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JULY 2019 I SMT007 MAGAZINE 83 lic formed with the aluminum. Figure 7 shows some cross-sections. As can be seen, while the solder wet and bonded well to the aluminum in most areas, voids were within the acceptable limit and are seen under the capacitor and battery holder's pad. These were further examined by doing an energy dispersive X-ray spectroscopy (EDS). Figure 8 shows an EDS of one such resistor pad. As can be seen in the EDS, there is evidence that the surface treatment results in the forma- tion of a silver-aluminum (Ag-Al) intermetallic with some presence of bismuth. Conclusions The surface treatment was shown to enable soldering to aluminum. Since solders vary in metal composition and flux, they each will have specific reflow profiles. Additional work may be needed to fine-tune reflow parameters for specific applications to get consistent wet- ting and good solder joints. Most new soldering applications would require such process devel- opment. Overall, this surface treatment has the potential to open the path for large scale use of Al-PET substrates. This could revolutionize the manufacturing of smart tags, RFID tags, and single-layer aluminum circuits. SMT007 References 1. Weast, R.C. Handbook of Chemistry and Physics: 66 th Edition, CRC Press, 1985. 2. Anixter Inc. "Copper vs. Aluminum Conductors." 3. Based on price listing on Market Insider in September 2018. Actual prices will vary on a daily basis. 4. MacDermid. "Metex 6811 Cyanide Free Liquid Zincate Datasheet." 5. Averatek. "Mina: Facile Soldering to Aluminum for RFIDs." 6. "Dielectric Constants at 20°C." 7. Omnexus. "Glass Transition Temperature Values of Several Plastics." This paper was first presented at the IPC APEX EXPO 2019 Technical Conference and published in the 2019 Technical Conference Proceedings. Divyakant Kadiwala is director of manufacturing at Averatek Corporation. Figure 8: EDS spectra from the pad side after pulling resistor from pad showing Ag-Al intermetallic.

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