BACKGROUND

Semiconductor die require effective thermal transport to prevent heat buildup that can impair performance of the die and permanently damage to the die. Various mechanisms have been used in the past to remove heat from die. The most common mechanism is the use of metallic fins that attach to the top of the die via thermally conductive adhesive. This has worked well in the past for single-board designs. However, with multi-board assemblies in which die are placed between two boards, there is no way to place metallic fins directly over the die.

Chemical Vapor Deposition Diamond (CVDD) has a very high thermal conductivity and can be formed in thin sheets. These sheets are commonly cut using special saws to obtain different shapes of diamond sheeting for use in a variety of commercial applications. Pastes made up of CVDD grains are much less expensive than CVDD sheets. Though diamond pastes have been used for thermal conveyance in the field of semiconductors, CVDD sheets and shapes have not been widely adopted because of their expense.

Accordingly, there is a need for a method and apparatus that is not overly expensive and that will provide sufficient thermal transport so as to prevent in heat buildup within individual die. Also, there is a need for a method and apparatus that can be used to convey heat away from die that can be used with multi-board assemblies.

BRIEF DESCRIPTION

A board assembly is disclosed that includes a circuit board, a semiconductor die electrically coupled to the circuit board, a Chemical Vapor Deposition Diamond (CVDD) window, and a layer of thermally conductive paste in direct contact with a first surface of the CVDD window along the full extent of the first surface of the CVDD window and in direct contact with the semiconductor die. The layer of thermally conductive paste is positioned so that it covers a hot-spot on the semiconductor die. The CVDD window has a footprint that is less than twenty percent of the footprint of the semiconductor die.

A method for forming a board assembly is disclosed that includes identifying a location of a hot-spot on a semiconductor die and cutting an opening in a circuit board corresponding to the location of the identified hot-spot. A CVDD window having a shape corresponding to the shape (and position) of the hot-spot is inserted into the opening. A layer of thermally conductive paste sufficient to ensure contact between the diamond window and the hot-spot (less than 40 μm thick) is then placed over the CVDD windows and the die is positioned over the layer of thermally conductive paste such that the CVDD window underlies the hot-spot and such that a surface of the semiconductor die is in direct contact with the layer of thermally conductive paste.

A method for forming a board assembly is disclosed that includes identifying a location of a hot-spot on a semiconductor die; attaching a CVDD window onto a surface of a thermally conductive plate, in a location corresponding to the location of the hot-spot on the semiconductor die; applying a layer of thermally conductive paste over the attached CVDD window; attaching a semiconductor die to a circuit board such that the semiconductor die is electrically coupled to the circuit board; and placing the thermally conductive plate over the semiconductor die so that the applied layer of thermally conductive paste is in contact with the semiconductor die and such that the CVDD window overlies the hot-spot.

Because of the high thermal conductivity of the CVDD windows and the positioning of the windows beneath hot-spots, heat is quickly and effectively removed from the die. Also, the CVDD windows have a surface area that is significantly less than the entire surface area of the die. Thus, the cost of the CVDD window material is significantly less than the cost would be if the lateral extent of the CVDD material were to be the same as the footprint of the die.

