Surface-Mountable PTC Over-Current Protection Device
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Solution Overview
Problem
Surface-mountable over-current protection devices struggle to withstand high voltages and maintain low resistivity and high hold current simultaneously, leading to issues with high voltage endurance and potential electric arcs due to defects in the PCB process.
Innovation Solution
A surface-mountable over-current protection device with a simple structure, using a PTC material layer and metal electrode layers, where the leads are bent into multiple portions for surface-mounting, and an insulating layer is added for flame-retardant and water-resistant properties, allowing for high voltage and power endurance without the need for a PCB process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the amount of conductive fillers is decreased for high voltage applications, then voltage endurance is improved, but resistance increases and hold current decreases
Solution Approach 1:
The patent changes the type of conductive filler from carbon black to metal powder or conductive ceramic powder with much lower resistivity. This parameter change allows maintaining low device resistance even with reduced filler content, thereby achieving both high voltage endurance and low resistance simultaneously
Solution Approach 2:
The patent uses composite PTC material comprising crystalline polymer and conductive filler (metal powder or conductive ceramic powder). This composite material structure provides both the voltage endurance required for high voltage applications and the low resistivity needed for high hold current
2Device complexity
If PCB process is used to form conductive paths, then device complexity is reduced, but defects such as etching inaccuracies and copper foil residue cause electric arcs and reduced voltage withstand ability
Solution Approach 1:
The patent extracts the device from the PCB process entirely. Instead of forming conductive paths through PCB etching, the invention uses a self-contained PTC material layer with metal electrode layers and bent leads that connect directly to terminals, eliminating PCB process defects and improving voltage withstand ability
Solution Approach 2:
The patent introduces an insulating layer as an intermediary between the PTC material layer and external environment. This insulating layer prevents electric arcs and protects against defects, serving as a mediator that enhances reliability without increasing device complexity
3Ease of manufacture
If carbon black is used as conductive filler, then manufacturing cost is reduced, but electrical conductivity is insufficient for low resistivity applications
Solution Approach 1:
The patent changes the material parameter of conductive filler from carbon black to metal powder or conductive ceramic powder. This substitution dramatically improves electrical conductivity and reduces resistivity, enabling the device to meet low resistivity requirements while maintaining manufacturing feasibility
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The device can sustain voltages up to 30V and 80W for extended periods without blowout, passing cycle life tests and ensuring reliable high voltage and power protection.
Implementation Method 1
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
Implementation Method 2
The PTC conductive composite material contains crystalline polymer and conductive filler. The conductive filler is dispersed uniformly in the crystalline polymer
Data Source
AI summary
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 500μΩ·cm. The surface-mountable over-current protection device can withstand a cycle life test of 300 cycles at 20V/40A without blowout.