How did you apply the TIM to the COB?
The Arctic MX I used comes in a large syringe and I was able to put a small bead to form a X from the corners then put a dab at the center. I then tightened the COB evenly by turning each screw in small increments from one to the other. The paste seem to squeeze out on all sides but I haven't removed the COB to check it.
No.
Of course that will "work" but as you say....does it?
Use blue masking tape and make a stencil. Use a stiff scarper, to lay in a TIM pad.
When it stiffens again you remove the tape (the best stuff, you work the material first, stirring it on a pallet board like you would mix epoxy)
Now for your question, I learned from Peilter Junction ruining
I need to butter tightly, the back of the ceramic, to fill the tiny air voids. It looks grayish instead of white, but still smooth.
So, now I lay a wet to wet surface by using a tool (butter knife, razor blade ??) to lay down to COB from one edge to the opposite. Hold the start edge with my finger to make sure there is no drift.
Now you know there are no voids. You can see it as you lay down the COB. You push all the air out, and get wet to wet contact.