In response to the challenges of automating the assembly of a CR2032 coin cell to a PCB, especially for a high-volume, low-cost application with a flush bottom requirement, here are some suggestions:
Custom Termination: As Kean mentioned, discussing with a battery supplier could be beneficial. They might offer custom termination and packaging solutions that are optimized for automated assembly at your production scale.
Conductive Glue: The use of conductive glue on the top-side pads before placing the tabbed cell could be an automated process. This method would require less handling and could potentially be integrated into your existing assembly line with minimal changes.
SMT Battery Holders: As tomgat pointed out, using Surface Mount Technology (SMT) battery holders can be an efficient solution. PNP (Pick and Place) machines can handle these quite well, and it might be worth exploring this option further, especially if you can ensure that the voltage area is isolated during reflow.
Avoiding PCB Pad Contacts: Psi's advice to avoid using PCB pads as battery contacts is crucial for reliability. The connection can become high resistance over time, leading to potential product failures. Sticking to tabbed cells, either through-hole (TH) or SMT, is recommended.
Wave Soldering with Custom Tabbed Cells: The idea of custom tabbed cells with leads trimmed to the PCB thickness is interesting. However, it might introduce additional complexity and cost. The rotating head on the TH placement machine can bend and cut the lead during assembly, which could be a more reliable approach.
SMT Approach: Considering the low BOM count and not being critical on density, an SMT approach could be more cost-effective. It would also avoid the complexities and regulations associated with shipping batteries.
On-Site Battery Insertion: If all else fails, using an SMT battery shell and then having a worker insert the batteries on-site after the boards have been assembled and tested could be a viable option. This would eliminate the need for dealing with batteries during shipping and could simplify the assembly process.
In conclusion, it seems that a combination of custom solutions, such as SMT battery holders or conductive glue, might offer the best path forward for automating the assembly of the CR2032 coin cell(e.g. [spam link removed])to your PCB. It's important to consider the entire production process, from assembly to testing to shipping, to find the most efficient and reliable solution. Prototyping and testing different methods will be key to finding the best fit for your specific application.