Flat packages such as QFNs (Quad Flat No-lead) and other MLFs (Micro Lead Frame) with outstanding thermal, inductive and capacitive characteristics increasingly are being incorporated into densely populated, space-saving assemblies. Unlike BGA components, QFNs do not provide a solder ball array for SMD assembly but must be soldered to the assembly with their contact pads attached directly to the metalized body (lead frames). This technology makes much higher demands compared to the handling of standard SMD components.
Therefore, the challenge is to apply fresh solder to the contact pad structure of the QFN component prior to placement and reflow. Typically, these packages are used in tight spaces where it is difficult to use conventional solder pasting methods (stencil and blade) because there is not enough real estate to place the stencil and draw paste over it. Direct dispensing of solder paste is not a viable option either. It is expensive, slow, and rarely available in rework environments.
As Horn will explain in his presentation, direct paste-pasting the component is the preferred method. Thin-film stencils, fixturing, and skillful hands can sometimes achieve wonders, but aren't we supposed to be getting our hands out of the way? In this scenario, someone is usually left juggling a pasted component upside-down, and trying to position it onto a nozzle prior to reflow without disturbing the pasted work. Reworking MLF or QFN components repeatedly with high yield requires more of a hands-off approach that can be integrated easily into the rework tool. What is needed is an equipment module that ensures that the paste process does not limit rework yield. Because stencils are available with less than 300 micron pitch for component sizes in the millimeter range, there is a limit to successful paste printing that relies on hand/eye dexterity.
For more information about FINETECH's Direct Component Printing (DCP) Module, visit http://www.finetech.de/enid/qfnrework
FINETECH is a leading manufacturer of innovative rework and micro assembly equipment for the latest advanced packages. The modular design of the FINEPLACER� platform enables a multitude of applications, from reworking SMDs to the highly accurate placement of flip chips or opto-electronic components. FINETECH is headquartered in Berlin, Germany, with offices in Tempe, Arizona, Shanghai, China and Penang, Malaysia.