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LP2985YPB mask opening

John Hudrlik
Prodigy 60 points
Other Parts Discussed in Thread: LP2985

We received the following from a TI FAE regarding the AN1112:

“LP2985 YPB is a 5 bumps, 0.5mm pitch WCSP with small solder balls.

Recommended NSMD land pattern is 0.165 +/- 0.02 mm
Solder Mask Opening is 0.265 +/- 0.02mm

We don’t want the solder mask opening to be too large to avoid
losing solder to the traces connected to the soldering pads.

The SMO in the current App Notes (0.35 +/- 0.025mm) is too large
that need to be updated. “ 

Can we get confirmation this is correct?

  • 0
    TI__Prodigy 240 points

      The solder mask opening for the small bump DSBGA as
    called on the SNVA009A App Report (old National AN-1112
    App Note) is indeed too large and should be corrected.

       This is particularly true for such a small pad. The
    more standard 0.002" (0.05mm) solder mask opening ring
    should be used. That would make the solder mask opening
    0.1mm larger than the pad or 0.265mm dia. as stated above

  • 0 in reply to Ernesto Rey
    Prodigy 60 points

    Two questions left...

    1. I'm assuming that the paste volume is in error to then? Please provide a nominal (The ANs list 0.3mm sq openings).

    2. There is a note to not exceed 2/3rds the pad width for traces at the pad connection. I was planning on doing a 5mil backoff (the trace width would be 2/3rds the trace width up to 5mils away from the pad connection. Is this sufficient/excessive?

  • 0 in reply to John Hudrlik
    TI__Prodigy 240 points

    John,
    Your question above relates to the separate thread available at:
    http://e2e.ti.com/support/power_management/linear_regulators/f/321/p/380727/1341074.aspx#1341074

    (1) Our apologies, the drawing (Note 3) points out to the incorrect App Report (SBVA017), it should refer to App Report SNVA009A. The latter has no reference to paste volume and deals with the smaller ball size and pitch devices.

    (2) Trace width will affect the spread of the solder from the pad along the trace up to the soldermask opening edge. This is turn will affect the standoff. Technically traces could be as wide as the pad but this will lower the standoff, so narrower traces are desirable. If connection to planes or very wide traces is needed, the SMD (Solder Mask Defined) approach is recommended.

       That being said, 0.127mm traces are fine as long as all four bumps use the same trace thickness and that any widening of the traces does not begin until beyond 2x the width of the soldermask clearance ring, to account for soldermask mis-registration exposing any large metal areas.