Document Type




Publication Date



Institute of Electrical and Electronics Engineers (IEEE)

Source Publication

IEEE Transactions on Components, Packaging and Manufacturing Technology

Source ISSN



This paper investigates using an SU-8 photoresist as an adhesive material for flip-chip bonding, assembling, and packaging microelectromechanical systems devices. An important factor, when using SU-8 as an adhesive material is to control ultraviolet (UV) exposure during fabrication to maximize bond strength due to material cross linking. This approach is much improved over previous efforts where SU-8 bake times and temperatures where changed to alter material cross-linking. In this paper, bake times and temperatures were maintained constant and total UV exposure energy was varied. Once fabricated, bond strength was systematically tested to determine the tensile loads needed to separate bonded structures. The resulting separation force was shown to increase with UV exposure and ranged from 0.25 (5-s exposure) to 1.25 N (15-s exposure). The separation test data were then analyzed to determine the statistical significance of varying UV exposure time and its effect on SU-8 cross-linking and bond strength. The data show that total UV exposure dose is directly correlated with the bond strength of SU-8 bonded structures. By varying only UV dose, the separation force data exhibited a statistically significant dependence on SU-8 cross linking with a 5% probability of error. Further, SU-8 etch resiliency increased by approximately 40%-60% as cross linking was increased with UV exposures ranging from 5 to 15 s.


Accepted version. IEEE Transactions on Components, Packaging and Manufacturing Technology, Vol. 5, No. 3 (March 2015): 301-306. DOI. © 2015 IEEE. Used with permission.

Ronald A. Coutu was affiliated with the Department of Electrical and Computer Engineering, Air Force Institute of Technology, Wright-Patterson AFB, OH at the time of publication.

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