Surface-Mount Package with Differential Softening Temperatures
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Solution Overview
Problem
Surface-mountable piezoelectric sound components face issues with stress and separation at bonded surfaces due to thermal expansion differences during high-temperature reflow soldering, leading to potential separation and decreased bonding strength.
Innovation Solution
A package design where the case has a softening temperature higher than the reflow temperature and the cover has a softening temperature lower than the reflow temperature, with both components formed from LCP, alleviating stress through thermal expansion compensation and using adhesives like epoxy or silicone to maintain bonding strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If both the case and cover have high softening temperatures (higher than reflow temperature), then the package structure maintains shape stability during reflow, but excessive stress is generated at bonded surfaces due to thermal expansion differences causing separation
Solution Approach 1:
The patent applies different softening temperature characteristics to different parts of the package structure. The case is designed with high softening temperature (higher than reflow temperature) to maintain overall shape stability, while the cover is designed with lower softening temperature (lower than reflow temperature) to reduce thermal expansion stress at bonded surfaces. This local differentiation resolves the contradiction between shape stability and bonding strength.
2Temperature
If the cover has high heat resistance (softening temperature higher than reflow temperature), then the package can withstand reflow temperatures, but thermal expansion stress causes separation at bonded surfaces during high-temperature reflow
Solution Approach 1:
The patent changes the softening temperature parameter of the cover material to be lower than the reflow temperature, while keeping the case material with softening temperature higher than reflow temperature. This parameter differentiation allows the cover to soften and accommodate thermal expansion stress during reflow, preventing bonded surface separation while still maintaining adequate heat resistance for the overall package.
3Adaptability or versatility
If lead-free solder is used for reflow at 250°C or more, then environmental compliance is achieved, but the thermal expansion stress between case and cover increases causing separation
Solution Approach 1:
The patent addresses the environmental compliance requirement for lead-free soldering by locally modifying the cover's thermal properties. The cover is designed with lower softening temperature than reflow temperature, allowing it to accommodate the higher thermal expansion stress inherent in lead-free soldering processes without causing bonded surface separation.
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
Prevents separation and maintains bonding strength during reflow and drop impact tests, ensuring stable acoustic performance and element characteristics.
Implementation Method 1
since the heat resistance or softening temperature of the cover is lower than the reflow temperature, the stress is compensated for by the softened cover
Implementation Method 2
a stress resulting from the difference in thermal expansion between the case and the cover is placed on their bonded surfaces
Data Source
AI summary
A package of a surface-mountable electronic component to be reflow-soldered to a circuit board at about 250° C. or more includes a case and a cover. The cover has a softening temperature lower than the reflow temperature, and the case has a softening temperature higher than the reflow temperature. In the package, softening the cover compensates for the stress on the bonded surfaces resulting from a difference in thermal expansion between the case and the cover caused during reflow.