Debunking An Old Myth: Those New Devices Will Fall Off The Board

by Paul L. Schimel PE, International Rectifier, El Segundo, Calif., How2Power Today, Sep 24 2010

Focus:
In the past, leadless semiconductor packages (those with no protruding pins) were avoided in the power electronics world. The "forbidden" leadless packages were the BGAs, flip chips, and PQFNs. Back then, you needed the leads protruding from the package for compliance. The coefficient of thermal expansion (CTE) for the plastic package was fairly different from that of the system consisting of the printed circuit board (PCB), traces and solder. Without leads that could flex a little, eventually the solder would fracture and failure would ensue. But, as this article documents, packaging materials have improved and the issue of CTE mismatch is no longer a reason to forego using leadless packages. This article presents data on the CTEs of packaging and board materials to assure designers that leadless semiconductor devices are now safe to use. The author explains why the CTE mismatch between older mold compounds and PCBs was too great for leadless packages, and contrasts the CTEs of the older molding compounds with the compounds currently in use.

What you’ll learn:

• How to understand why newer leadless packages are safe to use for power semiconductor

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