LM3242

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SNOSB48E – OCTOBER 2011 – REVISED AUGUST 2015

Layout Examples (continued)

Figure 36. Board Layer 4 – System GND Plane

10.3 DSBGA Package Assembly and Use

Use of the DSBGA package requires specialized board layout, precision mounting and careful re-flow

techniques, as detailed in Texas Instruments Application Note 1112. Refer to the section Surface Mount

Assembly Considerations. For best results in assembly, alignment ordinals on the PC board must be used to

facilitate placement of the device. The pad style used with DSBGA 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 SNVA009 for specific instructions how to do this.

The 9-bump package used for LM3242 has 250-micron solder balls and requires 0.225-mm pads for mounting on

the circuit board. The trace to each pad must enter the pad with a 90°angle to prevent debris from being caught

in deep corners. Initially, the trace to each pad must be 7 mil wide, for a section approximately 7 mil long, as a

thermal relief. Then each trace must neck up or down to its optimal width. The important criterion is symmetry.

This ensures the solder bumps on the LM3242 re-flow evenly and that the device solders level to the board. In

particular, special attention must be paid to the pads for bumps A3 and C3. Because VIN and GND are typically

connected to large copper planes, inadequate thermal reliefs can result in late or inadequate re-flow of these

bumps.

The DSBGA package is optimized for the smallest possible size in applications with red or infrared opaque

cases. Because the DSBGA package lacks the plastic encapsulation 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 sensitivity. However, the package has exposed die edges. In particular, DSBGA

devices are sensitive to light, in the red and infrared range, shining on the package’s exposed die edges.

Adding a 10-nF capacitor between VCON and ground is recommended for non-standard ESD events or

environments and manufacturing processes. It prevents unexpected output voltage drift.

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