Name: in situ surface temperature measurement in a conveyor belt furnace via inline infrared thermography
Uploaded: 2020-05-30T13:00:00
Description: Watch this Scientific Journal Video about In Situ Surface Temperature Measurement in a Conveyor Belt Furnace via Inline Infrared Thermography at JoVE.com

This work is supported by the German Federal Ministry for Economic Affairs within the project &#8220;Feuerdrache&#8221; (0324205B). The authors thank the co-workers that contributed to this work and the project partners (InfraTec, Rehm Thermal Systems, Heraeus Noblelight, Trumpf Photonic Components) for co-financing and providing outstanding support.

1. Installation of IR camera into a conveyor belt furnace
<ol>
	<li>Decide which part of the furnace should be measured by the IR camera. 
	NOTE: Here, the peak zone of the firing process is chosen (see the orange highlighted zone in the firing area of Figure 1A).</li>
	<li>Define the temperature range of interest that the IR camera should detect (e.g., 700&#8722;900 &#176;C, the typical peak temperature range of the firing process).</li>
	<li>Determine, or at least e...

<ol>
	<li>Xu, J., Zhang, J., Kuang, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Conveyor Belt Furnace Thermal Processing. , (2018).</li><li>Breitenstein, O., Warta, M. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Langenkamp Lock-in Thermography: Basics and Use for Evaluating Electronic Devices and Materials. , (2010).</li><li>Ravindra, N. M., Ravindra, K., Mahendra, S., Sopori, B., Fiory, A. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Modeling+and+Simulation+of+Emissivity+of+Silicon-Related+Materials+and+Structures.">Modeling and Simulation of Emissivity of Silicon-Related Materials and Structures.</a> Journal of Electronic Materials. 32 (10), 1052-1058 (2003).</li><li>Ourinson, D., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+Situ+Solar+Wafer+Temperature+Measurement+during+Firing+Process+via+Inline+IR+Thermography.">In Situ Solar Wafer Temperature Measurement during Firing Process via Inline IR Thermography.</a> Physica Status Solidi (RRL) - Rapid Research Letters. 13 (10), 1900270 (2019).</li><li>Ourinson, D., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In-situ+wafer+temperature+measurement+during+firing+process+via+inline+infrared+thermography.">In-situ wafer temperature measurement during firing process via inline infrared thermography.</a> AIP Conference Proceedings. 2156, 020013 (2019).</li><li>Cooper, I. B., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Understanding+and+Use+of+IR+Belt+Furnace+for+Rapid+Thermal+Firing+of+Screen-Printed+Contacts+to+Si+Solar+Cells.">Understanding and Use of IR Belt Furnace for Rapid Thermal Firing of Screen-Printed Contacts to Si Solar Cells.</a> IEEE Electron Device Letters. 31 (5), 461-463 (2010).</li><li>Schubert, G., Huster, F., Fath, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Physical+understanding+of+printed+thick-film+front+contacts+of+crystalline+Si+solar+cells-Review+of+existing+models+and+recent+developments.">Physical understanding of printed thick-film front contacts of crystalline Si solar cells-Review of existing models and recent developments.</a> Solar Energy Materials and Solar Cells. 90 (18-19), 3399-3406 (2006).</li><li>Rauer, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Aluminum+Alloying+in+Local+Contact+Areas+on+Dielectrically+Passivated+Rear+Surfaces+of+Silicon+Solar+Cells.">Aluminum Alloying in Local Contact Areas on Dielectrically Passivated Rear Surfaces of Silicon Solar Cells.</a> IEEE Electron Device Letters. 32 (7), 916-918 (2011).</li><li>Pawlik, M., Vilcot, J. -. 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Commonly, thermography temperature is corrected via measuring and adapting the optical parameters of the object, transmissive window and path, and environmental temperature of the object and transmissive window2. As an alternative method, a temperature correction technique based on thermocouple measurements is described in this protocol. For the latter method, knowledge of the parameters mentioned above is not required. For the application shown here, this method is sufficient. However, it cannot ...

Process control and quality assurance of objects processed in conveyor belt furnaces1 is important and accomplished by measuring the surface temperature of the object. Currently, the temperature is typically measured by a thermocouple1. As thermocouple measurements require contact with the object, thermocouples inevitably damage the object. Therefore, it is common to choose representative samples of a batch for temperature measurements, which are not further processed since they become damaged. The measured temperatures of these damaged objects are then generalized to the remaining samples from the batch, which are further processed. Accordingly, production must be interrupted for thermocouple measurements. Furthermore, the contact is local, needs to be readjusted after each measurement, and influences the local temperature.
Infrared (IR) thermography2 has a number of advantages over classic thermocouple measurements and represents a contactless, in-situ, real-time, time-saving, and spatially resolved temperature measurement method. Using this method, each sample of the batch, including those that are further processed, can be measured without interrupting production. In addition, the surface temperature distribution can be measured, which provides insight into temperature homogeneity during the process. The real-time feature allows correction of temperature settings on-the-fly. So far, the possible reasons for not using IR thermography in conveyor belt furnaces are 1) unknown optical parameters of hot objects (especially for nonmetals3) and 2) parasitic environmental radiation in the furnace (i.e., reflected radiation detected by the IR camera in addition to the emitted radiation from the object), which leads to false temperature output2.
Here, as a representative proof-of-concept example of IR thermography in a conveyor belt furnace, we successfully installed an inline thermography system into an IR lamp powered solar firing furnace (Figure 1), which is used during the contact firing process of industrial Si solar cells (Figure 2A,B)4,5. The firing process is a crucial step at the end of industrial solar cell production6. During this step, the contacts of the cell are formed7,8, and surface passivation is activated9. To successfully achieve the latter, the time-temperature profile during the firing process (Figure 2C) must be accurately realized. Therefore, sufficient and efficient temperature control is required. This protocol describes how to install an IR camera into a conveyor belt furnace, conduct a customer correction of a factory calibrated IR camera, and evaluate the spatial surface temperature distribution of a target object.

<table border="0" cellpadding="0" cellspacing="0" style="width:665px;" width="665">
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		<col />
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	</colgroup>
	<tbody>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Datalogger incl. Thermal barrier</td>
			<td style="width:121px;">Datapaq Ltd.</td>
			<td style="width:161px;"></td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">IR thermography camera &#34;Image IR 8300&#34;</td>
			<td style="width:121px;">InfraTec GmbH</td>
			<td style="width:161px;"></td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">IR thermography software &#34;IRBIS Professional 3.1&#34;</td>
			<td style="width:121px;">InfraTec GmbH</td>
			<td style="width:161px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Solar cells</td>
			<td style="width:121px;">Fraunhofer ISE</td>
			<td style="width:161px;"></td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Solar firing furnace &#34;RFS 250 Plus&#34;</td>
			<td style="width:121px;">Rehm Thermal Systems GmbH</td>
			<td style="width:161px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Sheath thermocouples type K</td>
			<td style="width:121px;">TMH GmbH</td>
			<td style="width:161px;"></td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Thermocouple quartzframe</td>
			<td style="width:121px;">Heraeus Noblelight GmbH</td>
			<td style="width:161px;"></td>
			<td></td>
		</tr>
	</tbody>
</table>

in situ surface temperature measurement in a conveyor belt furnace via inline infrared thermography

Measuring the surface temperature of objects that are processed in conveyor belt furnaces is an important tool in process control and quality assurance. Currently, the surface temperature of objects processed in conveyor belt furnaces is typically measured via thermocouples. However, infrared (IR) thermography presents multiple advantages compared to thermocouple measurements, as it is a contactless, real-time, and spatially resolved method. Here, as a representative proof-of-concept example, an inline thermography system is successfully installed into an IR lamp powered solar firing furnace, which is used for the contact firing process of industrial Si solar cells. This protocol describes how to install an IR camera into a conveyor belt furnace, conduct a customer correction of a factory calibrated IR camera, and perform the evaluation of spatial surface temperature distribution on a target object.

As shown in Figure 3B&#8722;D, the example object (here, a silicon solar cell; strictly speaking, a passivated emitter and rear cell [PERC]12; Figure 2A,B) can be clearly detected by the IR camera in different configurations4. The different configurations are monofacially metallized (Figure 3B), bifacially metallized13 (<strong ...

Watch this Scientific Journal Video about In Situ Surface Temperature Measurement in a Conveyor Belt Furnace via Inline Infrared Thermography at JoVE.com

In Situ Surface Temperature Measurement in a Conveyor Belt Furnace via Inline Infrared Thermography

This protocol describes how to install an infrared camera into a conveyor belt furnace, conduct a customer correction of a factory calibrated IR camera, and evaluate the spatial surface temperature distribution of an object of interest. The example objects are industrial silicon solar cells.

Measuring the surface temperature of objects that are processed in conveyor belt furnaces is an important tool in process control and quality assurance. ...

As it is crucial to measure the temperature of the objects processed in inline furnaces, here we present inline thermography as a promising alternative to classic temperature measurements by thermocouples. Thermocouples damage the object, measure the temperature locally, and require a production interruption. Our inline thermography camera however, measures the object temperature in a contactless, real-time, spatially-resolved manner.We use inline furnaces for contact firing of silicon solar cells. Therefore, we installed a thermography camera inline into our furnace to investigate these advantages. Select a camera with a detection wavelength range that matches the wavelength range of the highest emission of the object of interest in the temperature range of interest as much as possible.To install the camera outside of the furnace chamber, remove the furnace wall and isolation at the location where the optical path should be located, avoiding disturbing objects, such as infrared lamps, in the optical path. Close the hole with a window that isolates the furnace chamber thermally while being as transparent as possible for the detection wavelength range of the camera. Then, place the camera above the windows so that the camera has a visual on the moving belt.Avoid as much parasitic radiation detection by the camera as possible by avoiding nearby objects that emit or reflect radiation in the detection wavelength range of the camera. Then, examine the thermography image via the infrared camera software to check the resulting field of view of the camera. For a customer temperature correction for Silicon solar cells, first check the solar cell for local optical artifacts.As the temperature correction is based on thermocouples, to check the thermocouple validity, mount the thermocouple on the rear aluminum side of the wafer, and measure the time temperature profile for a standard firing process. If the time temperature profile shows a disruption in the form of a flatter curve at the aluminum silicon eutectic temperature of 577 degrees Celsius, the thermocouple is most likely correctly calibrated. Conduct thermocouple measurements with the validated thermocouple mounted on the rear side of the solar cell, and record the wafer with the infrared camera.Conduct multiple thermocouple measurements in the temperature range of interest at the same object spot and at spatially various random object spots to obtain statistically significant time temperature profiles. To determine the local uncorrected thermography solar cell temperature under the thermocouple, extract the local temperature at the position of the thermocouple. Log the measured temperatures via thermocouples against the determined temperatures via uncorrected infrared thermography, and obtain a curve fit as a general uniform global correction formula for the uncorrected thermography image.Then use this curve fit data to correct the uncorrected thermography image globally. To create a two-dimensional peak temperature distribution map, write a script in an appropriate programming language to track the surface temperature for each object's surface spot along the entire camera field of view to act as a virtual thermocouple placed at all of the wafer spots simultaneously. Then, extract the peak temperature value for each spot, and plot these temperatures in a corresponding 2D distribution map.To perform an average temperature distribution in the throughput direction, average the 2D temperature distribution in the dimension perpendicular to the throughput direction. To perform an average temperature distribution perpendicular to the throughput direction, average the 2D temperature distribution in the dimension in the throughput direction. As demonstrated in this figure, the corrected temperature of this Silicon solar cell can be clearly detected by the infrared camera in different configurations.Monofacially metalized, bifacially metalized, and non-metalized perk samples. In these analyses, the temperature range of interest resembled the typical peak temperature range of the firing process. As observed in this image, the contacting thermocouple on the rear side of the solar cell causes a temperature drop around itself, most likely due to heat dissipation and shading.The latter drop is important for estimating the cell temperature during firing without thermocouples, compared to the temperature measured by the thermocouple, as for this cell positioned onto a frame when contacted by a thermocouple. If placed directly on the belt, the infrared camera allows observation of the local heat dissipation of the cells by the conveyor belt. This image shows a representative two-dimensional spatial solar cell peak temperature distribution, and the deduced average distribution in and perpendicular to the transport direction.As we use inline furnaces for contact firing of silicon solar cells, we installed an infrared camera into our furnace to create an innovative thermography application. Obtaining spatially resolved peak temperature distributions during the firing process allows the investigation of temperature distribution correlations to the spatially resolved solar cell parameters that are significantly effected by the firing.

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