Figure 6 shows the exterior appearance of the packaged pressure sensor (sacrifice-replacement
approach) and its cross-section image at section A-A. The top surface of the sensing membrane was
entirely free of EMC contamination, so the effectiveness of the photoresist block in shielding the
silicon membrane of the pressure sensor was confirmed. The top surface of the silicon membrane was
fully exposed to freely sense the environment pressure through the sensing-channel of the packaged
pressure sensor. To ensure a full contact between the mold surface and all of the sacrificial photoresist
blocks, a very small interference value was deliberately designed between the depth of the mold cavity
and the total package height. Consequently, the top surface of the photoresist block was squeezed as
the transfer mold was closed. The concave appearance of the photoresist block was due to the mold
squeeze and can be improved with a proper interference design. The photoresist block also effectively
protects the sensing membrane of the pressure sensor from EMC bleeding, improving the yield of the
packaging process. As shown in Figure 6(b), the sidewalls of the sensing channel tapered slightly in
the outward direction. The opening size of the sensing channel on the topside is slightly larger than
that on the bottom-side. The slight geometry deformation in the cross-section of the sensing-channel has no negative influence on the pressure sensing of the packaged pressure sensor. The sacrificereplacement
approach was verified as useful for a pressure sensor application. Due to the process
requirement of cold-mount specimens, a clear epoxy (CMA1-K02, Pentad Scientific Co., Taiwan) was
used to fill the cold-mound mold during the specimen preparation process. The original space of the
open channel is a real cavity instead of the cold-mounted clear epoxy, as shown in the cross-section
image of the packaged pressure sensor [Figure 6(b)].