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Pi Case and Raspberry Pi 2 Broadcom die size


starfireprime
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I have Flirc's Pi case for my Model B+ and really love the product.  I've noticed that for the newly announced Pi 2, the Broadcom chip appears slightly larger, although in the same location on the board. 

 

Any thoughts on thermal issues if the Pi Case's aluminum heat sink only covers a majority, but not the entire surface of the chip?  I'm guessing no, but I thought I'd ask.  :)

 

 

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I would say no, it would still work as I guess, the biggest heat will be in the middle and the case will dissipate heat. I think it will cover at least 75-80% of the chip?

 

I don't think it would cause any problem with the PI 2. 

 

edit: well, if the chip is locate at the same place, but longer (no in the middle) I'm not sure now xD

 

PI2

0258000007884573-photo-raspberry-pi-2.jp

 

B+

1914-01.jpg

 

I hope they are the same height at least!

Edited by ChristTheGreat
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The biggest difference in layout between RPi B+ and RPi 2.0 B is not the CPU placement but the RAM placement. On pre-2.0 boards RAM is mounted on top of the CPU. On 2.0 board the RAM is on the other side of the board. Because of that the CPU on the 2.0 board is thinner than the CPU+RAM on pre-2.0 boards. I don't know how the thermal pad looks in the Flirc RPi case (I don't have one yet as I don't have RPi B+) but there is a risk that it won't even touch the CPU because of its thickness rather than the position or its size.

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There won't be any issues. We tested a few weeks ago. While the chip is a little bigger, the heat sink will do as its intended. The hot spot won't be at the end of the chip.

 

Thanks Jason.  Any thoughts/observations on yawor's comment as to the height of the CPU off of the board and the thickness of the thermal pad?  I don't recall the thickness of the pad in the case that I already received.

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Awesome, I have a feeling that my Flirc case might make it to the new Rpi 2 I just ordered, or do I need another case?  wouldn't want the B+ to be naked.... hmm decisions decisions.  This was definitely one of the first things I looked up with the announcement, great news, glad you got to test it already too!

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There won't be any issues. We tested a few weeks ago. While the chip is a little bigger, the heat sink will do as its intended. The hot spot won't be at the end of the chip.

 

Is the new CPU on the 2.0 board actually thicker than the CPU alone on the 1.x? Because with RAM removed from the top of the CPU and moved to the other side of the board I was afraid that the thermal pad might float a 1-2 mm above the CPU instead of touching it.

 

Anyway great news that you've tested and it fits :).

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Some data.

 

The chip on the Pi 2 is only about 0.2mm less in height than the chip on the Pi. It isn't, however, in the same place. It's slightly off to the left. The left edge of the Pi 2 chip is about 3mm out of the edge of the Pi chip, and subsequently, the heatsink. It actually does hang over on the right now. By how much cooling is affected all depends on what exactly is on those leftmost 3mm.

 

It is, however, an extreme bother to people with OCD, because it simply doesn't fit from a purely visual aspect. Saying that, will we see a revision of the Flirc case to accomodate the exact placement of the Pi 2 chip?

Edited by DocG
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Just a follow up - I received my Pi 2 today and already had my Flirc case.  The board fits fine in the case, but it did not appear as if the thermal pad made contact with the heatsink post at all.  The board easily rocked out of the case when I turned it on its side suggesting that there was not adhesion to the pad at all.  Also as DocG noted, the post is noticeably off center.

 

For now, I removed the pad an am just running the board in the case.

 

EDIT:

 

Without the thermal pad contact, temps run a little hotter (as one might expect with less air circulation and no direct thermal transfer).  My unscientific measurements:

 

                    In Case                 Alone (68F room)

Idle               40-42C                   38C

1 busy core     45C                     44C

2                      50C                    49C

3                      55C                    54C

4                      60C                    57.5C

Edited by starfireprime
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I doubt you'll be able to measure the gap, but if you go one up, i.e. 0.5mm from whatever the supplied pad is you should be good. You'd probably do well to not put the pad in the center of the post, but place it so that it covers more of the chip.

 

The problem with a thicker thermal pad is that it loses a lot of effectiveness, and starts to become more of an insulator then a conductor of heat.

 

Thermal pads don't actually help transfer heat amazingly well, the best solution would be two perfectly flat pieces of metal touching directly, but that's not possible, so we use thermal pads/paste.

Edited by Lukeroge
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The problem with a thicker thermal pad is that it loses a lot of effectiveness, and starts to become more of an insulator then a conductor of heat.

 

Thermal pads don't actually help transfer heat amazingly well, the best solution would be two perfectly flat pieces of metal touching directly, but that's not possible, so we use thermal pads/paste.

 

I think that it's still a better conductor than the air itself :). I think that gluing (using a thermal conductive glue of course) a thin flat piece of copper on the heat sink post may be doable. Then replace thermal pad with some good thermal paste like Silver Arctic 5.

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I think that it's still a better conductor than the air itself :). I think that gluing (using a thermal conductive glue of course) a thin flat piece of copper on the heat sink post may be doable. Then replace thermal pad with some good thermal paste like Silver Arctic 5.

 

Oh yeah, it's better than air for sure, I was just saying that in general, thermal pads are worse than direct contact (with paste).

Edited by Lukeroge
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Whiznot this is not a good idea. You would need to glue together multiple layers because cans are made from really thin sheet of metal. This aluminum-glue "sandwich" would probably be no better than a foam thermal pad. It would be best to find a sheet of copper of proper thickness. I don't know how thick it would need to be because I don't have the case nor RPi2 myself yet to do some measures. It would be best if the sheet is thick enough that it actually touches the CPU so you can use some good thermal paste (for example silver based like Silver Arctic 5) between the CPU and the copper pad.

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If I was serious about using the heatsink I'd start by sanding back the coating to expose the bare aluminium, then I'd pretty much do what yawor was saying.

 

As a side note, I thought the Flirc case looked pretty good, but then I took one and sanded back the outer coating. What a difference! Everything just looks so much better in brushed aluminium. :)

 

[Edit]

Did a slight variation with using a thicker thermal pad (http://oi62.tinypic.com/equrmo.jpg), and at least for my case can confirm that despite having slightly sanded back the post a 1.5 mm pad bridges the gap between heatsink post and processor.

Edited by DocG
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@DocG - thanks.  I'll try a 1.5mm pad and some stress tests to see how it works!

 

Edit:

 

Picked up a T-Flex 15mmx15mmx1.5mm pad off of ebay.  It fully covered the cpu.  I sanded off the paint on the post to expose the aluminum and gave it a shot.  Although the pad may have been touching the post slightly, I was unconvinced that there was good contact since the board still rocked out pretty easily.

 

So I took a rotary tool to the four screw posts to shorten then up a bit, reinstalled the board and was reasonably pleased there was contact between the pad and the post. 

 

Some stress numbers

 

Ambient ~ 64F  ~ 18C

 

Idle           29.3C

1 thread   32.6C

2              34.7C

3              36.9C

4              38.8C

 

So about 2.2 degC per loaded core and better overall performance.

Edited by starfireprime
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