Mounting the Chip Amp- Overtightening? - diyAudio
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Old 12th January 2004, 02:59 PM   #1
lgreen is offline lgreen  United States
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Default Mounting the Chip Amp- Overtightening?

In assembling my LM3886 Chipamp (inverting gainclone), I attached the LM3886 to a heatsink via a brass bar (as well as the standard mounting hole) like this:
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To get good heat transfer, I tightened the screws holding the brass bar very tight as well as the screw holding in the chip at the top. This thing is mounted good, very good, to the heat sink...

Then I read a datasheet (for something else) that gave a spec for max force applied to the package, that got me thinking...maybe I tightened this too much? Do you think that's possible? Anyone ever break a chip via overtightening? Recommendations? Worries?
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Old 12th January 2004, 03:34 PM   #2
lgreen is offline lgreen  United States
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Default Another pic

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Old 12th January 2004, 04:05 PM   #3
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Actually, I think what you've done is very clever--the part of the chip that will actually get the hottest, has the best contact with the heatsink. Well done!

There's probably not any danger in mounting it like that, unless you hear the chips crack. I don't think you're going to tighten them that much though.
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Old 14th January 2004, 11:16 AM   #4
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Talking My LM3886*12

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Old 14th January 2004, 11:58 AM   #5
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lgreen, I had a strange feeling of dejavu on reading this thread. Did you by any chacne happen to see one I started a month or so ago?

Another Clone Project.

P.S. how did you get the stainless steel mounting clips off your heatsinks?
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Old 14th January 2004, 12:05 PM   #6
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Quote:
Originally posted by bigparsnip

P.S. how did you get the stainless steel mounting clips off your heatsinks?

screwdriver...
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Old 14th January 2004, 12:07 PM   #7
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Nope, mine appear to be held on quite securely with a stainless pin pushed into the heatsink itself (i tried to drill them out and they blunted my drill bit, hitting them had just as much effect).
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Old 14th January 2004, 12:09 PM   #8
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Quote:
Originally posted by bigparsnip
Nope, mine appear to be held on quite securely with a stainless pin pushed into the heatsink itself (i tried to drill them out and they blunted my drill bit, hitting them had just as much effect).

heh.. his were different then.. lol
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Old 14th January 2004, 01:05 PM   #9
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I like how you have mounted the chips but after reviewing the National LM4731 datasheet I think that you have possibly over tightened the mounting screws. (the LM4731 is a simular package to the LM3886 and has detailed mounting instructions in it - page 12)
I like the clamp/bar, but if I was using it I would torque the single top mounting screw very lightly. As the package heats up and cools down it will flex some and the combination of clamp/top mounting arrangement might cause stress to the package.
I found a small dial torque wrench in a Pawn shop for $10.00 a few years ago and it has come in handy every so often.
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Old 14th January 2004, 01:23 PM   #10
miguel2 is offline miguel2  Portugal
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My GC only get very slightly warm in operation. I have 2 LM3875 on a L shaped aluminium bar, not a heatsink. So I guess that mounting these chips in order to get good heat transfer is not necessarilly a priority.
My 2 cts.

Miguel
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