I'm a R&D engineer, recently I'm doing some evaluation on thermal performance of exposed die paddle. The package outline for the exposed die paddle package remain the same, the only changes is deeper the downset of the die paddle until the bottom of the die paddle is exposed. People claimed that this will improve the thermal performance of the package, i.e. the junction to ambient temp should be lower (theta Ja). However, through the computer simulation (FEA) and also practical measurement, it show a worst off result, the junction to ambient temperature is increased (higher theta Ja). My explanation to this is when the die paddle is exposed, the distance between the inner leadframe with the die is far compare to the standard package which is almost parallel. The outer lead of the package would actually acts as an extended surface to help to dissipate heat from the package, in addition, the lead is connected to a PCB, and the copper trace layer of the PCB has a very good thermal conductivity (about 2.5X of leadframe), so the outer lead not only dissipated heat through convection but also conduction. When the die paddle is exposed, it actually degrade the thermal performance of the leadframe. Even though, the heat dissipation through the die paddle is improved, but the surface area of the exposed die paddle compare to the exposed surface of the leadframe is not significant, especially for the package with high leadcount. In addition, the heat dissipated from the exposed die paddle is only through convection compare to leadframe by convection and conduction. The convection rate of the exposed die paddle also limit by the convection coefficient of the still air. So the overall thermal performance of the exposed die paddle is being degrade, so a higher Theta Ja is expected. Please share with me your opinion regarding this issue. Thanks. Regards Cindy Hoe HC Hoe (Cindy) R&D Engineer (Package Analysis Section) E-Mail : [log in to unmask] Tel : 605-5262333 ext 304 Fax : 605-5265333 ################################################################ TechNet E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c ################################################################ To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body: To subscribe: SUBSCRIBE TechNet <your full name> To unsubscribe: SIGNOFF TechNet ################################################################ Please visit IPC web site (http://jefry.ipc.org/forum.htm) for additional information. For the technical support contact Dmitriy Sklyar at [log in to unmask] or 847-509-9700 ext.311 ################################################################