See this parts page: http://www.pchub.com/uph/model/0--35850-1/Vaio-SVF15-Series-Fit-Fit-15E-parts.html
There are several different ones (colors) and backlit and non-backlit versions. They call them the mainboard.
I cannot find Sony Vaio service manuals, so I'm going to use screen shots from two different HP 15-inch laptop models, the first of which has a "pop-in" keyboard that is not integrated into the "top cover" of the base of the PC:
and the second of which uses a "top cover" unit where the keyboard, mousepad, and surround are all part of one unit and are fixed to the plastic surround of the top in the same way you describe yours as being, with plastic studs that are heat melted to keep the metal (usually) keyboard retaining clip in place:
I just dealt with a Toshiba laptop that uses the all-in-one keyboard, mousepad, and surround top cover unit as shown in the second image above and it sounds like your Sony does the same, particularly based on what's at that parts page (at least some of the Sony models do).
Brian AKA Bri the Tech Guy (website in my user profile) - Windows 10 Home, 64-Bit, Version 1803, Build 17134
. . . the presumption of innocence, while essential in the legal realm, does not mean the elimination of common sense outside it. The willing suspension of disbelief has its limits, or should.
~ Ruth Marcus, November 10, 2017, in Washington Post article, Bannon is right: It’s no coincidence The Post broke the Moore story