On a fine pitch BGA (.8mm pitch, 384 balls, .5mm ball diameter) I am using a
.014" diameter land per TI's recommendation. I was thinking then of a .013"
square stencil aperture with .003" radiused corners on a 5 mil plate. This
seemed reasonable until I did an area ratio calculation per IPC-7525. The
result was .592, which fails compared to the acceptable value of >.66. The
aspect ratio is a solid 2.6, although IPC says I should not consider aspect
ratio in this case, only area ratio. If I reduce down to a .012" square
aperture I can get to an area ratio of .642. Still fails, but close. But,
reducing the aperture 2 mils compared to the pad seems extreme and violates
the recommendation in para. 3.2.2.4. So my question is, what do you guys and
gals use for an aperture design on a component like this? Do you go by the
IPC guidelines?

Thanks.

Bob

=======================
Robert Barr
Manufacturing Engineering
Formation, Inc.
Voice: 856-234-5020 x3035
Fax: 856-234-6679

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