Re: Drilling large finned heatsink
I've never liked fixing devices [whether semiconductors or conduction-cooled power-valves] to heatsinks using tapped holes; my preference has always been for the fixings to be free-floating within the heatsink through-holes (so as to allow the hot-device to 'settle' in good contact with the heatsink) and use nuts-and-bolts.
In the past I've had inconvenient fins milled away so as to provide access to a nut-runner so a hot-device can be properly bolted-down.
Also - side-note - properly torque the fixings: don't just 'do it up till it feels right', use the device-manufacturer's recommended torque. Getting it right can reduce the thermal-resistance of the device-to-heatsink interface by a good 10%,meaning cooler runningand longer life. [Equally, nothing good's been reported about cracking a Beryllium-Oxide thermal-conduction 'slab' because your technician thought he could do-it-without-a-torque-wrench]
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