Ultra-thin chip package (UTCP) and elastic circuit technologies for compact or conformable sensor and electronics assemblies

This contribution provides an overview of CMST's technologies on flexible ultrathin chip packaging and elastic electronic and sensor circuit technologies and applications

Flexible and stretchable electronics

Conventionally electronics circuits are produced by assembly of packaged components on flat, rigid printed circuit boards. However there is a growing demand for 2.5 dimensional (2.5D free form surfaces) or even full 3D electronics. Applications for such circuits are found in a vast range of fields: such circuits are desirable for comfort and ergonomic reasons (e.g. in wearable or implantable circuits), to respond to design and aesthetics considerations (e.g. 2.5D or 3D light sources), for ecological reasons (more efficient materials usage, less CO2 emissions in automotive applications) etc. In this contribution we will present two technologies, under development at our laboratory, which open the way to industrial production of randomly deformable circuits. These technologies are : • The ultra-thin chip package (UTCP) technology, by which bare Si (or other anorganic semiconductor based) chips are thinned down to a thickness of 20-30µm, embedded in a stack of spin-on polyimide layers, and provided with a fan-out metallization, resulting in an extremely miniaturized, lightweight and flexible chip package with a total thickness below 100µm • A number of technologies for dynamically stretchable (i.e. elastic) circuits, which are based on the interconnection of individual components or component islands with meander shaped thin-film or Printed Circuit Board (PCB) based metal wirings and embedding in elastic polymers like PDMS (silicone rubbers) or PU (polyurethanes). Process flow details, reliability data and applications for these technologies will be presented

Intermediary metabolism

Caenorhabditis elegans has orthologs for most of the key enzymes involved in eukaryotic intermediary metabolism, suggesting that the major metabolic pathways are probably present in this species. We discuss how metabolic patterns and activity change as the worm traverses development and ages, or responds to unfavorable external factors, such as temperature extremes or shortages in food or oxygen. Dauer diapause is marked by an enhanced resistance to oxidative stress and a shift toward microaerobic and anaplerotic metabolic pathways and hypometabolism, as indicated by the increased importance of the malate dismutation and glyoxylate pathways and the repression of citric acid cycle activity. These alterations promote prolonged survival of the dauer larva; some of these changes also accompany the extended lifespan of insulin/IGF-1 and several mitochondrial mutants. We also present a brief overview of the nutritional requirements, energy storage and waste products generated by C. elegans

Effect of overmolding process on the integrity of electronic circuits

Traditional injection molding processes have been widely used in the plastic processing industry. It is the major processing technique for converting thermoplastic polymers into complicated 3D parts with the aid of heat and pressure. Next generation of electronic circuits used in different application areas such as automotive, home appliances and medical devices will embed various electronic functionalities in plastic products. In this study, over-molding injection molding (OVM) of electronic components will be examined to insert novel performance in polymer materials. This low-cost manufacturing process offers potential benefits such as, reduction in processing time, higher freedom of design and less energy used when compared to the conventional injection molding method. This paper aims to evaluate the performance of this process and propose a series of alternative solutions to optimize the adhesion between and integration of electronics and engineering plastics. A number of methods are used to optimize the process so that the electronic circuits are not damaged during the over-molding, moreover to test the reliability of the system in order to control the continuity of connections between the electronic circuit foils and the electronic components after the OVM process. Correspondingly, we have performed specific tests for this purpose varying in some conditions: the type of injected plastic used, over-molding parameters (temperature, pressure and injection time), electronic circuit design, type of assembled electronic components, type of foils used and the effect of using underfill material below the electronic component. From these tests, first conclusions were made. We have also studied adhesion between the foil and the over-molding material. In this case, various types of engineering plastics have been tested; polypropylene (PP), 30% weight percentage glass,fiber filled polypropylene (GF-PP), Polyamide-6 (PA6) and 50% weight percentage glass fiber filled polyamide-6 (GF-PA6). It was proved that throughout the wide range of tested materials, (PA6) over-molded samples showed a better adhesion on the copper-polyimide foils than the rest. These plastics were over-molded on two types of polyimide (PP/Copper (Cu) tracks foils with and without an adhesive layer between PI and Cu. It was obviously clear that the foils with on adhesive layer between PI and Cu had more delamination in the Cu tracks than the foils without an adhesive layer. Furthermore, it was shown that the presence of an underfill material has on effect on the system as the foils that had an underfill material below their components successfully had a better connection than the folis without an underfill material. Finally, experiments were executed using the two probe method as an electrical measurement and microscope investigation as the visual inspection

A new low cost, elastic and conformable electronics technology for soft and stretchable electronic devices by use of a stretchable substrate

A growing need for ambient electronics in our daily life leads to higher demands from the user in the view of comfort of the electronic devices. Those devices should become invisible to the user, especially when they are embedded in clothes (e.g. in smart textiles). They should be soft, conformable and to a certain degree stretchable. Electronics for implantation on the other hand should ideally be soft and conformable in relation to the body tissue, in order to minimize the rejecting nature of the body to unknown implanted rigid objects. Conformable and elastic circuitry is an emerging topic in the electronics and packaging domain. In this contribution a new low cost, elastic and stretchable electronic device technology will be presented, based on the use of a stretchable substrate. The process steps used are standard PCB fabrication processes, resulting in a fast technology transfer to the industry. This new developed technology is based on the combination of rigid standard SMD components which are connected with 2-D spring-shaped metallic interconnections. Embedding is done by moulding the electronic device in a stretchable polymer. The reliability of the overall system is improved by varying the thickness of the embedding polymer, wherever the presence and type of components requires to. Manufacturability issues are discussed together with the need for good reliability of the stretchable interconnections when stress is applied during stretching

Multimode PDMS waveguides fabricated using a hot-embossing technique

A novel method for fabricating multimode PDMS waveguides is presented. This process is based on a hot-embossing technique and generates high quality optical waveguides without a substantial residual layer after embossing. Furthermore, the process allows for low-cost fabrication since it relies on a replication technique and additionally only commercially available materials are used. The measured propagation loss is smaller than 0.24dB/cm and can be further reduced by improving the master mould quality

Flexible and stretchable circuit technologies for space applications

Flexible and stretchable circuit technologies offer reduced volume and weight, increased electrical performance, larger design freedom and improved interconnect reliability. All of these advantages are appealing for space applications. In this paper, two example technologies, the ultra-thin chip package (UTCP) and stretchable moulded interconnect (SMI), are described. The UTCP technology results in a 60 µm thick chip package, including the embedding of a 20 µm thick chip, laser or protolithic via definition to the chip contacts and application of fan out metallization. Imec’s stretchable interconnect technology is inspired by conventional rigid and flexible printed circuit board (PCB) technology. Stretchable interconnects are realized by copper meanders supported by a flexible material e.g. polyimide. Elastic materials, predominantly silicone rubbers, are used to embed the conductors and the components, thus serving as circuit carrier. The possible advantages of these technologies with respect to space applications are discussed

Hurdles in investigating UVB damage in the putative ancient asexual Darwinula stevensoni (Ostracoda, Crustacea)

Ostracoda or mussel-shrimps are small, bivalved Crustacea. Because of their excellent fossil record and their broad variety of reproductive modes, ostracods are of great interest as a model group in ecological and evolutionary research. Here, we investigated damage and repair of one of the most important biological mutagens, namely UVB radiation in the putative ancient asexual ostracod Darwinula stevensoni from Belgium. We applied three different methods: the Polymerase Inhibition (PI) assay, Enzyme-Linked Immuno Sorbent Assay (ELISA) and dot blot. All three techniques were unsuccessful in quantifying UVB damage in D. stevensoni. Previous experiments have revealed that the valves of D. stevensoni provide an average UVB protection of approximate 60%. Thus, UVB damage could be too little to make quantitative experiments work. Additional variation between individual ostracods due to season and age most likely contributed further to the failure of the three used experimental approaches. In a second experiment, we investigated the influence of temperature on survival of D. stevensoni during UVB exposure. The estimated lethal UVB dose at 4°C was with 50 kJ/m2 significantly lower than at room temperature with 130 kJ/m2. This could either indicate adaptation to low temperatures and/or the presence of metabolic processes against UVB damage in D. stevensoni. These results could also explain why the estimated lethal UVB dose of D. stevensoni is similar to that of other non-marine ostracods where valves provide around 80% protection, although the valves of D. stevensoni provide less protection. If such metabolic processes can repair UVB damage fast, they might be an alternative explanation why we could not quantify UVB damage in D. stevensoni