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

Figure 3.21 SolderBrace Material Cleaning by Polishing Method
- UV-Defined cleaning: This method was similar to the one described in Section 3.4.1,
but the SolderBrace material was printed on the bumped wafer instead of spin coating
the wafer followed by the solder bumping. Figure 3.22 shows the partially printed 8”
wafer that was used to test this method as the start point. Due to the large size of the
wafer, it was first diced into small pieces or panels. With the pattern mask, UV
exposure and development, the material coated on the top of the solder balls could be
removed (see Figure 3.23). However, for an array of dies or the whole wafer of dies,
the size of the exposed areas was still not consistant which might be caused by the
non-uniform printing over the solder spheres. What is more, silica filler residue was
sometimes left on the solder ball after development (see Figure 3.24).
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