I’d like to touch on one last topic as a preview for the upcoming SiP printing webinar: stencil design. Just like solder paste and flux technology has evolved over the years to keep up with the smaller and smaller requirements for system-in-package applications, stencil technology has evolved as well. The first major advancement in stencil printing technology came with the advent of chemically etched stencils. The process involves applying a patterned mask to a sheet of metal, then using a chemical spray to dissolve the unprotected areas. However, the problem that arose with this type of etching was that the etch rates were different for large and small apertures.
The next evolution was laser-cut stencils. The precise laser showed no differences in etching for both the small and large apertures, so this type of stencil was great for SiP applications with the need to print smaller apertures. Once laser-cut stencils became commonly used, the next step was to improve upon the material. Laser-cut stencils with electroplated nickel on top of the stainless-steel stencil was shown to improve transfer efficiency with smaller components like 0201 components (right now Indium Corporation products are soldering 01005 and smaller!) and QFNs (quad flat no lead). The trade-off here is that electroform stencils cost much more than standard laser-cut and take longer to make. Laser-cut stencils have been making technological advances as well, such as with nano-coating, so be sure to choose the right stencil for your process needs.
Don't forget to tune in to my upcoming SiP printing webinar to learn more about stencil technology!