One very important part of materials testing is to find the usable limits of a material before it becomes a released product. Some customers like to use ball attach fluxes beyond the standard 8 hour recommendation – and in some cases this is possible.
I like to find the realistic limits of ball attach fluxes using our pin transfer unit. If flux has been left on equipment too long, the first sign of failure is generally bridging flux deposits that appear across the same pads print after print. Inspection of the pin transfer array should show a string of flux spanning the gap from pin to pin. The interesting thing about this phenomenon is that most ball attach fluxes in the industry have a threshold after which multiple bridges occur almost at once. This makes finding the ‘workable life’ of a flux much easier.