... Rotor yoke, 16... Rotor magnet, 17... Stator coil for motor drive, 18...
·Case. (A) (B) ← Manufacturing process? (Front view shown) 3JL - Cross section Figure 2 (A) (B) Honjosho 1: J
, 6 A front view of MR's dead body and his drunken face (A)
(B) (Front view L1 showing direct machining f!2 (A) (a) Front view showing J-) Jt; Blood diagram (A) (B) Front view of Bell rate OJv 'Bill surface diagram No. 6 Cross-sectional section of F'l in Figure 1 (A) (Japanese) B, b tome, normal form ■ Concave and υr surface diagram Figure A, 2nd disaster tf'l117 ) Hungry eye Figure 8 1B MR Hinzu and [-evening fI b σ diagram Figure 1Q Figure 5i Figure VTR motor and seven teeth 58 MR Jin's Rohi 11
(A) CB) Conventional MR model - I171 front view jp ratio 1 page rV Figure 15

Claims (1)

[Scope of Claims] 1) In a resin-molded magnetoresistive sensor in which a magnetic sensing portion made of a ferromagnetic thin film is not covered with a molded resin, an element pellet having a magnetic sensing portion and a terminal electrode portion on its surface has a magnetic sensing portion on its back surface. at least a portion of the terminal electrode is bonded on one surface of the lead island, and the terminal electrode and the lead are connected by a wire,
A magnetoresistive sensor characterized in that a thin elastic resin layer is formed on the other surface of the lead island. 2) The thickness of the thin resin layer is 50 μm or more and 300 μm
The magnetoresistive sensor according to claim 1, characterized in that: 3) The magnetoresistive sensor according to claim 1 or 2, wherein the thin elastic resin layer is embedded in another resin. 4) The magnetic sensing 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. Magnetoresistive sensor. 5) adhering an MR sensor pellet onto the lead island on at least a portion of the back surface of the pellet;
A step of electrically connecting the pellet and the lead by wire bonding, a step of applying or adhering an elastic resin to at least a portion of the back surface of the lead island, and a step of applying a magnetic sensing portion forming surface of the pellet to an upper mold. A step of pressing the surface of the resin with a pin provided in a lower mold to press the pellet against the upper mold so that the pellet adheres tightly, and a step of injecting the resin into the mold and molding the resin. A method for manufacturing a magnetoresistive sensor characterized by: 6) The method for manufacturing a magnetoresistive sensor according to claim 5, wherein the surface roughness of the mold surface is 1 μm or less at least in a portion against which the magnetic sensing portion forming surface is pressed. 7) The method for manufacturing a magnetoresistive sensor according to claim 5 or 6, further comprising the step of filling a resin on the opposite surface of the lead island to which the pellets are bonded after the resin molding step. (Margin below)