Fire Precursor Detection～ Detection of gases emitted from printed circuit boards ～Research Objective
In recent years, high-density packaging of electronic components on a printed circuit board has become
increasingly common due to the sophistication and miniaturization of electronic products as IoT becomes
more widespread. Long-term use or heat accumulation of such high-density PCBs can lead to a high riskof deterioration, which in the worst case could result in a fire. To prevent such accidents, various
protection devices such as fuses are commonly used. However, none of them is 100% effective, anddouble or triple safety measures are required for applications that require a high level of safety, such asdata servers and automobiles.
In this study, we attempted to use our semiconductor-type gas sensors, to detect the odorous gas
components generated by the heat produced when an overcurrent is applied to an electronic circuit board,and found the possibility of detecting the initial abnormal stage of the circuit board before it starts tosmolder or catch fire.

The gas sensors used in this study

TGS2600

TGS2602TGS2603
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Research Results
1. Analysis of volatile gases produced from circuit boards
Gas chromatography and mass spectrometry analysis was performed on the volatile gases
produced when five different types of circuit boards were heated to 250°C. The analysis identified
different types of gases for each type of circuit board.

The gases detected can be broadly classified into the following five groups of gases. ＊Reference 3)Classification(a) Alcohol(b) Amides(c) Acidic gases(d) Ketones(e) Aromaticcompounds

Chemicalstructural formula

Representativegas2Research Results
2. 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 concentrationof each representative gas was 10 ppm.
The sensitivity characteristics of each sensor model are shown in the radar graphs below.

TGS2600
Alcohol

Aromatic
compounds

Ketones

Acidicgases

AmidesAromatic
compounds

Ketones

TGS2602

TGS2603

Alcohol

Alcohol

Acidicgases

AmidesAromatic
compounds

Ketones

Acidicgases

AmidesFigure 1: Sensitivities to 10 ppm of representative gases at different heater voltages (axis: sensor resistance ratio)3

Research Results
2. Selection of sensor models and optimum heater voltage
The main sensitivity characteristics of each sensor model are as follows.

・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. This sensor shows a well-balanced
sensitivity pattern to all types of gases with increased sensitivity to aromatic compounds at the higher
working voltage.

・TGS2603
This sensor shows low sensitivity to aromatic compounds, but higher sensitivity to alcohols andketones at the higher working voltage.

The gas sensor characteristics required for this application are uniform sensitivities to various gases
rather than high sensitivity to a specific gas. In this respect, the TGS2602 operating at 5 V isconsidered to have the best characteristics.

4Research Results
3. Sensor responses to volatile gases generated from the circuit board

Sensor Resistance

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

Figure2: The sensor resistance change of TGS2602 as a response to volatile gases generated
from a circuit board and the changes in circuit pattern appearance by applying an overcurrent.

Immediately after the overcurrent was applied, a decrease in sensor resistance was observed,
indicating the generation of certain gases from the circuit board pattern. In addition, after 7 minutes,
production of a strong odor was detected, and a black discoloration was seen in the center of thecircuit pattern.
5Conclusion
This research suggests the possibility of detecting abnormal heat generation on a circuit board muchearlier than the time to smolder or catch fire by installing a gas sensor in an enclosed space or near apotential source of odorous gases.
For example, by installing a gas sensor and a shutdown circuit that operates on the sensor output signal
on a circuit board, it is expected that it will be possible to prevent system failures and minimize damage
from electrical fires by detecting abnormal conditions much earlier than current fire detection systems
commonly used to monitor large indoor areas.
*References.
1) Manabu Kanazawa , The Journal of the Institute of Electrical Installation Engineers of Japan, 37,866-869 (2017).
2) Hisao Kitaguchi , JETI, 50, 51-54 (2002)
3) Atsushi Horikawa , Yoshinobu Marumoto , The Japan Institute of Electronics Packaging , 34, 3B201 (2020).

For more information about a research or development collaboration with our company,
please contact us at figaro@figaro.co.jp
Conference presentations related to the contents of this document■ Society of Automotive Engineers of Japan, Inc.
Academic Meeting at 2021 Autumn Conference
October 13-15, 2021
Proceedings Issue date (Date of publication): October 8, 2021
■ 69th Chemical Sensor Symposium (September 8-9, 2021)

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