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|Experimental and Numerical Characterization of Panel Warpage for Low Cost Package Development on 1-Block Panel|
|Keywords: Warpage, 1-block panel, FBGA|
|1-block panel, a strip with single panel, is going to be the main stream blockcoming design as it can significantly improve the package output comparing with traditional 4-panel strip. For example, a 4-panel strip of 240x62.5mm2 can contain 64 units with package size of 13x13mm2, while the 1-block panel of 240x74mm2 can contain block to 85 units of the same package size, which is about 30% increment. However, the thermo-mechanical warpage is a big challenge in manufacture processing. The large warpage after molding might prevent the strip travel into the magazine, and it may also cause handling and processing issues during ball mounting and singulation processes. Therefore it is crucial to control the warpage at different stages. The objective of this study is to characterize and optimize the warpage of 1-block panel for Ball Grid Array package (BGA) at different stages. Firstly after molding, the strip warpage was measured from room temperature to high temperature (170oC), and then the strip was sent for post mold curing (PMC). After PMC, the strip warpage was measured again following previous method. Furthermore, the warpage at different temperature was measured block to reflow temperature (260 oC) to see the reflow effect on warpage. The measured warpage at above three stages were compared in order to identify potential process bottleneck. With the measured warpage data at different process stage, a thermo-mechanical model was created to simulate the warpage behavior with Finite Element Method (FEM). To select a proper material element in the simulation, some solid elements and shell elements were investigated. It was showed the element selection is also important, different element may result different warpage data and temperature sensitivity. While a good shell element selection can save a lot of computation resource. The warpage measured at different temperature and process stage was correlated to the simulation. Combining the simulation and experimental data, suggestions were proposed to improve the BGA 1-block panel warpage.|
|Yongbo Yang, Senior Engineer
United Test and Assembly Center