Transistors and the newbie scratching head - please help!

Hi! As the title says, I'm a diy newbie attempting to build a Firstwatt F2 and a couple of other devices and I am discovering all kind of stupid things that I don't know how to solve because of my total lack of knowledge / experience. Please help me clarify a few of them:

1. Regarding mounting the FETs on the heatsink, I have two options, please tell me what would be the best:
a) I found some mica locally, looks pretty good (thinness is about 0.05mm, with a few scratches) and I have some Arctic Silver Ceramique.
b) I bought from Mouser some Laird Technologies T-gard 5000, they don't look like those in the picture, are rectangular instead and just a bit larger than the IRFPs. I suppose they should be used without thermal compound, right?
EDIT: taking another look in the T-gard datasheet I see that "T-gardTM 5000 is ideal for applications that require a delta temperature across the interface of 2.0°C/watt or
higher on a TO-220 clip mounted @ 50 psi pressure." Not good enough for the ~70W heat / channel / 2 IRFP's of the F2, I suppose?!

2. Regarding the handling of the so called electrostatic sensitive devices, what kind of precautions do you take? Quite a few of the items I got from Mouser came in protection bags with a warning label: transistors, diodes & bridges, an integrated I needed for another power supply... Do I have to wear an antistatic wrist strap? Could it be a realistic / necessary and sufficient solution to manipulate them by only touching them with the material the ESD-safe bag is made of? Sorry, this is basic knowledge, I know, but I don't have it...

Thanks a lot!

For question nr.2, I found out all I needed to know.

What do you think about my first question? I must do a correction, I was wrong, the TO247 mica I could find locally is pretty thick, 0.1mm (0.004''). Also, what would be an acceptable temperature of the IRFP 240 / 9240 on the long term? I think I would get up to ~75 degrees Celsius at the surface of contact with the heatsink, is this too much?

I thought so. However, half of 150 degrees means 75 at the junction, and I think I remember reading that there's about 25 degrees difference between the junction and the contact surface of the transistor, I'm not very sure about that though... This would mean 50 C at this contact surface, and in a room at 30 C would require about 0.3 C/W total value of heatsink + mica & compound, for example, so it's not realistic. If the above is correct (which I'm definitely not sure of) then a more realistic target would be ~100 degrees at the junction. Is this right or I'm way off?

Emooze, I'm not sure I get it. The Laird pads have 1.26 C / square cm / W (see attachment), and the IRFP's are about 2 square centimeters contact surface. Doesn't this result in ~ 0.65 C / W / transistor, or ~ 22C temperature difference between transistor and heatsink? (0.65 x ~35W) Combining this with a heatsink thermal resistance of, say, 0.3 C / W, in a room at 30 degrees I would get 51 degrees heatsink at the contact surface and 73 degrees transistor at the contact surface. What is wrong with this calculation? On another forum somebody told me I'm misinterpreting the data in the Laird datasheet, but I didn't understand why.

Yes, the FETs need to be electrically isolated from the heatsinks.
I forgot to mention that I have no idea what is he thermal resistance of the mica that I have, all I know is that it's 0.1mm thick.

Yes, 70W heat / channel / 2 IRFP devices, so let's say 35W each (I'm not sure they are both dissipating the same power).

Please don't scare the **** of me! Your post got me depressed! 0.3C/W is a pretty good figure for the heatsink itself, and I think my huge diy one will achieve this figure, but the 0.1mm mica + compound might add some...not sure...0.4 or 0.5C/W for each transistor?

On the other hand, I see other people using Conrad MF30-2F-151.5 0.25C/W heatsinks or others which don't seem notably better and silpads or mica (see this log, this log and this picture). A heatsink temperature of 60C was usually considered OK. Perhaps there's a chance for me too? I understand it would be ideal to have half the max. temp. rating at the junction, but let's put it another way, what would be an acceptable figure? What about 90 or 95C? (not "negotiating" - lol - just trying to learn the proper and at the same time realistic - for me - way of doing it).

Thank you, thank you, thank you! I feel much better now. I had already ordered all the stuff from Mouser and ordering again from them, Digikey etc. some small things like the Bergquist pads is not very attractive because of the shipping costs. A Mouser representative erroneously told me I could get some out of stock TO247 mounting kits later without any additional shipping costs and I almost clicked the "Order" button when I saw I would have payed 40 Euro for the shipping of the small 1-2 Euro total value kits. Still, I feel more confident now, worst case I'll use the 0.1mm mica and see what happens.

By the way, the surface of the transistors doesn't need to be smooth sanded, does it?

Thanks again!

In the end I think I'll use the compound with the thinnest mica I can find, there is still some hope for thinner one locally.

Re. sanding the transistors, it's funny how I get two advices from the two guys who showed their willingness to help, and the 2 advices are opposite. Well, I suppose it's also normal, everyone has his / her own experience that can very well be different from the others'. The reason why I saw this idea recommended was because of the sometimes higher plastic edge of the transistor that could prevent a good contact of its metal surface to the sink. I will ask on other forums as well. In case I do sand them, I have sand paper up to 1500.

Thanks again for the help you offered me!