Review
New materials developed over the past year are bringing increased levels of thermal protection, electrical insulation, EMI shielding, and environmental protection to everything from individual components to entire pc boards. The materials play an important role in keeping end-products running smoothly and safely in the face of their higher operating frequencies and temperatures compared to the products's predecessors. Advances were also made in, among other things, adhesives used for holding components on boards prior to soldering and chemicals used in manufacturing boards. The following represents several examples of materials that debuted in 2003.
To keep EMI at bay in wireless systems and devices, W.L. Gore & Associates (gore.com) developed its Gore-Shield GS8000, a soft, highly conductive gasket material. Excellent cavity-to-cavity EMI shielding and excellent conductivity at low compressive forces are claims made for the conformable gasket material. The material has a nominal starting thickness of 1 mm that compresses to a thickness of 0.4 mm, and it can accommodate variations in gap heights of up to 2 mm.
Rolls of pressure-sensitive adhesive (PSA) have been developed by Adhesives Research (adhesivesresearch.com). They can replace liquid epoxy adhesives for encapsulating rigid and flexible OLEDs, LCDs, electronic papers, etc. The material is applied by first placing a layer of the pliable, instantly bonding PSA to the display and then exposing it to UV light. The result is said to be a high-strength bond between adhesive and display.
New thermally-conductive adhesive transfer tapes developed by 3M Electronic Adhesives and Specialties Dept. (3M.com) for securing heat-sinks to heat spreaders boast of increased mechanical strength, as well as improved surface wet-out for lower thermal impedance and higher adhesion. The tapes, the 88xx family, also are designed to withstand shock, while their high dielectric strength provides electrical isolation.
Gaps measuring up to 0.3 mm on pc boards can be filled with a new putty developed by Fujipoly of America (fujipoly.com). The thermally conductive, but electrically non-conductive Sarcon GR-Pm and XR silicone putties are available in sheet form and are said to be highly conformable.
Where electrical insulation with high thermal conductivity is required from a material, Master Bond (masterbond.com) has developed a two-part epoxy system that is said to do the job. The EP21AN material offers thermal conductivity in excess of 22 BTU-in/ft2-hr-°F, a dielectric strength of >400V/mil, and a volume resistivity greater than 1,013 ohm-cm. And it has been formulated with a non-critical 1/1 mix ratio, weight or volume, and cures readily at ambient temperatures.
And to help put the kibosh on EMI for enclosed electronics equipment, Chomerics (chomerics.com) has developed new fabric-over-foam gaskets that provide more than 90 dB of EMI attenuation from 20 MHz to 10 GHz and are UL 94V-0 flammability rated. And the Soft-Shield 7000 non-urethane soft foam core EMI gaskets are said to maintain physical and mechanical integrity in high operating temperatures for a service life exceeding 10 years.
—Joe DelGatto
Outlook
A Brew For Tomorrow's Electronics
Manufacturers are working with the composition of materials, as well as with their form (i.e., liquid and solid) and shape, in order to achieve the improved levels of performance required of the materials, as well as adhesives and chemicals scheduled for use in next-generation electronic products. New materials will withstand higher EMI/RFI levels and higher temperatures, have a longer use or flex life, and will be easier to use or install. New adhesives and encapsulants that cure or set faster and that have improved thermal and electrical insulative properties are also expected to soon find their way to market. And the EPA's ban on HCFC-141b should catalyze development of other alternatives to the banned dichlorofluoroethane solvents.
—JDG
