BGA with scaling of solder balls. BGA solder balls with a rough, crusty, dull surface appearance.
First, the visual appearance of a solder connection does not necessarily indicate the integrity/reliability of a solder connection. However, the external appearance of a solder connection can indicate the solidification phenomena (we are dealing with a molten metal!). For instance: * Movement of a solder connection results in surface ridges => a disturbed solder joint. * Extended/slow cool down ramps can result in surface texture => grainy solder joint.
Second, the "BGA scaling" could be a reflection of: * Too little heat (incomplete solidification) OR * Too much heat (excess grain growth/structure).
Either way, unless there is some kind of thermal issues with the assembly, you should not be getting the "scaling" effect. The reflow profile of the assembly needs to be corrected. Occasionly, we have seen scaling and resolved the issue by improving the reflow profile.