1.11.2020

Aluminum EMI Grease Open Source Invention Patent

So I want to make a grease that operates with a wide temperature range for an EMI shielded aluminum or magnesium box for electronic components.

The first thing to think about with these metals, if you are not making the box one solid piece hollowed out, is that oxidees form instantly on the surface which reduces electrical conductivity and thus reduces the functionality of the EMI shielding.  We want the grease to reduce that.

Also we want the grease to be stable at extreme cooling temperatures and also in hot temperatures if cooling is sub optimal.

Also we want the grease to resist moisture penetration into the box.

So I designed the following grease

PFPE oil.  Krytox states that a PFPE oil mixed with PTFE powder is what makes their grease.  So since we want conductive option instead of or in addition to PTFE or any other additive, we will add Aluminum powder, preferably around 5 micron depending on the surface finish of the aluminum parts we are joining.  Not copper or silver powder since these can cause galvanic corrosion with the aluminum since aluminum can act as an anode.  A good PFPE oil seems to be Krytox GPL101 rated for -70c up to 104c.  This range allows extreme cooling of the enclosure as well as hot temperatures if the box is insufficiently cooled.

Aluminum Powder.  As described above, the micron size should be a little bigger than the surface roughness.  So if surface roughness is minimum of  3.2 um, then a 5 um aluminum powder is perfect.

Barium Aluminate and/or other base.  This is an experimental additive.  We know that aluminum forms an oxide layer instantly upon exposure to oxygen.  So Barium Hydroxide is a strong base that will dissolve that aluminum oxide layer therefore theoretically reducing electrical resistance between the contact.  However barium hydroxide is a very strong base and may unpredictably dissolve the aluminum.  Therefore Barium Aluminate is a stabilized version (basically barium hydroxide pre-reacted with aluminum) that is still alkaline and should remove and keep off the oxide layer as it is in contact in the joint.

So an example recipe can be:

PFPE oil base (krytox gpl 101).

5um Aluminum powder added until paste like consistency.

Barium Aluminate added at | 1:4 | Barium Aluminate:Aluminum | wt:wt | powder.  This ratio is flexible and this is just a starting point.  We want enough to reduce the oxide layer on aluminum contacts (including aluminum powder particles) but not enough to add resistance.  Note that barium is heavier than aluminum.

Once experimentation is done a precise recipe can be developed.

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