Considerations For QFN Thermal Pad Solder Coverage
Authors: Thomas A. Adams, P.E. Company: Plexus Corporation Date Published: 10/16/2011
Abstract: Circuit designers have been exploiting the thermal performance of the exposed thermal pad die packages like the QFN (quad flat pack no leads). Manufacturers assembling these devices to the PCB (printed circuit board) seek clear acceptance criteria for allowable solder voiding in the thermal pad of QFNs. When the design of PCBA (printed circuit board assembly), choice of assembly materials, and processes cannot preclude the formation of solder voids, a level of acceptability must be determined. Solder workmanship and acceptance standards generally provide some guidance, but due to the thermal function of the exposed die pad, a fixed limit for allowable solder voiding is not valid for all applications. This research examines existing data and analysis of prior work that may provide guidance on acceptability criteria of voiding in the QFN BTC (bottom termination components). Voiding, depending on the heat transfer requirements, could lead to degradation of the electrical performance, life, and reliability of the IC (integrated circuit).