Shin-Etsu Support Jig Handles Thin Wafers for Reflow Soldering
Shin-Etsu Polymer Co. Ltd. has developed a jig for handling thin wafers that can endure 260 degrees C in a solder reflow furnace. The tool makes it possible to use a silicone film to attach solder balls to thinned wafers for 3-D stacked chips.
Kenji Tsuda, Asia Contributing Editor -- Semiconductor International, 1/5/2009
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Shin-Etsu Polymer Co. Ltd. (Tokyo) has developed a support jig for handling thin (&50 μm) wafers that can endure 260°C in a solder reflow furnace. The tool makes it possible to attach solder balls to thinned wafers for 3-D stacked chips. The method uses a silicone film, rather than adhesive materials for attachment and solvents for detachment, which eliminates damage to the wafer and reduces any burden on the environment.
To stack IC chips vertically, electrodes on the back surface of a wafer or chip with through-silicon vias (TSVs) must be connected with another solder-bumped chip or wafer. However, it is difficult to form solder bumps on a thinned wafer because the wafer tends to break. Although conventional support frames have not been able to endure high temperatures, the newly developed resin ring and its support substrate can be placed in a reflow furnace.
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| Shin-Etsu Polymer developed a support jig for thinned wafers, including thermoplastic resin substrate (left), and a double ring with silicone film (right). |
Thinned wafers are essential to reduce the cutting time during dicing and to enable a flexible wafer-level packaging (WLP) process. The thinned wafer is attached with a silicone rubber film of 100-200 μm, and fixed with double resin rings. The ringed wafer is put on the thermoplastic substrate and conveyed into a reflow furnace. The support substrate endures multiple cycles of ~300°C heat over short periods.
In the bumping process, solder paste is printed on a thinned wafer that is covered with a silicone film, and solder balls are mounted on it. The solder-ball wafer is placed into a reflow furnace, producing solder bumps on the wafer. The thickness variation of the heat-resistive silicone film is ±10 μm, but Shin-Etsu Polymer said it soon will be able to control it to ±2~3 μm.
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| The bump formation process requires jigs that can withstand high temperatures in a reflow furnace. |
Shin-Etsu Polymer plans to promote the support jig and related processes to chipmakers, assembly subcontractors and equipment makers. One goal is to find an equipment manufacturer that can develop an automated method to remove the wafer from the film, which is now done manually.
