Patent Application
20090224213
(A) Field of the Invention
The present invention relates to a variable impedance material, and more particularly, to a variable impedance material comprising a conductive powder, semi-conductive power, and an insulation adhesive.
(B) Description of the Related Art
Integrated circuits are externally fed with supply potentials and input signals to be processed and to have processed output signals received from them. In particular, the input signal terminals are very sensitive, since the conductor tracks that feed the potentials and signals lead directly to a gate terminal of an input switching stage. While the integrated circuit is being manually handled, or during the automated processing to solder the integrated circuit on a circuit board, there is risk that the sensitive input stage or output stage may be destroyed by electrostatic discharge. For instance, the human body may be electrostatically charged and then discharged via the terminals leading to the outside of the semiconductor component containing the integrated circuit.
Tools of automatic component-mounting machines or test equipment may also be electrostatically charged and discharged via the semiconductor component. As technology advances and the scale of pattern lines on the semiconductor body bearing integrated circuits becomes smaller, there is a need for protection against such electrostatic discharges. Integrated circuit devices are often provided with some protection against electrostatic discharge (ESD) with high input currents, such as electrical resistors connected in their input paths, thereby limiting the input current.
U.S. Pat. No. 6,642,297 discloses a composition for providing protection against electrical overstress (EOS) comprising an insulating binder, doped semiconductive particles, and semiconductive particles. The composite materials exhibit a high electrical resistance to normal operating voltage values, but in response to an EOS transient the materials switch to a low electrical resistance and limit the EOS transient voltage to a low level for the duration of the EOS transient.
U.S. Pat. No. 6,013,358 discloses a transient voltage protection device wherein a gap between a ground conductor and another conductor is formed using a diamond-dicing saw. Substrate material selection includes specific ceramic materials having a density of less than 3.8 gm/cm.sup.3 designed to optimize performance and manufacturability. An overlay layer can be provided to minimize burring of the conductors during formation of the gap.
U.S. Pat. No. 5,068,634 discloses a material and device for electronic circuitry that provides protection from fast transient over-voltage pulses. The electroded device can additionally be tailored to provide electrostatic bleed. Conductive particles are uniformly dispersed in an insulating matrix or binder to provide a material having non-linear resistance characteristics. The non-linear resistance characteristics of the material are determined by the inter-particle spacing within the binder as well as by the electrical properties of the insulating binder. By tailoring the separation between the conductive particles, thereby controlling quantum-mechanical tunneling, the electrical properties of the non-linear material can be varied over a wide range.
U.S. Pat. No. 6,498,715 discloses a stack up type low capacitance over-voltage protective device comprising a substrate, a conductive low electrode layer formed on the substrate, a voltage sensitive material layer formed on the conductive lower electrode layer, and a conductive upper electrode layer formed on the voltage sensitive material layer.
U.S. Pat. No. 6,645,393 discloses a material for transient voltage suppressors composed of at least two kinds of evenly-mixed powders including a powder material with non-linear resistance interfaces and a conductive powder. The conductive powder is distributed in the powder with non-linear resistance interfaces to relatively reduce the total number of non-linear resistance interfaces between two electrodes and, as a result, decrease the breakdown voltage of the components.
One aspect of the present invention provides a variable impedance material comprising a conductive powder, semi-conductive power, and an insulation adhesive, which presents a high resistance at a low applied voltage and a low resistance at a high applied voltage.
A variable impedance composition according to this aspect of the present invention comprises a conductive powder in an amount from 10% to 30% of the weight of the variable impedance composition, a semi-conductive power in an amount from 30% to 90% of the weight of the variable impedance composition, and an insulation adhesive in an amount from 3% to 50% of the weight of the variable impedance composition.
According to one embodiment of the present invention, the variable impedance material presents a high resistance at a low applied voltage and a low resistance at a high applied voltage. As the variable impedance material is positioned in a gap between two conductors of an over-voltage protection device, the over-voltage protection device as a whole presents a high resistance to a low voltage applied across the gap and a low resistance to a high voltage applied across the gap.
The objectives and advantages of the present invention will become apparent upon reading the following description and upon reference to the accompanying drawings in which:
In particular, a first conductive member 22′ is sandwiched between the substrate 12 and the first side-electrode 22, and a second conductive member 24′ is sandwiched between the substrate 12 and the second side-electrode 24. The first conductive member 22′ and the second conductive member 24′ can be plating metal layers or conductive through holes. Preferably, at least one of first protrusion 14A and the second protrusion 16A is a tapering protrusion with a tapering width. The second protrusion 16A faces the first protrusion 14A to form an arcing path 18 from the first protrusion 14A to the second protrusion 16A. Preferably, the first nonrectangular conductor 14 and the second nonrectangular conductor 16 are trapezoid and positioned on the substrate 12 in a mirror-image manner. In particular, the shape of the first nonrectangular conductor 14 can be different from that of the second nonrectangular conductor 16. The first protrusion 14A includes a first flat edge 14B and the second protrusion 16A includes a second flat edge 16B facing the first flat edge 14B.
Referring to
Referring to
Preferably, the conductive powder includes at least one element selected from the group consisting of Al, Ag, Pd, Pt, Au, Ni, Cu, W, Cr, Fe, Zn, Ti, Nb, Mo, Ru, Pb, and Ir, the semi-conductive powder includes zinc oxide or silicon carbide, and the insulation adhesive includes epoxy or silicone. In addition, the variable impedance material 28 may further include an insulation powder in an amount from 10% to 60% of the weight of the variable impedance material, and the insulation powder includes metal oxide such as aluminum oxide or zirconium oxide.
Referring to
Conventional over-voltage protection devices all have two rectangular conductors a gap between the two conductors of uniform width; therefore, the arcing path is unpredictable. In contrast, the present over-voltage protection device 10 comprises the first nonrectangular conductor 14 having the first protrusion 14A and the second nonrectangular conductor 16 having the second protrusion 16A facing the first protrusion 14A such that the distance between the first nonrectangular conductor 14 and the second nonrectangular conductor 16 is non-uniform. In particular, the gap between the first nonrectangular conductor 14 and the second nonrectangular conductor 16 is smaller at the protrusion portion than at other portions such that is the arcing path 18 is designed to be at the protrusion portion and the variable impedance material 26 covers the protrusion portion according to the embodiment of the present invention.
The above-described embodiments of the present invention are intended to be illustrative only. Numerous alternative embodiments may be devised by those skilled in the art without departing from the scope of the following claims.
