SMTA International Conference Proceedings


FINE-PITCH QFN REWORK

Authors: Neil O'Brien and Scott Kentner
Company: Finetech
Date Published: 10/4/2009   Conference: SMTA International


Abstract: It is clear that the future belongs to the ever shrinking component. The Micro Lead Frame (MLF) component and specifically Quad Flat No-Lead (QFN) packages, have gained wide scale acceptance. They typically appear in densely populated boards where real estate is at a premium. As with all components, size and pitch continue to narrow, leaving traditional hand rework behind.

QFN center thermal pads and fine-pitch outer pads continue to challenge the rework world. With 0.4mm pitch in production and talk of 0.3mm pitch coming, the challenges to a repeatable rework process will be examined.

The design, size and assembly process of QFN's present some unique rework challenges not seen with other components. This paper will focus on the complete rework process, including component removal, site preparation, component paste printing, and finally new component soldering. The stencil design and paste process will be looked at in depth and soldering results evaluated. Triple row QFN’s will be the test case.

Key words: QFN, MLF, Rework, Component Printing, Area Ratio.



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