Stencil Aperture Area Ratio Extension - Impact of Stencil Technology and Coating

ABSTRACT Continued miniaturization of personal computing systems with increasing densities, drives the need for consistent solder paste print deposits to ensure maximum first pass assembly yields and high product quality levels. The IPC stencil design guidelines recommends stencil area ratio to be ≥ 0.66 for acceptable print release [1]. In order to meet the product densification and mixed assembly requirements, stencils have to be designed with area ratio < 0.66, which can lead to less than acceptable print deposits. Review of the literature shows the varying impact of stencil manufacturing technology and stencil coatings on the print performance [2, 3, and 4]. In this work, the effects of stencil manufacturing technology and polymer nano coated stencils are examined and compared to conventional stainless steel laser cut technology in its ability to extend the area ratio guidelines. Print performance on a variety of components was evaluated using BGA, Passive and QFP components with varying stencil aperture area ratios. The experiments were conducted in two phases. Phase 1 used an anodized Aluminum board to print and measure solder paste and Phase 2 used a 32mil PCB to validate the findings from Phase 1. Statistical analysis was conducted to quantify differences between conventional stencil technology and polymer nano coated stencils. Results from this work will help to answer the following questions. 1. What is the advantage of stencil manufacturing technology and polymer nano coated stencils (additional print volume or consistent print performance) and 2. How far we can extend the stencil area ratio recommendation?