JPH0327321Y2 - - Google Patents

Description

[Detailed explanation of the idea] This invention relates to a protection element for semiconductor devices.

In order to prevent semiconductor devices (e.g. power transistors, power ICs, etc.) from being destroyed by overcurrent flowing through them, a metal wire for a fuse is installed that instantly blows out when a current slightly lower than the breakdown current flows. We are already seeing proposals for a configuration using a protection element.

Figures 1 and 2 show conventional protection elements of this type, where 1 is a metal wire for a fuse (for example, a solder wire, Al wire, Au wire, Ag wire, Al-Si wire, etc.), and 2 is a pair of metal wires. It is the lead. Each lead 2 is arranged so as to be located in the same plane as shown in FIG. Further, each end of the metal wire 1 is stretched by wire bonding between the tips of each frame-shaped lead 2. 3 is arc extinguishing resin, such as epoxy resin varnish, silicone resin varnish,
Polyester resin varnish, polyimide resin, etc. are used, and when an overcurrent flows through the metal wire and melts and scatters, it absorbs this. 4 is package,
For example, it is constructed by molding a resin such as epoxy or silicone phenol.

According to the protective element having such a configuration, the metal wire 1
When an overcurrent flows through the metal wire 1, the metal wire 1 melts and blocks the subsequent flow of current. Therefore, if lead 2 is connected in series to the semiconductor device to be protected,
It is possible to prevent the semiconductor device from being destroyed by excessive current flowing through it.

By the way, as mentioned above, when an overcurrent flows through the metal wire 1 and it melts, it is divided into two parts.If the gap created in the middle of the metal wire by this melting is short, the voltage applied to this gap will cause the wire to split into two. Arcing may occur. When such an arc occurs, not only is the overcurrent not interrupted, but the temperature around it rises, and as a result, the package 4 itself may explode. Therefore, conventional protection elements of this type have the inconvenience of not being able to be used in circuits where a large voltage is applied at the time of blowout.

In particular, when the metal wire 1 is covered with arc-extinguishing resin 3 as shown in the figure, unlike when it is supported in space, when it is fused, it is cut into pieces as if it were cut with scissors. Then, it melts in a round shape toward lead 2. Therefore, the fusing gap becomes wider as time passes, and there is a drawback that arc discharge continues in the fusing gap until the fusing gap becomes wide enough. If the metal wires are supported in space, all of them will melt instantly and the fusing gap will become wide enough to prevent arc discharge in a short time, so that this drawback can be avoided to a large extent.

Even if this device is used in a circuit with a large applied voltage, and even if the metal wire is covered with arc-extinguishing resin, it will ensure that overcurrent is interrupted and that it will not explode when it melts. The purpose is to

An embodiment of this invention will be explained with reference to FIG. Note that parts given the same reference numerals as in FIG. 1 indicate the same or corresponding parts. In the illustrated embodiment, two metal wires 1A and 1B are used, which are installed in series between the leads 2 via the intermediate lead 5. That is, the metal wire 1A is straddled between each lead 2 and the intermediate lead 5.
1B is stretched. Each lead 2, 5 is the second
As shown in the figure, they are on the same plane, and as shown in the figure, they are arranged side by side in a straight line. The outer ends of the leads 2 and 5 are led out to the outside of the package.

In the above configuration, connecting the lead 2 to the semiconductor device to be protected is the same as in the conventional case. Assume that an overcurrent flows between the leads 2, and as a result, one of the metal wires 1A is fused first.
If an arc occurs in the gap created between the metal wires 1A, an overcurrent continues to flow between the leads 2, and the other metal wire 1B is blown out by this overcurrent. Therefore, metal wire 1
Both A and 1B will be fused.

In this case, when the metal wire 1A is first fused, even if it takes a long time until the fusion interval of the metal wire 1A becomes sufficiently wide because the metal wire is covered with arc-extinguishing resin, By then, the metal wire 1B will be fused. Therefore, the time during which overcurrent flows is shorter than when one metal wire is used.

In addition, since the intermediate lead 5 is led out to the outside of the package 4, heat from the metal wire is conducted to the outside via the intermediate lead 5, which improves the current capacity of the metal wire. Since there are three wires, the mechanical strength of the entire device is improved, which is extremely convenient.

In addition, when this is mounted on a printed circuit board or the like, it is useful for determining whether or not a metal wire has fused due to the flow of an overcurrent. In other words, the package will not be destroyed by overcurrent, so it cannot be determined from its appearance. For this reason, a tester is used to determine if the metal wire is fused, but in that case, even if a test voltage is applied between the leads 2, current may flow through the external circuit connected to the leads 2. This makes it impossible to confirm metal wire melting.

On the other hand, if the intermediate lead 5 is provided and led out to the outside of the package 4 as in this invention, a test voltage can be applied between the lead 2 and the intermediate lead 5, and This voltage makes it possible to reliably determine whether or not the metal wire is fused during this period, even if an external circuit is connected.

In the illustrated embodiment, there are two metal wires, but there may be three or more metal wires, and they may be connected in series. However, when using three leads as shown in the figure, normally a frame and a mold for the transistor are used to package this type of element, so it is difficult to manufacture this type of protection element with a three-lead configuration. There is no problem.

As detailed above, according to this invention, even if the metal wire is covered with an arc-extinguishing resin, it is possible to reliably prevent arcing over a long period of time when the metal wire is fused. As a result, it is possible to reliably prevent failure to shut off overcurrent and explosion due to temperature rise, and it is possible to configure the package shape with the same thickness as the conventional one.Moreover, by using an intermediate lead, metal This has the effect that it is possible to reliably determine whether or not the wire is fused.

[Brief explanation of the drawing]

FIG. 1 is a plan sectional view of a conventional example, FIG. 2 is a sectional view of the same side, and FIG. 3 is a plan sectional view showing an embodiment of this invention. 1A, 1B...metal wire, 2...lead, 3...
Arc-extinguishing resin, 4...Package cage, 5...Intermediate lead.

Claims (1)

[Scope of utility model registration request] A pair of leads and an intermediate lead are arranged side by side in the same plane, a metal wire is stretched between the intermediate lead and each lead, and the metal wire is covered with an arc-extinguishing resin, Furthermore, a protection element for a semiconductor device, wherein the ends of the leads and the intermediate leads including the metal wire are placed in a molded package so that the outer ends of the leads and the intermediate leads are guided outside.