Vlad Domnich | Vibrantz Technologies: How does material patterning enable controlled electromagnetic radiation transmission in radomes?

What challenges arise when firing ruthenium dioxide resistors at temperatures exceeding typical recommendations?

The speaker discusses the materials used to create large-area surface resistors for radome applications. Ruthenium dioxide is a common choice for achieving the desired resistivity range. However, a key challenge is that ruthenium dioxide typically requires firing temperatures around 900 degrees Celsius.

The application requires firing at 1020 degrees Celsius, which is significantly higher than the recommended temperature for ruthenium dioxide. This elevated temperature could potentially lead to issues with the material's stability, microstructure, or electrical properties. Therefore, careful consideration must be given to the selection and processing of ruthenium dioxide to ensure it can withstand the higher firing temperature without compromising performance.

The speaker's approach involves using ruthenium dioxide with different surface areas (related to particle size) and a lumino-silicate glass binder. The glass binder's thermal expansion must closely match the substrate, and its softening point must be appropriate for the application. Additives are also used for additional control over thermal expansion, high-temperature viscosity, and the temperature coefficient of resistance (TCR).

In this short video, you can learn:
* The typical firing temperature limitations of ruthenium dioxide resistors.
* The potential issues associated with exceeding recommended firing temperatures.
* The speaker's approach to mitigating these issues through material selection and additives.
📋 **Clip Abstract** This segment addresses the challenges of using ruthenium dioxide resistors at high firing temperatures and outlines the speaker's strategy for overcoming these challenges through careful material selection and process control.
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Why is thermal expansion coefficient (CTE) matching critical for resistor performance on complex-shaped substrates?

The speaker explains that initial tests on flat substrates showed promising results with the developed resistors. However, when the customer began testing the materials in real-world applications on larger, complex-shaped substrates, cracking was observed. This cracking was attributed to a mismatch in the coefficient of thermal expansion (CTE) between the resistor material, the substrate, and any intermediate layers.

The CTE mismatch caused stress within the resistor film during thermal cycling, leading to cracking, especially on complex shapes where stress concentrations are more likely. To address this issue, the speaker's team modified the resistor formulation to lower its thermal expansion coefficient. The goal was to achieve a CTE that closely matched the CTE of the substrate and any coatings used in the application.

The final product, designated 279899GH, achieved a calculated CTE of less than 4 ppm and a measured CTE of less than 5 ppm. This close CTE matching eliminated the cracking issue observed in the initial tests. This highlights the importance of considering CTE matching when designing materials for applications involving complex geometries and thermal cycling.

In this short video, you can learn:
* How CTE mismatch can lead to cracking in resistor films on complex substrates.
* The importance of CTE matching between the resistor, substrate, and any intermediate layers.
* How the speaker's team modified the resistor formulation to achieve a low CTE and eliminate cracking.
📋 **Clip Abstract** This segment details the problem of cracking in resistors due to CTE mismatch on complex substrates and explains how the speaker's team solved the problem by reformulating the resistor material to achieve a low and well-matched CTE.
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