Hi, Jack,
I think you've probably travelled into that country where you have to
calculate your land pattern and try it for size. Use the formula near the
front of IPC-SM-782 or the on-line IPC calculator, if Hitachi themelves
cannot offer adequate advice.
What stencil thickness are you using for these, and what are the solder
balls made of - usual eutectic or something with a higher melting point? If
they're high melting point, you only need enough pad to allow a solder
fillet to form, since the ball will just be in point contact with the
board. On the other hand, if the solder is eutectic, the small pad may be
deliberate in order to try and maintain a reasonable stand-off height for
the component. The larger the pad, the lower the component is likely to
settle onto it, and also the greater the increase in variance of solder
joint volume unless your paste printing volume is very tightly controlled.
One other thought in conjuction with maintaining a maximised stand-off
height / minimised additional solder, is minimisation of the risk of short
circuiting between the contacts at that very small pitch. What ball
diameter do you have at that?.
I'm just hypothesising here, as I guess you realised, but I hope I've
triggered some more-useful thoughts.
Peter
Jack McNally <[log in to unmask]> 05/02/2003 08:52 PM
Sent by: TechNet <[log in to unmask]>
Please respond to "TechNet E-Mail Forum."; Please respond to Jack McNally
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cc: (bcc: DUNCAN Peter/Asst Prin Engr/ST Aero/ST Group)
Subject: [TN] BGA land pattern design for .65mm pitch device
Can anyone tell me where I can find land pattern design guidelines for
BGA's with .65 mm pitch? IPC-SM-782 only has pad dimensions for BGA's of
1.0 mm and greater.
I am placing a BGA which Hitachi calls its BP-240A package. The pad design
on the boards seems too small, only .0098" while the ball size according
to the spec is .0157".
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