PCB Embedding Technology for the Miniaturization of complex electronic systems

The technology to embed electrical components into build-up layers of printed circuit boards has considerably evolved during the past 20 years. Although the basic concept has been first described already in 1969, only 30 years later serious developments took place some of which have now reached full industrial maturity. At present there is not only a single embedding technology, but different approaches are used to embed components. Bare die embedding is nowadays industrialized and used as a packaging technology for a variety of different products. On the other hand, the embedding of surface mount devices into the build-up of the printed circuit board allows a high degree of miniaturization and improved robustness of more complex electronic systems. Although the principle is rather simple, it is far from being an established technology in a typical printed circuit board house. The focus of this presentation will be on the design, the types of components and processes for the surface mount devices embedding. The results of a representative variety of projects, which have been conducted at Fraunhofer IZM and TU Berlin during the past five years will be presented. In these projects highly integrated multi-component packages were fabricated in flexible and yet robust manner. It ranges from energy autonomous sensor node to record environmental data, which are transmitted wireless into an IoT data cloud. This module is equipped with a helix antenna, holds replaceable battery, and for the environmental data acquisition is equipped with a sensor that has an ambient access. Another example is an encapsulated sensor and control node integrated into the surface of an autonomous under water vehicle. In this module a single embedded layers contains about twenty passive components in various package types and a variety of active components like u-controller, orientation sensors, and CAN-transceivers (power and data transmission). As a third example an approach for embedded modules with a hermetic sealing which are used in harsh environments will be presented. The sealing of such modules realized by the integration of a ceramic platelet with electrical feedthroughs on top surface of the module, while all other surfaces of the module are fully covered with plated Cu. The ceramic platelet is connected to the wiring structure of the embedded build-up. Since the packing density of the embedded surface mount devices is typically very high, a tight and void-free encapsulation of the components with epoxy resin is critical during embedding process. In order to determine the appropriate prepreg stack for the build-up, detailed tests with respect to resin filling and the adhesion of resin and the surface mount devices were carried out. In some cases, surface treatments (wet cleaning, plasma, laser roughening) were used to improve the interface integrity. After initial fabrication runs to adjust process parameters and conduct first functional tests, typical production yields are in the range of 95 percent and higher, depending on the complexity of the embedded system.