Replacement T2

[/df]

I discovered (when one fell off recently) that the heat-sink in the centre of the HD-Fox T2 main board is actually fixed at the four corners with what appeared to be some industrial double-sided tape but might just have been glue baked for nearly a decade. The lack of a heat-sink didn't have any short-term effect, but possibly there are many units operating marginally with poor contact between the chip (with its layer of heat-sink compound) and its heat-sink. Without disassembling again, I assume that the heat-sink is protecting the SoC and that a similar arrangement applies to HDRs since the same chip is used.

 

[PerryM]

So I installed 'fan', set it to 60% (barely audible) and so far so good. It would thus appear that the standard fan mode is set to come on at too high a temperature for my box for whatever reason. The great news for me is that the fan is definitely working.
Thanks again for all the support.

 

[Black Hole]

I assume that... a similar arrangement applies to HDRs since the same chip is used.

I can help with that.

 

[Black Hole]

I can help with that.

I had a look at the mechanical mounting on a faulty one, but the fixing appeared strong and I didn't (at that occasion) go so far as to force the issue.

 

[/df]

Is the HDR heat-sink clamped or does it just sit on the board (like the first example in this useful list of attachment methods)?

 

[everthewatcher]

Is the HDR heat-sink clamped or does it just sit on the board (like the first example in this useful list of attachment methods)?

There's no clamping method and there seems to be no movement so I've assumed it's suck on the chip, in which case removal will probably go badly if it's an exposed die.

I've a hedgehog-style heatsink here that would glue nicely onto the existing one but I've seen no need to do so yet.

 

[/df]

With the one that fell off, the fixing (gluing) points were at the corners, quite far from the SoC itself, with a blob of heat-sink compound over the actual SoC.

 

[Black Hole]

if it's an exposed die.

No reason to suppose that - everything else is packaged, and I can't imagine it would be economic to make an exception for the SoC. It would need to be packaged to be compatible with normal pick-and-place machines.

Is the HDR heat-sink clamped or does it just sit on the board

I thought there were enough photos about to consult, eg:

...but if you need more:



(the "string" is the cotton cover for my thermocouple, cellotaped to the heatsink)

 

[/df]

Interestingly (or not) that's an entirely different heat-sink from the HD-Fox one, which is more finny, like the ones shown in the link that I posted above. Also interestingly, "finny" is a word in the browser's spell-check dictionary, but "heatsink" isn't!

So perhaps it was necessary to use a fancier heat-sink in the HD, whereas a simple flange sufficed in the HDR because of the residual ventilation due to the disk fan.

 

[Black Hole]

For reference (the HD-FOX heatsink), a standard extrusion:



Not visible in the photo is an adhesive bond to the PCB similar to the HDR-FOX.

 

[bottletop]

For reference (the HD-FOX heatsink), a standard extrusion:

View attachment 5547

There's no clamping method and there seems to be no movement so I've assumed it's suck on the chip, in which case removal will probably go badly if it's an exposed die.

I've a hedgehog-style heatsink here that would glue nicely onto the existing one but I've seen no need to do so yet.

Interestingly (or not) that's an entirely different heat-sink from the HD-Fox one, which is more finny, like the ones shown in the link that I posted above. Also interestingly, "finny" is a word in the browser's spell-check dictionary, but "heatsink" isn't!

So perhaps it was necessary to use a fancier heat-sink in the HD, whereas a simple flange sufficed in the HDR because of the residual ventilation due to the disk fan.

I didn't realise the HD-FOX uses a proper heatsink. In that case I will probably replace the crappy heatsink on my HDRs with a finned or headgehog heatsink in the future.

Edit: after see the next 2 comments, maybe this isn't a good idea!

 

[Black Hole]

I didn't realise the HD-FOX uses a proper heatsink. In that case I will probably replace the crappy heatsink on my HDRs with a finned or headgehog heatsink in the future.

Don't. As noted above (or in one of the other concurrent threads) the finned heatsink is not very efficient without forced air (and these fins are only about 4mm apart). The HDR-FOX heatsink (having a larger effective surface area) may well have a lower thermal resistance to free air.

 

[everthewatcher]

For reference (the HD-FOX heatsink), a standard extrusion

Bad choice of heatsink there - that style needs forced airflow plus it's mounted horizontally so the effective thermal resistance will be much higher than the figure the manufacturer gives. The one used on the HDR is called a heat spreader and is a much better choice with no forced or convection airflow.

 

[everthewatcher]

No reason to suppose that - everything else is packaged, and I can't imagine it would be economic to make an exception for the SoC. It would need to be packaged to be compatible with normal pick-and-place machines.

Flip chip BGA , where the back of the die is exposed like this Celeron Mobile package on WP.

 

[Ezra Pound]

everthewatcher said : if it's an exposed die.

No reason to suppose that - everything else is packaged, and I can't imagine it would be economic to make an exception for the SoC.

Bottletop's post here shows an exposed die

Internal Temperatures (SoC)

Using a early unit with horizontal RF sockets, thermocouple on SoC IC, wire coming through a specially-punched 3.5mm hole and cover fitted properly, unit not recording or playing back during test, fan set to 50%, ambient temp 20-20.5C throughout, HDD temps as reported by drive, figures after...

hummy.tv

 

[Black Hole]

Fair enough. So why is there so much clearance under the "heat spreader"?

 

[everthewatcher]

Fair enough. So why is there so much clearance under the "heat spreader"?

Not sure what's being asked here. Between heatsink/spreader and BGA substrate? If yes then surely it just means the die is thicker than the depression in the spreader.

 

[Black Hole]

If yes then surely it just means the die is thicker than the depression in the spreader.

So far as I can make out (digital calipers) there is about 1mm gap between the base of the spreader and the PCB, and the central depression (presuming it is the same 0.8mm thickness all over) adds another 0.8mm to that. 1.8mm seems a bit thick for a PCB-mounted die.

BGA

Do you mean that? I thought BGAs are ceramic (or am I out of date?).

 

[Black Hole]

Belay all that, posts in the other thread explain all (click through for pictures):

Pictures after removing the very sticky double sided heatsink adhesive.
The dental floss method works well for initial separation of the adhesive tape. Then it's gentle srubbing using fingernails or plastic spatula type tool.
As the adhesive was still very strong, I doubt it has suffered overheating.
Overheating will usually make the adhesive tape brittle - which this wasn't at all.
For anyone worried about using the dental flossing method - try it on something else first.
Eg anything that as has been mounted with strong adhesive tape.

Super! That explains a lot. So what I thought was a thick adhesive layer holding the spreader to the PCB is actually the BGA substrate.

 

[Ezra Pound]

So far as I can make out (digital calipers) there is about 1mm gap between the base of the spreader and the PCB, and the central depression (presuming it is the same 0.8mm thickness all over) adds another 0.8mm to that. 1.8mm seems a bit thick for a PCB-mounted die.