All I agree with Werner, I have never seen a failure in either of the IMC phases of the copper-tin IMC. However, failure due to intermetallic growth is common in the industry that operates between 150oC and 225oC. The mechanism is: The copper diffuses into the tin and forms a nice pure intermetallic compound. It leaves behind a debris layer between the copper and the IMC or forms a weak layer between the IMC and the solder composed of the other metals and debris in the solder besides tin. I have seen a failed layer on a board that was soldered with Sb5 (started with 5% Sb) to have a 20% Sb composition along with oxides, sulfides and other debris. Another type is where the cooper plating occludes too much of the plating additives and other contaminates such as iron and the fracture is between the copper and the IMC. I have seen one failure wherein a contaminated layer appeared between the IMC layers, I could not give this one a theory. The failure in not often seen with the common tin/lead solders because the remaining lead rich layer is still fairly strong and ductile. If you think you have problem with IMC, put your board in the oven for 100 to 200 hours at 150oC and do a tape test on some of the conductors. Try it several times in the same place. If the tape will pull it off you component leads are not far behind. Phil Hinton