Electromagnetic Interference EMI Shielding for Spray Coating And Dispensing

Bluetooth, Wi-Fi, 3G, LTE, wearables, and the internet-of-things (IoT) are all examples of technologies that have been introduced to mobile computing in recent years. These technologies and other types of wireless devices rely on different radio frequencies that can interfere with one another causing unwanted electromagnetic interference (EMI). Historically, “metal cans” or “lids” were used to create a localized Faraday cage to shield entire groups of sensitive components from interference. This is no longer feasible as manufacturers continue to design thinner, smaller devices that leave very little real-estate for such external structures. Thus, it has become increasingly important to develop new, reliable EMI shielding solutions built into the packages themselves.

In recent years, various methods have been used to apply very thin, silver-based coatings directly to the exteriors of the individual packages or components to create the exterior EMI shield. For complex System-in-Package (SiP) devices, there are sometimes interior structures built into these packages to create smaller Faraday cages around specific components prior to the final application of the exterior EMI shield coating. Currently, dispensing is used to create the interior SiP structures and sputter coating has been the dominant method for applying the exterior EMI shield coatings.  However, the capital cost, productivity, and thickness of the package sidewall coating from sputtering equipment have been stumbling blocks for widespread adoption of this technology to a wider array of applications, particularly for “odd-form” packages where selectivity of where the coating is applied is required. 

Recent improvements in fluid formulations for silver-based epoxies and inks have made it possible to apply EMI shield coatings by spraying as an alternative to sputtering. Nordson ASYMTEK has partnered with several fluid formulators to spray coat these materials for individual components on strips or wafers and “odd-form” SiP packages.  The addition of Nordson ASYMTEK’s industry-leading tilt applicator technology has also proven in multiple tests to increase sidewall coverage of these coatings while maintaining sub-15µm overall thickness.

Excellent Sidewall Coverage

Made with Loctite Abelstik EMI 8880S from Henkel	Made with AE5000-A5 from Tatsuta	System-in-Package (SiP) devices: Dispensed lines of conductive epoxy to create interior SiP structures

Benefits and capabilities include:

• Significantly lower capital equipment investment and minimal footprint
• Selective application of material around keep-out-zones and complex geometries - ideal for trench-fill applications
• Uniform coverage and thickness on side walls and top surfaces - typical ratio is > 0.7:1
• Shielding material thickness in the 3-6 µm range - with shielding performance comparable to sputtering
• Minimized or eliminated need for masking
• Minimized material waste

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