Inside the Apple Watch: Technical Teardown

I pointed this trend out to a guy who was whining about the "good old days" of through hole components and how hard it was to use surface mount stuff. There are a lot of motivations to go with chip on board tech, mostly the chips can be cheaper as you have removed an entire chunk of steps and fallout out of the production process. Interestingly for me, the reason this is becoming more popular is that because feature sizes are so small, the silicon cost of these parts is dominated by the pin pads, not the logic. So making the pads big enough to put solder balls on them for COB assembly doesn't materially increase the cost of the die, and yet saves packaging, bondout, and post packaging testing.