The process starts with the use of a ‘Magic Ingredient’, a water-soluble solder paste. This ‘Magic Ingredient’ is available though DigiKey and is made by Kester Solders. Buying of the product in itself is interesting as it must be kept refrigerated and will only be delivered if ordered for overnight delivery. Since the material is water based it must be stored in a cold place (refrigerator) and only ‘keeps’ for a few months. Starting with a clean board, the solder paste is applied from the syringe. The paste comes pre-loaded into a syringe however, the reader must order the plunger for the syringe and the applicator tips separately. Link.