Flat packages such as QFNs (Quad Flat No-lead) or other MLFs (Micro Lead Frame) with outstanding thermal, inductive and capacitive characteristics are being increasingly incorporated into densely populated, space-saving assemblies. Unlike BGA components, QFNs however do not provide a solder ball array for SMD assembly but have to 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.
QFN components do not provide own solder, at the same time a consistent application of new solder paste is barely possible on densely populated PCBs. Thus, the challenge is to precisely apply new solder to the contact pad structure of the QFN component before they can be soldered.
One possibility is to implement an additional work step with transfer plate and solder reflow. However, beside accuracy issues, exposing the QFN component to thermal stress not one but even two times must be considered a serious drawback. In comparison, paste printing the solder directly to the QFN component using a printing stencil is quicker, more precise and keeps the stress to the component at a minimum.
With the “Direct Component Printing (DCP) Module”, FINETECH offers an all-in-one solution for all FINEPLACER® rework stations. After the QFN component has been placed on the printing stencil using the FINEPLACER® beam splitter optics, new solder paste can be applied consistently with a mini squeegee. Afterwards the QFN is picked-up by the reflow arm and the printing result can be inspected with the patented vision alignment system. In a last step, the component will be aligned to the substrate and finally soldered. Implementing nitrogen into the process will improve the formation of an optimal solder meniscus.
This is a very effective and time-saving solution since all rework steps can be performed within one rework system. The uncomplicated step of printing the solder paste directly to the component helps avoiding a second reflow process. The thermal stress of the component corresponds to the one of the original assembly – no compromises. See the application note at http://www.finetech.de/enid/qfnrework.
Press release: "Twin Power Solder Removal" |
