FA3ST - Solder Mask


The solder mask covers the entire BGA substrate except for the fingers, rings and fiducials which must be exposed so that they can be wire bonded. Depending on your manufacturing process, the solder mask is either held back from the metal or overlaps the metal slightly. (Some mfgrs believe that overlapping the metal helps to secure it better to the substrate.

PBGA Rules
For Amkor's PBGA the solder mask is held back about 100 um from the fingers, rings and about 150um back from the fiducials. Since the power ring is only 200 um away from the finger tips and the ground ring is also 200 um from the power ring, a single large opening is used.

 pbgamsk.gif

The mask opening for the PBGA. Fingers and fiducials are shown in white.


SBGA Rules
SBGA rules have the solder mask overlapping the inner side of the fingers by about 50 um and clearing the outer side by about 100 um. The ground rings are overlapped by 50 um on one side and 150 um on the inner side.


mask1.gif


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