This post authored by John Coonrod originally appeared on the RogBlog hosted by Microwave Journal.

Outgassing is a concern for any electronic equipment intended for use in high-vacuum environments. It refers to the release of gas trapped within a solid, such as a high-frequency circuit-board material. The effects of outgassing can impact a wide range of application areas in electronics, from satellites and space-based equipment to medical systems and equipment. In space-based equipment, released gas can condense on such materials as camera lenses, rendering them inoperative. Hospitals and medical facilities must eliminate materials that can suffer outgassing to maintain a sterile environment.

In the vacuum of deep space, outgassing (also known as “offgassing”) has contributed to the degraded performance of charge-coupled-device (CCD) sensors in space probes, prompting NASA to develop exacting procedures for evaluating materials prior to their use in space. NASA test procedure SP-R-0022A, for example, is used to test composite materials such as circuit-board laminates. ASTM International, a well-respected materials standards organization, has developed procedures, such as ASTM E595-07, to gauge key material parameters such as total mass loss (TML) and collected volatile condensable materials (CVCM) for the purpose of evaluating the changes in mass of different materials in a vacuum environment as would occur due to outgassing. GSFC and other NASA centers have long endorsed a policy of selecting the lowest outgassing materials available for spacecraft and space applications, testing in accordance with ASTM E595-07 which outlines a test method for evaluating the changes of mass in a test specimen under vacuum at a temperature of +125°C for 24 hours. NASA’s target number for acceptable TML is less than 1% and for CVCM is less than 0.1%.

The term “vacuum” as used in these tests is somewhat subjective. Per the standards, testing does not have to proceed at the vacuum levels of deep space, which are typically 10-12 Pa (10-14 Torr). In fact, the ASTM standard specifies only that the vacuum for performing TML and CVCM testing should be less than 7 x 10-3 Pa (5 x 10-5 Torr) for 24 hours at +125°C. The high temperature was selected to be at least +30°C above any typical operating temperature, in order to create accelerated-lifetime conditions.

After the 24-hour vacuum/high-temperature period, the standard notes that a specimen should be weighed at +23°C and 50% relative humidity to minimize the effects of water vapor on the measurement accuracy. Specimens are placed in a glass vial during the 24-hour heating period and must be weighed within 2 minutes after opening the vial to minimize the loss of absorption of water vapor when exposed to an uncontrolled humidity environment. An additional test, for water vapor recovered (WVR), can be performed after measurements of TML and CVCM. Tests can be performed on materials in their “as received” condition or after they have undergone curing.

Low levels of outgassing are usually associated with high-quality materials as well as well-controlled manufacturing processes. Various circuit-board materials from Rogers Corporation, for example, have been tested according to NASA test procedure SP-R-0022A for TML, CVCM, and WVR and found well suited for spacecraft applications. The materials include RT/duroid® composites based on polytetrafluoroethylene (PTFE) with inorganic filler materials, such as glass and ceramic fillers, and TMM® series temperature-stable hydrocarbon composites. The specimens were etched free of copper foil prior to testing, and heated at +125°C for 24 hours in a vacuum. Sample sizes were 100 to 300 mg placed in copper enclosures. The exit port of each enclosure was heated to +125°C with a chrome-plated collector maintained at +25°C spaced 12.7 mm from the exit port.

For these measurements, in all cases, the RT/duroid and TMM circuit-board materials posted impressive numbers for TML and CVCM compared to NASA’s maximum recommended values of 1.0% and 0.1%, respectively. For RT/duroid 5880 laminate materials, with PTFE dielectric, glass-microfiber filler, and low relative dielectric constant of 2.20, the TML and CVCM values were 0.03% and 0.00%, respectively. RT/duroid 6010 laminates, with a considerably higher dielectric constant of 10.2 as a result of adding glass microfiber and ceramic fillers to the PTFE dielectric, posted the same TML and CVCM values of 0.03% and 0.00%, respectively. RT/duroid 6002 laminate, with PTFE dielectric but a lower concentration of glass microfiber and ceramic filler resulting in a relative dielectric constant of 2.94, had TML and CVCM values of 0.02% and 0.01%, respectively.

For all of the RT/duroid and TMM materials tested, the TML values were well below 0.1% and the CVCM values at or near zero. The TMM laminates, which are highly crosslinked thermoset hydrocarbon dielectric materials, feature characteristically low TML and CVCM values. The TMM 3 laminates, with low relative dielectric constant of 3.27, achieved 0.04% TML and 0.00% CVCM. The TMM 10 laminates, with higher 9.20 dielectric constant, had slightly higher 0.06% TML while maintaining a 0.00% CVCM. Of the materials tested, the highest value of TML was for 3001 bonding film, a thermoplastic chlorofluorocopolymer with relative dielectric constant of 2.28 designed for bonding layers of PTFE-based circuit boards to form multilayer circuits. Still, its TML tested at only 0.13%, or well below NASA’s high limit of 1.0%, while its CVCM was only 0.01% or one-tenth that of the NASA recommended maximum value. (A complete rundown of the TML and CVCM values, along with WVR results, for the full lines of RT/duroid, TMM, ULTRALAM® laminates, and RO4003C™ circuit materials can be found in application note 2.9.1 from Rogers Corporation.)

Outgassing is not a material characteristic of concern to all circuit designers. But for those involved in electronics for satellites and other spacecraft, it is not something to be taken lightly. For circuit-board materials, the most prudent choice is the material with the lowest TML, CVCM, and WVR values available.

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Ken Kozicki from BISCO® Silicones recently authored an article for Railway Technology International about the design considerations that go into creating comfortable railcar seat cushions.  How important are first impressions for seating when a passenger steps into the railcar? Obviously, if it’s the Orient Express or another high end rail system, the feeling of luxury must be present.  But even for standard commuter railcars, seat cushions do make an impression.  Ken notes:

“…the most prevalent and obvious fixture within any interior, rendering, brochure, or maze of booth exhibits is the seat or array of seats. The type of seat will vary from the most outrageously luxurious – slated for a VIP very high speed Oriental Express pod – to the simplest and ergonomic that allows for rows and rows of passengers in a configuration that would be suitable for the rush hour of London, Shanghai or San Paulo….What has taken teams of engineers and designers months, if not years, to conceptualise, design, prototype, test (and re-test), will be given a judgment in less than ten seconds. So from that, one could wonder just how important is the first impression of a railcar seat?”

In this article, Ken look at the design considerations that need to be factored in when choosing the right seat cushion for a railcar:  Ken highlights the following:

  • the number of seating positions per coach (as required by the transit authority)
  • materials’ standards for flame, smoke, and toxicity (FST)
  • type of train service (urban metro system versus suburban commuter), and
  • severity of usage.

Ken also discusses the new concerns of sustainability and end-of-life:

“This is being driven by questions related to the disposal of the seat: “What will become of a worn, damaged, or obsolete seat?” Will it be thrown into a land-fill? What are the decomposition ramifications of that seat in a land-fill?”

All good questions.  But what about the seat itself and the cushioning material? Are some better than others?  Ken suggests yes, there are differences between one cushioning material from another:

“…cushions have differences in profile, appearance and texture, it is not obvious that there are different types of materials used to fabricate the cushions. These materials are usually in the form of foam, such as a filled-polyurethane, silicone, and melamine. The foam which is specified for the fabrication of the cushion will have been tested to the various FST standards, ensuring the safety of the passengers. In addition, some of the foam materials may have been cycletested to simulate wear and usage, which brings us back to our earlier statement of first impressions. Often, seat cushion foam materials are tested and certified to a characteristic known as indention force deflection (IFD).”

2-D & 3-D view of thin profile seat with loaded urethane

“A typical IFD test method will be comprised of a disk of a determined diameter that compresses the foam material a certain percentage of its thickness, and then measures the amount of “pushback” force the foam has. This is its indention force deflection, and is directly related to the comfort of the seat. In production, the foam will be certified according to this test. If it is within the IFD tolerance range, the foam will be qualified for seat cushion fabrication.”

Of course, Ken highlights that the bigger test happens after many months of wear on the cushion, after the “pushback” force has been worn down.  Different materials, like silicone foam, do a better job over the life of a cushion than other materials.

To read Ken’s final recommendations, either view the article here (in a magazine viewer) or download a full PDF of the printed article.

Related Links

BISCO Material Selection Guide

Floating Floor Design Tool

Silicone Material Selection Guide

On December 2, 2010, in BISCO Silicones, by sharilee

Selecting materials for gasketing and sealing means taking a close look at critical specs, such as temperature, flammability, toxicity, vibration isolation, and sound damping. To make the process easier, the Silicone Material Selection Guide walks you through the options, helping you pick the right materials for your application.

Fire, heat, tearing, elasticity, EMI/RFI shielding – there are a lot of issues to consider. Hybrid Electric Vehicles (HEV), for example, need materials for environmental seals, vibration pads, antenna seals, battery cell cushions, and more. The goal is a design that performs at its peak over an extended period of time. This requires materials that keep harsh environmental elements out and provide low compression set and long term stress relaxation.

For mass transit applications, foam cushioning is one of the largest single combustible components. As a result, strict regulations are in place to ensure cushions meet flame spread, smoke density, and hazardous emissions standards.

Whether your design calls for resistance to temperature extremes, low flammability, or high tear strength, start your search with the Silicon Material Selection Guide. The Guide features BISCO Silicones — cellular, solid, and specialty materials that can be fabricated into gaskets, heat shields, fire stops, seals, cushions, and insulation for a wide variety of applications.

In the News

Rogers Corporation’s New PORON® ShockSeal™ Foam takes the Pain out of Dropped Handheld Devices

PORON® World’s Greatest Foam

Rogers Corp Reports 2010 Third Quarter Results

On November 24, 2010, in Corporate, by sharilee

The latest financials are in for Q3 2010. Record results were seen in the divisions based on high demand  for printed circuit materials for wireless infrastructure, high performance foams in mobile devices, power distribution for mass transit and wind systems, and more.

Read the Rogers Corp. 2010 Third Quarter Report

Download the Rogers Corp. Third Quarter Conference Call

Don’t miss this great interview from DesignCon with our very own John Coonrod.  In this brief video, John talks about the latest advances with high frequency laminates…

Some of the reasons why high frequency laminates work so well are:

  • Have higher dielectric constant, which makes for smaller wavelengths
  • Can make microwave features smaller, or even miniaturize the size, giving a faster signal over a smaller area
  • Build in multi-layers

Listen in on what else John is saying about high frequency laminates…

If you are having problems viewing this video, click here.