I want to make my circuit board very small. I have seen many smaller boards with complex circuit. But I am not sure how do they do it? Is it all Custom circuit implemented on VHDL or some micro controller core printed on circuit board like the Black portion on the image below. I am new to PCB designing. Any suggestion would be appreciated.
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Arjun
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If you need to ask what CoB is then you're too new to use CoB. Stick to BGA and/or WLCSP for now. – Ignacio Vazquez-Abrams Sep 06 '15 at 11:43
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I have already printed two boards at fab house in china, all i need is reduced PCB and reduced cost as well. I am required to drop down the PCB size as low as possible. – Arjun Sep 06 '15 at 11:45
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CoB requires specialized controlled-atmosphere attachment equipment; BGA and WLCSP use normal reflow. – Ignacio Vazquez-Abrams Sep 06 '15 at 11:47
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Can I print AVR microcontroller like this in china at FAB house? or do I need to have my custom processor? – Arjun Sep 06 '15 at 11:51
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You'll need to talk to your Atmel sales rep in order to find out which are available as a bare die. – Ignacio Vazquez-Abrams Sep 06 '15 at 11:56
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What is the difference between bare die and WLCSP package? – Arjun Sep 06 '15 at 12:14
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WLCSP is a "packageless" BGA. Bare die requires you to connect wires from the landings on the die to pads on the board. – Ignacio Vazquez-Abrams Sep 06 '15 at 12:15
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You might want to edit the title of the question to something more descriptive like "How to get to the smallest possible board size with an AVR MCU?" – bigjosh Sep 06 '15 at 16:02
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If you are using an AVR, you might be able to significantly reduce your footprint by using a Wafer Level Chip Scale package (WLCSP).
These can end up using even less board space than a Chip-on-board since you don't need room for the bonding wires. Instead, you fanout the connections from directly under the package, similar to a BGA.
The parts are much easier to work with than COB and you can order them from normal distributors like Digikey...
http://www.digikey.com/product-search/en?keywords=attiny%20wlcsp
You can read more about Atmel's WLCSP in this app note...
bigjosh
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