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Fine-Tuning the Stencil Manufacturing Process and Other Stencil Printing Experiments
March 4, 2014 |Estimated reading time: 1 minute
Abstract
Previous experimentation on a highly miniaturized and densely populated SMT assembly revealed the optimum stencil alloy and flux-repellent coating for its stencil printing process. Production implementation of the materials that were identified in the study resulted in approximately 5% print yield improvement across all assemblies throughout the operation, validating the results of the initial tests.
A new set of studies was launched to focus on the materials themselves, with the purpose of optimizing their performance on the assembly line. Using a similar test vehicle as the prior experiments, DOEs characterized key aspects of the stencil manufacturing process by varying the laser cutting parameters and coating materials. As the scope of the DOE grew, it also included evaluation of new materials and a comparison of microBGA aperture designs. Eventually, additional runs were added to investigate the effects of nanocoating on wipe frequency and compare two different stencil cutting processes.
Results of the prior tests are reviewed, and the new test vehicle, experimental setup, and results are presented and discussed.
Introduction
This study builds upon the results of a previous investigation that identified the best stencil technology for the production of a high-density, highly miniaturized PCB assembly. The test vehicle used in that study is shown in Figure 1.
Figure 1: Test vehicle used in previous tests (non-BGA circuitry on closeup is intentionally blurred).
The PCB design packed nearly 15,000 paste deposits in a 3 x 7 area; 8,500 of those were 0.5 mm microBGAs. The study used print yields, transfer efficiencies, and print volume consistency as metrics to evaluate a number of stencil technologies, including electroformed nickel stencils, electroformed nickel that had been laser cut, and two different types of laser-cut stress relieved stainless steel (SS). The study concluded that the best print quality was produced with laser-cut fine grain (FG) SS foils with two-part Self-Assembling Monolayer Phosphonate (SAMP) nanocoating applied.Read the full article here.Editor's Note: This article originally appeared in the February 2014 issue of SMT Magazine.