More And More, It's 'Cool' To Think Thermal

Electronic News, Sept 14, 1998 by Kevin McCullough, Bill Rife

But all that has changed in the short span of a few years. Now, thermal cooling is becoming one of the most critical performance issues facing the electronics industry today. And, the mature technology of passive heat-sink thermal cooling has not only been transformed radically, but the technology of thermal cooling has also been undergoing fundamental changes. Within this transformation, five key trends are emerging:

1. More components will require cooling. More and more chips now require cooling. Board speeds are getting faster, smaller and more heavily populated. Package densities are going up, performing more functions and, therefore, getting hotter. Chips are expected to do more in less space.

A lot more components on the board need cooling today than they did even six months ago. For example, memory chips never needed cooling, but now SRAM packages require their own cooling solutions. Video card processors didn't require cooling, but today many do, and so will the next generation. Hard drives and chipsets are now candidates for cooling. The typical PC now uses many more heat sinks.

Thermal cooling is also in demand because of the explosive growth of new embedded applications. Telecommunications equipment, printers, C&C machinery, networking equipment, video card processors, household "smart" appliances, and ATM machines are only a few of the products now driven by embedded CPUs. More are being added each day, and with the complexities of multiple functions, thermal cooling has become a necessity.

2. Cooling applications are often designed after the prototype. One major challenge facing thermal management companies is the ability to design cooling applications around what is already in place. Often, needs are discovered or developed after the prototype has already been designed. The challenge is to find ways to design solutions within already configured board space.

3. New innovative manufacturing processes save time and money. The need to do more in less space, in less time and with less money has spawned new manufacturing processes. For example, at ChipCoolers Inc., our new manufacturing process creates high-ratio extrusion heat sinks in ratios up to 15 to one (the industry standard is typically 10 or 12 to one). These increased ratios mean that the heat sinks are providing much more surface area without increasing the heat-sink size.

Another manufacturing development is the production of a higher cross-cut fin ratio that is now 0.080 by one-inch. The higher fin height on the heat sink groove is significant in that it produces up to 50 percent more surface area without occupying additional board space.

A third manufacturing process is producing higher ratio die casts that are not only dramatically lowering heat-sink costs to customers, but performing better.

4. Cooling technology of heat sinks: Customization is key to performance. With the variety of components now requiring cooling within very limited space, heat-sink customization is essential. No one type of heat sink can adequately meet cooling needs. While older applications may still be able to use off-the-shelf catalog parts, most new applications require customization, which must be delivered without time delays at no additional cost.

5. Rapid prototyping and fast delivery of final product. Perhaps nothing has impacted our industry more than the shortened prototyping and final product-delivery times. Last year, the standard industry delivery time for a prototype was several weeks; to produce finished manufactured products, the times could stretch from eight to 12 weeks. This has all changed. At ChipCoolers, rapid prototyping is a standard service. We produce prototypes within a few days, and typical delivery time of the finished component from start to finish is within 30 days.

Trends in CPU Configurations

These developments are set against a backdrop of changing configurations on boards. Surface mount technology is being seriously challenged by BGA (Ball and Grid Array Assemblies) because of increasing competition to do more on a board with less space. BGAs offer more pin count with less space than surface mounts.

But BGAs have caused new challenges for attaching heat sinks. With surface mount technologies, a "lip" or ledge surrounded the CPU, allowing for a variety of attachment methods including tapes, pads, clamps and clips. With the BGA configuration, the "lip" disappeared and heat sinks could no longer be easily attached. Many manufacturers were forced to develop new methods and retool.

However, systems using mounting clips with threaded screw attachments have had an easy transition from surface mount to BGAs. The heat sink can be screwed into the mounting clip, and the clip can be snapped directly onto the chip without the need for the ledge. Another advantage of this attachment system is that it offers consistent clamping pressure. This is necessary to keep thermal resistance low, while delivering excellent shock and vibration protection. Electrical conductivity problems are also eliminated with this system.