Datasheet

ADP2125
Rev. A | Page 14 of 16
PCB LAYOUT GUIDELINES
08774-022
Figure 22. ADP2125 Recommended Top Layer Layout
08774-023
Figure 23. ADP2125 Recommended Bottom Layer Layout
For high efficiency, good regulation, and stability, a well-
designed and manufactured PCB is required.
Use the following guidelines when designing PCBs:
•
Keep the low ESR input capacitor, C
IN
, close to VIN
and GND.
•
Keep high current traces as short and as wide as possible.
•
Avoid routing high impedance traces near any node con-
nected to SW or near the inductor to prevent radiated
noise injection.
•
Keep the low ESR output capacitor, C
OUT
, close to the FB
and GND pins of the ADP2125. Long trace lengths from
the part to the output capacitor add series inductance that
may cause instability or increased ripple.
To ensure package reliability, consider the following guidelines
when designing the footprint for the ADP2125. The
BUMPED_CHIP device footprint must ultimately be
determined according to application and customer specific
reliability requirements, PCB fabrication quality, and PCB
assembly capabilities.
•
The Cu pad on the PCB for each solder bump should be
80% to 100% of the width of the solder bump. A smaller
pad opening favors solder joint reliability (SJR) perfor-
mance, whereas a larger pad opening favors drop test
performance. The maximum pad size, including tolerance,
should not exceed 180 µm.
•
Electroplated nickel, immersion gold (ENIG) and organic
solderability preservative (OSP) were used for internal
reliability testing and are recommended.
•
Nonsolder mask defined (NSMD) Cu pads are recom-
mended for BUMPED_CHIP packages.
•
The solder mask opening should be approximately 100 µm
larger than the pad opening.
•
The trace width should be less than two-thirds the size of
the pad opening.
•
The routing of traces from the Cu pads should be symmet-
rical in X and Y directions. Symmetrical routing of the
traces prevents part rotation due to uneven solder
wetting/surface tension forces.
•
Stencil design is important for proper transfer of paste onto
the Cu pads. Area ratio (AR), the relationship between the
surface area of the stencil aperture and the inside surface
area of the aperture walls, is critically important. Stencil
thickness has the greatest impact on this ratio. AR values
from 0.66 to 0.8 provide the best paste transfer efficiency
and repeatability. The AR is calculated using the following
equation:
A
w
Ap
AR =
where:
Ap is the area of the aperture opening.
Aw is the wall area.