J.D. Rurup, E.B. Secor
Iowa State University,
United States
Keywords: printed electronics, additive manufacturing, process control, hybrid electronics
Summary:
Conventional flat, rigid PCBs consume space, add weight, and do not integrate will with curved 3D geometries of products spanning consumer, industrial, medical, and defense hardware. Emerging manufacturing methods enabling direct fabrication of electronics on 3D surfaces promise enhanced integration of biomedical sensors, increased sustainability in automotive and commercial aerospace industries, and improved functionality for defense and space electronics. The expanding Internet of Things increases the need for technologies capable of integrating circuitry onto diverse 3D surfaces, from everyday consumer devices to heavy manufacturing equipment. Aerosol jet printing (AJP) is especially compelling for conformal patterning, offering high resolution and high tolerance to standoff variability, but it suffers from several limitations: (1) process variability limits translation of promising prototypes into production and (2) existing printing systems do not support patterning on large surfaces or in confined geometries. We are addressing these challenges with (1) a real-time process monitoring system and (2) an AJP-equipped, small form-factor 6-axis robotic arm, increasing the manufacturing readiness level of conformal AJP towards viability at production scales. Aerosol jet printers employ two different atomization methods for aerosolizing functionalized liquid inks – ultrasonic and pneumatic. However, neither allows for explicit control over the amount of aerosol generated. Drift and variability in aerosol generation leads to inconsistency in the downstream deposition rate, even when process parameters remain the same, thus changing functional electronic properties. To detect and counteract this long term drift, we have developed an inline optical process monitoring technique based on light scattering to measure aerosol generation in real time. Employing this method, we have demonstrated closed loop control of ultrasonic atomization, improving process stability over prints lasting multiple hours [1,2]. Additionally, this real-time metric creates a new data stream for quality control by mapping deposition rate to spatial positions at sub-second timescales [3]. Ongoing efforts to translate this process monitoring system to pneumatic atomization have shown preliminary success, despite the added complexity of the atomization physics. Efforts are underway to examine closed loop control with pneumatic atomization, as well as prove the efficacy of the system over timescales consistent with production shifts. This novel process monitoring technique will play a critical role in gaining industry-wide confidence in AJP. A primary advantage of AJP over alternative patterning techniques is its large nozzle-substrate offset, making it highly suitable for conformal patterning on 3D objects. Typical commercial aerosol jet printers have 3-axis motion systems, limiting conformal patterning abilities, and 5-axis trunnion motion systems developed limit build area and increase motion planning complexity. As an alternative approach, we developed a custom printer employing a small 6-axis robot arm. To print on large or immovable objects, the entire print system can be moved to the substrate. Such a compact motion system further enables conformal aerosol jet printing in confined spaces, including the interior walls parts down to 100 mm in diameter. The versatility of a small 6-axis robotic arm, combined with the utility of aerosol jet printing, yields the opportunity to explore 3D circuitization of whole new types of substrates.