I need some help understanding the dimensions specified in the datasheet of an FPGA.

I am trying to figure out the pad/ball dimensions. From looking at the schematic, it looks like theta_b is the diameter, but then what are the theta_d and theta_e values? Additionally what is the C, A, and B value? I couldn't seem to find any reference to those.

I used the autocad libraries and it appears to be the .5 mm, but would like to have a better understanding/explanation. Is theta_d the radius and theta_e maybe the height?

FPGA Dimensions

  • \$\begingroup\$ They may be explained elsewhere in the datasheet ... which could usefully be linked in the question. \$\endgroup\$ Mar 17 at 13:19
  • 1
    \$\begingroup\$ What you call "theta_X" is read as "phi X", and means "diameter X". \$\endgroup\$ Mar 17 at 16:10

1 Answer 1


⌀b is the diameter of the solder ball: 0.6mm ±0.1mm

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This specifies the positional tolerances.
⌀ddd is the positional tolerance in respect to C, A and B.
⌀eee is the positional tolerance in respect to C.

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This is such a reference marker. I suppose you'll find something similar for A and B.

Unless you're a PCB manufacturer, I wouldn't lose sleep over these tolerances. It's more important that you're designing the solder pads according to the manufacturer recommendations.

Furthing infos regarding geometric dimentioning and tolerancing: Wikipedia

Picture: fictiv

enter image description here

PS: ⌀ is a diameter symbol and not related to θ.


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