Low Temperature Electroless Deposition of Hard Magnetic Alloys for the Metallization of Additive Manufactured Functional Microstructures

Abstract

In the last few decades additive manufacturing is finding applications in the field of microdevices production. Techniques like sterolithography (SLA), two photons lithography (TPL) and others [1] have the potential to reach the micrometric scale required for the realization of devices like polymeric based microelectromechanical systems (MEMS) or magnetically actuated microdevices. The most precise and versatile additive technologies however use polymers as materials. For this reason a fundamental step of the manufacturing process is the application of a metallic layer to provide conductivity, essential for MEMS, or to make sensitive the device to the presence of a magnetic field. Many different metallization methods can be applied, but one of the most attractive in terms of cost and flexibility is electroless deposition [2]. The use of this all-wet technique introduce however some major issues when plating on the resins usually employed in SLA or TPL. The main problem is in particular related to the temperatures typical of some electroless baths, which makes them incompatible with polymers that in some cases present reversible transition temperatures as low as 40 °C. To successfully metallize SLA and TPL resins a great attention must be devoted to the choice and optimization of compatible electroless processes. Between the possible metallic layers that can be applied in relation to the type of microstructure produced, hard magnetic alloys are of great interest. Such materials, and in particular their ability to retain magnetization, can be used to actuate or manipulate different classes of devices. Examples may include magnetically actuated microswitches, sensors or others [3]. In the present work two processes to deposit hard magnetic CoNiP, operating at two different temperatures, are presented and applied to the plating of microsized functional structures. The main advantages or disadvantages of using one temperature with respect to the other are discussed as a function of the target application. Some general problems related to the plating of stereolithography printed small structures are analyzed as well. These include difficulties coming from the chemical and physical properties of the resins, from the activation step or from the solution itself. [1] M. Vaezi, H. Seitz, S. Yang; Int. J. Adv. Manuf . Technol. (2013) 67, 1721–1754 [2] Y. Yan, A. A. Bettiol, Photonics Global Conference (PGC), 2010, pp. 1 – 4 [3] S. Kim et al.; Adv. Mater. 2013, DOI: 10.1002/adma.201301484