Study On B₄C Ceramic Composites And Their Fine Machining Processes

The development of IC technology is changing with each passing day.The increase of chip integration and packaging density has set higher demands on properties of electronic packaging materials.Electronic packaging materials should have high thermal condunctivity,CTE matched to those of semiconductors and low density.In addition,low dielectric constant and dielectric loss are needed in some cases.Boron carbide has excellent properties such as high melting point,high hardness,low density,and good neutron absorbability,it is also one of the most promising high-temperature thermoelectric materials.Boron carbide is main research object of this paper.Possibility of using it as electronic packaging substrate material was researched. The 'Polymetric Sponge' process was used to prepare B₄C reticulated porous ceramic in this paper.The results showed that ceramic slurry of good rheological behavior was prepared using distilled water as solvent,silica sol as a binder,calcium betonite and CMC to improve the rheology,and ethanol to remove air bubble.Highly porous B₄C ceramic with an open, three-dimensional network structure and large pore diameter was prepared after immersing sponge in ceramic slurry,evaporation and sintering process.This kind of porous ceramic can be used as preform for preparing metal matrix composites.B₄C-AlN composite ceramic was prepared in this paper using B₄C and AlN as stuff,Y₂O₃ and CaF₂ as sintering aids by molding and sintering process.The results showed that linear shrinkage of composite ceramic increased with the increasing of AlN content from 0 to 10wt%;hardness of composite ceramic decreased with the increasing of AlN content from 10wt% to 50wt%;thermal conductivity of B₄C-50AlN composite ceramic decreased with the increasing of temperature from room temperature to 350℃,maximum of thermal conductivity is 27 W/(m·K),and the main reason for low thermal conductivity is that composite ceramic sintered body did not obtain a compact structure;B₄C-20AlN composite ceramic sintered body had a regulative grain shape and clean interface;the presence of Ca3Al2O6,Ca11N8 phase was found besides the main phase B₄C,AlN and additive CaF₂ in B₄C-10AlN ceramic sample by XRD analysis.Aluminium was infiltrated in B₄C-AlN composite ceramic preform to prepare B₄C-AlN/Al cermet in this paper.The results showed that structure of this composite distributed uniformly,ceramic and metal phase combined compactly in general,the presence of Al₃BC,YAlO₃,B₂YC₂ phase was found besides the main phase B₄C,AlN and Al in composite sample.To apply ceramic to electronic packaging substrate material depends on improvements of its micro-machining properties.This paper carried out primary research on scribing of B₄C and Al₂O₃ ceramic surface using lasers.The results showed that laser machining capability can be enhanced in a certain extent by increasing laser power, however, machining quality would decline;laser machining effect would be affected by changing defocus distance.The width of scribing line on ceramic surface was thinnest when electric current was lower than 100A;change of the width of scribing line was not distinct when increasing electric current from 100A to 250A.Microcosmic laser machining area was formed on surface of the sample;precision of the width of scribing line could be controlled in micron scale; both of the depth of scribing line and the shape of profile could be regulated by changing technical parameter. .