JPH0510799B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to general electronic circuits using integrated circuits, and is directed to an electrostatic charge protection system that protects the circuits from electrostatic pulses that enter from the outside through power supply lines, input/output signal lines, etc. This relates to a destruction prevention device.

Conventional Structures and Their Problems In recent years, as electronic equipment becomes more highly integrated and consumes less power, each circuit unit used therein is required to have high reliability against electrostatic damage.

A conventional electrostatic damage prevention device will be described below with reference to the drawings.

Figures 1, 2, and 3 are circuit diagrams of conventional electrostatic damage prevention devices. Figure 1 is a circuit using an RC trap, Figure 2 is a circuit using a surge absorption element, and Figure 3 is a circuit diagram using a surge absorbing element. The figure shows a circuit with a spark gap, but Figures 1 and 2 show the most general-purpose electrostatic damage prevention device. 1 is an input/output terminal for connecting to an external circuit, and 2 is an internal terminal of the circuit. Wiring coupled to the elements includes a resistance element 3, a capacitor 4, and a surge absorption element 5.

In FIG. 1, when static electricity is applied to terminal 1, the transient voltage level of static electricity is integrated by the resistance value of resistor element 3 and the capacitance value of capacitor 4, so the potential of wiring 2 is It hardly increases to the extent that it causes electrostatic damage to integrated circuits, etc.

In addition, in FIG. 2, when static electricity is applied to terminal 1, the transient voltage level of static electricity is absorbed by surge absorbing element 5, so the potential of wiring 2 does not increase and it is connected to wiring 2. The integrated circuits used are protected from static electricity.

However, if the circuits shown in Figures 1 and 2 above are used, the dimensions of the wiring board on which they are mounted will increase, and the number of elements will increase in circuits with many input/output terminals. Therefore, it is difficult to adopt it in a unit that requires miniaturization, so the configuration shown in FIG. 3 has been conventionally used. Its operation will be explained below. In Fig. 3, 6 is a resistive element of several kilohms, 7 is an input/output terminal for connecting to an external circuit, 8 is a wiring connected to an integrated circuit, 9 is a spark gap part, 10 is an integrated circuit, and 11 is an integrated circuit. 10 is a capacitor of about 5 to 10 PF with reverse bias of a diode to prevent electrostatic damage, and 12 is an integrated circuit 1.
This is the internal wiring of 0. When static electricity (hereinafter referred to as 250PF charge, which is considered to be approximately equivalent to the capacity of the human body) is applied to the input/output terminal 7, the energy of the static electricity is 300 to 500 V. Because the static electricity is small, it does not cause a spark in the spark gap part 9, and the potential of the wiring 8 is lower than the static electricity voltage level of 300~
However, since the integrated circuit 10 connected to the wiring 8 has a built-in capacitor 11 which is an electrostatic damage protection circuit, the voltage will rise to 300 to 500V.
It has an electrostatic withstand voltage inside the device, and will not cause electrostatic damage.

In addition, when static electricity with a voltage level of about 3 to 5 KV or more is applied, the potential of the wiring 8 is
Since the resistance element 6 has a resistance value of several kilohms,
The capacitor 11 for preventing electrostatic discharge does not rise until dielectric breakdown occurs, and there is a distance of about 3.5 mm between the soldered parts on the wiring board at both ends of the resistor element 6, and the spark gap of the terminal 7 The distance between the insulating parts on the wiring board of section 9 is 0.5 mm, the minimum value possible on a normal wiring board, and the gap is sharper, so that static electricity is caused by sparks in the spark gap section 9, which has low impedance with respect to ground. wake up

For the above reason, in FIG.
If a resistor having a resistance value of several kilohms is used, even if static electricity at a voltage level of 20 kV is applied to the terminal 7, the integrated circuit 10 will not be damaged by static electricity.

Fig. 4 is a perspective view of a unit using the configuration shown in Fig. 3, in which 13 is a wiring board, 14 is a metal case connected to the ground, 15 is a lead wire for supplying power voltage, and 16 is a ground. The lead line 17 is a lead line for input/output signals. FIG. 5 is an enlarged view of the wiring board 13.
8, 19, 20 are resistance elements, 21 is a power supply voltage terminal, 22 is a ground terminal, 23 is an input/output signal terminal,
24 is the spark gap part of the input/output signal terminal, 2
5 is the spark gap part of the power supply voltage terminal.
It is assumed that the terminal 21 is connected to the lead wire 15, the terminal 22 is connected to the lead wire 16, and the terminal 23 is connected to the lead wire 17. Since the wiring board 13 is completely covered by the metal case 14 connected to ground,
Terminal 2 is protected from static electricity to earth.
By protecting only the circuit boards 1 and 23 from static electricity with respect to the ground using the method shown in FIG. 3, the wiring board 13 can be provided with an electrostatic withstand voltage of about 20 KV as explained above.

However, in the above configuration,
When supplying power supply voltage to an integrated circuit that requires a current value of several mA or more due to its circuit configuration, the resistor element 18,
Using a resistance element of several kilohms for 19.
A large voltage drop will be generated across the resistive elements 18 and 19, making it impossible to supply the power supply voltage necessary to the integrated circuit.
8 and 19 depend on the circuit configuration of the integrated circuit used,
In many cases, it is limited to those with an impedance of 100Ω or less.

In other words, in Fig. 3, when resistor element 6 is used with a resistance value of 100Ω or less, when static electricity is applied to terminal 7, the voltage level of the static electricity is about 3KV. Even if the resistance value of the resistance element 6 is low, the potential of the wiring 8 increases, and the capacitor 11 for preventing electrostatic discharge damage temporarily causes a slight dielectric breakdown, so the potential of the wiring 8 increases. instantaneously becomes ground potential, which induces a trigger action, and the static electricity passes over the surface of the resistive element 6, and the internal circuit of the integrated circuit 10 connected to the internal wiring 12 of the integrated circuit 10 is exposed to the static electricity. This had the problem of causing destruction.

OBJECTS OF THE INVENTION The present invention provides an electrostatic damage prevention device that can protect general electronic circuits using integrated circuits from electrostatic pulses that enter from the outside through power supply lines, input/output signal lines, etc. The purpose is to provide

Composition of the Invention In order to achieve the above object, the electrostatic breakdown prevention device of the present invention is such that a terminal connected to an external circuit on a wiring board and an integrated circuit are connected via a resistive element, and the integrated circuit is connected via a resistive element. A highly reliable electrostatic withstand voltage measure is taken by providing a ground wiring on the lower wiring board that causes static electricity passing through the surface of the resistor element to spark and escape to the ground side.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS.
This will be explained with reference to FIG. Figure 6 shows the circuit configuration of the electrostatic damage prevention device of the present invention, where 26 is a number.
A resistive element having a resistance value of about 10Ω, 27 an input/output terminal for connection to an external circuit, 28 a wiring connected to the integrated circuit, and 29 a ground wiring.

FIG. 7 shows the main parts of a circuit mounting board embodying the above circuit configuration, 30 is a wiring board, 31,
32 and 33 are resistance elements, and this resistance element 3
1 and 32 are connected to the power supply voltage terminal 34 side, and one end of the resistance element 33 is connected to the input/output terminal side, and these resistance elements 31, 32, 33
The other ends are respectively connected to other wirings 38 connected to an integrated circuit 39 or the like.

37a, 37b, 37c, 37d are wiring boards 3
This is the ground wiring provided on the ground wiring 37.
a, 37d are below the resistance elements 31, 32, 33, and ground wirings 37b, 37c are below the resistance elements 31, 33.
32 and 33 and another wiring 38.

Further, the wiring board 30 in FIG. 7 is entirely covered by a metal case connected to ground, similar to FIG. 4.

The operation of the electrostatic damage prevention device configured as described above will be described below.

In FIG. 7, the integrated circuit 39 has a circuit configuration that requires a constant current of about 10 mA, so the number of resistive elements 31 and 32 inserted into the power supply wiring is limited to several.
A resistor with a resistance value of 10Ω was used. Furthermore, the resistive element 33 is inserted into the wiring for input/output signals, and in this embodiment, one having a resistance value of about 10 KΩ was used because there was no problem with the circuit configuration. When anti-ground static electricity with a voltage level of 300 to 500 V is applied to the power supply voltage terminal 34 and the input/output signal terminal 36, since static electricity has little energy, it does not cause a spark and the resistance element 31,
32 and 33 and is transmitted to the integrated circuit 39. However, the integrated circuit 39 has a built-in electrostatic damage protection circuit and has an electrostatic withstand voltage of about 300 to 500V. It will not lead to electrical damage. Next, apply a voltage level of 3 to 5KV to the input/output signal terminal 36.
When static electricity with respect to the earth is applied to the input/output signal terminal 36, the spark gap is not formed in the input/output signal terminal 36, but the normally used resistive elements 31, 3
The length of 2 and 33 is approximately 3.5 mm, and ground wirings 37a and 37d are formed near the soldering lands, so that one soldering land connected to the input/output signal terminal 36 of the resistive element 33 Since the ground wiring 37a is formed very close to each other with an insulation interval of 0.5 mm, an apparent spark gap is formed, and in the conventional example shown in FIG. Since this is the same as when a resistor having a resistance value of several kilohms is used, static electricity will not cause sparks in the ground wiring 37a and the integrated circuit 39 will not be damaged by static electricity.

In addition, the voltage level 3~5KV is applied to the power supply voltage terminal 34.
If a static electricity of more than 100% is applied to the ground, the resistance value of the resistive element 32 is low, so that the resistive element 3
The potential of the terminal of the integrated circuit 39 connected via 2 increases, and the electrostatic breakdown prevention capacitor connected to that terminal inside the integrated circuit 39 temporarily causes a slight dielectric breakdown, and the terminal It instantly becomes ground potential, which acts as a trigger, and the static electricity attempts to pass over the surface of the resistance element 32, but is prevented from passing through by the ground wiring 37d provided on the wiring board 30 below the resistance element 32. A spark is generated between the ground wire 37d and the integrated circuit 39.
does not lead to electrostatic damage.

As described above, according to this embodiment, the resistance element 3
High reliability against electrostatic damage is achieved by the ground wirings 37a and 37d provided on the wiring board 30 on the lower surface of the wiring boards 1, 32, and 33.

Effects of the Invention As is clear from the above description, the present invention provides a wiring board in which a terminal connected to an external circuit and an integrated circuit are connected via a resistance element, and a wiring board below the resistance element. By providing a ground wire on the top, when high-voltage static electricity flows to the power supply voltage terminal, etc., the static electricity that passes over the surface of the resistor element is sparked and released to the ground wire. By inserting the above-mentioned device, it is possible to obtain an electrostatic withstand voltage of 20 KV against the earth, which is of great industrial value, even if the intruding electrostatic voltage withstand voltage is 1 KV or less.

[Brief explanation of the drawing]

Figures 1, 2, and 3 show conventional electrostatic damage prevention devices, and Figure 1 is an RC trap circuit configuration diagram.
Figure 2 is a circuit configuration diagram using a surge absorption element, Figure 3 is a circuit configuration diagram using the spark gap method,
FIG. 4 is a perspective view of a unit using the configuration shown in FIG. 3, FIG. 5 is an enlarged view of a conventional wiring board using the configuration shown in FIG. 3, and FIG. FIG. 7 is an enlarged view of a circuit mounting board in an embodiment of the electrostatic breakdown prevention device of the present invention using the circuit configuration of FIG. 6. 26... Resistance element, 27... Input/output terminal, 28
... Wiring, 29 ... Earth wiring, 30 ... Wiring board, 31, 32, 33 ... Resistance element, 34 ... Power supply voltage terminal, 35 ... Earth terminal, 36 ... Input/output terminal, 37a to 37d... ...Earth wiring, 38...
...Other wiring, 39...Integrated circuit.

Claims (1)

[Claims] 1 On the wiring board, a terminal connected to an external circuit and an integrated circuit are connected via a resistance element, and static electricity passing through the surface of the resistance element is sparked on the wiring board below the resistance element. An electrostatic damage prevention device that has a ground wiring that releases to the ground side.