Printed multilayer and multi-material electronic devices and structures are suitable for applications in sensing, advanced packaging, RF antennas and tags, programable surfaces, power transfer coils, large-area intelligent surfaces, and biomedical microdevices. Differences in the coefficient of thermal expansion (CTE) for each material, uniformity of temperature across the device while processing and differences in thermal resistance of structures will cause stress gradients in printed FHE devices. These stress-induced effects are even intensified when multiple post-processing steps (reflow soldering, sintering, flip-chip bonding, etc.) are needed. In devices with a high density of interconnects and traces, power dissipation could also lead to performance problems in FHE devices caused by thermal strains. The 3D FHE device development often requires multiple design and process iterations and corrections to handle these stress effects, particularly when considerable power handling, structures with embedded components and cavities, or ultra-thin structures are needed. We have designed, developed, and characterized resistive microheater elements and Resistive Temperature Detectors (RTD) elements that can be 3D printed on or embedded in 3D-printed FHE structures. Our 3D-printed resistive heater linear array enables specific temperature profiles across the array and creates a controlled heat flow directly integrated into an FHE. The same resistive elements can accurately measure the temperature (RTD) or heat flow in different parts of the FHE device. We used the inkjet printing (NanoDimension DragonFlyTM IV) method to print our resistive array. We studied the resistance as a function of varying thicknesses of conductive Ink (CI) layers (1- 20 layers corresponding to ~ 1-20 µm AgCite® NP) for the resistive elements of the printed array (5x7), achieving resistances in the range of 1-20Ω per resistive element (Q-pixel). We have demonstrated individual control over the Q-pixels, turning ON (I=1-80 mA) the desired patterns (combination of pixels) at desired temperatures where the thermal emissions are visible in an IR camera and achieving temperatures of 25-120 C. Using a PID-controlled thermal stage, we measured the temperature coefficient of resistance (TCR) for the printed RTDs to be 1.898×10^(-3)/C (1898 ppm/ C) measured in the range of 30-50 C. The developed Q-pixel array can be used for many applications ranging from sensing and packaging to biomedical device research and micro-robotic E-Skin for thermal conductivity probing. The integrated heat source and the RTD sensors allow the realization of microcalorimetric devices such as scanning microcalorimeters, thermal conductivity sensors, and thermal diffusivity sensors. The embedded Q-pixels in the FHE devices will allow thermal management in the FHE packages, measure and correct for environmental effects, and characterize the power handling and Ovenization in Package (OiP) for sensitive components.
