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Enhanced Polymer Passivation Layer for Wafer Level Chip Scale ...

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Figure 3.7 SolderBrace film thicknesses as a function of spin speed<br />

3. Soft baking: Right after the coating, the wafer was pre-baked at 100 o C on a hot plate <strong>for</strong><br />

5 minutes to remove all of the solvents from the material. After soft bake completion, the<br />

hotplate was turned off and the wafer cooled slowly to room temperature. The softbake<br />

time and temperatures were optimized based upon the film thickness and sample stability.<br />

Prolonged dry times and higher temperatures decreased the via size and cured the film<br />

prior to exposure.<br />

4. Edge bead removal: It is a standard requirement <strong>for</strong> a lithographic process. Without any<br />

intervention, the material may accumulate at the edge of the wafer, up to several times<br />

51

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