Kari Rönkä

Interfacial reactions between Sn‐based solders and AgPt thick film metallizations on LTCC

Purpose – This paper aims to investigate the metallurgical reactions between two commercial AgPt thick films used as a solder land on a low temperature co‐fired ceramic (LTCC) module and solder materials (SnAgCu, SnInAgCu, and SnPbAg) in typical reflow conditions and to clarify the effect of excessive intermetallic compound (IMC) formation on the reliability of LTCC/printed wiring boards (PWB) assemblies.Design/methodology/approach – Metallurgical reactions between liquid solders and AgPt metallizations of LTCC modules were investigated by increasing the number of reflow cycles with different peak temperatures. The microstructures of AgPt metallization/solder interfaces were analyzed using SEM/EDS investigation. In addition, a test LTCC module/PWB assembly with an excess IMC layer within the joints was fabricated and exposed to a temperature cycling test in a −40 to 125°C temperature range. The characteristic lifetime of the test assembly was determined using DC resistance measurements. The failure mechan...

Hot Laminated Multilayer Polymer Illumination Structure Based on Embedded LED Chips

The dominant technology for manufacturing backlight illumination structure (BLIS) is typically based on the use of individually packaged surface mount device light emitting diodes (LEDs) and special light guide plate (LGP) and diffuser films. The prevailing BLIS package, however, contains several separate diffuser films, which results in a thick and costly structure. In addition, the light coupling from LED to the LGP is sensitive to alignment errors causing nonuniform and inefficient illumination. We have demonstrated a novel hot laminated packaging structure for backlighting solutions, which is based on inorganic LED chips and multilayer polymer structure. The main advantages of the implemented system compared to the traditional light guiding system are easy optical coupling with high efficiency in an integrated and thin package. The performed designs of 3×3, 5×5, and 5×7 LED chip matrices, verified by test structure implementations and characterizations, showed that the final thickness of the BLIS depends on the required uniformity of illumination, allowed LED device pitch and efficiency of the diffuser. The final BLIS demonstrator size was 50×75 mm2 consisting of six 25×25 mm2 modules. Each module consisting 5×5 LED devices resulting in total number of 150 LED devices with 5-mm pitch. The measured key characteristics of the demonstrator were as follows: average brightness 11.600 cd/m2 (ILED = 2 mA), luminous efficiency 22 lm/W, color temperature 5550 K, commission on illumination values (x = 0.331, y = 0.411), Color Rendering Index ≥ 70, and total power conversion efficiency of 6.3%. The combination of the developed Matlab performance simulation tool and cost-of-ownership cost evaluation tool enables us to estimate the manufacturing cost of a specific BLIS element against the required performance, assisting decision-making in different applications and specific individual customer cases.

Demonstrators for autonomous automotive and signage applications by bonding flexible solar cells, batteries and LED elements on large area polycarbonate backplanes

Autonomous systems are pursued in automotive and signage applications due to easy installation and achieved energy savings. In addition, reduction of cabling decreases system weight, which is especially pursued in automotive applications due to the decreased fuel consumption. Naturally, autonomous systems require some kind of energy harvesting and energy storing systems. In order to achieve required autonomy operation time of over 15 hours, four flexible Li-Ion batteries of 1200 mAh total capacity in automotive demonstrator and four flexible Li-Ion batteries of 3200 mAh total capacity in signage demonstrator were required. The dimensions of batteries were 295 mm × 29 mm and 295 mm × 119 mm. The energy harvesting for autonomous operation was based on flexible commercially available amorphous silicon solar cells, types MP3-25 and MPT6-150 manufactured by Power Film. The dimensions of the solar cells were 114 mm × 29 mm and 114 mm × 150 mm. The pursued autonomy time of demonstrators resulted to a large surface area requirement for the backplane substrates. The dimensions of the assembled automotive demonstrator were 2400 mm × 35 mm × 0.95 mm and the dimensions of the assembled signage demonstrator were 2550 mm × 144 mm × 0.95 mm. The large size of both the components and the substrates produced challenges for assembly and bonding processes. As the bonding method hot bar bonding or oven curing were used, the experimental procedure being compatible with the guidelines of the material suppliers. Daisy chain test structures were used to study the interconnections between the foils. Thermal humidity testing at 85°C/85%RH and thermal cycling between −40….+85°C were used as the environmental tests for the test structures processed before final selection of the bonding materials and processes for demonstrators manufacturing. Both manufactured demonstrators were operational after assembly and bonding processes. The energy produced by the solar cells was guided to the Li-Ion batteries by a specific charge regulator. Batteries were able to supply power to the automotive and signage LED elements so that the systems autonomous operation was successfully demonstrated.

Printed hybrid systems

This paper presents research activities carried out at VTT Technical Research Centre of Finland in the field of hybrid integration of optics, electronics and mechanics. Main focus area in our research is the manufacturing of electronic modules and product structures with printed electronics, film-over-molding and polymer sheet lamination technologies and the goal is in the next generation of smart systems utilizing monolithic polymer packages. The combination of manufacturing technologies such as roll-to-roll -printing, injection molding and traditional component assembly is called Printed Hybrid Systems (PHS). Several demonstrator structures have been made, which show the potential of polymer packaging technology. One demonstrator example is a laminated structure with embedded LED chips. Element thickness is only 0.3mm and the flexible stack of foils can be bent in two directions after assembly process and was shaped curved using heat and pressure. The combination of printed flexible circuit boards and injection molding has also been demonstrated with several functional modules. The demonstrators illustrate the potential of origami electronics, which can be cut and folded to 3D shapes. It shows that several manufacturing process steps can be eliminated by Printed Hybrid Systems technology. The main benefits of this combination are small size, ruggedness and conformality. The devices are ideally suited for medical applications as the sensitive electronic components are well protected inside the plastic and the structures can be cleaned easily due to the fact that they have no joints or seams that can accumulate dirt or bacteria.

Hybrid in-mould integration for novel electrical and optical features in 3D plastic products

Next generation of smart systems in different application areas such as automotive, medical and consumer electronics will utilize various electronic, optical and mechanical functions integrated in plastic product structures. In this study, hybrid in-mould integration of electronic and optoelectronic modules was examined in order to embed novel functionality into polymer matrix. The feasibility to converge the printed electronics, component assembly and injection moulding manufacturing processes was examined by simulations, experimental tests and by realizing three demonstrators: over-moulded optical touch panel, plastic embedded flexible organic light emitting diode (OLED) foil and disposable healthcare sensor with over-moulded flexible printed circuit (FPC) connector. The demonstrators proved that hybrid in-mould integration could be feasible technology enabling seamless integration of optical, electrical and mechanical features into 3D plastic products.

Freeform and flexible electronics manufacturing using R2R printing and hybrid integration techniques

Printed electronics and other large-area roll-roll - compatible processes are opening up the new opportunity for cost-efficient mass manufacturing of electronics among other functionalities, on large-area and flexible substrates such as plastic, paper, metal foils, glass and fabrics. Data processing power and other functionalities still require high performance microelectronics circuits and therefore, also traditional electronic/semiconductor technology are also needed. These needs lead to technical manufacturing requirements that can be fulfilled best with concept of utilization combination of printed electronics and hybrid integration of silicon electronics to flexible printed platforms. Extending the continuous roll-to-roll manufacturing approach as far as possible (in air or/and in vacuum) in the manufacturing process to assembly and bonding, the manual assembly and handling phases can be almost fully eliminated. In this paper recent development to manufacture freeform and flexible electronics components and systems using printing and hybrid integration processes is presented. Production examples of hybrid integration will be presented for 1) LED display, 2) a large area roll-to-roll processed LED luminaire, 3) over-moulded optical touch panel and 4) over-moulded OLED subassembly.

Backlight illumination structure based on inorganic LED devices and laminated multilayer polymer substrate

The dominant technology for manufacturing backlight illumination structures is typically based on use of individually packaged Surface Mount Device (SMD) Light Emitting Diodes (LEDs). The optical power from sources is coupled to the light guide having a special structure to couple light out so that uniform illumination is achieved to the illuminated component, typically LCD display. In practice the structure contains several separate diffuser films, which results to a thick and costly structure. In addition, the light coupling from LED to the light guide is sensitive to alignment errors causing nonuniform and inefficient illumination. The developed alternative packaging structure for backlighting solutions is based on inorganic LED devices and multilayer polymer substrate. Polycarbonate substrate material was used, which is highly transparent at visual band allowing low absorption and has good lamination properties in hot lamination process allowing compact integrated structures. In the manufacturing process the individual polymer sheets with an individual thickness of 100 µm were printed with conductive patterns produced by screen printing using silver-based thick film pastes. The final integrated multilayer structure containing embedded LED devices was produced in a hot lamination process. Two types of LED devices were embedded within the laminated structure, namely blue LED, type C470RT290 and green LED, type C527RT290. The bottom area of the chip was 300 µm × 300 µm and the thickness 115 µm. The devices were manufactured by Cree. Test samples containing 3 × 3, 5 × 5 and 5 × 7 LED devices were designed, implemented and characterized. The final laminated structure thickness was typically 300 µm. The performed designs verified by test structure implementations and characterizations showed that the final thickness of the backlight illumination structure depends of the required uniformity of illumination and allowed LED device pitch and used diffuser efficiency. The main advantages of the implemented system compared to traditional light guiding system are easy optical coupling with high efficiency in an integrated and thin package. The developed technology seems to be suitable to produce backlight illumination structures for applications in which thin, lightweight, efficient and cost-efficient backlight illumination structure is essential, such as, hand-held devices. In addition, the developed technology seems to be possible to apply in several other applications, such as, information tables, signboards and displays.