10.1.1 DSBGA Package Assembly and Use

Use of the DSBGA package requires specialized board layout, precision mounting and careful reflow techniques, as detailed in the AN-1112 DSBGA Wafer Level Chip Scale Package application report. For best results in assembly, alignment ordinals on the PC board should be used to facilitate placement of the device. The pad style used with DSBGA package must be the non-solder mask defined (NSMD) type. This pad type means that the solder-mask opening is larger than the pad size which prevents a lip that otherwise forms if the solder-mask and pad overlap when holding the device off the surface of the board causing interference with mounting. For specific instructions on how to do this, refer to the AN-1112 DSBGA Wafer Level Chip Scale Package application report.

The 6-bump package used for LM3241 has 300 micron solder balls and requires 10.82 mil pads for mounting on the circuit board. The trace to each pad should enter the pad with a 90° angle to prevent debris from being caught in deep corners. Initially, the trace to each pad should be 7 mil wide, for a section approximately 7 mil long, as a thermal relief. Then each trace should neck up or down to its optimal width. The important criterion is symmetry which ensures the solder bumps on the LM3241 reflow evenly and that the device solders level to the board. In particular, special attention must be paid to the pads for bumps A2 and C2. Because the VIN and GND pins are typically connected to large copper planes, inadequate thermal relief can result in late or inadequate reflow 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 exposed die edges of the package.

TI recommends connecting a 10-nF capacitor between the VCON pin and ground for non-standard ESD events or environments and manufacturing processes. This capacitor prevents unexpected output voltage drift.