To make bPiShift as compact as possible, we decided to mount both the male and female header pins along the edge of the board, even though they were originally designed for through-hole mounting.

At our small in-house lab, we have a basic SMT assembly setup that includes a manual frameless stencil printer, a small pick-and-place machine, and a reflow oven. We mainly use this setup for rapid prototyping, and we’ve previously used it to place and reflow components on both sides of a PCB. The real challenge this time was figuring out how to mount those edge header pins efficiently - preferably without manual soldering.

Our first idea was to mount all standard SMD components using the usual process on the top side, without applying solder paste to the header pin pads. This would allow us to mount all SMD components first, then apply solder paste on the backside for both the SMD components and the header pins. We could then insert the header pins before baking the board in the reflow oven. However, this method would only solder the header pins on one side, leaving the other side to be soldered manually - something we wanted to avoid.

So, we tried a different approach altogether. We first created a frameless stencil to apply solder paste for both sides of the PCB, leaving out openings for the header pins. This allowed us to complete SMT assembly on both sides using our usual process. After that, we made a custom plastic stencil specifically for applying solder paste to the header pin pads once both sides were assembled. Using this stencil, we applied solder paste to both sides of the board, manually inserted the header pins along the edge, and then reflowed the board in the oven.

This method worked beautifully - it allowed us to achieve consistent, even solder joints on both sides of the PCB without any manual touch-up. The result is a cleaner, more professional finish while keeping bPiShift’s footprint as small as possible.