Juha Niittynen

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.

Comparison of laser and intense pulsed light sintering (IPL) for inkjet-printed copper nanoparticle layers

In this contribution we discuss the sintering of an inkjet-printed copper nanoparticle ink based on electrical performance and microstructure analysis. Laser and intense pulsed light (IPL) sintering are employed in order to compare the different techniques and their feasibility for electronics manufacturing. A conductivity of more than 20% of that of bulk copper material has been obtained with both sintering methods. Laser and IPL sintering techniques are considered to be complementary techniques and are highly suitable in different application fields.

Capability of inkjet technology in electronics manufacturing

The past decade has seen a growing interest in additive manufacturing and printable electronics. The main markets are expected to be among low-cost mass production of radiofrequency identification (RFID) tags, antennas, keyboards, displays, sensors, and smart packages, but also high-performance products. This paper focuses on process improvement and capability analysis of inkjet technology in electronics manufacturing using six sigma methodology. It provides not only tools and roadmaps for technical development and process improvement, but also a systematic program management tools for technology development also in industrial-academic collaboration. This paper focuses on the printing accuracy and quality issues in inkjet printing technology. The scaling of the image and the alignment capability of the process is analyzed by printing several dot matrixes on polyimide substrates and measuring the places of the inkjetted drops from substrates and comparing those onto the locations of the dots in printfile. This data is used to generate a mathematical model, which was used to correct the shifting and scaling of the image yielding to improved process capability.

Inkjet-Printed Graphene/PEDOT:PSS Temperature Sensors on a Skin-Conformable Polyurethane Substrate

Epidermal electronic systems (EESs) are skin-like electronic systems, which can be used to measure several physiological parameters from the skin. This paper presents materials and a simple, straightforward fabrication process for skin-conformable inkjet-printed temperature sensors. Epidermal temperature sensors are already presented in some studies, but they are mainly fabricated using traditional photolithography processes. These traditional fabrication routes have several processing steps and they create a substantial amount of material waste. Hence utilizing printing processes, the EES may become attractive for disposable systems by decreasing the manufacturing costs and reducing the wasted materials. In this study, the sensors are fabricated with inkjet-printed graphene/PEDOT:PSS ink and the printing is done on top of a skin-conformable polyurethane plaster (adhesive bandage). Sensor characterization was conducted both in inert and ambient atmosphere and the graphene/PEDOT:PSS temperature sensors (thermistors) were able reach higher than 0.06% per degree Celsius sensitivity in an optimal environment exhibiting negative temperature dependence.

Reliability of ICA attachment of SMDs on inkjet-printed substrates

Abstract Printable electronics has been attracting considerable attention in recent years as a technology for flexible production of low-cost electrical devices on flexible substrates. Due to the additive nature of the production process, printable electronics offers to be a simple and effective method to manufacture electronics. Because the complexity and functionality of all-printed electrical devices is highly limited mainly by the low performance of semiconductive inks, external components are necessary for complex functionalities required in today’s electrical devices. Such components must be attached to printed structures with connections having adequate electrical and mechanical performance and good long-term reliability. This study evaluated the reliability of isotropically conductive adhesive connections on inkjet-printed substrates and viewed ICA component connections as viable options for attaching SMD components on inkjet-printed circuits.

Functional fluid jetting performance optimization

Abstract The manufacturing method utilizing digital printing technology offers alternatives to create electronic structures to be used even in microelectronic applications. Material deposition based on digital inkjet technology offers advantages over both traditional mask-etch technologies and other printing methods. Inkjet technology works in an additive manner, reducing material consumption and the amount of created waste. Additionally, the digital nature of the process allows flexible production, e.g., rapid design changes, quick prototyping, and small, customized series. This research paper introduces ink jetting performance optimization utilized in a concept where discrete components and bare silicon chips were integrated in a single module with ink jetted interconnections. Jetting optimization of fluids enhances the droplet placement and volume accuracy that is a critical issue when forming interconnections for dense IC circuits. The overall drop placement error in jet printing is a combination of several error sources such as mechanical, dynamical and material related issues. However, the largest error portion is induced by a single printhead. The printhead related errors can be detected by observing the flight behavior after firing from the printhead nozzle. This paper focuses on optimizing the performance of ejected droplets during flight, i.e., drop formation sequence and minimum flight time variance. The average drop velocities of drops fired from separate printhead nozzles can be used to evaluate the difference in placement on substrate, which in worse case may lead to electrical wiring failures. The performance optimization was done by analyzing the initial state, modeling the drop velocity during flight, optimizing the process parameters to satisfy the model, and accepting the model after verification. Two inks, conductive and dielectric, were evaluated and improvement in placement accuracy was achieved through enhanced uniformity in drop average velocities, a dimensionless number, coefficient of variation was enhanced from 0.051 to 0.040,with conductive ink and from 0.111 to 0.049 with dielectric ink, thus decreasing the velocity related drop placement error.

Inkjet printing in manufacturing of stretchable interconnects

Stretchable circuits have the potential to enable integrating electronics in everyday objects, but also skin-like, imperceptible electronic applications. However, manufacturing stretchable electronics requires developing novel manufacturing methods and using novel materials at least as substrate. Since the elastic materials for stretchable electronics are relatively soft, using traditional manufacturing methods becomes more problematic, whereas contactless material deposition by inkjet-printing is unaffected by such material properties. This study concentrates on feasibility analysis of using inkjet printing in manufacturing of stretchable electronics. First, printing related challenges are evaluated by manufacturing test structures with inkjet-printer using silver nanoparticle ink on elastic thermoplastic polyurethane substrate and sintering structures in convection oven. Adhesion between ink and substrate, but also sheet resistance, is evaluated. A minimum sheet resistance approx. of 26 mΩ/□ was obtained, and peak strains of inkjet-printed conductors are found to be between 1.0 % and 1.5 %, but conductivity is observed to be almost fully reversible when strain is released.

Characterization of Laser Sintering of Copper Nanoparticle Ink by FEM and Experimental Testing

In the last few years, inkjet printing of functional materials for electronics applications has been studied intensively, and significant progress has been made in developing ink materials and deposition techniques. Though sintering, the process of turning liquid nanometallic ink into its final and functional form, has also been studied, the traditional convection-oven-based heat treatment yet remains the common sintering method. High process temperature and long process time both limit the usability of inkjet printing as they restrict the selection of substrate materials and consume most of the overall fabrication time. Several sintering methods have been studied as alternatives for thermal sintering, but so far none of them have been widely adopted. We studied laser sintering of copper nanoparticle ink to gain an understanding of the process and the main variables affecting it. Laser sintering was also studied by thermal modeling, and the results are used to explain the behavior of process. Process parameters comprised substrate material and thickness, application of an insulator layer on top of the silicon wafer, laser scanning speed and optical power, and thickness of the printed structure. Comparison of modeling and test data shows that though the temperature of the printed structure can be used to plan the sintering process, it alone cannot explain the test-based conductivity results.

Characterization of ICA attachment of SMD on inkjet-printed substrates

As electronics industry is moving more and more towards flexible substrates and products more knowledge is needed on new additive production technologies enabling simplified and cost-efficient fabrication of these flexible products. Printable electronics in general is expected to reshape the manufacturing of low-cost mass production of low-end products such as RFID-tags, antennas, keyboards, wireless sensors and displays. This paper focuses on analyzing component attachments of traditional SMD components on inkjet-printed substrates with electrically conductive adhesive and evaluating the variables affecting the component attachment performance. Component attachments electrical performance was evaluated by varying several fabrication parameters and analyzing the changes in the component attachment resistance. The final conclusion reached in this paper is that adequate electrical performance can be achieved with both of the tested materials and both of the tested component sizes as long as proper production parameters were used.

Capability Assessment of Inkjet Printing for Reliable RFID Applications

In this paper, inkjet-printed silver traces and interconnections produced with the print-on-slope technique were used in an radio-frequency identification (RFID) structure operating in the ultra-high-frequency range. Underfill material was used to attach silicon RFID chips onto flexible, 125-