How to make a Chip on Board (CoB)?

I’ve noticed that many electronic devices wich are cheap (Toys, Famiclones) contain a big black blob with a microcontroller die inside, Is this comparable to for example, an ATMEGA328p. How do these work? Can I make my own?In the case of the Famiclone, there is a (very) big chip whit a lot of pins (80?) I think it contains the entire system “CPU” inside because it’s next to a big ROM chip. In case of the toys, they mostly have a rectangle sized PCB with the chip in the middle with 10 pin terminals that is used to control the sound and the lights. But it doesn’t have any other component on the PCB, I guess all the required components are already built-in.

You need to weld a wire onto the silicon and them take it to the coper pad and connect. This is beyond my ability. Machines do this.

ronsimpson said:

You need to weld a wire onto the silicon and them take it to the coper pad and connect. This is beyond my ability. Machines do this.
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Is this type of microcontroller comparable to an ATMEGA328p or any programmable mic.?

If the device is produced in large quantities the chip under the blob is likely an ASIC - Application Specific Integrated Circuit. No, you would not be able to produce it.

The controller chip for a simple LCD is a Hitachi HD44780, or similar.

The connections are made using the same machines as for assembling bare silicon dies in to the leadframes of conventional IC packages.

The link wires usually then end up buried in the epoxy encapsulation, but can be seen in ICs with "window" tops such as UV erasable EPROM and MCUs with internal erasable EPROMs.






The automatic wire bonding machines start at around $25000 from what I can find, and go to millions...



There is of course nothing to stop you having boards made with normal surface mount MCUs or FPGAs etc., then adding a blob of black epoxy over the IC to make it look like a COB assembly!

I expect that there are contract manufacturers out there that have COB capability.

ChrisP58 said:

I expect that there are contract manufacturers out there that have COB capability.

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I would imagine so, but how many tens of thousands does the OP want?

I would imagine many Universities would have the capabilities as well?, they often have chip fabrication capabilities - my daughter had to make solar cells for her clean room certification, and her husband was involved in making acceleration sensors.

There are quite a few issues when manufacturing COB -




Regards, Dana.