Electronics Assembly Knowledge, Vision & Wisdom
Dispensing EMI Shielding Materials: An Alternative to Sputtering
Dispensing EMI Shielding Materials: An Alternative to Sputtering
The development of a spray coating process to apply EMI shielding materials to the exterior surfaces of components on strips and larger SiP packages.
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Authored By:
Garrett Wong
Nordson ASYMTEK
Carlsbad, CA

Jinu Choi
Henkel Electronic Materials LLC
Irvine, CA

Summary
Shielding electronic systems against electromagnetic interference (EMI) has become a hot topic. Technological advancements toward 5G standards, wireless charging of mobile electronics, in-package antenna integration, and system-in-package (SiP) adoption are driving the need to apply more effective EMI shielding and isolation to component packages and larger modules. For conformal shielding, EMI shielding materials for exterior package surfaces have mostly been applied with a physical vapor deposition (PVD) process of sputtering, leveraging front-end packaging technologies to back-end packaging applications. However, sputtering technology challenges in scalability and cost along with advancements in dispensable materials are driving considerations for alternative dispensing techniques for EMI shielding.

The authors will discuss development of a spray coating process to apply EMI shielding materials to the exterior surfaces of individual components on strips and larger SiP packages. Using newly developed and enhanced materials and equipment for this industry, a process was demonstrated that provided uniform coating on packages in the sub-10nm thickness range with consistent coating thicknesses around package corners and package sidewalls, producing a top surface-to-sidewall thickness ratio of 1:1. Further investigation showed decreased production costs for applying EMI shielding to component packages by increasing spray-coating productivity and by selectively applying the coating to specific areas of packages. Additionally, low capital-equipment expense and shorter lead times for spray coating equipment improved the ability to scale up production capacity compared to sputtering equipment.

In mobile electronics packaging, several SiP-module manufacturers are challenged to isolate components within the SiP from each other and from their exterior for EMI shielding. Trenches are cut around the interior components and conductive paste is dispensed into the trenches to form smaller Faraday cages within the package. As trench designs become narrower, it becomes imperative to control both the volume and placement accuracy of the material filling the trenches. The latest, advanced jetting products provide control of the volume while the narrow, in-air stream width delivers accurate trench-fill. In a final step, the tops of these paste-filled trenches are connected by applying exterior EMI shield coating. Spraying overcomes challenges faced when using sputtering equipment and harnesses the improvements in both the EMI shielding materials and the equipment for depositing it, so that SiP packages can be manufactured using efficient back-end packaging techniques.

Conclusions
Sprayed EMI shielding has become a viable and attractive alternative to sputter coating. Advancements in material formulations as well as the methods of applying these materials allow for comparable performance and thickness as sputter coating. In addition, spray coating offers far more flexibility for different types of substrates that can be coated as well as allowing for greater selectivity for placement of the shielding material. Through optimizing the spray coating process and patterning, spray can achieve comparable or better cost per unit when compared to sputter coating. Spray coating further offers superior scalability for growing production capacity with low capital investment. Lastly, further innovation in the dispensing of shielding materials is leading the way for highly precise shielded areas and conductive trace creation through jet dispensing.

Initially Published in the SMTA Proceedings

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