Experimental investigation of laser parameters in molded interconnect devices manufacturing via laser direct structuring

Abstract

In today's technology, products are becoming smaller but also more complex, with increased functions. As they contain many electronic components in a limited design area, they may require three-dimensional solutions. Conventional printed circuit boards (PCBs) cannot fulfill this expectation. Therefore, Molded Interconnect Devices are a technology that can bridge this gap in PCBs, by combining mechanical and electrical functions in a single component. MIDs are a technology that enables the integration of conductive circuits onto a polymer that can combine mechanical and electrical functions into a single part. There are several MID manufacturing methods such as two-shot molding, hot stamping, aerosol jet printing, film insert molding, and laser direct structuring. The predominant method for applying MID through laser assistance is laser direct structuring (LDS), which has a market share of over 50%. This selective metal plating technique is used for thermoplastic polymers. The LDS process involves three key steps: molding or printing the polymer components, laser structuring of the components, and metallization for conductivity activation. As laser has many parameters that affect the manufacturing of LDS, it is necessary to investigate the effects of these parameters on the polymer surface. The knowledge obtained from industry standards and scientific research does not fully cover the effects of LDS process parameters on the dimensional accuracy, quality, and reliability of MID-LDS products. Additionally, the relationship between the LDS process and its parameters is not fully understood. The effect of laser on the material can vary depending on the substrate and its constituents. The literature contains several studies that investigate the impacts of these factors. Some of them focus on LDS parameters, metallization quality, LDS prototyping, and the methods used, while others address the development of additional methods due to the higher cost of LDS polymers compared to market polymers. In this study, the laser-polymer relationship in two dimensions was examined using two different polymers and manufacturing methods, and the effect of all laser parameters on polymers was determined. The parameters to be selected to improve the metallization quality were determined. The study was conducted on polyphthalamide (PPA) and polycarbonate (PC) materials. PPA samples were produced by plastic injection, and PC samples were produced by fused filament fabrication (FFF). Then, the required shapes for characterization of the parts were determined, these shapes were structured using fiber laser, and then metallized with copper. Surface roughness before metallization, Fourier-transform infrared spectroscopy (FTIR), and the width of the single laser beam scan (track width) were measured for each parameter value. After metallization, metallization thickness and sheet resistance were measured for each parameter value. Images of the samples were taken using an optical microscope and 3D profilometer for characterization. Through the characterization studies conducted, it has been observed that as the laser power increases, the track width also increases, while the increase in laser scanning speed and frequency has a negative effect. The track width increases with the increase in laser fluence but reaches higher values at lower speeds. The increase in laser energy density (dose) also increases the track width, especially at lower frequencies. Generally, the metallization thickness of the materials increases with the increase in laser power, while a decrease is observed with the increase in frequency. The laser speed causes a decrease in metallization thickness at low power levels, while it causes an increase at high power levels. It has been observed that the increase in track width of single scan laser beam is related to the metallization thickness but has a negative effect for both polymers after a certain point. The relationship between width and the ratio of speed to frequency (v/f) has been determined. An increase in this ratio causes a decrease in the track width.