1. Field of the Invention
The present invention relates to a process for firmly soldering difficulty solderable metal of iron, nickel, copper or an alloy thereof having an oxide surface with a solder alloy.
2. Description of the Prior Arts
It has been difficult to directly apply a solder to an oxide surface of iron, nickel, copper or an alloy thereof.
FOR EXAMPLE, A LEAD FRAME OF AN ELECTRON DISPLAY TUBE WHICH IS USED FOR DISPLAYING NUMERICAL SYMBOLS IN A PORTABLE COMPUTER ETC., IS MADE OF NICKEL OR IRON ALLOY THEREOF AND THE SURFACE THEREOF IS OXIDIZED SO AS TO HAVE HIGH AFFINITY TO A SOLDER GLASS IN THE CASE OF AIR-TIGHT SEALING OF THE DISPLAY TUBE. Accordingly, it is difficult to directly solder the conventional Pb-Sn type solder to the lead frame. Accordingly, an auxillary lead piece made of nickel or copper is welded to the lead frame and then the terminal is soldered to the auxiliary lead pieces.
Instead of welding, it has been known to solder a solder alloy by removing a part of oxide membrane by treating a lead frame with an acid and bonding the solder alloy with a flux which contains a strong acid such as hydrochloric acid and then removing the flux by washing it with water. These methods have needed many steps and a complicated step and cause low efficiency in the soldering operations.