Datasheet

ADP2126/ADP2127 Data Sheet
Rev. B | Page 16 of 20
PCB LAYOUT GUIDELINES
09658-031
Figure 31. ADP2126/ADP2127 Recommended Top Layer Layout
09658-032
Figure 32. ADP2126/ADP2127 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
connected 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 ADP2126/ADP2127. 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 ADP2126/ADP2127. 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) performance,
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 recommended
for the BUMPED_CHIP package.
•
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 symmetrical
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 from
Aw
Ap
AR =
where:
Ap is the area of the aperture opening.
Aw is the wall area.