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Warpage Control of Thermally Enhanced PBGA Package with Internal Heat Spreader during Reliability Test
Keywords: Warpage, Temperature Cycling, BGA
Thermally enhanced PBGA package with internal heat spreader (TEPBGA-II) is becoming more and more popular due to the ever growing power dissipation requirement of the advanced CMOS Logic devices. The additional stiffness provided by the Cu heat spreader also helps the package to remain flat during SMT reflow process. However, it has been observed that, in some cases, TEPBGA-II package would show larger warpage than regular PBGA in accelerated stress test such as air temperature cycling (AATC). The excessive warpage may increase yield loss during test. It could also cause the violation of the criteria set by JEDEC for component temperature cycling (JESD22-A104C). In this work, two types of Cu alloys were evaluated for the heat spreader of TEPBGA-II packages. The packages went through simulated SMT reflow and were then stressed in air temperature cycling at -55~125oC and 0~125oC, respectively. In-situ deformation monitoring with strain gages attached on the heat spreader showed that either plastic or elastic behavior of the package can be expected depending on the Cu alloy and cycling condition. Laser profilometer measurement confirmed that the package with plastic deformation would show excessive warpage after temperature cycling. The hardness of the Cu materials was evaluated before and after the stressing and its correlation to the package deformation will be discussed. A finite element model was also created to assess the impact of cycling condition on the thermal stress and driving force for package warpage. The results of these analyses will be used to generate criteria for selecting heat spreader material to ensure the flatness of TEPBGA-II package in temperature cycling. Finally, the packages were assembled to PCB board and solder joint reliability tests were performed to understand the impact of Cu heat spreader material on SJR.
Min Ding, Senior Packaging Engineer
Freescale Semiconductor
Austin, TX

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