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When designing a modern package it is critical to know the net of each die pad.
Many of the routing rules are net based. Power and grounds are of course treated
much differently than IOs. Yet many IC designers persist in sending the packaging
designer the pad information without the proper net names. At right you can see a typical pad coordinate table provided by an IC desginer. In fact, sometimes the die pads don't even have numbers -- all that is provided is the center coordinates of the pad! |
1 -685 420 2 -685 300 3 -685 180 4 -685 60 5 -685 -60 6 -685 -180 7 -685 -300 8 -685 -420 9 -420 -685 10 -300 -685 11 -180 -685 . . . 28 60 685 29 -60 685 30 -180 685 31 -300 685 32 -420 685 |
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Power & Ground Nets are Crucial! If nothing else, the IC designer should assign the power and ground nets. Give all nets that are to be connected to a common metal ring the same net name. For the rest of the IO pads, give each die pad a unique name. The package design software assumes that any pads that share a common net name will be connected together! |
vss 1 -685 420 io1 2 -685 300 io2 3 -685 180 io3 4 -685 60 vdd 5 -685 -60 io4 6 -685 -180 io5 7 -685 -300 vddint 8 -685 -420 io6 9 -420 -685 io7 10 -300 -685 vss 11 -180 -685 . . . io8 28 60 685 nc 29 -60 685 vdd 30 -180 685 io10 31 -300 685 io11 32 -420 685 |
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Verification using Connectivity If a proper name is assigned to each die pad, upon completion of the package, the package designer can create a netlist derived from the actual connectivity that matches up each die pad with the ball it is attached to. This makes verifying that the package is correctly designed more accurate. Many companies have found to their chagrin, that a completed package connects to the wrong ball pads. The error was not caught during package design because the designer had to hand edit the netlist provided by the IC designer to add in the signal names. |
vss 1 - io1 2 A5 io2 3 B4 io3 4 C4 vdd 5 - io4 6 E5 io5 7 F4 vddint 8 - io6 9 G3 io7 10 G4 vss 11 - . . . io8 28 H3 nc 29 - vdd 30 - io10 31 J4 io11 32 J5 |