Surface-mountable over-current protection device

Abstract

A surface-mountable over-current protection device comprises at least one chip, a first lead and a second lead. The chip comprises a PTC material layer and two metal electrode layers disposed on upper and lower surfaces of the PTC material layer. The first lead is bent into multiple portions comprising a first electrode connecting portion connecting to one of the two metal electrode layers of the at least one chip and a first soldering portion for surface-mounting. The second lead is bent into multiple portions comprising a second electrode connecting portion connecting to another one of the two electrode layers of the at least one chip and a second soldering portion for surface-mounting. The PTC material layer comprises crystalline polymer and conductive filler dispersed therein, and the conductive filler has a resistivity less than 500 μΩ·cm. The surface-mountable over-current protection device can withstand a cycle life test of 300 cycles at 20V / 40 A without blowout.

Description

BACKGROUND OF THE INVENTION(1) Field of the Invention[0001]The present application relates to an over-current protection device, and more specifically, to a surface-mountable over-current protection device.(2) Description of the Related Art[0002]A positive temperature coefficient (PTC) composite material has an extremely low resistance at a normal temperature; however when an over-current or an over-temperature occurs in the circuit, the resistance instantaneously increases to a high resistance state (i.e., trip) to diminish the current for circuit protection. When the temperature decreases to room temperature or over-current no longer exists, the over-current protection device returns to low resistance state so that the circuit operates normally again. Because the PTC over-current protection devices can be reused, they can replace fuses and are widely applied to high-density circuitries.[0003]In general, the PTC conductive composite material contains crystalline polymer and conduct...

AI Technical Summary

Benefits of technology

The present patent application describes a surface-mountable over-current protection device that can withstand high voltages and powers without damage. By using bending instead of a PCB process to make leads, the device has enhanced voltage endurance due to no etchant residues. The device can withstand at least 20V without blowout and can withstand a voltage of 30V or 60V for at least 24 hours without damage. The device is optimized for its PTC composition, metal electrode layer thickness, and chip size.

Problems solved by technology

However, carbon black only exhibits low electrical conductivity and therefore cannot meet the demand of low resistivity in recent applications.

This however increases the resistance and decreases hold current of the device, and cannot meet the requirements of high voltage endurance and high hold current simultaneously.

However, in the event of, for example, inaccurate positions of etching, copper foil residue due to incomplete etching or defective connections of conductive through holes, an electric arc may occur.

In addition, if etchant remains after process, the ability to withstand voltages would be diminished.

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