Don't worry, I'd use soldering silicon mat that have tiny rectangles area to store the screw. I am to scared to grouping the screw by it's size, so I just separating the screw, and put back where it belong.Be careful with the screws. The screws are all different length, and when I opened mine I was following a guidance that there are two groups, but found it to be wrong as my phone seemed to have at least four groups of different screws. It was too late, however, because mine were already mixed within two groups I created. So, I would advise to create a diagram of screw location and keeping track of which screw goes where. I think that many times this phone is taken apart and put together, without this tracking, some screws end up too long for where they were placed and holding parts loosely, thus adding to the flex that might be cracking the older brittle thermal interface.