>Kirk VanDreel >05/19/97 11:25 AM >Does any one have the capability to produce 50 um lines and spaces with 2 >um fused solder over the traces? Experiments have shown a dewetting of the >solder into balls on the traces, however, the wetting angle is not bad. Is >there a physical constraint we are running into which is causing this >globbing of the solder? > Hello Kirk, I have seen this problem on fine traces caused by excess tin-lead rather than dewetting. When you etch, the undercut reduces the copper trace width under the tin-lead. A 50um trace reduced to 40um will effectively give 20% more tin-lead thickness when fusing, and above a certain thickness it will bunch up due to surface tension and produce a solder ball. Having said that, I would not expect this problem with 2um tin- lead. Can you do the following:- Minimise undercut by using thin copper foil Optimise etching parameters- (<8.5 pH in ammoniacal etch - 8.2 optimum) Plate the tin-lead as thin as possible - (3-4um should be okay). One final thought,if your trace edges are not covered with solder after fusing, you are leaving more tin-lead on the surface. Check the solder conditioning and fusing flux. Good Luck, -- Paul Gould Teknacron Circuits Ltd [log in to unmask] Isle of Wight,UK *************************************************************************** * 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] * ***************************************************************************