Sep 17, 2009 
The need for cleanliness under individual components increases as the spacing between connector leads decreases and power increases. The low standoff height of QFNs traps flux between the ground pad and component leads. Entrapped flux under the QFN is a reliability concern. The purpose of this presentation is to make an argument for removing the residue under the QFN post-rework and present cleaning process options for meeting this cleaning challenge.
The QFN is similar to the Quad Flat Package (QFP), but the leads do not extend from the sides of the package. The perimeter leads are located on the bottom of the package, providing the electrical connection. Another unique characteristic is the existence of a center thermal pad, which provides an efficient heat transfer path when soldered to the PCB, helping to increase the thermal performance of the part. This package type was introduced specifically for applications where size, weight, thermal and electrical performance is important. The QFN, however, does offer some technical challenges, specifically in a lead-free environment, due to its unique structure and low standoff. This session will highlight some of these challenges, specifically relating to the rework process and post-rework cleaning of this unique package type.
Kyzen is a leading supplier of precision cleaning chemistries to the worldwide electronics, metal finishing, medical, semiconductor, and optical industries. Founded in 1990, Kyzen offers superior cleaning chemistries, technical support, application and analytical services throughout the world. Kyzen has won numerous industry awards for its exceptional products and all products are RoHS compliant. For more information, visit http://www.kyzen.com.
