I have a few development boards I was working on and I noticed that a few of the microchips have a completely mirror-like surface on top of the chip. The chips tend to be very small, just a few millimeters wide and deep. What is on the surface of these chips and why?
Electronic – Why do some microchips have a mirror-like surface
microchip
Best Answer
These are probably chipscale packages. So you're looking at the top of the actual silicon die. The bottom is processed so that there are solder balls for connection to the PCB.
If you've ever seen a silicon wafer you know that it's polished to a mirror like silvery-gray finish.
One issue you can sometimes have with CSP devices is that they can be sensitive to light, since the silicon is exposed.