Perception? vs. Reality!

"Here are some things we thought you should know"

Perception — A bonded fin heatsink can offer fin ratios as high as practical, up to 30:1 (fin height to fin gap) and beyond.

Reality — Fin height is based on one thing: Physics! After a ratio of 20:1 in most cases all you are buying is material, not performance. Let Dau size your next bonded fin heatsink project.

Perception — Standard catalog extrusions save cost and delivery time.

Reality — The packaging of your product will have the biggest impact on both final cost and performance. Why buy more or less than what you need. Dau will work with you to develop a thermal package. Our skilled craftsman can produce prototypes in 1 to 3 weeks so you have the most time for testing of your units

Perception — An air-cooled heatsink can be made of copper, but it will be heavy and the cost will be typically three times that of aluminum.

Reality — If your package size is too small, or your heat dissipation is too high for an aluminum bonded fin product, copper is a very cost effective alternative. Copper has a thermal transfer rate two times greater than aluminum. Yes, copper is heavier, but in most applications where copper is used the heatsink is much smaller, due to the performance of the material, than a comparable aluminum product.

Perception — Pin Fins have more surface area to remove heat and therefore are better heatsinks.

Reality — If the slot width cut thru the extruded fins is the same size as the extruded slot width - the surface area is exactly the same. What is missing? The removed metal cannot conduct heat to the air stream, so the total temperature difference(Î"T) is smaller than with the original extrusion(Î"T).

Perception — The tDau "thermal Resistance" (Junction to Case) Rj-c. is gospel and should never be exceeded.

Reality — This tDau Rj-c is an estimate, because today's chips don't resemble the early 3-pin transistors. The only practical way of not exceeding the actual case temperature limit is to be conservative and derate the target temperatures in designing heatsinks.

Perception — Fans always operate at the published CFM or air flow rate.

Reality — The published CFM rating for a fan is "free blowing" on a string in a room with still air. The actual CFM operation point of the fan is a combination of system pressure losses and the losses thru the heatsink itself. Often, system pressure losses greatly exceed the heatsink pressure losses. The published fan curve details what CFM a fan can move against resistance.

Perception — Aluminum heatsinks will always remove the necessary excess heat, even when product power is increased.

Reality — Within a given volume or by not allowing heatsink size changes as it becomes modified (read "more power"), aluminum may no longer cool to desired temperatures. A copper heatsink with a thermal transfer rate twice that of an aluminum heatsink might provide the only solution. The cost difference becomes small, since you may want the product to work over its entire life.