Circuit package with thermal expansion relief chimney

Claim 1

A circuit package comprising: an electrically insulating thermally conductive substrate; circuit means, including heat generating electrical components, mounted on top of said substrate; a housing covering said substrate and extending upwardly therefrom and having a downwardly opening cavity over said electrical components; a first electrically insulating coating material covering said electrical components in said cavity in said housing, said first coating material being pliable and remaining pliable upon heating by said heat generating electrical components, but being subject to thermal expansion; a second electrically insulating coating material covering said first coating material in said cavity in said housing, said second coating material being more rigid than said first coating material and less subject to thermal expansion; a chimney extending downwardly through said housing into communication with said first coating material, said chimney having a lower opening above said substrate and below the interface of said first coating material with said second material, such that said chimney provides a thermal expansion relief passage for said first coating material upon heating thereof to prevent said substrate from being pushed away from said housing by said first coating material during thermal expansion thereof, and reduce undesirable forces against said electrical components.