Due to the very small amounts of solder on the contacts of QFNs the use of residual solder on the PCB pads is not recommended.

The pads need to be cleaned and normally it would be very difficult to applying new solder to them.

Either applying solder to the pads of the components or printing solder paste onto the QFN pads are the best options.

With the QFN prebumping method solder paste is applied to the pads and the QFN is then reflowed to ensure solder is firmly attached.

The Pre Bumping process is easy with the tools supplied by Martin and specially developed for use with the Minioven.

MARTIN can supply custom stencils, the necessary solder pastes as well as other tooling.

Place the QFN in the frame and the stencil over the top of the QFN.
  Apply the solder paste with the squeege.
  Then once reflowed in the Mini oven, the QFN is ready to be reworked with the rework station.