mounting of outputs to heatsink

[bigpanda]

Hi,

Can anyone show a picture of the mounting screws for the outputs going thru the ridge (or fins) instead of the trough of the heatsink? How difficult could it be to drill thru the ridge? Tks

[Stocker]

The main difficulty is holding a drill steady. With a drill press, you can easily mount your devices anywhere on a suitably flat heatsink mounting plane.

[bigpanda]

Hi,

I do have a drill press. Drilling from the flat side of the heatsink for the screw to pass thru do not create any problem. But drilling from the fins side, making clearence for the nut or the screw-head is not as easy as it might be. That's why I would like to see how other people are doing.

[richie00boy]

I thought the idea was the device is mounted on the flat side and the screw inserted from that samde side. The the heatsink is tapped rather than an oversize hole made. You don't need nuts then.

[AndrewT]

Hi,
drill and tap from the flat side.

With care you can drill into the fin and thus hide the end of the screw from external inspection.

Use a tapping lubricant to stop the tap snagging and breaking.

[Flodstroem]

It is difficult to mount To-3 devices on a flat surface heat sink without to degrade the heat conduction transferring (the thermal resistance could easily be to high). I have found this mounting method to have an acceptable ( in fact very) low thermal resistance for the heat generated in To-3 devices.

It is also very simple to un-bolt whole assembly if need be for service (unbolt 4 or 5 bolts and you will have whole power stage in your hand).

Besides flat and slim design it is also an easy job to design the PCB for the output devices
(a sort of surf mount board)

here is my solution as a pdf-file

Regards

[Flodstroem]

AndrewT:

drill and tap from the flat side.

With care you can drill into the fin and thus hide the end of the screw from external inspection.

Use a tapping lubricant to stop the tap snagging and breaking.

You should do it exactly as AndrewT describe it her. This is the way to go when you should mount the Alu-bars to the heat sink as I suggested in the drawing.

Regards

[bigpanda]

Hi,

Tapping the heatsink is one of the things I tried to get away with. Alu is too soft and in time with frequent loosing and tightening, they might get worn easily.

[AndrewT]

Hi,
most grades of aluminium (alloy) will take repeated re-bolting without suffering from excessive thread wear, particularly with the coarse pitch used in metric threads.

Go ahead and do it. But stick close to the correct tapping drill. Do not be tempted, as a recent poster suggested, to use a tapping drill that is bigger than recommended for aluminium. You might get away with this when tapping steel but it would still be bad practice.

[bigpanda]

Hi Flodstroem

Tks for the tip but I am more of thinking the TO-264 (such as super leach clone by Delta audio). The way I am thinking of is to mount the outputs to an extra Alu plate by sunk-head and cover the heads by the flat side of the heatsink, bolted by another set of screws. In this case, 1 group of screws confine to the output arrangement while the other group to the profile of the fins. Hope that dosen't increase the thermal resistance.