Effects of Aspect Ratio of Photoresist Patterns on Adhesive Strength between Microsized SU-8 Columns and Silicon Substrate under Bend Loading Condition

Abstract

The adhesive strength between microsized SU-8 columns and a silicon substrate under the bend loading condition has been studied to clarify effects of the columnar aspect ratio. The maximum tensile stresses at the root are almost the same within the range of high aspect ratios (1.4–2.1) of the SU-8 columns, in which delamination cracks are opened by bend loading (mode I). This result shows that the delamination is induced by the maximum tensile stress at the root. On the other hand, the maximum tensile stress irregularly changes within the range of low aspect ratios (0.8–1.1) of the specimens and features of the delamination surfaces differ from those within the range of high aspect ratios. This result suggests that the delamination mode must change from mode I to mode II or the complex mode. All the results show that the adhesive strength of a SU-8 column with the range of high aspect ratios of 1.4 and more obtained from the adhesive bend test can be analyzed as the maximum tensile stress at the root (the adhesive bend strength) in this study.

Influences of pretreatment and hard baking on the mechanical reliability of SU-8 microstructures

“…This paper focuses on revealing the influences of pretreatment and hard baking on the adhesion strength and the tensile fracture strength. The pretreatment processes that we have considered are O 2 plasma ashing and primer coating, which are said to affect the mechanical properties of SU-8 as with hard baking [24][25][26][27][28]. O 2 plasma ashing is the process for removing organic materials from the top surface of a wafer.…”

Effects of Specimen Dimensions on Adhesive Shear Strength between a Microsized SU-8 Column and a Silicon Substrate

“…Figure 1 shows the columnar shapes of adhesive test pieces with four different diameters (50, 75, 100, and 125 m) on a substrate for the purpose of obtaining four different aspect ratios of the SU-8 columns on a Si wafer under the same processing condition. 25,26) A film of SU-8 with 50 m thickness (Nippon Kayaku SU-8 3000 film) was selected to easily control the resist thickness on Si. A silicon wafer was diced into three pieces of 15 mm 2 using a dicing saw.…”

“…The loading point is approximately 10 m, within the aspect ratio of less than 0.2 in this study; thus, the generated bend stress at the columnar root is much smaller than the adhesive bend stress. 22,25) Therefore, the effects of bend stress on the delamination should be negligible; in other words, the delamination should occur by shear force in the shear-type test. In addition, the measured force includes only the shear component using a load cell, which can detect only the shear force direction.…”

“…1) to clarify effective factors of the adhesive strength. [21][22][23][24][25] Both bend and shear loading modes were available for the adhesive testing method (Fig. 2).…”

“…In our previous study, the adhesive bend strength, which was obtained from the bend-type mode test, was slightly changed with the columnar aspect ratio. 25,26) In particular, in the range of the aspect ratio within 1.2, the effect became too large to ignore, because the compression and shear components, which are included by the applied force, increase with decreasing aspect ratio.…”