Issue link: https://iconnect007.uberflip.com/i/1467185
84 DESIGN007 MAGAZINE I MAY 2022 An advantage of not soldering to make con- nections is that the component lands can be treated as microvias and the free space can be used for increased routing. When all the required interconnections and circuits are added, the assembly can be partially machined in areas where bending is performed to thin the metal carrier sufficiently to allow the residual metal to easily bend. If le, the residual metal can serve as a ground layer for the assembly. If isolation is required or desired, the residual metal can be etched using chemistry appro- priate for the metal used as a carrier. Alkaline chemistries such as dilute sodium hydroxide and sodium gluconate solutions are suitable for aluminum, but other chemistries such as ferric chloride are more universal in their potential application. ere are many proprietary chem- istries which can be used as well. e patented process concept is illustrated in Figure 1. Accepted flex circuit design practices sug- gest that the number of circuit layers through the areas where flexing or bending is required should ideally be limited to one or two metal layers. at aside, the processes described offer significant potential benefits for increased reli- ability and reduced overall cost. Conclusion e continuing challenge of making lead-free solder work in electronic assembly has given rise to new ways of looking at circuit assembly and fabrication, using methods that could elim- inate solder and its myriad issues altogether. What has been offered for the reader to pon- der is just the tip of the iceberg. My mind (and perhaps now yours) lights up daily with ideas and ways to integrate packaged chips with the interconnections they require to carry out their mission. Improved approaches to assem- Figure 1: Example of a possible aluminum rigid-flex manufacturing process. (Source: U.S Patent 10,285,270)