Laser bonded microjoints between titanium and polyimide for applications in medical implants

Abstract

Bioencapsulation of medical implant devices, and neural implant devices in particular, requires development of reliable hermetic joints between packaging materials that are often dissimilar. Titanium-polyimide is one of the biocompatible material systems, which are of interest to our research groups at Wayne State University and Fraunhofer USA. We have found processing conditions for successful joining of titanium with polyimide using near-infrared diode lasers or fiber lasers along transmission bonding lines with widths ranging from 200 to 300 microm. Laser powers of 2.2 and 3.8 W were used to create these joints. Laser-joined samples were tested in a microtester under tensile loading to determine joint strengths. In addition, finite element analysis (FEA) was conducted to understand the stress distribution within the bond area under tensile loading. The FEA model provides a full-field stress distribution in and around the joint that cause eventual failure. Results from the investigation provide an initial approach to characterize laser-fabricated microjoints between dissimilar materials that can be potentially used in optimization of bio-encapsulation design.

Chemical and Physical Properties of Polyimides: Biomedical and Engineering Applications

“…A. Main et al have been tested laser joined titaniumpolyimide samples for bond strength, andwas observed that the laser bonding parameters such as laser power and feed speed affect the bond strength of all material systems [35]. The applicability of laser joining for a specific material combination and the selection of the appropriate approach depends on the optical properties of the materials.…”

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.…”

“…In our previous study, we have analyzed the laser-fabricated titanium/polyimide (TiPI) joints, and observed the presence of a sharp interface based on the creation of chemical bonds between Ti, and O and C contained in PI. 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.…”

Fibre laser joining of highly dissimilar materials: Commercially pure Ti and PET hybrid joint for medical device applications

“…Successful laser joining of metals to plastics has been demonstrated for a range of material combinations. Examples include CFRP-zinc coated steel [4], CFRP-SS304 [5], HDPE-SS304 [6], PA6-SS304 [1], PA66-SS304 [7], PET-A5052 [8,9], PET-AZ91D [10], PET-Cu [9], PET-SS304 [9,[11][12], PET-SS316L [13], PET-Ti [14,15], PMMA-SS304 [16] and PI-Ti [17]. Katayama et al [11] applied continuous wave (CW) diode laser to join SS304 and PET and reported that high strength plastics and metal joints can be fabricated by laser heating due to the formation of mechanical, physical and chemical bonds (e.g.…”

“…They employed response surface methodology (RSM) to establish mathematical relationships between different process parameters (i.e., laser power, joining speed and stand-off distance) and joint strength. Mian et al [17] applied CW diode, Nd:YAG and fibre lasers to join the Ti with PI. They developed a FEA model to predict the joint strength and the predicted values were in good agreement with the experimental results.…”