Materials Science & Technology

Open Degradation on ITO Lines for an LCD Driver Peter Jacob, Empa Dübendorf Dept. 173

Setup „ „ „

LCD-driver IC directly glued onto connecting ITO lines on LCD glass Glue includes silver particles 2-step protector: soft silicone gel and hard top mould compound Mould compound

Silicone gel LCD Driver Chip

Au bump

ITO Line

LCD Glass Carrier

Empa, ,

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Failure Description „ „ „

Empa, ,

After some time of operation, repeatingly LCD segments failed to display correctly Electrical analysis has shown that always the same ITO line to the LCD driver was open No specific or unusual setup, current density or other observations were made considering this line

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Optical setup, image taken through the glass Optical microscope inspection has always shown the same attack points: one small line right from the big one was completely open, the wider line right from the thick one never was attacked

Empa, ,

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Voltage Potentials and electrochemical evaluation of the situation

0-3V ?

Accu 1

+8.6V VLCD

Border line of inner mold

Empa, ,

Accu 2

0 3 V

VLCD is the line with the maximum potential onsite. Compared to neighbour potentials, electrolytic cells have been generated, consuming material of the „minus“ side.

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Cross sectional drawing Humidity enclosure, acting as an electrolyte Hard mould compound

Silicone gel Au bump LCD Driver Chip

Glue with conductive balls

Empa, ,

ITO Line

ITO Open LCD Glass Carrier

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Conclusions „

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Empa, ,

Humidity and electrical field strength can generate electrolytical reactions on LCD-ITO lines – finally causing opens Device and ITO/ LCD layout should consider to arrange pins in a manner which avoids abrupt potential changes of neighboured lines. Vdd and Vss lines are best arranged at corners, where enough space is available to reduce field strength After a suiable redesign enhancing critical spaces, no further reliability problems occured 7