2009/11/23學 生：陳立偉指導教授：林克默

1. Introduction 2. Experimental 3. Results and discussion 4. Summary

1. Introduction According to the EU (RoHS) Directive on the restriction of the

use of certain hazardous substances, it is believed that requirement of environment- friendly ribbon assembled in the crystalline silicon solar system should be an important issue in the near future.

Before the characteristic study on electronics packaging, little work has been done on the wettability of solders on solar cells. Herefore, it is of great interest to study the wettability of two lead (SnAgPb (SAP) and SnPb (SP)) and one lead-free (SnAgCu (SAC)) solders, and the effects of soldering temperature were also monitored for comparison in this paper.

2. Experimental Solders ： Sn–28Pb 、 Sn–2.6Ag–24.3Pb and

Sn–3.5Ag–0.8Cu in at%.Low-solid non-clean flux (Kester, 955).The temperatures at 190–240 for lead solders and at ℃

230–280 for lead-free solder.℃

Analyzed by the contact angle (CA) system (VCA-2500XE, VISUAL CONTACT ANGL-236).

Microstructure analyses were performed using scanning electron microscopy (Hitachi S-4800).

Composition analyses were carried out by energy-dispersive spectrometry (EDX).

3. Results and discussion

Fig. 1. Contact angle measurement of solders detected at high temperatures.

Fig. 2. Contact angle measurement of solders at room temperatures.

Fig. 3. Contact angles of solders on substrates measured at various temperatures.

Fig. 4. Cross-sectional images of SnAgPb soldering with Ag paste at (a)190 , and higher ℃ magnification of (b).

Fig. 5. Cross-sectional BEI micrographs of SnPb soldering with Ag paste at (a) 190 and (b) its local higher magnification, at (c)215 and (d) its local℃ ℃ higher magnification.

Fig. 6. Cross-sectional image of SnAgCu soldering with Ag paste at (a) 255 , (b) 280 , and higher magnification of (c). ℃ ℃

(Pt.1) has mostly Sn (76.7%), high amounts of Cu (19.0%), and low Ag (4.3%). (Pt. 2) mostly Ag with minor amounts of other alloy elements dissolved in.

4. Summary 1. Lead-free SAC solder generally has lower CA values

than lead SP and SAP solders, implying that SAC solder has better wettability.

2. CA values of SAC solder decreased with increasing soldering temperatures; conversely, leaded SP and SAP solders have higher CA values when soldered at high temperatures.

3. Based on the BEI micrographs, IMC was significantly observed in the SAC solder/busbar interface, while no evidence of IMC formed between the SP solder and the substrate was detected.

Thank you for your attention