2 Use a dedicated work holder with 'pockets' milled out to accommodate the components on the first side of the board after reflow. Some prefer a pallet that runs all the way through their process. So, these pallets: * Feature hold downs that are flush with the top side of the board so you can use it to support and accurately, repeatably locate the board in the screen printer and a not interfere with placement. * Can be conveyed. * Allow for using pick and place board support and tooling pins. * Insulate the first pass components and help keep them from reflowing during the second pass. * Additionally, would not add thermal mass to avoid running the oven at a higher temperature to compensate for the mass of the pallet.
Although, flexible tooling could also be used, a well designed dedicated tool generally provides superior results. [One of those "pay me now or pay me later" things. Yano?]