New Capability Offers Improved Step Stencil Quality for Challenging Assemblies
December 3, 2015 – Continuing to invest in the most advanced stencil production technologies, FCT Assembly’s Fine Line Stencil division today announced that it has added a next-generation micro-milling system to its operation to enable production of highly-accurate step -- or multi-level -- stencils.
Step stencils are used for a variety of applications and have seen demand rise as component footprints shrink. Miniaturization and certain assembly configurations challenge traditional, single-thickness coplanar stencils. Step stencils provide flexibility for ensuring proper solder paste height and volume for fine-pitch components that are distributed over a wide area; or, for heterogeneous assemblies that incorporate small devices alongside larger components which require more paste volume.
“We have offered step stencil manufacture for some time,” explains Brent Nolan, FCT Assembly Vice President, “but the products were produced using a chemical etching process which constrains transitional thickness flexibility, has reduced surface quality and limited accuracy. Board designs are becoming more complex and now dictate very stringent feature control, which is why Fine Line Stencil has invested in a state-of-the-art micro-milling platform that allows exceptional accuracy and repeatability.”
The standard chemical etching process takes anywhere from one and a half to two hours, on average, to produce a single 1 mil (25 µm) step. Numerous repeat processes are required to chemically-etch multiple steps and, because of this ongoing repetition, the accuracy across the entire process window can be compromised. Alternatively, the micro-milling system now employed by Fine Line Stencil, leverages the most advanced optics to deliver exceptional positional accuracy for extremely tight tolerances in half the time. In fact, per 25 µm of depth, there is less than 3 µm of variance from feature to feature.
The ability to finely mill the various stencil steps ensures that the transition from one level to another are smooth and that the surface roughness of the steps are consistent with that of the rest of the stencil. This results in a more repeatable and accurate printing process, less paste smearing and reduced stencil underside paste extrusion.
“The micro-milling process produces more precise multi-level stencils as compared to chemical etching,” says Nolan in conclusion. “Our customers will benefit from these quality products, which enable production of high-yield assemblies that incorporate challenging components such as micro BGAs, 0.3 mm CSPs, 0201s and fine-pitch QFNs.”For more information, visit www.finelinestencil.com or call 719-510-6000.