INTERCONNECTMATERIALS
Ribbons from vendor 1 were soaked in MEK for 16 hours, and FTIR was performed in an effort to identify the potential material removed from the ribbon by the MEK. Subtracting the spectrum from MEK, the scan in Figure 11 identifies the ribbon contaminants as a range of aliphatic carboxylic acids.
Expanding the chemistry Applying knowledge from the “rubber like improved” material, two additional ECA materials were developed. To provide the fastest application of adhesive in the assembly process, jet dispense technology is an attractive option. Jet dispensable ECAs require unique rheology characteristics to ensure repeatable dispensability.
A “rubber like improved” ECA with jet dispensable rheology characteristics was developed and tested for resistance stability with damp heat conditioning. In addition, a rigid higher strength adhesive with a Tg
of around 70°C was developed with the “improved” corrosion resistance technology. Both chemistries along with the “rubber like improved” ECA were tested on a 3rd
(96.5/3.5) ribbon and on a 100% pure tin coated ribbon. The results are shown in Figure 12.
Employing the technology that was developed in the “rubber like improved” version, the jettable and rigid ECAs also demonstrated stable contact resistance through damp heat conditioning. Despite subtle differences, all samples demonstrated at least a 50% drop in the total resistance across the 12 interfaces indicating that the resistance stability is attainable in both a rigid or rubberlike ECA. Furthermore, the strong performance was not affected by the ribbon composition. Tin coated ribbon alone performed comparable to tin silver ribbon.
vendor’s tin silver coated
Figure 11. FTIR of residue from ribbon from vendor 1
Conclusion
A reliable, stable interconnect is essential to assuring long term life of a PV panel. The reliability of the interconnect can improved by mitigating the risk of both stress and corrosion. Stress concerns with the ECA are addressed with a relatively low Tg ECA. An ECA with a low Tg
reduces the
temperature range in which the significant stresses develop in the glassy region of the polymer. However, low Tg
materials have been problematic
concerning corrosion resistance on nonnoble substrates when subjected to damp heat conditioning. A new stable rubber like ECA has been demonstrated that exhibits the damp heat stability on tin and tin silver coated ribbon. With the tandem properties of low interfacial stress and corrosion resistance the new rubber like ECA enables the thin film industy with the ability to provide more flexible solutions with long term reliability. Furthermore, potential utility in c Si applications can be realized when interfacial stress of a solder interconnect is a potential problem.
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Further reading REFERENCES [1] M. Powalla, M. Cemernjak, J. Eberhardt, F. Kessler, R. Kniese, H.D. Mohring, International PVSEC 14 (2004) 1 4.
[2] B.R. Olaisen, M. Edoff, A. Holt, 24th European Photovoltaic Solar Energy Conference, 21 25 September (2009) 3007 3010. [3] D. Lu, C.P. Wong, Proceedings International Symposium on Advanced Packaging Materials (1999) 288 294. [4] H.K. Kim, F.G. Shi, Microelectronics Journal 32 (2000) 315 321. [5] Q.K. Tong, G. Fredrickson, R. Kuder, D. Lu, Proceedings of the 49th Electronic Components and Technology Conference (1999) 347 352.
[6] J. Bicerano, Prediction of Polymer Properties, 3rd Ed. Marcel Dekker, Inc. NY, 2002. [7] C.P. Wong, Daoqiang Lu, Quinn K Tong, IEEE Transactions of Electronics Packaging Manufacturing, (1999) 228 232. [8] Y.L. Li, C.P. Wong, Materials Science and Engineering R 51 (2006) 1 35. [9] J. Lange, S. Toll. J.E. Manson, Polymer 36 No. 16, (1995) 3135 3141.
[10] C. Brahatheeswaran, V.B. Gupta, Polymer 34 No. 2, (1993) 289 293. [11] K.W. Allen, International Journal of Adhesion & Adhesives 23 (2003) 87 93. [12]
J.Kim, K.S. Kim, and Y.H. Kim, Mechanical Effects in Peel Adhesion Test, J. Adhesion Sci. Technol. 3 (1989) 175 187.
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