In recent years, the widespread adoption of IoT (Internet of Things: a technology that enables devices to connect to and interact via the internet by integrating communication functions) has accelerated the advancement and miniaturization of electronic devices.

Along with this trend, printed circuit boards, which serve as essential components for electronic devices, are increasingly required to achieve higher density packaging to accommodate complex component mounting within minimal space.

High-Density Design of Printed Circuit Boards (PCBs) and Fire Risk

High-density printed circuit boards have the increased risk of quality degradation due to long-term use, heat accumulation, etc.

The deterioration of resin or wiring insulation on the PCBs and electronic components can potential cause short circuits, in the worst-case scenario, this can lead to fire.

To prevent such accidents, various protective components, such as fuses (safety devices that cut off the circuit to prevent damage to electronic circuits when excessive current flows), are commonly used. However, for applications requiring a high level of safety, such as data servers and automobiles, additional safety measures are necessary.

Gas Emission Due to Heat Generation in PCBs to be detected by Gas Sensors

FIGARO's semiconductor gas sensors have the potential to detect odor components generated due to the evolution of heat caused by an overcurrent at an early stage, allowing for the detection of abnormalities before the circuit board begins to emit smoke or catch fire.

Through the research presented in this article, it was confirmed that FIGARO's semiconductor gas sensors can detect odor components generated by heat evolution on a printed circuit board.

The gas sensors used in this research

[Research Details] Sensitivity Characteristics of FIGARO's Gas Sensors for Each Target Gas

Analysis of volatile gases emitted from circuit boards

Gas chromatography and mass spectrometry analysis were performed on the volatile gases emitted when five different types of printed-wiring boards were heated to 250°C. The analysis identified different types of gases for each type of printed-wiring board.

The gases detected can be broadly classified into the following five groups of gases.

(Reference) Atsushi Horikawa, Yoshinobu Marumoto, The Japan Institute of Electronics Packaging, 34, 3B2 01 (2020).

Selection of sensor models and optimum heater voltage

The sensitivity characteristics of each sensor model to the five gas groups at different working voltages (heater voltages) were studied to determine the optimum working voltage. The concentration of each representative gas was 10 ppm.

The sensitivity characteristics of each sensor model are shown in the radar graphs below.

Sensor responses to 10 ppm of representative gases at different heater voltages (axis: reciprocal of the sensor resistance ratio)

(TGS2600)
The sensitivity to each gas type is relatively low at both working voltages, but well balanced.

(TGS2602)
TGS2602 shows a similar sensitivity pattern to TGS2603. At a higher working voltage, it exhibits increased sensitivity to aromatic compounds while maintaining a well-balanced sensitivity pattern to all types of gases.

(TGS2603)
This sensor shows low sensitivity to aromatic compounds but higher sensitivity to alcohols and ketones at a higher working voltage.

The gas sensor characteristics required for fire precursor detection prioritize uniform sensitivities to various gases rather than high sensitivity to a specific gas. In this respect, TGS2602 operating at 5 V is considered to have the best characteristics.

Sensor responses to volatile gases emitted from a printed-wiring board

Changes in the sensor resistance of TGS2602 and appearance changes of the wiring pattern with a line width of 1 mm, a line length of 50 mm, and a copper thickness of 35 μm printed on a printed-wiring board were examined when applying an overcurrent of 12A to the printed-wiring board placed inside a sealed container.

Changes in the sensor resistance of TGS2602 in response to volatile gases emitted from the circuit board and the appearance changes of the wiring pattern due to overcurrent application

Immediately after the overcurrent was applied, a decrease in sensor resistance was observed, indicating the generation of certain gases from the wiring pattern.

In addition, after 7 minutes, the production of a strong odor was detected, and a black discoloration was seen in the center of the wiring pattern.

[Research Results] Gas Sensors for Detecting Abnormal Heat Generation in Printed Circuit Boards

This research suggests the possibility of detecting abnormal heat generation in a printed circuit board much earlier than the time it takes to smolder or catch fire by installing a gas sensor in an enclosed space or near a potential source of odorous gases.

For example, it is expected that it will be possible to prevent system failures and minimize damage from electrical fires by installing a gas sensor and a shutdown circuit that operates based on the sensor output signal on the circuit board.

(References)
- Manabu Kanazawa, The Journal of the Institute of Electrical Installation Engineers of Japan, 37, 866-869 (2017).
- Hisao Kitaguchi, JETI, 50, 51-54 (2002)
- Atsushi Horikawa, Yoshinobu Marumoto, The Japan Institute of Electronics Packaging, 34, 3B2 01 (2020).

FIGARO's Gas Sensors Contributing to Fire Safety with Early Gas Detection

FIGARO's gas sensors, which have high sensitivity to various gases, can detect gas emissions significantly earlier than conventional fire detection systems for wide indoor area monitoring, such as thermal cameras. This allows for quick alerts at the initial stage of a fire emergency.

High-sensitivity TGS 26 series Gas Sensors

FIGARO's TGS 26 series gas sensors utilize relative value detection --a method that detects air contamination by measuring changes in sensor resistance relative to the sensor resistance in clean air. This enables control that closely mimics human perception.

These sensors are long-lasting, cost-effective, and easy to use with simple electronic circuits. Additionally, we introduce three sensor models that comply with RoHS2 directive.

Figaro Engineering Inc. offers a wide range of high-quality products to meet various customer needs and to enhance safety, security, and comfort in daily life with our high-sensitivity and highly reliable gas sensors.