Improved Lead Frame Structure for Surface-Mounting Package
Original Publication Date: 1986-Nov-01
Included in the Prior Art Database: 2005-Mar-09
Solder wicking along leads of surface mount packages during reflow is recognized as an important problem leading to improper fillet formation, weak joint strength and, thereby, short fatigue life. This seems more serious with plastic leaded chip carrier (PLCC)-type packages having J-leads than with other types of packages, such as small outline IC and flatpack. Solder wicking is also concerned in case of rework, where solder application and the reflow process are less controllable. Solutions presented here are based on an idea of retaining solder at surface-mounted pads by various surface treatments of lead frames. The drawing shows an exemplary PLCC package having lead beams with narrow strips of surface-treated area (hatched portions) to prevent solder wicking along leads during reflow or rework.