These are some pics I took with my cheap USB microscope, so they are not that special, but hopefully you’ll get the idea.
This chip has been sitting on my bench for a few months, so I cleaned it as best I could with Metholated Spirits before taking the pics below.
The actual chip came from arrow.com where I purchased 10 units for $0.90 AUD each as they were ‘overstocked’.
The package is a WLCSP64 and is approximately 4.5 mm x 4.5 mm on each side and 0.38 mm thick with 64 solder blobs for pins (BGA).
The entire chip is silicon and the size of the actual DIE, there is no plastic or any other case material, and no copper pins.
This to my mind represents the state of the art in miniaturization, where the connections are via solder blobs onto metallized tracks which connect to the pads on the die periphery.
When I looked at this chip under my 40x microscope it took my breath away because I could see under the silver and gold metallization into the chip itself. That’s right, the parallel lines which look a dull gold in my picture, looked shiny and like they are made of solid GOLD in the microscope.
I’ve never seen anything as breathtaking as this before and I’m used to looking at chips with microscopes and lighting that make the “wire bonding” wires look the size of lamp posts.
Capability:
This STM32L162RD is just JAM PACKED with peripherals, it is mind boggling!
https://www.st.com/resource/en/datasheet/DM00039232.pdf Ultra-low-power 32-bit MCU Arm® Cortex®-M3
384KB Flash
48KB SRAM
12KB EEPROM
LCD, USB, ADC, memory I/F, AES
Low Power, 305 nA Standby mode
So is it the perfect chip ?
Probably not, but it's sure pretty, and perhaps represents the state of the art.
This type of package is quite fragile, open to light so needs to be sealed underneath after reflow soldering. The solder balls are VERY close to the silver tracks so I imagine BEST BGA practices would be needed to use it.
I could easily scrape the silver metallization off the base with a knife using virtually no force, tho this is not a fair criticism because I’m a 100 ton giant compared to this tiny silicon chip.
Note: I'm not connected to STM or arrow.com in any way and I receive no payment of any kind from them. I do however love STM32 MCU's.