Pyroelectric Infrared Sensor Assembly for High-Temperature Reflow
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Solution Overview
Problem
Existing pyroelectric infrared sensors face issues during reflow processes due to peak temperatures exceeding the Curie temperature of the pyroelectric element, leading to potential remelting of solder pastes and electrical malfunctions.
Innovation Solution
A pyroelectric infrared sensor design using a pyroelectric element with a Curie temperature higher than 295°C, connected to an internal board with high melting point solder paste for internal components and low melting point solder paste for external connections, along with conductive adhesives to secure critical components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high melting point solder paste is used for capacitor element connection, then resistance to remelting during reflow is improved, but manufacturing complexity increases due to using different solder pastes for different components
Solution Approach 1:
The patent applies different solder paste types to different locations within the sensor assembly: high melting point solder paste is used specifically for the capacitor element connection to prevent remelting, while low melting point solder paste is used for the pyroelectric element connection to enable proper reflow bonding. This localized differentiation resolves the contradiction by providing targeted protection only where thermally sensitive components are present.
2Ease of manufacture
If standard reflow temperature of 220°C is used, then compatibility with low melting point solder paste is maintained, but insufficient heating time prevents reliable soldering of large electronic components
Solution Approach 1:
The patent performs preliminary protection by applying high melting point solder paste to the capacitor element connections before the reflow process. This preliminary action ensures that when extended heating is applied to achieve reliable soldering of large components, the capacitor element connections remain protected from remelting, thus preventing electrical malfunctions while enabling adequate heating time.
3Ease of manufacture
If extended heating time is applied during reflow, then reliable soldering of large components is achieved, but peak temperature exceeds Curie temperature causing potential damage
Solution Approach 1:
The patent implements local thermal protection by selectively applying high melting point solder paste to thermally sensitive areas (capacitor element connections) while allowing other areas to experience the full extended heating cycle. This localized approach enables the necessary peak temperatures and heating duration for reliable soldering of large components without causing damage to temperature-sensitive components.
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 design prevents remelting of solder pastes and maintains electrical integrity during high-temperature reflow processes, reducing malfunctions and ensuring reliable operation.
Implementation Method 1
a pyroelectric element having a composition of PbCa(MnSb)TiO3 and connected to the first electrode pad
Data Source
AI summary
A pyroelectric infrared sensor comprises an internal board, a pyroelectric element and a capacitor element. The internal board is provided with a first electrode pad and a second electrode pad. The pyroelectric element has a composition of PbCa(MnSb)TiO and is connected to the first electrode pad. The capacitor element is connected to the second electrode pad with a high melting point solder paste which has a liquidus temperature equal to or more than 240° C.