JP2001257311A - Electrostatic protective circuit for semiconductor device and method of using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrostatic protective circuit for a semiconductor device, which can effectively prevent the breakdown of a semiconductor IC due to electrostatics which is most likely to occur under the conditions where the semiconductor IC is handled as a single unit, in other words, from an assembly-selection-shipping process to a packaging-mounting on substrate process, and which can be separated from an inner circuit during operation, and to also provide a method of using the same. SOLUTION: The electrostatic protective circuit, which is a series combination of a fuse 1 and a capacitor 2 is inserted between a signal terminal and the inner circuit. After mounting the semiconductor device on a substrate, an AC signal is inputted into the signal terminal to melt the fuse 1, thereby separating the electrostatic protective circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrostatic protection circuit for a semiconductor device for securing transmission of a high-frequency signal and preventing electrostatic breakdown, and a method of using the same.

[0002]

2. Description of the Related Art Hitherto, an electrostatic protection circuit for protecting an internal circuit from a high voltage input due to static electricity or the like applied to a signal input terminal or a signal output terminal of a semiconductor integrated circuit has been proposed.

The destruction of a semiconductor integrated circuit due to static electricity occurs most frequently in a situation where the semiconductor integrated circuit is handled as a single unit, ie, during an assembly process, a sorting process, a shipping / packing process, and a mounting process on a substrate. . After mounting on the circuit board,
The signal terminals are connected to other semiconductor integrated circuits and passive elements,
Since the impedance is lowered or the possibility of intrusion of static electricity from the outside is reduced, the necessity of the electrostatic protection circuit is reduced.

Japanese Patent Application Laid-Open No. 5-121662 discloses a semiconductor integrated circuit having an electrostatic protection circuit as shown in FIG. As shown in FIG. 2, the electrostatic protection circuit has a configuration in which a fuse 3 is inserted between an electrostatic protection diode 4 and a circuit to be protected. When a breakdown voltage is applied to the diode 4, a current flows in the reverse direction, so that the internal circuit can be protected.

After mounting the semiconductor integrated circuit, a large direct current is applied to the fuse 3 to blow the fuse 3. As a result,
By separating the electrostatic protection circuit from the signal terminal, even when a high-speed signal is input to the signal terminal, the capacitance component of the electrostatic protection circuit is not affected, and the high-speed performance of the input signal is not impaired. .

[0006]

However, in the electrostatic protection circuit shown in FIG. 2, it is necessary to flow a large direct current in order to blow the fuse 3, and in this case, since the diode 4 is provided, it is necessary to supply IN to IN. It is necessary to set GND to the positive side. However, IN is connected to an internal circuit, and a large direct current from GND flows not only through the diode 4 but also through the internal circuit.

[0007] Therefore, it is necessary to flow a very large current, and the chip generates heat, or a bonding wire for connecting an electrode on the surface of the chip to a lead electrode outside the package, or the wiring is broken. There is also a risk of electromigration. After the semiconductor integrated circuit is mounted on the substrate, it is often difficult to apply a positive potential from the GND side in consideration of system restrictions.

In FIG. 2, the diode 4 is inserted in the reverse direction so that current does not flow under normal voltage application conditions. was there. Therefore, various inconveniences as described above have occurred.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and effectively prevents the destruction of an internal circuit due to static electricity in an assembling process, a sorting process, a shipping / packing process, and a mounting and assembling process on a board. On the other hand, it is an object of the present invention to provide an electrostatic protection circuit for a semiconductor device which can be separated from an internal circuit during actual operation of the semiconductor device, and a method for using the same.

[0010]

In order to achieve the above object, according to the present invention, there is provided an electrostatic protection circuit for a semiconductor device provided between a signal terminal and an internal circuit. Is characterized in that a fuse and a capacitor are arranged in series.

According to a second aspect of the present invention, in the first aspect of the present invention, when the AC signal is input to the fuse, the electrostatic protection circuit is disconnected from the signal terminal.

According to a third aspect of the present invention, in the second aspect, the AC signal is inputted from a signal terminal side.

The invention according to claim 4 is the invention according to claim 2 or 3.
In the invention described above, the AC signal is input to a signal terminal at an arbitrary point in a semiconductor device manufacturing process.

The invention according to claim 5 is the invention according to claim 2 or 3.
In the invention described above, the AC signal is input to a signal terminal after the semiconductor device is mounted on a substrate.

According to a sixth aspect of the present invention, in the first aspect of the present invention, the AC signal is inputted to the signal terminal for a predetermined time.

According to a seventh aspect of the present invention, there is provided a method of using an electrostatic protection circuit for a semiconductor device, wherein a fuse and a capacitor are arranged in series between a signal terminal and an internal circuit. And disconnects the electrostatic protection circuit from the signal terminal.

An eighth aspect of the present invention is characterized in that, in the seventh aspect of the present invention, an AC signal is inputted from a signal terminal side.

The ninth aspect of the present invention is the seventh or eighth aspect.
In the invention described above, an AC signal is input to a signal terminal at an arbitrary point in a manufacturing process of the semiconductor device, and the electrostatic protection circuit is disconnected from the signal terminal.

According to a tenth aspect of the present invention, in the seventh or eighth aspect, after mounting the semiconductor device on the substrate, an AC signal is input to the signal terminal to disconnect the electrostatic protection circuit from the signal terminal. It is characterized by.

The invention according to claim 11 is the invention according to claims 7 to 1
0. The invention according to any one of 0, wherein an AC signal is input to the signal terminal for a predetermined time to disconnect the electrostatic protection circuit from the signal terminal.

[0021]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 is a circuit diagram illustrating an electrostatic protection circuit of a semiconductor device according to an embodiment of the present invention.
Fuse 1 to GND from between signal terminal IN and internal circuit
And the capacitor 2 are connected in series.

The static electricity applied to the signal terminal is an instantaneous current pulse,
A current flows through ND. Therefore, it is possible to suppress a current from flowing through the internal circuit due to static electricity. Since the rise time of the static electricity is about several nanoseconds to several microseconds, the high frequency component becomes large. On the other hand, since the impedance of the capacitor 2 is low, it is easy to pass a current. Since the static electricity is a short-time current pulse, the fuse 1 is not blown.

Next, a method of using the electrostatic protection circuit of the semiconductor device according to the embodiment of the present invention will be described. Usually, during the process from assembly to mounting of a semiconductor integrated circuit,
It is highly possible that static electricity is applied to the signal terminals. On the other hand, if the electrostatic protection circuit is not separated from the semiconductor device after mounting, there is an adverse effect that the capacitor 2 of the electrostatic protection circuit blunts the waveform of the input signal.

After mounting the semiconductor integrated circuit, a high-frequency AC signal is input to a signal terminal. The higher the frequency of the capacitor 2, the easier the current flows, so that the fuse 1 can be blown by applying an AC signal with a sufficiently high frequency. When the fuse 1 is blown, the capacitor 2 is cut off from the internal circuit, and the input signal is not affected.

The fuse has a property of being blown when the applied current exceeds the rated value for a certain period of time. Therefore, even if an AC signal is applied to the signal terminal during the test of the semiconductor integrated circuit, the fuse 1 is not blown because the time during which the signal is applied is short.

An actual example is shown below.
Assuming 1 pF and the frequency at the time of disconnection f = 100 MHz, the impedance (capacitive reactance) of the capacitor is expressed by the following (Equation 1).

1 / (2πfC) = 1592 (Ω) (Equation 1)

As can be understood from (Equation 1), the impedance of the capacitor changes depending on the frequency of the applied AC signal. For a low-frequency AC signal, almost no current flows because the impedance increases. However, for high frequency AC signals,
Since the impedance is reduced, it flows freely through the capacitor. In the case of a DC signal, no current flows after charging.

When the power supply voltage is 5 V, the value of the current flowing through the electrostatic protection circuit is 3 mA according to the following (Equation 2).

5/1592 = 0.003 (A) (Formula 2)

Here, assuming that the resistance of the fuse is 10Ω, the electric power W generated by the fuse is 15 mW as shown in the following (Equation 3).

W = 5 × 0.003 = 0.015 (W) (Equation 3)

Therefore, the fuse may be designed to be cut at 15 mW.

In the configuration of the present invention, the diode 4 of the conventional electrostatic protection circuit is replaced with a capacitor 2. In the prior art, when the reverse voltage applied to the diode 4 reaches a certain limit (breakdown voltage),
Utilizing the characteristic that a current flows rapidly, a high-frequency signal that destroys an internal circuit is discharged to GND.

On the other hand, in the present invention, the low-frequency signal of the capacitor 2 is hard to pass, and the high-frequency signal is easy to pass.
Can play a role. As described above, the effect is the same when the semiconductor device is a single device before mounting.

However, when the fuses 1 and 3 are blown, the difference becomes remarkable. In the prior art, since the diode 4 is provided, a large direct current must be supplied from the GND side to blow the fuse 3. On the other hand, according to the present invention, the fuse 1 can be blown only by applying an AC signal from the signal terminal side IN.

Further, even if a high-frequency signal is applied when the semiconductor device is a single unit before mounting, the fuse 1 is kept in the fuse 1 for a predetermined time.
If the high-frequency signal is not applied, the fuse 1 does not blow and the electrostatic protection circuit does not separate.
How long the fuse 1 to be blown is used is determined on the basis of how much frequency signal needs to be applied in a test or the like before mounting.

The above-described embodiment is shown as an example of a preferred embodiment of the present invention, and various modifications can be made without departing from the gist of the present invention.

[0040]

As is apparent from the above description, according to the electrostatic protection circuit for a semiconductor device and the method of using the same according to the present invention, a capacitor is connected to the signal terminal of the semiconductor integrated circuit from the assembly to the mounting process. Because of this, internal circuits can be prevented from being damaged even when static electricity is applied. When an AC signal is applied to the signal terminal for a predetermined time after mounting, a current flows through the capacitor, so that the fuse can be blown. When the fuse is blown, the influence of the capacitance of the capacitor can be eliminated.

When the fuse is blown, the capacitor is disconnected from the signal terminal, so that a high-frequency signal can be transmitted to the internal circuit. In particular, signal terminals that handle high frequencies are weak against static electricity because no capacitor is provided. However, the present invention is also effective for protecting such signal terminals as static electricity.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an electrostatic protection circuit according to an embodiment of the present invention.

FIG. 2 is a circuit diagram showing an electrostatic protection circuit according to the related art.

[Explanation of symbols]

 1 Fuse 2 Capacitor 3 Fuse 4 Diode

Claims (11)

[Claims] 1. An electrostatic protection circuit for a semiconductor device provided between a signal terminal and an internal circuit, wherein the electrostatic protection circuit includes a fuse and a capacitor arranged in series. Electrostatic protection circuit. 2. The electrostatic protection circuit for a semiconductor device according to claim 1, wherein the electrostatic protection circuit is disconnected from the signal terminal when an AC signal is input to the fuse. 3. The electrostatic protection circuit according to claim 2, wherein the AC signal is input from the signal terminal side. 4. The electrostatic protection circuit for a semiconductor device according to claim 2, wherein the AC signal is input to the signal terminal at an arbitrary point in a manufacturing process of the semiconductor device. 5. The electrostatic protection circuit according to claim 2, wherein the AC signal is input to the signal terminal after mounting the semiconductor device on a substrate. 6. The electrostatic protection circuit for a semiconductor device according to claim 2, wherein the AC signal is input to the signal terminal for a predetermined time. 7. It is provided between a signal terminal and an internal circuit,
A method for using an electrostatic protection circuit of a semiconductor device in which a fuse and a capacitor are arranged in series, wherein an AC signal is input to the fuse to disconnect the electrostatic protection circuit from the signal terminal. How to use the electrostatic protection circuit of the device. 8. The method according to claim 7, wherein the AC signal is input from a side of the signal terminal. 9. The semiconductor device according to claim 7, wherein the AC signal is input to the signal terminal at an arbitrary point in a manufacturing process of the semiconductor device, and the electrostatic protection circuit is disconnected from the signal terminal. 9. A method for using the electrostatic protection circuit for a semiconductor device according to claim 8. 10. The semiconductor device according to claim 7, wherein after mounting the semiconductor device on a substrate, the AC signal is input to the signal terminal to disconnect the electrostatic protection circuit from the signal terminal.
9. A method for using an electrostatic protection circuit for a semiconductor device according to item 8. 11. The signal processing apparatus according to claim 7, wherein the AC signal is input to the signal terminal for a predetermined time to disconnect the electrostatic protection circuit from the signal terminal.
13. A method for using the electrostatic protection circuit for a semiconductor device according to the item.