Dear TechNet forum member Does any one has experience with the Intermetallic layer build between Immersion Gold/Nickel and Tin Lead eutectic ? The Nickel (4-6 microns) applied on the PCB surface contains 6-8% Phosphorus. The Goldflash is 0.08 microns thick. We observed a 0.5 to 2 micron thick intermetallic layer between Nickel and the Tin Lead Ball after Reflow soldering . It seems not to be the well known Ni3Sn4 phase, because it is to thick and irregulary. Gold could not be detected as well (SEM-Analysis). The reliability of the BGA joints seems to be in a straight correlation to this brittle intermetallic layer.