Warpage Control Technology using 300 mm Waffle Wafer Evaluated by High-Precision FEM Analysis

We will discuss warpage control using a novel waffle wafer to ensure the processing of COW for chiplet integration. Conventional COW, with thick mold resin, causes wafer warpage due to CTE mismatch, limiting processes such as BEOL and the multi-stack of wafers. It has been observed that the total volume of mold resin predominantly determines warpage, and the use of the waffle wafer helps reduce it. By using the waffle wafer after die bonding, with a mold thickness of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">70\ μ m</tex> , the wafer warpage was reduced by about <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">100\ μ m</tex> compared to non-waffle wafer usage. For trench depth uniformity of the waffle wafer, even with the same volume of mold, the lowest warpage is estimated when the trench depth is localized at the outer region of the waffle. According to these results, the use of the waffle wafer is suitable for reducing warpage in the COW process, and controlling trench depth can further minimize warpage.