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Evaluation of Potential Printed Wiring Board Materials: Thermoplastic Polyimide + Polymer Liquid Crystal Blends

Published online by Cambridge University Press:  10 February 2011

Witold Brostow ,
Nandika Anne D'Souza ,
Bhaskar Gopalanarayanan  and
Elizabeth G. Jacobs
Witold Brostow
Affiliation:
Department of Materials Science, University of North Texas, Denton, TX 76203-5310
Nandika Anne D'Souza
Affiliation:
Department of Materials Science, University of North Texas, Denton, TX 76203-5310
Bhaskar Gopalanarayanan
Affiliation:
Department of Materials Science, University of North Texas, Denton, TX 76203-5310
Elizabeth G. Jacobs
Affiliation:
DSPS Packaging Development, Texas Instruments Inc., P.O. Box 655012, MS 477, Dallas, TX 75265
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Abstract

Polymer liquid crystals (PLCs) have potential applications as printed wiring board materials and in other aspects of plastic packaging. They have a number of desirable properties such as low moisture absorption, thermoplastic behavior, and low thermal expansivity. However, PLCs can have significant anisotropy in expansivity with negative expansivities in the drawing or molding direction and relatively low positive expansivities in the transverse directions. By incorporating PLCs into an engineering polymer (EP) matrix, in our case a thermoplastic polyimide (TPI), we expected to be able to control the expansivity of the resulting blend – thereby aiding in long-term service performance and reliability. Properties such as low moisture absorption, dimensional stability at elevated temperatures, good adhesion properties, and reworkability were also sought. In this paper, we report on our work to process a TPI/PLC blend and characterize the thermal properties of the blends.

An amorphous TPI was chosen over a semicrystalline one because of a thermo-irreversible cold crystallization in the latter, causing undesirable changes in the morphology and poor adhesion to metals. Our evaluations of TPIs through thermally stimulated depolarization (TSD) and temperature-modulated differential scanning calorimetry (TMDSC) reveal sub-glass transition relaxations. We have investigated the selected semicrystalline TPI + PLC pair in the entire composition range, and concluded that the narrower range, up to 30 wt. % of the PLC, is sufficient for the achievement of our objectives. The glass transition temperature Tg = 240°C of the TPI determined by DSC is unaffected by variations of the PLC concentration. The cold crystallization temperature of the semicrystalline TPI decreases with increasing PLC concentration but upon formation of the LC-rich islands this effect becomes smaller. All the blends exhibit degradation onset temperature over 520°C. The thermal conductivity of the amorphous TPI + PLC blends varies as a function of the PLC concentration. The blends show very good film formability. The addition of the PLC improves the processability of the TPI. Thermomechanical analysis (TMA) reveals that the desired control of the expansivity of the blends is also achieved by varying the PLC concentration.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 515: Symposium J – Electronic Packaging Materials Science X , 1998 , 125
Copyright
Copyright © Materials Research Society 1998

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References

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