Cooling High-End Video Cards
On-line games are hot and, without careful thermal management, so are the video chips that run them. This popular phenomenon has created an extremely fast-paced, competitive market for the video chip manufacturer, and has provided unique cooling challenges for the thermal expert.
•The Background
•The Problem
•The Solution
•Conclusion
It is easy to understand why on-line gaming is extremely popular: it is free and available to anyone with a computer linked to the web with no other software necessary. Just log on and go—provided your video card is up to it.
Previously, in order to achieve blinding colors at dizzying speed, gamers added 3-D accelerators to their PCs. Newer video card designs incorporate the accelerators, but perception is very important here. In the mind of the gamer, these new cards are great, but perhaps the game would respond even faster if another accelerator were added anyway. Advertisements for the accelerator cards encourage users to add a second card to double their performance.
The high-quality gaming images and sophisticated web site graphics increase the amount of heat that must be removed from the system, and the added accelerator cards block the natural airflow paths, compounding the problem. Whether or not the increased heat affects performance of the video chip may be in question, but there is no argument that, over a period of time, too much heat will affect the reliability of the computer.
In order to plan effective cooling for today's high-end video cards, the thermal designer must be aware of the video manufacturer's business challenges as well as the thermal challenges. Market-driven demands for increased functionality present special hurdles for cooling. More than many other elements in the computer industry, video chips and the accompanying video cards are a commodity business. Time-to-market means everything to the success of a new product. Typically, designs are upgraded every six months. This quick turn-around leaves little time for board redesign, making a drop-in cooling solution desirable.
Frequently, the addition of features generates a corresponding increase in power output. Currently, a video-chip power output is anywhere from four watts to as high as 12 W. A simple extrusion is usually adequate to cool four watts, but more complex solutions are required as the power level rises. An example is shown in Figure 1, where micro-fins give the heat sinks 20% more cooling ability than a standard cross-cut heat sink.
More heat to dissipate necessitates a larger heat sink, which puts greater importance on the heat sink's method of attachment. Adhesive strips may be adequate to hold very small heat sinks, but the added weight of a larger heat sink may cause it to slip out of place or fall off completely. Even if the adhesive is strong enough to hold the heat sink in place, it can affect the ease with which the board can be repaired or upgraded. If the adhesive is still viable, attempts to remove the heat sink could damage the video card. If the card is upgraded to accommodate a more powerful chip and only enough room is left to attach a heat sink with adhesive, a complete redesign of the video card may be necessary to accommodate a new means of attachment for a larger heat sink.
Heat sinks that attach with spring-loaded pins onto pre-drilled holes on the board are now available. An example is shown in Figure 2. Key to this concept is standardization of the spacing pattern for the pre-drilled holes. Working with the heat-sink manufacturer to locate these holes is advantageous for both the graphic-card manufacturer and the heat-sink manufacturer, since larger heat sinks, or fan heat sinks, such as the one in Figure 3, can easily be incorporated as required by advanced video chip designs. Collaboration encourages incorporating thermal management into the card's design process from the beginning. The spring-loaded pins improve reliability by relieving stress on the ball connections in BGA-style packages. The springs allow the heat sink to self-align to the package, improving the thermal interface between the two. The pins also provide a quick, easy means of attachment and removal, while reserving real estate on the board to accommodate future upgrades.
These factors combine to save valuable time for the release of new products. Even if later design optimization or improvements in IC efficiency allow the return to a smaller heat sink, no time will be wasted on redesign solely to accommodate increased cooling capabilities. The new product will get to the market as quickly as possible. The only thermal adjustment necessary will be the substitution of a different heat sink.
High consumer demand for better on-screen graphics with faster response times creates heat-removal challenges. Not only is market pressure forcing video-card manufacturers to upgrade to increasingly more powerful video chips that generate more heat, but also PC users are adding 3-D accelerator cards that can interfere with natural airflow.
The optimum heat-removal method is one that permits rapid, easy upgrades in cooling ability without major redesign of the video card, allowing the video-card manufacturer to get the newest offering to market quickly.
Aavid Thermal Technologies, Inc., One Eagle Square, Suite 509, Concord, NH 03301. Tel: (603) 224-1117; Fax: (603) 224-6673.