Hi-res X-Ray of Raspberry Pi Pico
High resolution X-Ray of the Raspberry Pi Pico microcontroller, launched on 21 January 2021.
At the top is a view of the whole board, which is roughly 51m (2") long. Below that is an even higher resolution view of the processor chip. The actual silicon chip - 2mm x 2mm of sandy goodness - is the small square in the middle.
A note on the physical construction of integrated circuits: the silicon chip is fragile and you can't solder to it. The chip is therefore stuck to a metal 'base plate' and surrounded by carefully shaped fingers of metal that together are known as the 'lead frame' - that's lead as in cable, not as in heavy metal. The big ends of the fingers form the pins of the IC package. The thin ends are as close together as possible, though still far too big to physically connect to the silicon. Tiny, incredibly thin metal wires (known as 'bond wires' and made from gold or aluminium) are ultrasonically welded to the fingers and to specially-prepared areas on the chip, thus providing an electrical path from the chip to the outside world. Finally, it's all surrounded by a precision-moulded plastic case.
In the lower part of the image you can clearly see the fine bond wires that go from the silicon out to the leadframe. The tiny dots on the wires at the chip end are microscopic balls, formed when the wire is ultrasonically welded to the chip's metallisation. I estimate that the wires are about 20µm thick (0.02mm) and the pads on the chip are about 65µm apart, or roughly the width of a human hair. I said this was a high resolution X-Ray!
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