Рет қаралды 205,841
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: sci-hub.se/10.1016/J.JEURCERA...
60W laser cutter: www.ebay.com/itm/294386493292
Ceramic sheets at McMaster: www.mcmaster.com/alumina/nonp...
Ceramic PCB prototypes: ceramic-pcb.com/product/alumi...
Quickfire kiln: kruegerpottery.com/products/p...
Raspberry Pi picoReflow oven controller: apollo.open-resource.org/miss...
Silver powder: www.ebay.com/itm/122525930519
Glass glaze: www.amazon.com/dp/B0044SCR6O
Macor: www.mcmaster.com/materials/ma...
Dupont silver paste: www.dupont.com/content/dam/du...
Binders for ceramic powder: digitalfire.com/article/binde...
PVA mold release: www.tapplastics.com/product/f...
Very complete study of laser machining of ceramics: www.research.manchester.ac.uk...
Applied Science on Patreon: / appliedscience