Pyroelectric Infrared Sensor Solder Layout for High-Reflow Reliability
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Solution Overview
Problem
Existing pyroelectric infrared sensors cause electrical malfunctions in electronic devices due to remelted solder pastes during reflow processes when peak temperatures exceed the expected 220°C, affecting components other than the pyroelectric element.
Innovation Solution
The pyroelectric infrared sensor is designed with a capacitor element connected using a high melting point solder paste and other components using a low melting point solder paste, while the pyroelectric element is adhered with a conductive adhesive, ensuring the sensor operates effectively even at peak temperatures up to 250°C.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a low melting point solder paste (liquidus temperature about 220°C) is used to connect components on the main board, then the soldering process can be completed at the expected temperature, but the solder paste may be remelted when the peak temperature exceeds 220°C during reflow, causing electrical malfunctions
Solution Approach 1:
The patent applies different solder paste melting points to different functional areas: low melting point solder paste (about 220°C) is used for general component connections on the main board, while high melting point solder paste (about 250°C or higher) is used specifically for the pyroelectric element and its associated components. This local differentiation ensures that critical components remain stable during reflow processes that exceed 220°C, preventing remelting and electrical malfunctions while maintaining ease of manufacture for other components.
2Reliability
If the heating time is extended to reliably solder large electronic components, then the soldering reliability is improved, but the peak temperature in the reflow oven may reach up to near 250°C, causing remelting of low melting point solder paste
Solution Approach 1:
The patent changes the key parameter of solder paste melting point from low (about 220°C) to high (about 250°C or higher) specifically for the pyroelectric element and critical components. This parameter change allows the system to withstand peak temperatures of 250°C or higher that occur during extended heating cycles required for soldering large components, preventing remelting and maintaining electrical functionality throughout the reflow process.
3Adaptability or versatility
If the pyroelectric infrared sensor is mounted on the main board with other components, then the device can be manufactured using standard reflow processes, but the sensor components may be affected by temperatures exceeding the expected 220°C reflow temperature
Solution Approach 1:
The patent implements local quality by using high melting point solder paste (about 250°C or higher) specifically for the pyroelectric element and its immediate components, while other components on the main board can use standard low melting point solder paste. This localized approach allows the sensor to be manufactured using standard reflow processes with adaptability, while simultaneously protecting the temperature-sensitive pyroelectric components from harmful effects of temperature excursions above 220°C.
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 configuration prevents remelting of solder pastes and maintains electrical functionality by using high melting point solder paste for critical components, reducing malfunctions and ensuring reliable operation under high temperatures.
Implementation Method 1
a pyroelectric infrared sensor comprising a pyroelectric element which has a high Curie temperature
Implementation Method 2
the pyroelectric element is adhered with a conductive adhesive
Implementation Method 3
a capacitor element connected using a high melting point solder paste
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
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.