A great deal of attention has been paid in recent years to the integration of two and three-dimensional integrated electronic parts into plastics, both for their potential applications in modern human lives and for their outstanding properties, which include the ability to reduce product weight and space while increasing product reliability. The development of integrated electronic devices into plastics is advancing rapidly, owing to advancements in methodology and manufacturing techniques, which have significantly raised researcher interest in this topic. In-mold electronics (IME) is a term that describes an injection molding technology that integrates a printed foil with electrical components into a plastic part during the molding process. It is a revolutionary way to form two and three-dimensional products using electronic printed circuits. IME technology is comprised of three fundamental disciplines of study: electronics, materials science, and plastic manufacturing processes. Therefore, this review article aims to summarize the knowledge of these three primary fields to present an overview of in-mold technology. This article covers background history, a description of the In-mold process flow, and summarizes the recent real-life applications. Additionally, this article discusses some of the present technology challenges that must be overcome.

With the increasingly high demand for flexible microsystems, their embedding technologies have become more and more important. In this paper, we present the developments of over-molding technology to realize polyimide–copper (PI/Cu) electronic circuits embedded in plastics. The circuit consists of Cu interconnections on a PI substrate with assembled electronic components, which is inserted in a flat mold of a tensile specimen shape in an injection molding machine. This substrate is over-molded on one side with polyamide-6 (PA6). We have investigated two main properties of the circuits: the adhesion with the over-molded plastic and the effect of the over-molding on the electronics, measured after the molding process. Different Cu cladding foils were used in this study to optimize the adhesion between the foil and PA6. It was shown that the adhesion between the PA6 and the PI–Cu foil with acrylic as an adhesive layer is superior compared to the adhesive-less and the epoxy-based foils. Moreover, to check the electronics, 0 Ω resistors were assembled to evaluate the influence of over-molding on the electronics interconnections. The measurements of the acrylic foil were taken in three steps: before over-molding, after partial over-molding process without plastic injected, and finally after a complete over-molding cycle with plastic injection. The data presented showed that the fabrication process is suitable to integrate electronic components via over-molding and still have a functional electronic circuit on PI–Cu foil. Additionally, simulations were done to prove the same concept on a theoretical base, showing that the resistors should be functional after over-molding. Finally, we demonstrated our findings with a simple functional circuit where Near-field communication (NFC) etched antenna and a chip can wirelessly power assembled LEDs. Moreover, a long-term reliability test was performed and proved that such test structures could be used in long-term applications.

Over-molding has been proposed in recent years as an integrated functional flexible circuit board in a plastic part. This method uses the conventional process for film insert technology. Over-molding has attracted significant attention across many industries due to its potential to deliver different electrical functions in a variety of different part geometries, especially in automotive interiors and home appliances. While it has great application potential, manufacturing challenges continue throughout foil fabrication and injection molding. This raises challenges for designers and researchers responsible for maintaining the reliability of such electronic flexible circuits. Therefore, the purpose of this research paper is to improve some of the over-molding process parameters. On 0805 and 1206 over-molded zero-ohm resistors, electrical, mechanical, and failure characterization was performed. Those components were mounted in parallel, perpendicular, and 45° angled arrangements on two different polymer substrates, polyimide (PI) and polyethylene terephthalate (PET) using lead-free solder, low-melt solder, and conductive adhesive paste. Moreover, as an over-molding material, polycarbonate (PC) with medium viscosity was used. The effect of using different mold shapes (corner mold, 2 mm flat mold, and 3 mm flat mold) and injection molding process parameters (injection speeds and melt temperature) was studied.

The integration of assembled foils in injection-molded parts is a challenging step. Such assembled foils typically comprise a plastic foil on which a circuit board is printed and electronic components are mounted. Those components can detach during overmolding when high pressures and shear stresses prevail due to the injected viscous thermoplastic melt. Hence, the molding settings significantly impact such parts’ successful, damage-free manufacturing. In this paper, a virtual parameter study was performed using injection molding software in which 1206-sized components were overmolded in a plate mold using polycarbonate (PC). In addition, experimental injection molding tests of that design and shear and peel tests were made. The simulated forces increased with decreasing mold thickness and melt temperature and increasing injection speed. The calculated tangential forces in the initial stage of overmolding ranged from 1.3 N to 7.3 N, depending on the setting used. However, the experimental at room temperature-obtained shear forces at break were at least 22 N. Yet, detached components were present in most of the experimentally overmolded foils. Hence, the shear tests performed at room temperature can only provide limited information. In addition, there might be a peel-like load case during overmolding where the flexible foil might bend during overmolding.