Risto Rönkkä

Inkjet printed System-in-Package design and manufacturing

Additive manufacturing technology using inkjet offers several improvements to electronics manufacturing compared to current non-additive masking technologies. Manufacturing processes can be made more efficient, straightforward and flexible compared to subtractive masking processes, several time-consuming and expensive steps can be omitted. Due to the additive process, material loss is minimal, because material is never removed as with etching processes. The amounts of used material and waste are smaller, which is advantageous in both productivity and environmental means. Furthermore, the additive inkjet manufacturing process is flexible allowing fast prototyping, easy design changes and personalization of products. Additive inkjet processing offers new possibilities to electronics integration, by enabling direct writing on various surfaces, and component interconnection without a specific substrate. The design and manufacturing of inkjet printed modules differs notably from the traditional way to manufacture electronics. In this study a multilayer inkjet interconnection process to integrate functional systems was demonstrated, and the issues regarding the design and manufacturing were considered.

Evaluation of Inkjet Technology for Electronic Packaging and System Integration

The main trend of the electronic packaging industry has been on increasing the packaging density and increasing the functionality, but now also the interest on flexible manufacturing has grown. In this paper, we discuss the utilization of the inkjet technology for the electronic packaging and system integration. Inkjet technology provides fully-additive non-contacting deposition method that is suitable for flexible production. In this paper, we demonstrate the capability of the inkjet technology for the printable electronics through a highly-integrated RF SiP application, which is manufactured partly by inkjet printing. The SiP contains discrete components and an ASIC with a minimum pitch of 136 mum and the size of pads is 65 mum. The width of lines/spaces is designed with a rule of 75 mum/75 mum, but also narrower lines can be printed. The width of lines depends on the properties of surface, ink, and drop volume. The properties of the surface can be manipulated with proper surface treatment. In this paper, almost 20% decrease in a diameter of drop is reported when the surface treatment is used.

Molded Substrates for Inkjet Printed Modules

Ever increasing demand for high-performance, miniaturized, low-cost, and more environmentally conscious targets set high requirements for electronics packaging and manufacturing. Digital drop-on-demand printing of materials is an interesting approach for electronics manufacturing allowing several advantages compared to subtractive methods to manufacture electronics. Additive processing by means of digital printing offers new possibilities to electronics integration, by enabling direct writing on even nonplanar surfaces, and interconnection without specific substrate for components. A module utilizing additive deposition of conductive metallic nanoparticle inks and dielectrics using inkjet printing was designed. Conventional laminate-based or ceramic interconnection substrate, i.e., printed wiring boards was not used as often in electronics modules. Chip-first modules made using a particular encapsulation method were constructed of molded substrate with embedded components and without any wiring. The molding process and the characteristics of molding material were examined using real product samples, material characterization methods, and modeling. The interconnection process using inkjettable metallic nanoparticle and dielectric inks set strict requirements for molding materials; the surface characteristics should be suitable for the inkjetting of conductive and dielectric materials. Additionally, material must withstand the harsh process conditions that include several heating cycles in relatively high temperatures for organic materials. The surface characteristics of the molding material should be adjusted to ensure good control of inkjetted fluids on a surface enabling high-yield inkjetting of fine-pitch patterns. Furthermore, the mechanical properties of molding material and molding material surface have an effect on the interconnection process yield and reliability of the inkjetted lines and interconnections. The characteristics of molded modules working as substrate for additively processed patterns is a crucial role in the manufacturing of a highly integrated printed module.

Wide-band Electrical Characterization of printable nano-particle copper conductors

Copper nano-particle ink suitable for printing is a promising substitute for silver- or gold-based inks for consumer electronics applications. However, oxidization must be controlled during the manufacturing and sintering processes. In this work conductors created from a copper nano-particle ink are characterized. In order to mitigate oxidation effects, the ink was formulated in inert atmosphere. Sintering is achieved by exposure to a short light pulse, which, due to the short time scales (ms) and added benefit of photoreduction, can be done in air. Wide-band electrical characterization results up to 20 GHz for copper nano-particle conductors are presented. Structural analysis using scanning-electron microscope (SEM) complements the characterization. Based on high-frequency measurements, wide-band material parameter extraction techniques, and modeling-based analysis of measurement results, the conductivity was found to be of the order of 0.7·107 S/m. All loss mechanisms including impurities deposited within the metal, porosity, surface roughness, and variation in structure geometry are attributed to the conductivity. The electrical performance was found almost comparable to that of silver-based inks. Also the average measured direct-current (dc) conductivity 1.37·107 S/m is similar to that of typical nano-metal conductors.

Object detection for dynamic adaptation of interconnections in inkjet printed electronics

A computer vision system for automatic detection of interconnection points in inkjet printed interconnected electronics modules during the manufacturing process is described. The location data can be used for calculating the amount of misalignments and the required corrections. The method uses a local filtering operation for finding candidate regions, from which the false matches are filtered out by classification using an artificial neural network. Experiments show that atypical false match rate is as low as 0.18%. The location data is later used for correcting the wiring that is inkjetted on top of the layout to connect the connectors correctly.

Point pattern matching for 2-D point sets with regular structure

Point pattern matching (PPM) is a widely studied problem in algorithm research and has numerous applications, e.g., in computer vision. In this paper we focus on a class of brute force PPM algorithms suitable for situations where the state-of-the-art methods do not perform optimally, e.g., due to point sets with regular structure. We discuss of an existing algorithm, which is optimal in the sense of brute force testing of different point pairings. We propose a parameter choosing scheme that minimizes the memory consumption of the algorithm. We also present a modified version of the algorithm to overcome issues related to its implementation and accuracy. Due to its brute force nature, the algorithm is guaranteed to return the best possible result.

Dynamic adaptation of interconnections in inkjet printed electronics

Printed electronics is a new technology for manufacturing miniature electronics modules. The basic principle is that the integrated circuits are molded into a background material such that the connectors are left visible on top. After the background substrate has hardened, the wiring is printed on top of the module using conductive ink. The technology allows flexible manufacturing of significantly smaller modules using wide range of new materials. Typically the components and their connection points are slightly displaced when the background material hardens. This paper proposes a method for adjusting the wiring to match the displaced components. Experiments show that correction reduces the number of false or missing connections significantly thus providing necessary yield improvement for the manufacturing process.