Thermal stress cracking can be completely avoided by CO2 laser cutting thin alumina sheets underwater. I also show how to formulate and apply silver paste, then sinter in a kiln to produce double-sided ceramic printed circuit boards with conductive vias.
60W CW CO2 laser at 80% power. 10mm/sec. Standard lens focal length (50mm). 2mm water above ceramic. 180 passes to cut through 0.75mm thick alumina.
Silver paste: 97% silver powder, 3% glass powder by mass. Particle size 1 micron or less. Add poly vinyl alcohol mold release until desired consistency reached.
Paste applied with 4 mil thick vinyl stencil. Dried in air 10 minutes, then rapidly brought up to 900*C, held for 10 minutes, then rapidly brought back down to room temperature. Total cycle about 45 minutes.
I measured electrical conductivity of the finished traces from my process with vinyl stencils: 4 milliohms per square at 10 micron final thickness. This is pretty close to the Dupont published spec ( less than 2 milliohm/sq at 16 micron thick)
Underwater CO2 laser cutting reference: https://sci-hub.se/10.1016/J.JEURCERAMSOC.2011.06.015
60W laser cutter: https://www.ebay.com/itm/294386493292
Ceramic sheets at McMaster: https://www.mcmaster.com/alumina/nonporous-alumina-ceramic-sheets-and-bars/
Ceramic PCB prototypes: https://ceramic-pcb.com/product/alumina-pcb-al2o3-pcb-prototypes-online/
Quickfire kiln: https://kruegerpottery.com/products/par_quikfire6
Raspberry Pi picoReflow oven controller: https://apollo.open-resource.org/mission:resources:picoreflow
Silver powder: https://www.ebay.com/itm/122525930519
Glass glaze: https://www.amazon.com/dp/B0044SCR6O
Dupont silver paste: https://www.dupont.com/content/dam/dupont/amer/us/en/transportation-industrial/public/documents/en/LF131.pdf
Binders for ceramic powder: https://digitalfire.com/article/binders+for+ceramic+bodies
PVA mold release: https://www.tapplastics.com/product/fiberglass/mold_releases/tap_pva_mold_release_liquid/67
Applied Science on Patreon: https://www.patreon.com/AppliedScience
