spring clip instead of screw for mounting fets

[nieles]

i was browsing on farnell, and came across these clips:

http://www.farnell.com/datasheets/67092.pdf

searching a little bit more i found these:

http://nl.mouser.com/ProductDetail/Aavid-Thermalloy/MAX08G/?qs=IQR8xM2KsGgn8sWnGiROuQ%3d%3d

pro;
will not lose pressure
easier to attach

con;
if a clip is lost => blown fet


what do you guys think? will these be reliable enough to use?

 

[CamLight]

I've used clips for years (MAX07 and MAX08) and will never use anything else. They are MUCH more reliable than any screw mount method unless you also use a belleville washer with the screw. And almost no one does that, or even knows how to spec a belleville washer.

Even if the clip's mounting screw loosens a bit, there's still clip pressure. If you're just using a screw to mount the FET, even a bit of loosening is bad. And, with just screws, you also have to worry about overtightening. Clips don't care how much you tighten the screw. You still get the same pressure.

Lastly, if you want more pressure, you can "stack" clips on the FET.

 

[bigmoose]

Clips are very good, and recommended by IR in App Note 997. I can't fly clips however. On TO-247's I use a flat washer, than a bellville washer nearly equivalent to McMaster Carr part
9712K12 but in stainless. The nut gets Loctite, 222-MS.

Type 9712K12
Belleville Disc Springs
Material - Steel
Steel Type - Grade 1074 High-Carbon Steel
Minimum Inside Diameter - .138"
Maximum Outside Diameter - .281"
Thickness - .0130"
Overall Height - .021"
Load - 24 lbs.
Deflection at Load - .004"
Flat Load - 43 lbs.

 

[CamLight]

I can't fly clips however.

 

[bigmoose]

Prime customer's design requirements that are non negotiable. It's the industry that ruined my ability to design cost effective components!

 

[CamLight]

Ahhh...thanks.
But, when have avionics ever been cost-effective?

 

[liveforphysics]

Spring clips make a lot more sense for most applications than a screw and plastic insulator washer.

Screw and plastic has a number of flaws. Insulator washers have creep properties, and a screw changes tension over thermal expansion, and thermal cycles can loosen things (or deform the sinks threads).


Bellville washer fixes all the problems of a screw, including insulator creep, because it has the ability to maintain pressure over a large linear displacement.

Clip is still my favorite though.

 

[nieles]

Thanks for all the input!

i will order some on my next mouser order.