Investigating the Copper Peel and Solder Joint Shear Strength on Biodegradable Substrates

The amount of electronics waste is increasing rapidly, and replacing traditional electronics materials with biodegradable alternatives is essential where possible. Four types of biodegradable substrates with $35 \mu \mathrm{~m}$ thick laminated copper layer have been analysed in this research work. All the substrates are based on polylactic acid laminates with flax reinforcement. The first type is a pure PLA laminate. The second, third and fourth types incorporate polymer interlayers (polypropylene or polyamide) to facilitate the adhesion between the copper layer and the substrate. Note that the interlayers are not biodegradable but will be swapped with biodegradable alternatives in the future. Copper peel strength was measured using a standard test pattern described in IPC-TM650. The copper layers were peeled off using an Instron 5965 test equipment, and the applied load was recorded automatically. A custom sliding sample holder was designed, allowing the vertical peeling of the copper layer. In addition to the copper peeling test, surface-mounted resistors in different sizes were assembled with low-temperature reflow soldering, and the shear strength of their solder joints was investigated.