• Journal of Welding and Joining
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• v.31 no.5
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• pp.59-63
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• 2013

A bendable electronic module has been developed for a mobile application by using a low-cost roll-to-roll manufacturing process. In flexible embedded electronic module, a thin silicon chip was embedded in a polymer-based encapsulating adhesive between flexible copper clad polyimide layers. To confirm reliability and durability of prototype bendable module, the following tests were conducted: Moisture sensitivity level, thermal shock test, high temperature & high humidity storage test, and pressure cooker tester. Those experiments to induce failure of the module due to temperature variations and moisture are the experiment to verify the reliability. Failure criterion was 20% increase in bump resistance from the initial value. The mechanism of the increase of the bump resistance was analyzed by using non-destructive X-ray analysis and scanning acoustic microscopy. During the pressure cooker test (PCT), delamination occurred at the various interfaces of the bendable embedded modules. To investigate the failure mechanism, moisture diffusion analysis was conducted to the pressure cooker's test. The hygroscopic characteristics of the encapsulating polymeric materials were experimentally determined. Analysis results have shown moisture saturation process of flexible module under high temperature/high humidity and high atmosphere conditions. Based on these results, stress factor and failure mechanism/mode of bendable embedded electronic module were obtained.

• Proceedings of the KWS Conference
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• 2009.11a
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• pp.71-71
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• 2009

전자제품의 다양한 기능들의 융복합화 및 휴대 편의성 경향은 이제 더 이상 새로운 것이 아니다. 이러한 추세에 따라 전자부품들은 모듈화 되고, 휴대하기 용이해 지고 있다. 또한 다양한 제품 디자인에 적용하기 위해 제품에 장착되는 부품의 기구적 위치 배열의 한계 또한 제약 받고 있다. 따라서 최근의 전자부품은 모듈화 되고 있으며, 기구적 한계를 극복하기 위한 Flexible 모듈의 사용이 증가하고 있다. 또한 양산측면에서 Roll-to-Roll(R2R) 방식을 적용함으로써 생산성을 극대화 하고 있다. 이때 R2R 적용을 위해서는 제품이 굴곡 될 수 있도록 유연성이 보장되는 Bendable 전자모듈의 개발이 필수적으로 요구되고 있다. Flexible 기판은 더 이상 새로운 기술이 아니지만, Felxible 기판 내부에 칩이 내장되고, 회로가 형성되어 자체적으로 기능을 수행할 수 있도록 한 Bendable 전자모듈을 R2R 방식으로 제조하는 기술은 매우 새로운 접근이라 할 수 있다. 이러한 기술개발이 현실화 된다면, Wearable Electronics 및 Flexible Display 등 다양한 전자제품에 응용될 수 있을 것으로 기대된다. 그러나 이러한 제품의 상용화를 위해서는 Bendable 전자모듈에 대한 신뢰성이 확보되고, 제품으로써의 수명이 보증되어야 한다. 신규 개발되는 제품의 신뢰성 검증항목이나 수명평가 모델은 현재까지 제안되지 않고 있는 실정이다. 또한 다양한 사용 환경에서 고장(Failure) 발생을 유발하는 스트레스 인자(Stress Factor)를 도출함으로써, 가속시험 또는 신뢰성 검증을 위한 인가 스트레스를 선정할 수 있다. 그러나 이러한 고장물리를 기반으로 스트레스 인자를 해석한 결과는 아직 보고되고 있지 않다. 따라서 본 연구에서는 $50{\mu}m$ 두께의 Si Chip에 저항변화를 관찰하기 위한 회로를 형성한 후 폴리이미드 기판을 이용하여 Si Chip이 임베딩된 Bendable 전자모듈을 제작하였다. 전자모듈의 실사용 환경에서의 수명예측을 위한 사전단계로써 고장물리에 기반한 고장모드와 고장메카니즘을 해석하는 것이 최우선 수행되어야 하며, 이를 바탕으로 고장을 유발하는 스트레스 인자를 도출 하였다. 고장도출을 위해 시제품은 JEDEC J-STD-020C의 MSL시험, 고온가압시험, 열충격시험 및 고온저장시험을 각각 수행하였으며, 이로부터 발생된 각각의 고장유형을 분석함으로써 스트레스 인자를 도출하였다. 또한 모아레(Moire) 간섭계를 이용하여 제작된 샘플의 온도변화에 따른 변형해석을 수행하였고, 동시에 Half Symetry Model을 이용한 유한요소해석(FEA)을 수행하여 변형해석 및 스트레스 유발원인을 도출하였다. 이 결과로 부터 고장물리 기반의 고장해석과 Moire 분석 그리고 시뮬레이션 해석 결과를 바탕으로 Bendable 전자모듈의 고장유발 스트레스 인자를 해석할 수 있었다.

• Journal of IKEEE
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• v.20 no.3
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• pp.330-332
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• 2016

In this study, we investigate the influence of channel length of bendable a-Si:H thin film transistors (TFTs) on their electrical characteristics as a function of bending strain. Under a tensile strain of 1.69%, $8{\mu}m$-channel-length TFT has the threshold voltage shift up to 5.25 V, while $100{\mu}m$-channel-length TFT operates stably.

• Journal of the Microelectronics and Packaging Society
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• v.19 no.3
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• pp.15-20
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• 2012

In electronics industry, the coming electronic devices will be expected to be high integration and convergence electronics. And also, it will be expected that the coming electronics will be flexible, bendable and wearable electronics. Therefore, the demands and interests of bonding technology between flexible substrate and chip for mobile electronics, e-paper etc. have been increased because of weight and flexibility of flexible substrate. Considering fine pitch for high density and thermal damage of flexible substrate during bonding process, the micro solder bump technology for high density and low temperature bonding process for reducing thermal damage will be required. In this study, we researched on bonding technology of chip and flexible substrate by using 25um Cu pillar bumps and Sn-Bi solder bumps were formed by electroplating. From the our study, we suggest technology on Cu pillar bump formation, Sn-Bi solder bump formation, and bonding process of chip and flexible substrate for the coming electronics.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.5
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• pp.619-624
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• 2013

A bendable electronic module is developed. In this module, thin silicon electronic chips are embedded in a polymer-based encapsulating adhesive between flexible copper-clad polyimide layers. During the qualification test of a harshly thermal-hygroscopic complex loading condition, delaminations occur inside the module layers. A finite element model is developed for the module. To investigate the effect of hygroscopic stress on delamination, the results of the thermal and thermal-hygroscopic loads are compared. The analysis results reveal that the hygroscopic effect more strongly affects delamination than does the thermal effect. The potential failure mechanisms of the module are investigated based on the stress analysis.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.5
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• pp.523-528
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• 2012

A bendable electronic module is developed for a mobile application by using a low-cost roll-to-roll manufacturing process. In the module, a thin silicon chip is embedded in a polymer-based encapsulating adhesive between flexible copper clad polyimide layers. A set of tests are conducted for the purpose of qualification: thermal shock, high temperature storage, and autoclave tests. During the autoclave test, delamination occurs at many places within the module layers. To investigate the failure mechanism, moisture diffusion analysis is conducted for the interior of the module under the autoclave test condition. For the analysis, the hygroscopic characteristics of the encapsulating materials are experimentally determined. Analysis results indicate the moisture saturation process in the interior of the module under the autoclave test condition.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.61-61
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• 2011

Polymer solar cells have become one of the rising next generation solar cells due to their potential for lightweight and bendable plastic solar modules. Recently, the power conversion efficiency of polymer solar cells has reached ~8 %, which can make ~6 % plastic solar modules when it comes to the modular aperture ratio of ~80 %. Although this efficiency is far behind that of conventional inorganic solar cells, the plastic solar modules are expected to create new energy market into which the inorganic solar modules could not make inroads. In the near future, the plastic solar modules can be integrated with consumer electronics that should overcome the regulation of energy consumption. For this application, the polymer solar cells should be fabricated in a variety of module shapes, which can be resolved by employing conventional and/or advanced coating and molding technologies of plastics products. In this tutorial, the fundamental aspect of polymer solar cells will be briefly introduced and then recent trends in terms of materials and devices will be reviewed together with showing recent results in organic nanoelectronics laboratory.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.66 no.10
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• pp.1494-1498
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• 2017

In this study, we investigate the influence of an overlap between the gate and source/drain regions of silicon nanowire (SiNW) CMOS (complementary metal-oxide-semiconductor) inverter on bendable plastic substrates and describe their electrical characteristics. The combination of n-channel silicon nanowire field-effect transistor (n-SiNWFET) and p-channel silicon nanowire field-effect transistor (p-SiNWFET) operates as an inverter logic gate. The gains with a drain voltage ($V_{dd}$) of 1 V are 3.07 and 1.21 for overlapped device and non-overlapped device, respectively. The superior electrical characteristics of each of the SiNW transistors including steep subthreshold slopes and the high $I_{on}/I_{off}$ ratios are major factors that enable the excellent operation of the logic gate.

• Current Photovoltaic Research
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• v.2 no.3
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• pp.79-83
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• 2014

Dye-sensitized solar cells (DSSCs) are applied in the emerging fields of building integrated photovoltaic and electronics integrated photovoltaic like small portable power sources as demands are increased with characteristic advantages. Highly flexible dye-sensitized solar cells (DSSCs) prepared on single stainless steel mesh were proposed in this paper. Single mesh DSSCs structure utilizing the spraying the chopped glass paper on the surface treated stainless steel mesh for integrating the space element and the electrode components, counter electrode component and photoelectrode component were coated on each side of the single mesh. The fabricated single mesh DSSCs showed the energy-conversion efficiency 0.50% which show highly bendable ability. The new single mesh DSSCs may have potential applications as highly bendable solar cells to overcome the limitations of TCO-based DSSCs.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.244.1-244.1
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• 2016

Recently, the technology for flexible electronics such as flexible smart phone, foldable displays, and bendable battery is under active development. With approaching the real commercialization of flexible electronics, the electrical and mechanical reliability of flexible electronics have become significantly important because they will be used under various mechanical deformations such as bending, twisting, stretching, and so on. These mechanical deformations result in performance degradation of electronic devices due to several mechanical problems such as cracking, delamination, and fatigue. Therefore, the understanding of relationship between mechanical loading and electrical performance is one of the most critical issues in flexible electronics for expecting the lifetime of products. Here, we have investigated the effect of monotonic tensile and cyclic deformations on metal interconnect to provide a guideline for improving the reliability of flexible interconnect.