FBGA User’s Guide
54
Version 4.2, November 1, 2002
PC Board Surface Finish
Another design consideration is the selection of the surface finish for the board. While hot air solder
leveled (HASL) boards have been successfully used for FBGA, it is generally felt that the domed
shape of the pads makes it more difficult to achieve consistent assembly yields. On the other hand,
excellent yields have been achieved with both Ni/Au plated pads and also with bare copper pads
coated with organic solderability preservatives (OSP). In the case of Ni/Au plated pads, it is important
to control the plating quality to prevent embrittlement of the solder joint. This can occur if the gold is
too thick; gold thickness of 5 mils maximum is recommended. There has been some concern in the
industry that certain kinds of nickel plating can cause embrittlement—your PCB supplier should be
able to give advice on this subject.
Recommended Board Design Dimensions
Figure 7-2. Recommended Dimensions for the AMD 0.30 mm Solder Ball
Dimension
Function
Recommended Design Value
0.30 mm
Solder Ball
0.35 mm
Solder Ball
0.60 mm
Solder Ball
A
Solder Mask Opening
on the Package
0.25 ± 0.03 mm
0.30 ± 0.03 mm
0.50 ± 0.03 mm
B
Copper Pad Dimension
0.23 ± 0.01 mm
0.27 ± 0.015 mm
0.40 ± 0.03 mm
C
Copper Pad to
Solder Mask Clearance
0.075 ± 0.025 mm
0.075 ± 0.025 mm
0.075 ± 0.025 mm
—
Trace Width
0.125 ± 0.25 mm
0.125 ± 0.25 mm
0.125 ± 0.25 mm
Package side is mask defined
Solder wets only the pad
A
B
Package Side
Printed Circuit Board
C