Thin (50 to 100 µm) ceramic spacers for multi-layered electronic devices such as flash RAM require large numbers of small via holes drilled in them to perform their function. The preferred hole diameter is currently in the range of 100 µm but is expected to become smaller.
These ceramics may be easily drilled with a laser prior to firing. So called “green” ceramic is comprised of fine refractory particles in an organic binder. The Base plate Thermal Vias binder, which burns off during firing, gives the material the consistency of a weak flexible tape. The green ceramic, consequently, is applied to a poly (ethylene terephthalate) (PET) film for ease of handling.
Drilling of PET-backed green ceramic with conventional CO2 lasers causes severe melting of the PET backing, making it impossible to separate the ceramic from the backing. We have examined the use of a 9.4 µm CO2 laser for this process. The 9.4 µm wavelength is absorbed more strongly in the PET than is 10.6 µm light, reducing the dimensions of the heat-affected zone in the PET. Drilling with this type of laser produces greatly improved results in this process.