Underwater laser cutting and silver sintering to make ceramic circuit boards
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 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:
60W laser cutter:
Ceramic sheets at McMaster:
Ceramic PCB prototypes:
Quickfire kiln:
Raspberry Pi picoReflow oven controller: :resources:picoreflow
Silver powder:
Glass glaze:
Macor: ~glass-mica-ceramic/
Dupont silver paste:
Binders for ceramic powder: for ceramic bodies
PVA mold release:
Very complete study of laser machining of ceramics:
Applied Science on Patreon:
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