2016 Reports

Broadband Printing II: Step Stencil Design Evaluations
Author:  Michael Meilunas
        Broadband printing is the term often applied to an electronic assembly process in which both fine and large pitch componentry is assembled through a stencil printing process. Broadband printing applications may require step stencils in order to effectively deposit solder paste over both large and small features. Step stencil design guidelines may be found in IPC-7525B, which was released in 2011. The standard includes recommendations for minimum step edge to aperture spacing and, by extension, minimum step region width. In the ensuing years, significant advances in step stencil fabrication and solder paste technology have occurred, potentially allowing for even tighter step edge to aperture spacing and ultimately, furthering the miniaturization of electronic assembly. The following report describes an experiment which utilized a 120 micron thick stencil with 20 and 45 micron thick step downs of varying width and multiple step edge to aperture spacing, including distances which were significantly less than IPC-7525B recommendations. Multiple print processes were used to screen a type 4.5 solder paste over test boards which were then examined using an automated solder paste inspection system to collect solder paste area and volumetric data. Data analysis was performed to determine which designs and process factors resulted in acceptable printing.
Thermal Cycling Reliability of Underfilled Assemblies on TB2013
Author:  Pericles A. Kondos
        Four different underfills from various suppliers were used to underfill many different types of components on the front side of the main section of TB2013 test boards. The process details have been described in previous reports. The assemblies were subjected to accelerated thermal cycling (ATC) and the results are presented here together with failure analysis. The main purpose of this project was to compare the ATC performance of each underfilled component type with that of the non-underfilled, but comparison between underfills was attempted too. It was found that no underfill was consistently better across the board, although some trends did emerge.

Effect of Low Volume Solder Paste Deposit Outliers on BGA/CSP Assembly and Reliability Expectations
Authors:Sai Sriperumbudar, Martin Anselm and Michael Meilunas
      The goal of this experiment was to determine the acceptable lower limit for solder paste volume deposit tolerance during stencil printing processes to ensure achieving both assembly yield and reliability expectations with BGA / CSP componentry. The experiment was conducted with the assumption that the current minimum acceptability limit for a BGA or CSP solder paste deposit is -50% of stencil aperture volume. Based on this assumption, low-volume outliers in the range of -50 to -80% of stencil aperture volume were generated for assembly yield analysis and ultimately reliability analysis using accelerated thermal cycle testing. The results show that the low-volume outliers had no impact on the assembly and, contrary to traditional thought, had no negative impact on the accelerated reliability of the devices investigated.

Evaluation of PariPoser Anisotropic Conductive Elastomer
Author: Michael Meilunas

    This report documents the characterization and reliability evaluation of PariPoserTM, a thin, electrically conductive film designed for electronic packaging interconnects and may be used as a substitute for surface soldering in some applications.