Electrical resistors – Resistance value responsive to a condition – Current and/or voltage
Reexamination Certificate
1997-10-01
2001-01-09
Bradley, Paula (Department: 2833)
Electrical resistors
Resistance value responsive to a condition
Current and/or voltage
C338S021000, C439S086000, C361S111000
Reexamination Certificate
active
06172590
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to over-voltage protection devices used to protect electronic circuits from overvoltage transients caused by lightning, electromagnetic pulses, electrostatic discharges, ground loop induced transients, or inductive power surges. The present invention relates particularly to an electrical protection device capable of being mass produced cost-effectively and utilized as a discrete component.
BACKGROUND OF THE INVENTION
Voltage transients can induce very high currents and voltages that can penetrate electrical devices and damage them, either causing hardware damage such as semiconductor burnout, or electronic upset such as transmission loss or loss of stored data. The voltage transients produce large voltage spikes with high peak currents (i.e, over-voltage). The three basic over-voltage threats are electrostatic discharge, line transients, and lightning. However, electrostatic discharge can result from metallic instruments brought into near contact with devices, from vibrations created as the device moves along a conveyor or assembly line, or from being vibrated in a carrier. Electrostatic discharge occurs, for example, when static charge dissipates off the body of a person in direct physical contact with an operating electronic system or integrated circuit chip. Line transients are surges in AC power lines. Line transients can also occur due to closing a switch or starting a motor. Lightning strikes can strike stationary objects, such as a building, or mobile objects such as aircraft or missiles. Such strikes can suddenly overload a system's electronics. At peak power, each of these threats is capable of destroying the sensitive structure of an integrated circuit chip.
Various overvoltage protection materials have been used previously. These materials are also known as non-linear resistance materials and are herein referred to as such. In operation, the non-linear resistance material initially has high electrical resistance. When the circuit experiences an overvoltage spike, the non-linear resistance material quickly changes to a low electrical resistance state in order to short the overvoltage to a ground. After the overvoltage has passed, the material immediately reverts back to a high electrical resistance state. The key operational parameters of the non-linear resistance material are the response time, the clamp voltage, the peak current and the voltage peak. The time it takes for the non-linear resistance material to switch from insulating to conducting is the response time. The voltage at which the non-linear resistance material limits the voltage surge is called the clamp voltage. In other words, after the material switches to conducting, the material ensures that the integrated circuit chip, for example, will not be subjected to a voltage greater than the clamp voltage. The voltage at which the non-linear resistance material will switch (under surge conditions) from insulating to conducting is the trigger voltage. These materials typically comprise finely divided particles dispersed in an organic resin or insulating medium. For example, U.S. Pat. No. 4,977,357 (Shrier) and U.S. Pat. No. 4,726,991 (Hyatt et al.) disclose such materials.
Non-linear resistance materials and components containing non-linear resistance materials have been incorporated into overvoltage protection devices in a number of ways. For example, U.S. Pat. Nos. 5,142,263 and 5,189,387 (both issued to Childers et al.) disclose a surface mount device which includes a pair of conductive sheets and non-linear resistance material disposed between the pair of conductive sheets. U.S. Pat. No. 4,928,199 (Diaz et al.) discloses an integrated circuit chip package which comprises a lead frame, an integrated circuit chip protected by an electrode cover which is connected to ground on one side, and a variable voltage switching device including the non-linear resistance material connected to the electrode cover on the other side. U.S. Pat. No. 5,246,388 (Collins et al.) is directed to a device having a first set of electrical contacts that interconnect with signal contacts of an electrical connector, a second set of contacts that connect to a ground, and a rigid plastic housing holding the first and second set of contacts so that there is a precise spacing gap to be filled with the overvoltage material. U.S. Pat. No. 5,248,517 (Shrier et al.) discloses painting or printing the non-linear resistance material onto a substrate so that conformal coating with non-linear resistance material of large areas and intricate surfaces can be achieved. By directly printing the non-linear resistance material onto a substrate, the non-linear resistance material functions as a discreet device or as part of the associated circuitry.
It is commonly known in the art that the thickness of the non-linear resistance material and volume of the material are important to performance. See U.S. Pat. No. 4,977,357 issued to Shrier, U.S. Pat. No. 4,928,199 issued to Diaz et al. and U.S. Pat. No. 4,726,991 issued to Hyatt et al. Likewise, it is known that the clamp voltage is reduced or the non-linear resistance material can short out if put under pressure. See U.S. Pat. No. 5,248,517 issued to Shrier et al.
U.S. Pat. No. 5,262,754 (Collins) discloses an overvoltage protection element that can replace discrete devices presently used in protecting electronic circuits. The overvoltage protection element includes a layer of insulating material having first and second spaced major surfaces spaced a predetermined distance to determine the thickness of the element, a plurality of spaced holes extending between the major surfaces, and a overvoltage protection material contained within the holes formed in the layer of insulating material and extending between the spaced major surfaces. The spaced holes are formed by perforating the layer of insulating material by mechanical punching, laser processing and cutting, chemical etching, etc. The holes are formed in a pattern and should be wider than about one-half the width of the associated electrical circuit to which the holes will overlay. The spacing of the holes is determined by the spacing of the leads in the electrical circuit.
The above U.S. Patents referred to are incorporated herein by reference.
SUMMARY OF THE INVENTION
The present invention provides a mass-producible, cost-effective discrete electrical protection device that utilizes a small gap between two electrically conductive members attached to a substrate to provide over-voltage protection to an electrical device. In one aspect, the electrical protection device is a surface mountable device. In another aspect, the device has through-holes for accommodating leads on an electrical connector.
In one of its aspects, the present invention is an electrical protection device comprising a substrate having a first surface and a second surface, a first pad attached to the second surface of the substrate, a second pad spaced from the first pad and attached to the second surface of the substrate, a third pad attached to the first surface of the substrate and being in electrical communication with the first pad, a fourth pad spaced from the third pad and attached to the first surface of the substrate, the fourth pad being in electrical communication with the second pad.
In another of its aspects, the present invention is a method for making at least one electrical protection device, comprising the steps of providing an electrically insulating substrate having electrically conductive layers on opposite sides thereof, forming at least two through-holes in the electrically insulating substrate and the electrically conductive layers, forming electrically conductive paths between the electrically conductive layers through the through-holes, and forming electrically conductive pads around the through-holes, the electrically conductive pads being spaced from each other.
In another of its aspects, the present invention is a method for making at least one electrical protection device, comprisin
Behling Gerald R.
Felps Jimmie D.
Intrater James B.
Joshi Kailash C.
Olla Mike
Bradley Paula
Burns Doane , Swecker, Mathis LLP
Davis Katrina
SurgX Corporation
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