LM3691TL-0.9 NSC [National Semiconductor], LM3691TL-0.9 Datasheet - Page 16

• Manufacturer Part Number: LM3691TL-0.9
• Description: High Accuracy, Miniature 1A, Step-Down DC-DC Converter for Portable Applications
• Manufacturer: NSC [National Semiconductor]

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MICRO SMD PACKAGE ASSEMBLY AND USE
Use of the Micro SMD package requires specialized board
layout, precision mounting and careful re-flow techniques, as
detailed in National Semiconductor Application Note 1112.
Refer to the section Surface Mount Technology (SMD) As-
sembly Considerations. For best results in assembly, align-
ment ordinals on the PC board should be used to facilitate
placement of the device. The pad style used with micro SMD
package must be the NSMD (Non-Solder Mask Defined) type.
This means that the solder-mask opening is larger than the
pad size. This prevents a lip that otherwise forms if the solder-
mask and pad overlap, from holding the device off the surface
of the board and interfering with mounting. See Application
Note 1112 for specific instructions how to do this.
The 6-bump package used for LM3691 has 300–micron sol-
der balls and requires 10.82 mils pads for mounting on the
circuit board. The trace to each pad should enter the pad with
a 90° entry angle to prevent debris from being caught in deep
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corners. Initially, the trace to each pad should be 7 mil wide,
for a section approximately 7 mil long or longer, as a thermal
relief. Then each trace should neck up or down to its optimal
width. The important criteria is symmetry. This ensures the
solder bumps on the LM3691 re-flow evenly and that the de-
vice solders level to the board. In particular, special attention
must be paid to the pads for bumps A2 and C2, because GND
and V
The micro SMD package is optimized for the smallest possi-
ble size in applications with red or infrared opaque cases.
Because the micro SMD package lacks the plastic encapsu-
lation characteristic of larger devices, it is vulnerable to light.
Backside metallization and/or epoxy coating, along with front
side shading by the printed circuit board, reduce this sensi-
tivity. However, the package has exposed die edges. In par-
ticular, micro SMD devices are sensitive to light, in the red
and infrared range, shining on the package’s exposed die
edges.
IN
are typically connected to large copper planes.