JPS633516B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a structure of a condenser microphone having a semiconductor device.

Conventionally, a microphone with a semiconductor device called an electret condenser microphone consists of a metal plate called a back plate that is electrically connected to the signal input electrode of the semiconductor device, and an electret that is placed opposite the metal plate with a space between it. It has a structure in which a capacitor is formed in the space sandwiched between the metal plate and the electret film. The operating principle is that when the electret film vibrates in response to the vibrations of the air, the potential of the capacitor changes in response to the vibration, and this change in potential is transmitted from the back plate to the signal input electrode of the semiconductor device. Then, the change in the input potential is converted into a current signal and output to the outside.

A conventional electret condenser microphone (hereinafter abbreviated as ECM) having such a function, as shown in FIG. , electret film 1
is a cylindrical aluminum case 5 that encloses the ECM with an insulator 4
insulated from In addition, a back chamber 6 is provided on the rear surface of the back electrode plate 2, and a field effect transistor (hereinafter referred to as FET) 7 sealed with molded resin is fixed in the ECM with an insulating ring 8, and the gate lead 9 of the FET 7 is Adhere to the back electrode plate with paste etc. to make electrical contact. Next, the drain and source leads 10 of the FET 7 are connected to the printed board through an insulating rubber plate 12 for insulating the gate lead 9, source and drain leads 10 of the FET 7, the cylindrical aluminum case 5, and the printed board 11. 11 with solder 13.

As is clear from FIG. 1, such a conventional ECM structure has the disadvantage that it requires a large number of built-in parts, making the device complex and large. This is because semiconductor elements (transistors) are susceptible to adverse effects such as contamination of impurities from the external atmosphere and must be hermetically sealed from the outside using resin sealing. It was also necessary to create a means for connecting each of the electrodes, a back chamber, etc., and the shape of the ECM inevitably became larger. Also, the ECM
Because it consists of a back plate to which the gate electrode of the FET is connected and forms one electrode of the capacitor, as well as many other parts, manufacturing costs are high, making it extremely difficult to manufacture at a low price.

SUMMARY OF THE INVENTION The object of the present invention is to provide an electric condenser microphone (ECM) structure which eliminates the above-mentioned drawbacks and which has an extremely simple structure and can be manufactured at low cost.

The electret condenser microphone of the present invention is
A metal plate that faces the electret film and forms one end surface of the capacitive element forms one plane of the semiconductor device, and the input electrode of the semiconductor device is connected to the metal plate on this one plane, and the semiconductor It is characterized by a space called a back chamber facing the device.

Hereinafter, one embodiment of the present invention will be described in order of manufacturing steps with reference to the drawings. In the lead frame 13 shown in FIG. 2, the tip of the lead 14 which becomes the gate terminal is the other lead 1 which becomes the drain and source terminals.
A field effect semiconductor element (FET) is die-bonded to the chip mount part 17 on the gate lead 14 of this lead frame 13 using normal semiconductor device assembly technology, and each lead is Electrical connection is made by wire bonding. After this, each lead terminal 14 to 16 and
The FET chip is sealed with resin and formed as shown in FIG. The molded resin part 18 has a cylindrical outer shape, and the lead connection part of the lead frame 13 and a part of the lead connected to this connection part are exposed from one flat surface, and the gate lead 1 is exposed on the opposite flat surface 19.
4 is exposed, and the tip 20 and the flat surface 19 form the same flat surface.
If the tip portion 20 and the flat surface 19 are not on the same plane after resin sealing, they may be polished using a known polishing technique or the like so that they become on the same plane. Further, projections are formed in advance on the casting mold so that after molding, a recessed space called a back chamber 21 having an opening is formed in the flat surface 19. At this time, the protrusions formed on the casting mold can be easily installed by shaping the knockout pin used to release the molded product from the mold into a desired shape. Next, a metal coating is deposited on the entire surface of the flat surface 19 by a normal vapor deposition method or the like. At this time, the metal coating and the tip 20 are electrically connected, and the metal coating is connected to the gate electrode of the semiconductor element. Before or after forming the metal coating, the connecting portion of the lead frame 13 is cut to obtain a molded semiconductor device.
FIG. 4 shows a cross-sectional view of the semiconductor device shown in FIG. 3 actually incorporated into an ECM. The semiconductor device 22 is insulated and fixed from an aluminum case 27 by an insulating material 26, and the semiconductor device 22 is The coating 23 can be used as it is as a back electrode plate. That is, the electret film 24 forms a capacitor with the metal coating 23 via the spacer 25, and is electrically connected to the metal coating 23.
An input signal is supplied through the gate electrode of the FET,
Source and drain terminal 1 according to this input signal.
Outputs are obtained from 5 and 16. The back chamber 21 formed in the center of the semiconductor device 22 controls the sound quality characteristics, and is created during molding using the aforementioned knockout pin. Furthermore, the source,
The gate lead projecting to the output end along with the drain terminals 15 and 16 is unnecessary and is therefore preferably removed.

According to this embodiment, the back chamber, which was conventionally formed between the back electrode plate and the semiconductor device, is formed so as to protrude into the inside of the semiconductor device, and this back chamber is created at the same time as the semiconductor device is formed. That is, the back plate
Since the connection with the gate electrode of the FET can be made extremely easily, the structure of the ECM is extremely simple, and its manufacture is also easy, which greatly reduces the manufacturing cost and provides a low-cost ECM.

In this example, an example was presented in which a lead frame was used as the lead terminal of the FET, but a round wire or the like may also be used as the lead terminal. By forming the outer periphery of the evaporation surface (the outer periphery of the flat part 19 in FIG. 3) so that no metal is evaporated, it is possible to further improve the insulation effect between the outer case and the semiconductor. There may be no insulating member between the device and the case.

Further, as a method of forming the semiconductor device and the back electrode plate, a method as shown in FIGS. 5 and 6 may be used.

FIG. 5 shows a structure at the time of resin sealing in the semiconductor device manufacturing process as another embodiment of the present invention. A semiconductor element (FET) is mounted on a lead frame having the structure shown in FIG. 2 by die bonding and wire bonding using known techniques, and this lead frame 13 is placed with the lead tips facing down into a mold into which molding resin is injected. Insert it almost vertically to 30. At this time, a conductive resin 31 such as silver paste is previously spread on the bottom of the mold 17 with approximately the same thickness, and by inserting the lead terminals 14 of the lead frame 13, the gate lead The tip of 14 is immersed in conductive resin 31 to establish electrical contact. At this time, the thickness of the conductive resin should be equal to or less than the length of the protrusion of the gate lead 14 so that the other source and drain leads 15 and 16 of the lead frame 13 do not come into electrical contact with the conductive resin 31. . Next, the conductive resin 3
A non-conductive resin 32 as a molding material is placed on top of the lead frame 1, and the lead frame is fixed by casting, and the semiconductor element is hermetically sealed. At this time, a metal protrusion 33 is inserted from the bottom of the mold 30 to form a back chamber.

FIG. 6 is a cross-sectional view of the molded FET shown in FIG. 3 taken out of the mold and assembled into an ECM.
A spacer 34, an electric film 35, and an insulating plate 36 are attached to the resin-sealed FET, and the FET is wrapped in a cylindrical aluminum case 37.

Even in such embodiments, the formation of the back electrode plate, the formation of the back chamber, and the connection between the back electrode plate and the FET are performed during the manufacture of the semiconductor device.
It is possible to connect to the gate lead of the ECM, making it extremely easy to create a semiconductor device for ECM, and also to miniaturize the ECM structure.
It is possible to achieve lower prices. The height of the cylindrical ECM created in this example was reduced from 9.8 mm to approximately 5 to 6 mm, which is approximately half the size of the conventional one.

The metal coating as the back electrode plate shown in FIG. 4 may be any conductive material that has good adhesion to the molding resin, such as gold, titanium, platinum, etc.
The conductive resin shown in FIG. 5 may be any resin other than silver paste that has good adhesion to the mold resin and is conductive. Further, the thickness of these back electrode plates may be as long as it can function as one electrode of a capacitor, and may be several microns or more. Furthermore, the molding resin may be epoxy, silicone resin, or the like.
As an active element molded into a semiconductor device, a bipolar transistor may be used instead of a MOS FET.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view of a conventional electret condenser microphone including a semiconductor device, Fig. 2 is a shape diagram of a lead frame for a semiconductor device showing an embodiment of the present invention, and Fig. 3 is an embodiment in which a semiconductor device is molded. FIG. 4 is a sectional view of essential parts of an electret condenser microphone showing one embodiment of the present invention; FIG. 5 is a process diagram showing another embodiment of molding a semiconductor device; FIG. This figure is a cross-sectional view of the semiconductor device produced in accordance with FIG. 5 applied to an electret condenser microphone. 1... Electret film, 2... Back plate, 3... Spacer, 4... Insulator, 5... Cylindrical aluminum case, 6... Back chamber, 7... Field effect transistor, 8... Insulation Ring, 9...gate lead, 10...source/drain lead, 11...
...Printed board, 12...Insulating rubber plate, 50...
Solder, 13...Lead frame, 14...Gate lead, 15...Source lead, 16...Drain lead, 17...Die bonding part, 18,
32...Mold resin, 19...Flat surface, 20...
...gate lead tip, 21...back chamber, 22...
Semiconductor device, 23... Metal coating (back electrode plate), 24,
35...electret film, 25,36...
... Spacer, 26 ... Insulator, 27, 37 ... Aluminum case, 30 ... Mold, 31 ... Conductive resin, 33 ... Knockout pin, 34 ... Insulating plate.

Claims (1)

[Claims] 1. A resin structure that encapsulates a transistor element, has a recessed space on one end surface, and has an input electrode of the transistor element led out to the one end surface, and a resin structure that is adhered to the one end surface of the resin structure and a conductive film connected to the input electrode of the transistor element;
A condenser microphone comprising: a metal thin film that is disposed opposite to and spaced from the conductive film, and forms a capacitive element together with the conductive film.