SMT007 Magazine

SMT007-Aug2019

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86 SMT007 MAGAZINE I AUGUST 2019 ing. Trenches are cut around the interior com- ponents and conductive paste is dispensed into the trenches to form smaller Faraday cages within the package. As trench designs become narrower, it's imperative to control both the volume and placement accuracy of the mate- rial 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 sput- tering equipment and harnesses the improve- ments 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. Introduction: Growth of EMI Shielding EMI shielding has become a topic of signif- icant interest in recent years. As 5G wireless technology is approaching mass-market accep- tance and the future capabilities 5G standards will enable for the internet of things (IoT) and mission-critical communications, there is a sig- nificantly increasing need to effectively shield electronics and components from EMI. With the upcoming 5G wireless standards, signal frequencies of 600 MHz to 6 GHz [1] and mmWave bands will become increasingly more common and powerful as the technol- ogy is adopted. Some of the proposed uses and implementations include window pan- els for office buildings or public transporta- tion to help deal with shorter range commu- nications. Other proposed implementations include home and office building repeaters to provide adequate coverage due to 5G frequen- cies having difficulties passing through walls and other solid objects [2] . All of this activity will lead to an increased prevalence of signals in the 5G frequency range and a higher risk of exposure to EMI in these frequency ranges and their harmonics. Fortunately, EMI can be shielded on com- ponent and system-in-package (SiP) devices through the application of thin coatings of con- ductive metal to the exteriors of such devices (Figure 1). Historically, EMI shielding has been applied through placing stamped metal cans around groups of components or by applying EMI shielding tapes to specific components. However, as packages and end devices con- tinue to become miniaturized, such shield- ing methods become prohibitive due to size constraints as well as the flexibility to handle diverse, non-orthogonal packaging concepts that are becoming more common in mobile and wearable electronics. Likewise, some leading-edge package designs are moving toward selective coating of only certain areas of a package for the EMI shielding rather than a complete shell over the full exterior of the package. In addition to the external coating for the EMI shielding, new SiP devices are further requiring additional inte- grated shielding to be built directly into the package to properly isolate individual compo- nents from each other in a single package. Sputtering: A Method of Applying EMI Shielding The predominant method for creating EMI shielding on molded component packages or molded SiP devices has been through sputter- ing multiple layers of metals over the surface. With sputtering, it has been possible to apply Figure 1: Example SiP unit with sputter coating and integrated EMI shielding structures.

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