Example 2: AIF Die File with Ball Assignments

Example 2: Adding Ball Assignments July 6, 2001
In this example we show how the addition of the ball assignments is done. In many cases the product engineer (whether he be a die designer or package designer) knows which signals on the die go to which balls on the package. This is usually because a new design is not built in a vacuum but is likely an update for an existing design for which there are already ball assignments for the signals. Since the end user of the device would rather not completely re-layout his PCB, these signals must appear in the same positions as in the previous design.		We've taken the same AIF file that describes the die (see example 1) but this time we've added one more column of data - the JEDEC ball number. The rule is as follows: If a die pad goes to a single ball then enter the ball's JEDEC number in the 6th column of data. If a die pad goes to more than one ball (typical of VCC and VSS nets) then put a dash in the 6th column. Balls which go to such nets as power and ground (or even no-connect) are enumerated independently from the die pads. Use dashes as place holders for the die pad, pad stack and coordinates.

testdie_24_w_balls.txt

This is the same 24 pad die as before but now we have added JEDEC ball assignments. (We assumed an 8x8 array with a 4x4 depopulation, a 500 um pitch and a 7000x7000 package outline...)

This is the ideal set of information for the package designer. From this data he can import his die, the netlist and the package pin information directly into his package design tool (Cadence APD, Avanti Encore, Zuken CR-5000) without any need to massage the data.

Basically he is ready to place his fingers, rings and start routing.

To see what this might look like in a CAD system click on the DXF file below: testdie_24_w_balls.dxf

Balls that are connected together such as those for VCC, VCCINT and VSS nets are listed separately in the [NETLIST] section. Every ball should be accounted for in the AIF file and a ball should only be referenced once - either when it is listed on the same line as a die pad or when it is listed separately.

When listing the ball separately you must use dashes ( - ) to hold the place for the die pad, die pad stack and die coordinates. The AIF parser knows that data in column 6 is the ball assignment.

view of the BGA with ball assignments and rats.

At left you can see how a tool such as FA4ST would import this AIF file. Based on the ball assignments and the BGA information it can not only draw the die but can draw the array and build a rats nest from die pads to balls.

This is the basic starting information that any package designer needs and Artwork has developed modules that will import this AIF file directly into these tools.