Intel 740, Руководство по конструкции, Страница: 152 / 246

Intel740™ Graphics Accelerator Thermal Design Considerations
4
Application Note 653
2.2 Power
In previous generations of graphics accelerators where Quad Flat Pack (QFP) packages have been
the primary package type, the majority of power dissipation has been through the plastic case of the
package into the surrounding air. With the advent of Ball Grid Array (BGA) packaging for
graphics accelerators, the majority of the thermal power dissipated by the chipset typically flows
into the motherboard where it is mounted. The remaining thermal power is dissipated by the
package itself. The STBGA used for the Intel740 graphics accelerator continues this trend by
further enhancing the package’s ability to channel heat into the motherboard.
The amount of thermal power dissipated, either into the board or by the package, varies depending
on how well the motherboard conducts heat away from the package and whether the package uses
thermal enhancements. While package thermal enhancements typically serve to improve heat flow
through the case via a heat sink, how well the motherboard conducts heat away from the package is
strictly a function of motherboard design. The following should be taken into account by system
designers when developing new systems:
•
How well the thermal balls are connected to the inner planes of the motherboard. It is
recommended that:
— One via per ground ball be used.
— Minimum width of the trace connecting the motherboard ground pad to the via be 10 mil.
— Plated Via Size for ground balls be 14 to 16 mil in diameter on a 24 to 27 mil pad. A larger
via is more efficient in channeling heat.
— Do not use Thermal Relief Patterns on the inner plane connections of the thermal balls.
•
How well the inner planes conduct heat away from the package. Good ground paths to other
areas of the board will distribute heat more efficiently.
•
The size of the motherboard, number of copper layers and the thickness of those layers.