1 Introduction

This study examines the potential impact to solder joint quality and solder joint reliability for leads overhanging the land pad on a PCB during the SMT process when the exposed metal of the lead is extended on a QFN package without changing the PCB. A chip-on-lead test vehicle was selected and PCBs designed to simulate varying levels of overhang were used. For each overhang amount, a representative sample size underwent temperature cycling board-level reliability testing to assess solder joint reliability. Data on the solder joint thickness and cross-sectional images of the solder joints were taken for quantitative and qualitative assessments of solder joint formation and performance when subjected to extended stress.

This type of assessment has not been previously performed for non-leaded packages. This study was prompted by a need to extend the exposed metal of leads for better die support in chip-on-lead QFN packages—changing the package footprint—while still maintaining a given package designator for customer continuity.