Purpose of the black tape on certain motherboard areas?

[amn]

Hi all,

Upon disassembly of my Thinkpad T I see that certain areas of the motherboard are taped with a thin black surface (tape material), mostly where the ventilation holes under the case would be. Also on the die around the GPU chip core. Is this for moisture isolation, electric isolation, both or none? One thing I seem certain of, in my infinite ignorance, is that it hardly helps cooling, also because of the strong adhesive of that tape...

[aaa]

Electrical insulation most likely.

On the gpu? I don't see why it would be on the gpu. Maybe you're thinking of some other black stuff, there's black thermal material for the gpu.

[amn]

Electrical insulation most likely.

On the gpu? I don't see why it would be on the gpu. Maybe you're thinking of some other black stuff, there's black thermal material for the gpu.

Well, the motherboard has three distinct units - the CPU, the Intel something and the Intel something else. It is a GMA965 chipset (T61), and it is cooled by the heatsink, so I take it the GPU is in that die, along with whatever else GMA965 does, since it is a whole platform.

Why would one need electronic insulation on only SOME areas? The whole motherboard AFAIK uses electricity...

Do other Thinkpads have it too?

[rkawakami]

Yes there is electricity on the entire motherboard but only selected areas can be contacted by something else, which if it is conductive, can cause problems. For example, the area under the PCMCIA card slot can be protected by a plastic sheet. Same with the disk drive bay. The insulating pieces of tape or spongy material are placed onto the motherboard or certain parts if the designers believe that there may be a chance for an electrical short or for some other reason (heat transfer, vibration, noise, etc.).

For your example of tape being in the area of the ventilation holes, I'd say that someone thought that there was a distinct probability of damage occurring if one were to accidentally insert a piece of metal into that area when the system was on.

[amn]

Ok, thanks, that was informative enough.

But what worries me more is the tape that surrounds the GPU core. Now, the GPU has some small resistors or some -istors under it, can those be the reason tape insulates these from the copper heatsink that sits atop it all?

Here is a link to the image:
http://i44.tinypic.com/2u5q4vm.jpg

And here is the GPU without the tape:
http://i39.tinypic.com/t8u8f9.jpg

[aaa]

Yes, that would also be for insulation, and is not blocking heat transfer. As you can see the die itself has no plastic on it, and that's where all the heat is.

[rkawakami]

I would guess that those "-istors" on top of that IC are actually capacitors. They are normally used to smooth out or filter the supply voltage(s). They reduce, but usually do not totally eliminate, brief voltage spikes caused by the device's need for additional power (i.e., current consumption jumps) for time periods that are measured in nanoseconds or microseconds. Capacitors are connected between the "hot" leg of the power supply (the positive voltage side) and system ground. As such, the exposed metal endcaps of the capactiors would have those voltages on them. Having the insulating layer of tape between them and the metal heat sink keeps the possibility of shorting out the power supply(ies) to about zero.