BGA Heat Sinks and Bonded Grid Arrays

BGA heat sinks support demanding applications. There are a variety of heat sink styles and attachment methods available. Four primary mechanisms are used for cooling.

Natural convection heat sinks are made from cast or machine alloys, extruded aluminum, or aluminum or copper sheet. They are passive in nature. These BGA heat sinks do not rely upon local air velocity for the application of heat dissipation.

Forced air velocity is required for forced convection BGA heat sinks. The air velocity is incorporated through system level or dedicated fans to increase the thermal efficiency. Board level coolers, high fin density assemblies, or fan heat sinks are configured for impingement or cross flow environments.

Re-circulating BGA heat sinks normally employ looped heat pipes that allow heat transfer exchange through condensation and evaporation. Heat sink technologies are integrated to increase thermal efficiency when physical size restrictions or greater density requirements exist.

Channeled cold plates are used to comprise liquid cooled applications. A pump system and heat exchange are used to circulate fluids past the source of heat. Liquid cooled technology is reserved for high heat flux density applications or where phase change systems or forced convection cannot dissipate the power demanded.

In silicon die packaging, no package is considered the best package. Packaging takes up valuable space and introduces time delays. The cost increases as does the defect potential. Packaging is needed, however, to give easily damaged devices a degree of environmental and mechanical protection. Bonded grid arrays of solder balls are attached to the bottom of the carrier or package.

Plastic bonded grid arrays are the most common type. Typically, the die is wire bonded to the top of the surface of the carrier and over molded with epoxy based plastic.  Ceramic bonded grid arrays consist of a die attached to the surface top of a multilayer ceramic carrier. The die can have an active side up wire bonding or attached in a flip-flop configurations with the active side down.

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