Leadless Device Placement

shallow depth-of-field image of green computer circuit board
shallow depth-of-field image of green computer circuit board

Leadless Device Placement

Leadless chip carriers, also known as MicroLeadFrames, continue to be a popular package for surface mount applications. QFN and DFN packages offer a variety of benefits including reduced lead inductance, a small footprint, thin profile and low weight. Designers should note that special considerations are needed to properly design the board and to mount the package. For enhanced thermal, electrical and board-level performance, the exposed pad on the package must be soldered to the board using a corresponding thermal pad on the board. Also, for proper heat conduction through the board, thermal vias need to be incorporated in the PCB in the thermal pad region. Clearance considerations depend on the application.

Some of the factors that can affect the mounting of the leadless package to the board and the quality of the solder joints are as follows:

  • Type of vias
  • Board thickness
  • Surface finish on the board
  • Lead finish on the package
  • Type of solder paste used
  • Amount of solder paste applied
  • Stencil design
  • Reflow profile