In a message dated 97-07-04 01:59:40 EDT, you write: >One of our customers has an engineer who believes that reflowed tin/lead >has a significant reliability advantage over SMOBC. > I have no hard data on testing, but can tell you something about fused (reflowed) Tin/Lead that may assist in understanding. Fused Tin/Lead starts out as electroplated Tin/Lead, and the ratio of Tin to Lead varies with the current density in plating. The implications of this are that the Tin/Lead ratio will vary on the panel (board), and that the Tin will be lowest in the lowest current density areas, which are typically the holes, and the greater the aspect ratio (hole depth to diameter), the worse the problem becomes. This clearly implies that the current density problems are going to be a greater issue on modern boards. Further this can mean that unless a sufficiently high temperature is used, the high Lead areas will not fuse, and thus will be very prone to corrosion. 63/37 Tin/Lead fuses, in theory at just under 400 F. IF the ratio of Tin to Lead varies from that 63/37 ratio, the minimum temperature required increases. However it increases much more, and much faster if the deposit is high in Lead, versus being high in Tin. And of course, SMOBC, or HASL solder is generally pretty uniform, and always totally fused, or alloyed, as it starts out that way. A side note, if the Tin/Lead is not perfectly fused, you can get real nice galvanic corrosion forming, and the unfused areas will corrode quite quickly. So, although Solder is Solder is Solder, my suspicion is that in the real world, with current densities not closely watched, or controlled, the fused (reflowed) panels would have much higher incidence of corrosion potential, than SMOBC (HASL) panels, simply because you can depend on all the solder on an SMOBC panel being alloyed, this is not necessarily the case on a fused panel. Rudy Sedlak RD Chemical Company *************************************************************************** * TechNet mail list is provided as a service by IPC using SmartList v3.05 * *************************************************************************** * To subscribe/unsubscribe send a message <to: [log in to unmask]> * * with <subject: subscribe/unsubscribe> and no text in the body. * *************************************************************************** * If you are having a problem with the IPC TechNet forum please contact * * Dmitriy Sklyar at 847-509-9700 ext. 311 or email at [log in to unmask] * ***************************************************************************