Low Sodium Chip-Joining Process
Original Publication Date: 1985-Jan-01
Included in the Prior Art Database: 2005-Feb-18
The technique decreases the amount of sodium contamination found in chip-joining processes, by substituting the isopropyl alcohol rinses with either distilled alcohol or through the use of a vapor degreaser filled with isopropanol. The current chip-joining process consists of the following chemical treatments: 1. Isopropyl alcohol rinse. 2. Flux application. 3. Heat to reflow. 4. Flux softener application. 5. Xylene rinse. 6. Isopropyl alcohol rinse. It has been found that these alcohol rinses (isopropanol) and the flux produce large amounts of sodium, approximately 2 x 1012 Na+/cm2, whereas xylene is much cleaner at approximately 0.5-2.0 x 1011 Na+/cm2 . The reason is that isopropanol is more miscible in water than xylene and sodium is present as a water-soluble salt or oxide.