Exposed copper coupled with silver final finish is causing opens.

Figures 1 and 2 show two images of the same problem: one x-ray, the other optical. In both cases it’s the result of sulphur corrosion on the surface of copper and silver surfaces. Both surfaces remain exposed after a soldering operation, and in the presence of sulphur, it is possible to witness corrosion. In time it can result in an open connection, as the figures show. Figure 1, taken on a Dage x-ray system, shows different degrees of corrosion on the tracking just below the solder joint fillet. In failure investigations it’s important to see and record as much as possible without change or damage to the sample. On one joint there was an open connection on this QFP device.

Routing flash has EMI implications. Don’t rush.

Memory comes in different types, and one key distinction is whether the memory remembers anything once the system is shut down. Nonvolatile memory stays around for the next session, while volatile memory lives up to its name and melts away between uses.