“Harsh Environment Impact on Resistor Reliability”
Abstract: The industry has observed an increase in corrosion failures at data centers located in harsh industrial environments and in geographies with atmospheres high in sulfur-bearing gaseous contamination. Several failing signatures have been observed, including creep corrosion of copper plating on printed circuit boards and resistor terminal corrosion. Resistor terminal corrosion results in electrical opens as the corrosion product, silver sulfide, builds and consumes the terminal metallurgy. Reaction to these corrosion failures has included three key efforts: to investigate the source of the sulfur-bearing gases and to take actions to reduce exposure of the electronics to these corrosive gases; to increase component robustness to sulfur-bearing gases either through a change in component construction or by applying gas-impervious barriers, and to develop a laboratory-accelerated corrosion technique to predict and compare the life of the components in harsh field conditions.
This paper discusses work in each of these three areas. Environmental conditions in numerous data centers were assessed and steps recommended to improve air quality. Component manufacturers have developed alternative materials or constructions to improve component robustness when exposed to high sulfur environments. Mitigation techniques to apply a barrier such as a conformal coating have been developed and evaluated for effectiveness, and laboratory evaluation techniques have been explored to assess and rank component robustness for use in high sulfur environments. (SMTAI, October 2010)
“Laser Direct Imaging Method of Creating Electric Connections on High Density PCBs”
Abstract: A laboratory system for laser direct imaging conductors and spaces on PCBs with a minimum width distance of 50/50 µm is reviewed. This research used photoresist with 50 µm resolution, but laser photoresists with better resolution (e.g., 25µm) make it possible to image fine-line conductors (25/25 µm). The LDI consists of a diode UV laser, optical scanner head, telescope and XY planar table. (XVII International Symposium on Gas Flow and Chemical Lasers & High Power Lasers, September 2008)
“Biobased Composite Resins Design for Electronic Materials”
Abstract: Biobased materials developed from triglycerides contain a large variety of structures, which makes it difficult to predict their properties. This study used a structure–property relation to design biobased materials, both theoretically and experimentally. A general equation to predict the crosslink density in terms of the level of chemical functionalities of the triglycerides was derived and used as a design rule for high-crosslinked polymer materials. The twinkling fractal theory and the Clausius–Mossotti equation were used to guide two approaches of synthesis to improve the properties of the biobased thermosets: The biobased resin acrylated epoxidized soybean oil (AESO) was either crosslinked with divinylbenzene (DVB) or chemically modified by phthalic anhydride. The DVB-crosslinked resins had a 14–24°C increase in their glass-transition temperatures (Tg′s), which was dependent on the crosslink densities. Tg increased linearly as the crosslink density increased. Phthalated acrylated epoxidized soybean oil (PAESO) had an 18–30% improvement in the modulus. The dielectric constants and loss tangents of both DVB-crosslinked AESO and PAESO were lower than conventional dielectrics used for printed circuit boards (PCBs). These results suggest the new biobased resins with lower carbon dioxide footprint are potential replacements for commercial petroleum-based dielectric materials for PCBs. (Journal of Applied Polymer Chemistry, July 13, 2010)
“IPC-4761 Via Plugging Guideline: Careful What You Ask For”
Author: Saturn Electronics; saturnelectronics.com/via-plugging.htm.
Abstract: IPC-4761 reflects IPC’s work toward standardizing the via plugging process. The document classifies seven different types of via plugs. Two are dedicated to the use of dry film solder mask, which now has only limited usage and applications, primarily older military applications. The remainder could be separated between via plugging and via-in-pad, as these two types of via plugs serve very different purposes. (Company white paper, October 2010)
This column provides abstracts from recent industry conferences and company white papers. With the amount of information increasing, our goal is to provide an added opportunity for readers to keep abreast of technology and business trends.