Isothermal Cage PCB Reduces Thermal Gradients
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Solution Overview
Problem
Infrared (IR) sensors on printed circuit boards (PCBs) are highly sensitive to thermal gradients, leading to poor repeatability and false signals due to temperature variations, which existing solutions like large thermal masses cannot effectively mitigate without increasing size and cost.
Innovation Solution
An isothermal cage formed from thermally conductive material surrounds the IC seat, with thermally conductive dots and vias that match thermal time constants to reduce thermal gradients, ensuring consistent temperature readings across the sensor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a large thermal mass is used on the sensor package to reduce thermal gradient effects, then thermal gradient sensitivity is reduced, but the size and cost of the sensor increases
Solution Approach 1:
The thermal management function is segmented between the sensor package and the PCB. Instead of concentrating thermal mass in the sensor package, the patent divides the thermal mass into two parts: a small thermal mass in the sensor package and a larger thermal mass in the form of copper pours and thermal vias on the PCB. This segmentation allows the system to achieve thermal gradient reduction without increasing the sensor package size.
Solution Approach 2:
The patent moves the thermal mass from the three-dimensional sensor package volume to the two-dimensional PCB plane. By using extensive copper pours and thermal vias on the PCB, the system creates an alternative thermal management path that does not require increasing the sensor package volume. This dimensional shift resolves the contradiction between thermal gradient reduction and package size.
2Ease of manufacture
If conventional PCB layouts with linear and symmetrical trace patterns are used, then manufacturing is simplified, but thermal gradients cause poor repeatability and false signals in IR sensors
Solution Approach 1:
The patent creates an equipotential thermal environment around the IR sensor by surrounding it with copper pours on the PCB. These copper pours act as thermal reservoirs that maintain a uniform temperature potential around the sensor, eliminating thermal gradients that would otherwise cause measurement errors. This equipotential approach maintains signal reliability while preserving conventional PCB manufacturing simplicity.
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 solution significantly reduces thermal gradient-induced variations, improving the stability and accuracy of IR sensor output by maintaining consistent temperature across the sensor, as shown by reduced variance in sensor voltage across varying temperatures.
Implementation Method 1
an isothermal cage that substantially surrounds the IC seat, wherein the isothermal cage is formed at least in part of a thermally conductive material
Data Source
AI summary
With infrared (IR) sensors, repeatability and accuracy can become an issue when there are thermal gradients between the sensor and an underlying printed circuit board (PCB). Conventionally, a large thermal mass is included in the sensor packaging to reduce the effect from such thermal gradients, but this increase costs and size of the sensor. Here, however, a PCB is provided that includes an isothermal cage included therein that generally ensures that the temperature of the underlying PCB and sensor are about the same by including structural features (namely, the isothermal cage) that generally ensure that the thermal time constant for a path from a heat source to the thermopile (which is within the sensor) is approximately the same as thermal time constants for paths through the PCB.