TY  - EJOU
AU  - Cheng, Hsien-Chie  
AU  - Huang, Ho-hsiang  
AU  - Lu, Su-Tsai  
AU  - Chen, Wen-Hwa  

TI  - Hygro-Thermal Behaviors of an ACF-typed Ultra-thin Chip-on-Flex Interconnect Technology
T2  - The International Conference on Computational \& Experimental Engineering and Sciences

PY  - 2011
VL  - 19
IS  - 2
SN  - 1933-2815

AB  - Due to the strong demand of electronic products with light-weight, flexibility and
portability and rollability from consumers, the development of flexible electronics
with flexible interconnects is presently underway. Flexible electronics is a technology
that extends electronics devices beyond the rigid form factor. It is highly
recognized that it can bring a very vigorous drive toward the new flourish of economic
growth in the electronics industry.  <br/>
In the study, a flexible interconnect technology based on an ultra thin chip and
a very thin flexible polyimide (PI) circuited substrate is developed, as shown in
Fig. 1. The electrical interconnects and also thermal-mechanical connections of
the technology are formed through a piece of anisotropic conductive film (ACF).
It is thus termed ACF-typed ultra-thin chip-on-flex (UTCOF) interconnect technology
(i.e., ACF-UTCOF in abbreviation) throughout the study. The technology is
promising and potential for a variety of flexible electronics applications, such as
flexible display, paper-thin smart labels, particularly the RFID labels, miniaturized
medical electronic systems, E-paper, E-label and memory chip stacking etc. Before
the full and successful realization and implementation of the ACF-UTCOF
technology, many technical challenges need to be resolved, including reliability
and bendability. <br/>
Thus, the study aims at the investigation of the hygro-thermal behaviors of the advanced
ACF-UTCOF technology during high temperature and humidity condition
through transient moisture content model analysis of the Fick law using finite element
(FE) modeling and experimental validation. The considered hygro-thermal
behaviors include moisture saturation time, moisture diffusion rate, moisture concentration,
moisture diffusion coefficient, saturated moisture concentration. To
achieve the goal, an ACF-UTCOF test vehicle is first constructed for subsequent
testing and characterization, and the humidity property of the PI substrate is determined
by measuring the weight gain during moisture absorption, shown in Fig.
2. Next, the dependences of the relative humidity and saturated moisture concentration
and also the moisture diffusion rate of the ACF applied on temperature are
characterized through moisture absorption experiments, as shown in Fig. 3. In addition,
strains/stresses induced from hygro-thermal effects are examined through
three-dimensional (3D) transient moisture analysis of the Fick law. Finally, the
influences of the hygro-thermal stress relaxation of the ACF on the hygro-thermalinduced
mechanical behaviors. <br/>
FE simulation results reveal that most of moisture diffuses into the ACF layer directly
through the substrate side rather than the periphery of the ACF. As shown in
Fig. 4, the ACF-UTCOF test vehicle is saturated after about twenty hours under an
85C/85% relative humidity condition test. Most importantly, from the experimental
results, it is found that the moisture effect would play a much more significant role
in reliability than the thermal effect.
KW  - 

DO  - 10.3970/icces.2011.019.057