LPKF
Exciting news from LPKF’s process engineers: StencilLasers can now produce high-precision steps in solder paste stencils, given suitable process control. The process will be presented at SMT 2013 in Nuremberg by the Garbsen, Germany-based specialists in laser-based micro machining and is described in detail on the company’s website.
The trend toward miniaturisation in electronics is placing ever greater demands on soldering processes, which have to produce reliable, conductive connections between the electronic components and the board. Use of a soldering iron to solder the tiny components has long been obsolete in industrial production. Now solder paste is applied to the board, the components are positioned on it, and the entire assembly is heated in a furnace.
The solder paste is applied to the board via a printing process. A squeegee forces the solder paste through holes cut in a stainless steel stencil to coincide precisely with the soldering points. Critical to this process are suitable hole contours and exact positioning. The amount of solder paste required differs depending on the part. Small ICs with numerous connections have closely spaced contacts, making positioning and solder paste application much more demanding. Because too much paste nearly inevitably results in short circuits, stencils with reduced thickness in the regions where less solder paste is required are used. A stencil with a typical thickness of 120 µm has a thickness of around 100 µm in the IC regions, making it 20 µm finer.
These step downs were previously produced by etching or milling prior to laser cutting of the apertures. Stencil shops usually had to purchase prestructured stencils from external suppliers.
Through a clever combination of process parameters, the LPKF StencilLasers can generate these steps during the cutting process. LPKF has published research on this topic on the company website at www.lpkf.com/stepdown-stencils/, which is available for free download.