I am a newbie in ASIC design process and have a question. What is difference (or pros and cons) of shorting the voltage supply pins(which have the same voltage requirements) in package level or in die(chip)level?
Thanks G
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Well on the die level they'll all be tied together anyway in the power grid. That doesn't mean you only need one power and ground pin though. You have to understand the power draw of your chip to know how many pins you really need. Perhaps you need many because you have a fast DDR4 bus so you need the impedance of the package to be very low (more pins in parallel lowers your impedance). Same would apply if you have power hungry core logic. Or maybe you need pins on all sides to help with losses from IR drop.
There's actually a lot that goes into designing the power portions of chips and packages, but it's a broad topic.
answered Jun 26, 2015 at 19:03
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\$\begingroup\$ Thanks for your reply. Let me make it more specific. Lets say you have sensitive analog circuit such as a PLL which requires a clean VCC supply lets call it as cl_VCC and say you have digital logic supply (d_VCC) let say both 1.2 V. Would you short them on die? package or PCB? \$\endgroup\$ Commented Jun 26, 2015 at 19:35
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1\$\begingroup\$ My personal preference would be the PCB, to allow the impedance of the package itself to attenuate any noise between the two. Actually I wouldn't tie them directly, on the board I'd probably have a little filter and then connect to power. If it was a really sensitive part I'd probably use separate copper floods to star route gnd and power back to my voltage source. \$\endgroup\$ Commented Jun 26, 2015 at 19:57
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1\$\begingroup\$ I Agree with Some Hardware Guy, if you short the supplies on-chip there's not much you can do in case the logic disturbs the PLL. So separate pins is the way to go. Maybe even separate grounds ! In my work we have extremely sensitive circuits that cannot even handle the noise of a switching supply so we use a separate linear regulator for their supply. Other circuits can handle some noise so there we use a switching supply. \$\endgroup\$ Commented Jun 26, 2015 at 21:16