"Fountain" Soldering -- Its Background and Development

Old, tried, and true principles are described as they have been applied to a modified "fountain" soldering technique, to virtually eliminate "drossing" (tin and lead oxidation) and to reduce contamination to a minimum. A history is given of the development of this technique at Sanders, dating from the early days of the "Tinkertoy" program. An early sheet-aluminum stencil and "solder boat" dipping method is discussed, with relation to the long time-cycle and the trapped-gasses problem. Mentioned, is an improvement of bringing the solder to the work in solder cups, but which was mechanically grotesque and faced with the twin problem of thermal-loss and dross-formation. A one-shot pump modification is credited with being the forerunner of the true "fountain". Presented as the final solution, is a positive-displacement pump that supplies solder through a baffled manifold to selected tube sizestgiving a steady flow of solder which "fountains, to a uniform height above the tubes. Advantages of the "fountain" technique are listed, with emphasis being placed on accurate temperature control and lower soldering temperatures. A refinement is introduced in the form of an anti-oxident oil layer to control drossing, as used in the tinware industry in the "flow-brightening" of electrodeposited tin. Other precautions are outlined which reduce contamination. Growing out of this soldering technique for printed wiring, a resistor-wafer soldering machine is described (for stacked-wafer modules using standard resistors). Also presented, is a "piledriver" soldering machine for wafers using printed silver patterns and printed component parts.