Lead frame fanning and broken connecting bars elimination through design change and molding optimization

Designing of a leadless package is very challenging as there are many manufacturability considerations that need to be considered prior to designing the lead frame. The concerns are lead frame warpage, high sawing burr, lead frame delamination due to insufficient mold locking and etc. During the development of a dual leadless package of 7mm×7mm, these concerns were being addressed by design features such as half etched connecting bars to reduce copper loading during package sawing, additional stress relief slots and mold locking holes. Dummy leads were also designed in to balance the copper material on both sides of the connecting bars as the package design has a non symmetry land pattern. However due to the complicated lead and DAP design structure that restrict the mold compound flow, higher molding pressure is required in order to avoid any incomplete filling. This high transfer pressure eventually caused fanning of connecting bars and broken tie bars which also caused offset cutting and high saw burr. In this paper, we studied on how the combination of lead frame design, molding process optimization and package sawing process improvement could help to resolve the issue. This was done by lead frame warpage simulation and design of experiment on molding parameters and design of experiment on sawing process parameter and type of blade used.