thermal pad on the back of the mobo

[eadmaster]

I am considering buying a passively-cooled motherboard+CPU combo (ASRock Q1900M).

Do you think adding a thermal pad between the back of the motherboard (over the CPU socket) and the case would help dissipate the heat?

With this Intel Atom miniPC the trick reduced the temperature by about 15 degrees.

Side question:
is there any problem with my case (NZXT Nemesis) not designed for passive heat dissipation?

[quest_for_silence]

Do you think adding a thermal pad between the back of the motherboard (over the CPU socket) and the case would help dissipate the heat?

Who knows? The mobo you're looking at looks not that bad at cooling (not that great too), so apparently the mobo underside should not be that hot.

Personally I'd bet that a 600rpm 80mm fan strapped on the CPU heatsinks would help in a more efficient way (as well as a more effective TIM than stock one).

With this Intel Atom miniPC the trick reduced the temperature by about 15 degrees.

That's because the CPU/Ram area was actually barely dissipated (I'd dare to say, it was not dissipated at all), so that the whole SoC board run rather hot (given also the very small volume): the ASRock cooler is way more substantial than the Pipo's tiny fins, the NZXT thermals are way higher than the shy Pipo casing, so I don't expect the CPU will heat up the whole board.
As a personal guessestimate, there would be almost no chance that you will observe a 15°C temp reduction with a similar mod on the proposed setup.

is there any problem with my case (NZXT Nemesis) not designed for passive heat dissipation?

Well, I'd say no. The only one I see ATM is that you might have problems to find out an enough thick thermal pad. Providing you find it, probably that would be not so effective, but it's not a problem, in case. All in all, I don't see any *real* problem.

[Irrelevant]

Do you think adding a thermal pad between the back of the motherboard (over the CPU socket) and the case would help dissipate the heat?

I doubt it. The PiPO X7 is pretty unusual. Its standoff height is about half that of most ATX/mITX/mATX cases, so it should conduct heat twice as well to its mobo tray, and even if you found a case with a standard form-factor that had equally short standoffs, it wouldn't make much difference because the surface area of a mobo tray is actually pretty small in comparison to most aftermarket CPU coolers.

is there any problem with my case (NZXT Nemesis) not designed for passive heat dissipation?

Hmm ... doesn't look good to me. When you're cooling passively, what you really want in a case is openness, at least at the top and bottom, and the Nemesis looks a little closed up from the photos I briefly scanned. I've never done passive cooling, though (it either won't fit in my budget or won't allow for powerful enough hardware), so take that with a grain of salt.

[eadmaster]

Actually i was thinking about adding a case fan too, but i don't want it running all the time, so i hope i will be able to turn it off via software.

About the case: since i'm using a picoPSU i've left the ATX PSU space on the top opened and i've put a dust filter.
There is also a 5.25-inch slot opened in the front, so air ventilation shouldn't be a problem...