Typical FC bump pitch of 250 micron, for a bump 100-125 microns in diameter yields a standoff of 70-100 microns measured from top of board solder mask to surface of die passivation.   At 200 micron pitch and finer, bumps are smaller and standoff is reduced.  Wetted bond pad area varies significantly due to pad etch tolerance (typ +/- 20%), solder mask opening resolution (typ +/- 25 microns), and solder mask to etch feature alignment (typ +/- 50 microns).  This can cause the 70-100 micron standoff variation by itself.

Regards,
Leo Higgins

-----Original Message-----
From:   Erat, Wolfgang [SMTP:[log in to unmask]]
Sent:   Thursday, July 06, 2000 2:22 PM
To:     [log in to unmask]
Subject:        [TN] Flipchip underfill

Hello

What are recommendations / experience for optimal standoff height for Flipchip designs out there(distance top of substrate to bottom of chip) ?

Factors I would expect to be effected by this variable are: undefill flow / reliability / potential for voids in underfill

Went through the web but could not get much in terms of hard numbers.

Thanks in advance

Wolfgang