Activatable Thermal Fuse With Mechanical Blocking Element
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Solution Overview
Problem
Existing thermal fuses cannot be reliably integrated into printed circuit boards during reflow soldering processes due to their temperature triggering characteristics, leading to costly and error-prone manual assembly procedures.
Innovation Solution
An activatable thermal fuse with a mechanically displaceable bridge element, held in place by a thermally sensitive member and biased by a biasing member, which allows for a disabled state during reflow soldering and triggers only when activated mechanically, ensuring the fuse is not prematurely triggered by high temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thermal fuse with triggering temperature below 240°C is used, then it can provide thermal protection, but it cannot withstand reflow soldering temperatures and will be triggered during the soldering process
Solution Approach 1:
The patent applies preliminary anti-action by introducing a blocking element that prevents the bridge element from moving to the interrupted position during soldering. The blocking element is designed to counteract the thermal expansion or movement that would normally trigger the fuse at lower temperatures, thereby preventing premature triggering during the high-temperature soldering process while maintaining the fuse's thermal protection function.
Solution Approach 2:
The patent implements preliminary action by pre-positioning the bridge element in a held state before soldering occurs. The blocking element is already in place to restrain the bridge element, and only after the soldering process completes and the blocking element is removed (or becomes ineffective) does the thermal fuse become active. This ensures the fuse survives soldering and then provides thermal protection.
2Reliability
If manual placing and special soldering procedure is used for thermal fuses, then the fuse can be properly installed, but the production process becomes expensive and error-prone
Solution Approach 1:
The patent applies self-service by designing the thermal fuse to be automatically activated after standard reflow soldering without requiring manual intervention. The blocking element is designed to be removed or become ineffective automatically after soldering, allowing the bridge element to respond to thermal conditions. This enables the fuse to install itself through standard soldering processes without special procedures or manual placement.
Solution Approach 2:
The patent uses preliminary action by pre-configuring the blocking element to be in place during soldering but designed to automatically retract or become ineffective after the soldering process. This preliminary setup allows standard automated pick-and-place and reflow soldering equipment to install the fuse correctly without requiring special manual procedures, thereby simplifying manufacturing while ensuring proper installation.
3Reliability
If additional electrical contacts and subsidiary fuse wire are added for activation, then the thermal fuse can be activated after soldering, but additional space and conductor paths are occupied
Solution Approach 1:
The patent applies merging by combining the activation function with the existing soldering process. Instead of requiring separate activation contacts and conductor paths, the design integrates the activation mechanism into the bridge element and blocking element structure. The blocking element serves dual purposes: preventing premature triggering during soldering and enabling automatic activation after soldering by its removal or transformation, thereby eliminating the need for additional space-consuming activation circuitry.
Solution Approach 2:
The patent extracts the activation function from the traditional electrical contact approach and embeds it within the mechanical structure of the bridge element and blocking element. By removing the requirement for separate activation contacts and conductor paths, the design reduces space occupation on the circuit board while maintaining the ability to activate the thermal fuse after soldering through the mechanical interaction of the bridge and blocking elements.
4Reliability
If the bridge element is held in first position by thermally sensitive member, then the fuse remains closed during normal operation, but the member must be released at predetermined temperature to trigger the fuse
Solution Approach 1:
The patent introduces the blocking element as an intermediary between the bridge element and the triggering mechanism. This blocking element mediates the interaction between thermal conditions and the bridge element's position, preventing direct thermal triggering during soldering while allowing controlled activation afterward. The blocking element acts as a temporary constraint that modifies the thermal response characteristics without adding complex control systems.
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
Enables the thermal fuse to withstand reflow soldering temperatures without activation, then reliably interrupts the current path when triggered, providing effective thermal protection without occupying additional space or requiring external current sources.
Implementation Method 1
a thermally sensitive member holding the part in the first position and releasing the part as soon as the thermally sensitive member is exposed to a predetermined temperature value
Implementation Method 2
a biasing member biasing the part towards the second position
Data Source
Figure 1.a~1.d
Figure 2.a~2.d
Figure 3.a~3.d
AI summary
Activatable thermal fuse (10) comprising - a first (1) and a second (2) electrical terminal, - an electrically conductive bridge element (3) being in a first electric contact with said first terminal and being in a second electric contact with said second terminal, - at least a part (4) of said bridge element being displaceable from a first position in which said first contact is established to a second position in which said first contact is opened, - a thermally sensitive member (5) holding said part in said first position and releasing said part as soon as said thermally sensitive member is exposed to a predetermined temperature value, - a biasing member (6) biasing said part towards said second position, and - a mechanically displaceable activating element (7) blocking displaceability of said part in said first position in a first position of said activating element and enabling said displaceability of said part in a second position of said activating element. The invention is further directed to a method of manufacturing a printed circuit board with an activatable thermal fuse, a method of monitoring an activatable thermal fuse and to an electronical circuit comprising an activatable thermal fuse.