> I agree there has got to be a better way to select projects than random.
Provably random? It really seems like "random" is just a way of saying "we're not going to discuss our decision process".
> The requirement to use caravel ... but all I heard was "we want to see how people use it".
That makes no sense.
I'll give them credit for one thing: the way they're doing the WLCSP packaging far-backend run is very slick and cool. Ordinarily WLCSP packaging costs a fortune, and you have to run your own boat of wafers from the MPW to get it. By forcing everybody to use WLCSP with the same pinout EVERYBODY gets this cool option at a reasonable price.
But they could very easily have simply said "your UBM layer must be identical to the Caravel padframe's UBM layer" (UBM is the layer that says where the top level of chip metal interfaces with the Under Bump Metallization of the WLCSP package). Basically just say you pins have to be in the same place as Caravel but you don't need to use the rest of it.
Compared to what, a bare die? WLCSP is usually cheaper than plastic packages...
Edit:
Maybe that's only true in volume? I guess throwing a handful of dies on a wirebonder is easy compared with designing and fabbing the interposer, and who cares if the plastic costs a few cents more.
WLCSP unit cost is very low, but there is a very high fixed cost.
Also WLCSP packaging must be done a wafer-at-a-time. With an MPW, you don't get a whole wafer of your chips -- they cut up the wafer and send the chips with your design to you, and the chips with other peoples' design to the other people.
So ordinarily on an MPW if you want WLCSP, you have to pay the fab to run a whole second "boat" of wafers just for you, so those wafers can be run through the packaging process before they are cut up. This often costs more than the MPW booking does!
Provably random? It really seems like "random" is just a way of saying "we're not going to discuss our decision process".
> The requirement to use caravel ... but all I heard was "we want to see how people use it".
That makes no sense.
I'll give them credit for one thing: the way they're doing the WLCSP packaging far-backend run is very slick and cool. Ordinarily WLCSP packaging costs a fortune, and you have to run your own boat of wafers from the MPW to get it. By forcing everybody to use WLCSP with the same pinout EVERYBODY gets this cool option at a reasonable price.
But they could very easily have simply said "your UBM layer must be identical to the Caravel padframe's UBM layer" (UBM is the layer that says where the top level of chip metal interfaces with the Under Bump Metallization of the WLCSP package). Basically just say you pins have to be in the same place as Caravel but you don't need to use the rest of it.