Residual stress relief in Al ₂O ₃-poly-tetra-fluoro- ethylene hybrid thick films for integrated substrates using aerosol deposition

Low temperature fabrication of Al ₂O ₃-based polymer composite thick films was performed for integrated substrate applications using the aerosol deposition (AD) process. Although AD is capable of fabricating dense ceramic films at room temperature, residual stress occurs in the deposited ceramic films due to the nature of the film growth, which is based on solidification through the impact and fracture of a starting powder. In order to solve this problem, we obtain residual stress relief by adding poly-tetra-fluoro-ethylene (PTFE), which has superior elongation and dielectric properties when used as an electronic substrate. The Al ₂O ₃-PTFE composite thick films were deposited by the AD method on copper foil substrates using a mixed starting powder at room temperature. The size of the Al ₂O ₃ crystallites in the Al ₂O ₃-PTFE composite thick films was 10 times larger than the crystallites in the Al ₂O ₃ thick films due to the cushioning effect of the soft PTFE. The Al ₂O ₃-PTFE composite thick films had a low dielectric constant (≈4.5) and loss tangent (≈0.002), and electrical properties that were nearly frequency independent after a low temperature annealing at below 300 °C. In addition, the Al ₂O ₃-PTFE composite thick films showed a superior chemical resistance during the patterning process due to the extraordinarily high chemical resistance of the PTFE.