Fred Dimock, Manager Process Technology. BTU International

Surface finish is applied on to copper (Cu) integration scheme on printed circuit boards (PCBs). Choice of surface finish is critical especially for next generation HDI, high frequency PCBs because the performance and reliability of the electronic assemblies depends on the right selection. There are several options available in the market and one (OEM, PCB manufacturers, PCB designers, EMS) needs to consider the following critical selection criteria,

1. Insertion loss: Next generation electronic assemblies require HDI, high frequency PCBs. Right choice of surface finish is critical to attain optimum signal integrity with minimal insertion loss.

2. Solder joint reliability: Few surface finishes options (i.e. ENIG, etc.) tend to form brittle solder joints with lead-free solder. Also, Ni based surface finishes form Sn-Ni intermetallics/solder joints which are less strong to Sn-Cu intermetallics. Can the surface finish participate in ensuring smaller intermetallics and robust solder joints? The choice of the surface finish is critical in ensuring robust solder joints in your final assembly.

3. Shelf life: Looking at the current pandemic situation going on around the world, longer shelf life is critical due to supply chain disruptions across the world.

4. Reflow cycles during assembly: With ever-increasing complexity of the electronic assemblies, it is paramount to have the surface finish that can withstand multiple reflow cycles (3+).

5. Cost-effective: It is also critical to review cost during the selection of the surface finish. There are few options that involve use of precious metals, i.e. Ag, Au, Palladium (Pd). Thickness of these precious metals based surface finishes are critical to ensure cost-effectiveness.

Overall performance and reliability of electronic assemblies depends on the right material selection of every component involved. The surface finishes on the PCBs are critical piece to ensure the optimum performance and reliability of the electronic assemblies. Pay attention while selecting surface finishes for next generation PCB technologies.