Application of package-level high-performance EMI shield material with a novel nozzleless spray coating technology

摘要

The need for EMI (electromagnetic interference) shielding at the package-level is increasing as highly sensitive circuit assembly components become more tightly packed in items like smart phones and Internet of Things (IoT) devices. Traditionally, EMI shield coatings have been applied to individual components by sputtering or plating. The ideal properties for this EMI shield is a thin metallic layer less than 10 μm in thickness that provides the required shield effectiveness, adheres to the component surface, and ensures that the laser markings on the component surface are visible. New, high-performance EMI shield coatings have been developed that meet these requirements and can be applied using a direct spray process.These new sprayable coatings will provide highly effective EMI shield performance if they are applied uniformly and conformally to the package surfaces at the required thickness of generally less than 10 μm. A novel spray application method, T-CAT (ultra-Thin Coating Application Technology), can be used to apply a uniform, ultra-thin layer, while reducing the process cost by up to 60%.[1] This new spray technology consists of a novel nozzle-less ultrasonic spray head coupled with a precision motion and positioning platform, precision liquid delivery system, and substrate transport system.A new high-performance EMI shield coating has been developed specifically for application by the spray coating process. This new material consists of a combination of silver nano particles and silver coated copper micron-size particles suspended in an epoxy resin binder. The epoxy resin binder has excellent adhesion to the surface of the individual components without the need for special surface treatment. The material is also capable of providing the same EMI shield effectiveness as a coating layer applied by sputtering as long as the coating is applied in a uniform and conformal layer to the top and side surfaces of the components.There are significant challenges connected with the application of EMI shield coatings to individual components in a production process. The coating application system must be able to keep the coating material properly mixed as well as apply it at the required thickness uniformly and repeatably over time.This paper demonstrates the viability of T-CAT in conjunction with a unique metal and resin formulation technology to enable a thin EMI shield layer with superior performance compared with existing sputtering and plating methods. Performance characteristics of the coating material and the coating application process will be examined.