A Study on Over-Molded Copper-Based Flexible Electronic Circuits

Abstract

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.

Parameter Study on Force Curves of Assembled Electronic Components on Foils during Injection Overmolding Using Simulation

“…Figure 2a shows an assembled foil fabricated according to the design developed in [9] comprising 18 components oriented in three directions (0 • , 90 • , and 45 • ) with copper tracks used for the connection. A PET-based GTS-MP (Furukawa Electric Co., Ltd., Tokyo, Japan) foil was used with the layer structure and thicknesses given in Figure 2b.…”

“…Bakr et al [9] developed an assembled foil design comprising 18 zero-ohm resistors oriented at 0 • , 45 • , and 90 • for overmolding in a flat or corner-shaped mold. The design was also used in this study.…”

“…To that end, the foil design developed by Bakr et al [9] was utilized (illustrated in Figure 1a), and virtual parameter studies were made using AMI. Here, the influences of the mold thickness, melt temperature, and injection speed on the forces on 1206-sized components when overmolded with PC were investigated.…”

“…A Python script accessing the AMIs Synergy Application Programming Interface [15] was developed to calculate and visualize the tangential (F t ) and normal forces (F n ) on the components during filling (Figure 1b). The experimental results obtained in [9] were extended with additional injection molding tests, and the number of detached components after overmolding was counted (Figure 1c). In addition, the shear and peel strength values were assessed in mechanical tests (Figure 1d).…”

“…The findings were then combined to extract guidelines for injection molding of assembled foils (illustrated in Figure 1e). The foil design with soldered resistor components developed in [9] (a) was numerically simulated in parameter studies in which the normal (F n ) and the tangential forces (F t ) on the components during filling were investigated (b). Additional injection molding tests were conducted on the results in [9], and the detached components were counted after overmolding (c).…”