Adhesion evaluation of the heat resistant pressure sensitive adhesives at elevated temperatures for MEMS gyroscope testing

Abstract

Due to the requirement of high throughput, functional testing of MEMS gyroscopes should be performed on wafer level while the wafers are still on the carrier tape. In addition, it is often required that the functional characterization is carried out also at elevated temperatures, up to 150°C. The fact that comprehensive characterization of gyroscopes can take tens of minutes sets stringent requirements for the tapes where they are mounted. In this work the applicability of five different commercial back-grinding tapes of Si wafers were evaluated based on the following criteria: thermal stability, change in adhesion with increase in temperature, and the amount of residues on peeled surfaces. The adhesion on three surfaces (polished silicon, polymer, and brushed steel) was measured and evaluated in terms of adhesion strength and adhesion work. The adhesive polymer on all five base films was modified acrylic with different compositions of additives and the base film was ethylene vinyl acetate, polyethylene terephthalate, or polyolefin. Two of the tapes were UV curable. Four of five tapes passed the thermal stability test without noticeable changes in appearance. The adhesion strength was measured by employing the tensile test (T: 80, 100, 125 and 150°C; t: 0.5, 1, and 1.5 h) and the adhesion work was determined based on the stress-strain measurements. The results were analysed by the Analysis of Variance and Bonferroni all-pairwise mean comparison test. The following conclusions were made: i) the surface material affects adhesion significantly, ii) the non-UV tapes can sustain elevated temperatures better than the UV tapes, iii) as the temperature was increased the adhesion of all tapes increased until about 100 °C, after which it decreased notably with further increase in temperature, iv) the adhesion remained stable for about 60 minutes after which a decrease in adhesion was recorded. The detachment work and the amount of residue showed strong correlation as they are both dependent on the amount of adhesive fibrillations formed during detachment.