Performance of laser bonded glass/polyimide microjoints in cerebrospinal fluid

Abstract

In this paper, laser bonded microjoints between glass and polyimide is considered to examine their potential applicability in encapsulating neural implants. To facilitate bonding between polyimide and glass, a thin titanium film with a thickness of 2 microm was deposited on borosilicate glass plates by a physical vapor deposition (PVD) process. Titanium coated glass was then joined with polyimide by using a cw fiber laser emitting at a wavelength of 1.1 microm (1.0 W) to prepare several tensile samples. Some of the samples were exposed to artificial cerebrospinal fluid (aCSF) at 37 degrees C for two weeks to assess long-term integrity of the joints. Both the as-received and aCSF soaked samples were subjected to uniaxial tensile loads for bond strengths measurements. The bond strengths for the as-received and aCSF soaked samples were measured to be 7.31 and 5.33 N/mm, respectively. Although the long-term exposure of the microjoints to aCSF has resulted in 26% reduction of bond strength, the samples still retain considerably high strength as compared with the titanium-polyimide samples. The failed glass/polyimide samples were also analyzed using optical microscopy, and failure mechanisms are discussed. In addition, a two dimensional finite element analysis (FEA) was conducted to understand the stress distribution within the substrate materials while the samples are in tension. The FEA results match reasonably well with the experimental load-displacement curves for as-received samples. Detailed discussion on various stress contours is presented in the paper, and the failure mechanisms observed from the experiment are shown in good agreement with the FEA predicted ones.

Study of two different thin film coating methods in transmission laser micro-joining of thin Ti-film coated glass and polyimide for biomedical applications

“…The biological implants need to be packaged so that the system does not degrade when exposed to a biological environment. The applicability of laser bonded micro-joints between glass/ polyimide and titanium/ polyimide in encapsulating neural implants was also studied by our group (Newaz et al, 2006;Mian et al, 2007). As the findings from those studies were very promising, research was continued to further improve the joint strength and some of the results are presented in this study.…”

“…Furthermore, this joining process is flexible, has shorter processing time, can provide consistent quality and is repeatable. Earlier studies by our group in transmission laser microjoining of dissimilar materials like polymers to metals or polymers to metal film coated glass was proven to be successful (Bauer et al, 2004;Newaz et al, 2005;Mian et al, 2005Mian et al, , 2007. Glass, titanium and polyimide were used in those studies as they are proven biocompatible materials and are potential candidates in encapsulating devices for neural implants (deCharms et al, 1999;Gilleo, 2001;Grigorian, 2007;Lee et al, 2004;Metz et al, 2001;Wise et al, 2004).…”

Bonding mechanisms of laser‐fabricated titanium/polyimide and titanium coated glass/polyimide microjoints

“…4) were loaded in tension in a six-axis submicron tester 4,5,22 for bond strengths. The machine is fully controlled by a computer and can be operated both, in displacement and load controls, along 6 degrees of freedom, i.e.…”

“…5,6 Titanium is believed to interact primarily with the oxygen double Bonding mechanisms of laser-fabricated microjoints 507 bonds to carbon in the carbonyl groups (>C O), which form part of the PI molecular chains, and to form bonding configurations of the type Ti-O-C. 5,6 In our other related works, we have presented the mechanical characterization of titanium coated glass/polyimide (TiGPI) bonds. 4,7,8 In this case, the glass substrate was coated with a thin titanium layer because the reactivity of titanium with PI was already verified through Refs 5 and 6. Among many other advantages, titanium coated substrates have shown better surface characteristics and biocompatibility.…”

Finite element modeling of transmission laser microjoining process

“…With the advent of biomedical implants and their encapsulation, the laser bonding technique has potential to become a unique joining process for its high precision and biocompatibility property, as no additional adhesive materials are required in this case. Our research group in collaboration with Fraunhofer USA has been studying the applicability of laser fabrication process in joining dissimilar and biocompatible materials [6][7][8][9][10][11][12][13][14].…”