A Small “Dead-Area” Packaging Approach for Front Side Illuminated Photodiode

To increase the density of packaging, we propose a novel three-dimensional high-aspect-ratio packaging approach for conventional front side illuminated photodiode, which is able to fabricate a narrow spacing between the edge of package and the edge of die. Sliver-epoxy adhesive is used as conductive layer and formed over the SU8 photoresist by fluid dispensing or stencil printing process. In addition, a package substrate is designed and fabricated. The electro-optical properties of photodetectors, which is based on silicon photomultiplier, are measured, such as current-voltage characteristic, dark count rate, photoelectron spectrum, and photon detection efficiency. The test results show that there is no significant differences of electro-optical characteristics between this packaging approach and conventional wire bonding. Meanwhile, the minimum area of photodetector packaged successfully is 11.02 mm2 (3.36mm×3.28mm) and it is not 1.2 times greater than that of the chip before packaging. This packaging approach is promising for compact packaging, where the flip-chip and TSV are hard to carry out, and this technology, at the same time, makes it possible to obtain succinctly and cost-effectively a chip-scale package.