Spring-Loaded LED Holder for Thermal Expansion Mismatch
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Solution Overview
Problem
The lifetime of LED-based light-emitting devices is often limited by the mismatch in thermal expansion between the LED-module and the circuit board, leading to premature failure due to defects in the solder connection, and replacing the regular PCB with a ceramic-based board increases costs and limits design flexibility.
Innovation Solution
A light-emitting device design that uses a connection board with a substrate and conductor pattern, featuring an interconnecting arrangement with electrically conducting springs that allow movement between the connection pad and the conductor pattern, and an LED-holder that applies a spring force to press the LED-module against a heat dissipator, providing both robust electrical and thermal connections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a regular PCB is used for the connection board, then the device cost is low and design flexibility is high, but the lifetime is limited due to thermal expansion mismatch causing solder connection defects
Solution Approach 1:
The connection board is segmented into a substrate and a separate conductor pattern layer that can move independently. This allows the conductor pattern to accommodate thermal expansion differences while the substrate maintains structural integrity, resolving the contradiction between using low-cost regular PCB materials and achieving long device lifetime.
Solution Approach 2:
The conductor pattern is designed to be movable relative to the substrate, creating a dynamic connection that can adapt to thermal expansion mismatches. This dynamic structure allows the use of cost-effective regular PCB materials while maintaining reliable electrical connections over the device lifetime.
2Reliability
If a ceramic-based circuit board is used to match thermal expansion, then the lifetime is extended, but the cost increases and design flexibility is restricted
Solution Approach 1:
By separating the conductor pattern from the substrate, the invention enables the conductor layer to move independently to accommodate thermal expansion. This eliminates the need for expensive ceramic substrates while maintaining long device lifetime and preserving design flexibility.
Solution Approach 2:
The invention changes the physical state and movement parameters of the conductor pattern, allowing it to shift position relative to the substrate. This parameter change enables the use of flexible, low-cost substrates while achieving the thermal expansion matching effect previously only possible with rigid ceramic boards.
3Stability of the object's composition
If a rigid solder connection is used between LED-module and PCB, then the electrical connection is stable, but thermal expansion mismatch causes connection defects over time
Solution Approach 1:
The conductor pattern is designed as a movable element that can dynamically adjust its position relative to the substrate during thermal cycling. This dynamic capability maintains stable electrical connections while accommodating thermal expansion differences, preventing solder connection defects and extending device lifetime.
Solution Approach 2:
The movable conductor pattern acts as an intermediary between the rigid substrate and the LED-module, absorbing thermal expansion stresses through its own movement. This intermediary structure protects the solder connections from stress-induced defects while maintaining electrical stability.
4Strength
If the LED-module is firmly fixed to the connection board, then the electrical connection is secure, but thermal stress accumulates causing premature failure
Solution Approach 1:
The connection structure transitions from a static, rigid fixation to a dynamic system where the conductor pattern can move relative to the substrate. This dynamic design maintains strong electrical connections while allowing thermal expansion accommodation, preventing stress accumulation and extending device lifetime.
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
This solution extends the lifetime of LED-based light-emitting devices at a lower cost than prior art, offering greater design flexibility and reliability by maintaining a secure electrical connection and efficient heat dissipation despite thermal expansion mismatches, while minimizing contact surface wear and corrosion risks.
Implementation Method 1
the LED-holder exerts a spring force to press the LED-module against the heat dissipator
Implementation Method 2
a heat dissipator for dissipating heat generated by the LED when in operation
Implementation Method 3
Due to mismatch in the thermal expansion behavior of the LED-module and the PCB, temperature cycling may eventually result in defects in the solder connection
Data Source
AI summary
A light-emitting device (1), comprising an LED-module (3) comprising at least one LED mounted on a carrier and at least one connection pad (10a-b) for electrical connection of the LED module (3), a heat dissipator (2) for dissipating heat generated by the LED when in operation, a connection board (4) comprising a substrate having a conductor pattern for enabling provision of external power to the LED module (3), an interconnecting arrangement (7a-d) comprising at least one connection spring (7a-d) attached to the connection board (4) electrically interconnecting the at least one connection pad (10a-b) of the LED module (3) with the conductor pattern of the connection board (4), and an LED-holder comprising at least one holding spring (7a-d) attached to the connection board (4) exerting a spring force there by pressing the LED-module (3) against the heat dissipator (2) to provide a thermal connection between the LED-module (3) and the heat dissipator (2). The interconnecting arrangement (7a-d) is configured to allow movement between the conductor pattern of the connection board (4) and the at least one connection pad (10a-b). The at least one connection spring (7a-d) constitutes the at least one holding spring (7a-d), to simultaneously electrically interconnect the at least one connection pad (10a-b) of the LED-module (3) with the conductor pattern of the connection board (4) and press the LED-module (3) against the heat dissipator (2).