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Old 16th October 2005, 05:38 PM   #11
anatech is offline anatech  Canada
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Hi jleaman,
I use a thin coat of grease with sil pads. Mica and grease seems to have a lower thermal resistance on average. The use of "Belleville" is recommended. I have an artical from Motorola I can send you. Just PM me, it's a PDF around 870 Kb. The file is named "SOLDERRM-D.PDF".

-Chris
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Old 16th October 2005, 05:47 PM   #12
jleaman is offline jleaman  Belgium
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Quote:
Originally posted by anatech
Hi jleaman,
I use a thin coat of grease with sil pads. Mica and grease seems to have a lower thermal resistance on average. The use of "Belleville" is recommended. I have an artical from Motorola I can send you. Just PM me, it's a PDF around 870 Kb. The file is named "SOLDERRM-D.PDF".

-Chris

I dont like sil pad's i have blown up 2 amps from them dead short from a small metal shaving.. so now i only use ceramic ones.. BUt i could use some really hi end grease
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Old 16th October 2005, 06:21 PM   #13
anatech is offline anatech  Canada
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Hi Jason,
First rule: don't use exotic things (=unobtainium). Standard good quality grease and mica work great. If you want to decrease thermal resistance, then finish the heatsink to make it flatter and smoother. You can do the same to the part. The special washers move with expansion and contraction keeping a semi-constant pressure. Use threadlock on the screws to prevent them coming loose, machine screws work the best. I drill and tap the heatsink (just snapped a tap off in the heatsink - DARN )

Do you want the artical?

-Chris
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Old 16th October 2005, 06:24 PM   #14
jleaman is offline jleaman  Belgium
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Quote:
Originally posted by anatech
Hi Jason,
First rule: don't use exotic things (=unobtainium). Standard good quality grease and mica work great. If you want to decrease thermal resistance, then finish the heatsink to make it flatter and smoother. You can do the same to the part. The special washers move with expansion and contraction keeping a semi-constant pressure. Use threadlock on the screws to prevent them coming loose, machine screws work the best. I drill and tap the heatsink (just snapped a tap off in the heatsink - DARN )

Do you want the artical?

-Chris

Yes..

I also like nelson's way of mounting a fet with a nice large washer..

My amps have not failed at all. You guys have to remember this is not my amp that failed it is a friend's..
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Old 16th October 2005, 06:31 PM   #15
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Actually the Ceramic/ Alumnium oxide insulators are extremely easy to get and are available from at least several places that all of you normally buy parts from... I would hardly call them exotic and they make darn good sense to use, they also cut the thermal transfer loss in half over mica. I am in the middle of offering TO-247 Ceramic/Alumnium oxide pads to the KSA-50 group and once they are content and have what they need I will also offer them to the Pass group. I can get them for 50 cents each whcih is considerably less expensive than the normal price. I will sell them for my cost(50 cents each U.S. currency) plus shipping plus PayPal and I will only work with PayPal. Now Beryllium oxide... I might consider that exotic in this day and age, and darn dangerous as well.

The pads in the photo are all spoken for but I will have at least several hundred more on Monday morning.

Mark

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Quote:
I drill and tap the heatsink (just snapped a tap off in the heatsink - DARN )
Just get it anodized. The tap will completely vanish leaving the partially tapped hole.... you can then finish tapping the hole. Probably a dull tap or not using the correct tapping fluid also carbon steel taps are a no-no as they generally snap off easily no matter what... use high speed steel taps only!
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Old 16th October 2005, 06:36 PM   #16
jleaman is offline jleaman  Belgium
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Quote:
Originally posted by Mark A. Gulbrandsen
Actually the Ceramic/ Alumnium oxide insulators are extremely easy to get and are available from at least several places that all of you normally buy parts from... I would hardly call them exotic and they make darn good sense to use, they also cut the thermal transfer loss in half over mica. I am in the middle of offering TO-247 Ceramic/Alumnium oxide pads to the KSA-50 group and once they are content and have what they need I will also offer them to the Pass group. I can get them for 50 cents each whcih is considerably less expensive than the normal price. I will sell them for my cost(50 cents each U.S. currency) plus shipping plus PayPal and I will only work with PayPal. Now Beryllium oxide... I might consider that exotic in this day and age, and darn dangerous as well.

The pads in the photo are all spoken for but I will have at least several hundred more on Monday morning.

Mark

P.S.


Just get it anodized. The tap will completely vanish leaving the partially tapped hole.... you can then finish tapping the hole. Probably a dull tap or not using the correct tapping fluid also carbon steel taps are a no-no as they generally snap off easily no matter what... use high speed steel taps only!


Can i buy some of these off you ?
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Old 16th October 2005, 06:38 PM   #17
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Jason,

I just sold the last 100 to Jacco but check back with me on Tuesday. I will pick at least several hundred more up tommrrow. I don't like to sell something I don't have in my posession. There is a bag of 1000 more available!

Mark
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Old 16th October 2005, 06:38 PM   #18
fcel is offline fcel  United States
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Mark,
I want some. Can I put my name on the list now, since I won't know when the KSA 50 groups are content.
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Old 16th October 2005, 06:40 PM   #19
anatech is offline anatech  Canada
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Hi Mark,
I was actually referring to some of the specialized greases out there.

Ceramic won't help a rough surface, and are special order for most people. Surface flatness is the ultimate factor in heat transfer. The grease only helps by forcing out the air in the gaps. So the goal is to eliminate the gaps between the mounting surfaces. At that point a ceramic insulator may help heat transfer.

Sorry for not being more clear, and your point is well taken. I haven't used ceramic yet myself and so have no comment on them. Do they break if you drop them? I do drop things often as of late.

-Chris
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Old 16th October 2005, 06:40 PM   #20
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Would both you guys e-mail me so I know how many you want.....

Thanks!

Quote:
Do they break if you drop them? I do drop things often as of late.
I have yet to break any of them by excess pressure or dropping or what ever. I'm sure that you oculd crush one with a pliers though. They are actually amazingly strong. They are also incredibly flat and smooth. I use them with a small amount of grease. Lapping heatsinks so theya re flat is no big deal for a DIY'er but not practical in large scale manufacturing. I think you'd be amazed at how much resistance these things cut down on even if the sinks are not perfectly flat.

Mark
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