Heatsink Flatness Specification
Heatsink Flatness Specification
(OP)
Hello All,
I'm hoping for some input on flatness specifications for extruded heatsinks (typically with a machined mounting surface) for electronics applications. Module vendors will recommended flatness over a length of 100µm (e.g., http://www.infineon.com/dgdl/Infineon-AN2010_06_Mo... ) or per inch (e.g., http://www.pwrx.com/pwrx/app/mount%20pwr%20modu.pd...). The heatsink vendors will tend to have either a total flatness spec for the whole extrusion face or on limited basis (e.g., table B of http://www.aavid.com/product-group/extrusions-na/d...). My impression is that modern drawings using GD&T methods call out flatness for the total surface (e.g., http://www.gdandtbasics.com/flatness/).
My question: is there a straightforward way to equate these callout methods or to scale the flatness for differing dimensions? I'm a little confused on how to consider this when accounting for tolerance build-up, and this doesn't seem like a straightforward unit conversion exercise. If a surface met the 0.001 in/in requirement, it would seem to easily meet 0.002 in/2 in. More concretely- What would 0.001 in/in equate to in µm/100µm? What's the total flatness of a 6" by 12" plate with flatness of 0.001 in/in? Maybe I'm overthinking this?
Many thanks!
-Jack
I'm hoping for some input on flatness specifications for extruded heatsinks (typically with a machined mounting surface) for electronics applications. Module vendors will recommended flatness over a length of 100µm (e.g., http://www.infineon.com/dgdl/Infineon-AN2010_06_Mo... ) or per inch (e.g., http://www.pwrx.com/pwrx/app/mount%20pwr%20modu.pd...). The heatsink vendors will tend to have either a total flatness spec for the whole extrusion face or on limited basis (e.g., table B of http://www.aavid.com/product-group/extrusions-na/d...). My impression is that modern drawings using GD&T methods call out flatness for the total surface (e.g., http://www.gdandtbasics.com/flatness/).
My question: is there a straightforward way to equate these callout methods or to scale the flatness for differing dimensions? I'm a little confused on how to consider this when accounting for tolerance build-up, and this doesn't seem like a straightforward unit conversion exercise. If a surface met the 0.001 in/in requirement, it would seem to easily meet 0.002 in/2 in. More concretely- What would 0.001 in/in equate to in µm/100µm? What's the total flatness of a 6" by 12" plate with flatness of 0.001 in/in? Maybe I'm overthinking this?
Many thanks!
-Jack





RE: Heatsink Flatness Specification
It is somewhat difficult to compare a total flatness and unit flatness, you have to work out the worst case surface allowed by the per unit tolerance. It will be more than just the flatness per unit multiplied by the size. Hopefully someone can dig up an example, I don't have one handy.
----------------------------------------
The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.
RE: Heatsink Flatness Specification
Section 5.4.2.2
RE: Heatsink Flatness Specification
It appears to be part of the Aluminum Extruders Council publication available at http://www.aec.org/?page=lib_designmanualjump
This article is also interesting - different style of heatsink, but interesting http://www.aec.org/?page=lib_almagledheatsink
You may also come across ANSI H35.2, bur I think it does not apply to custom aluminum shapes; instead to industrial standards.
RE: Heatsink Flatness Specification
I think the result is not linear - that a delta/length for a give length <> 2delta/2length.
The proof is that one can take a circle and divide it into 4 equal arcs. Pick one vertex as an origin and then draw a line from the origin to each of the other vertices. Use that as the baseline and measure the deviation to the circle. The first is a small amount; the second delta will be the radius of the circle; and the third is almost the diameter of the circle.
It is likely the effect is less pronounced on smaller amounts of the arc, but I would not be surprised to see that it is noticeable.
RE: Heatsink Flatness Specification