ADP2127 datasheet(16/20 Pages) AD

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ADP2126/ADP2127

Rev. A | Page 16 of 20

PCB LAYOUT GUIDELINES

Figure 31. ADP2126/ADP2127 Recommended Top Layer Layout

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, CIN, 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, COUT, 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

AR =

where:

is the area of the aperture opening.

is the wall area.

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