Method for the controlling of certain second phases in aluminum nitride

A sintered aluminum nitride body product having a depletion zone for preventing the formation of particles in surface and subsurface microstructures of aluminum nitride bodies made by the process of:

• (a) providing a greensheet comprising aluminum nitride powder, a sintering aid and a binder;
• (b) providing a paste over said greensheet comprising a refractory metal powder, a binder and a compound selected from the group consisting of 3CaO.Al2O6, Ca3Al2O6, Ca12Al14O33, CaAl4O7, and CaAl12O19in an amount sufficient to reduce formation of particles in surface and subsurface microstructures of aluminum nitride bodies when applied on said greensheet and sintered;
• (c) applying said paste to at least a portion of a surface of said greensheet;
• and
• (d) heating said greensheet and paste for a time and temperature sufficient to form a sintered greensheet and paste such that a depletion zone substantially free of said particles having a thickness of about 10 to about 200 microns deep from a surface of said sintered greensheet and paste is formed.

A sintered aluminum nitride body comprising:

• a substrate of a sintered aluminum nitride having a microstructure containing a compound of aluminum oxide and calcium oxide;
• a paste layer of a sintered mixture of a refractory metal, a binder, and a compound selected from the group consisting of 3CaO-Al2O3, Ca3Al2O6, Ca12Al14O33, CaAl4O7, and CaAl12O19, said paste layer adapted to form a depletion zone when disposed on a portion of said substrate in an amount sufficient to reduce formation of a precipitated yttrium aluminate compound in a surface and subsurface of said microstructure except in said depletion zone of said substrate when applied on said greensheet and sintered;
• and
• said depletion zone substantially free of said precipitated yttrium aluminate in said surface and subsurface of said microstructure.

A sintered aluminum nitride body product having a depletion zone substantially free of particles in surface and subsurface microstructures of aluminum nitride bodies made by the process of:

• (a) providing a greensheet comprising aluminum nitride powder, a sintering aid and a binder;
• (b) providing a paste comprising a refractory metal powder, a binder, a compound selected from the group consisting of Ca12Al14O23, CaAl4O7, and CaAl12O19in an amount sufficient to reduce formation of particles in surface and subsurface microstructures of aluminum nitride bodies when applied on said greensheet and sintered, and about 1 to about 50 volume percent of aluminum nitride powder;
• (c) applying said paste to at least a portion of a surface of said greensheet;
• (d) heating said greensheet and paste for a time and temperature sufficient to form a sintered greensheet and paste;
• and
• (e) forming a depletion zone substantially free of said particles having a thickness of about 10 to about 200 microns deep from a surface of said sintered greensheet and paste.

A sintered aluminum nitride body product having a depletion zone substantially free of second phase particles in surface and subsurface microstructures of aluminum nitride bodies made by the process of:

• (a) providing a greensheet comprising aluminum nitride powder, a sintering aid and a binder;
• (b) providing a paste comprising a refractory metal powder, a binder, tricalcium aluminate in an amount sufficient to reduce formation of particles in surface and subsurface microstructures of aluminum nitride bodies when applied on said greensheet and sintered, and about 1 to about 50 volume percent of aluminum nitride powder;
• (c) applying said paste to at least a portion of a surface of said greensheet;
• (d) heating said greensheet and paste for a time and temperature sufficient to form a sintered greensheet and paste;
• and
• (e) forming a depletion zone having a thickness of about 10 to about 200 microns deep from a surface of said sintered greensheet and paste.