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Bonding of metals to transparent materials (glasses, crystals, etc.) is commonly used for several applications in modern defence manufacturing including for hermetic sealing and precision optics mounting. Common methods include the use of organic adhesives or glass frit interlayers as well as diffusion, anodic and arc bonding. Such techniques are typically esoteric and operator skill dependent. They can introduce large heat input risking the device integrity or are subject to post-process creep and volatile components outgassing, which can lead to contamination of optical surfaces and subsequent device degradation. Adhesives in particular are not truly hermetic and so are largely unsuitable for electro-optics and miniature lasers fabrication. They are sensitive to environment, swelling in the presence of moisture, softening at high temperatures or becoming stiff and brittle at low temperatures. All of the above are highly undesirable. Apart from limiting the range of material combinations possible to join, such bonding often ends up as a lengthy, error prone manufacturing step. This explains why so many manufacturers would like to replace such bonding with a more deterministic process.
Recently [1] direct microwelding of glass to metal (BK7 and fused silica to Al) has been demonstrated utilising ultrafast lasers which offer non-contact fabrication with high precision, high process speed and very small heat affected zones. In this paper we will showcase a purpose-built ultrafast laser prototype for laser microwelding of 10-20mm thick bulk optics (lenses, waveplates, prisms) to flat aluminium or stainless steel mounts with sufficient bond strength for use in advanced manufacturing for defence applications. Various demonstrated case studies in aerospace electro-optics assemblies and flexible electronics hermetic sealing for device encapsulation will be discussed in detail including bond strength shear test characterisation, thermal and vibration cycling. This laser microwelding tool is suitable for early adoption of this microwelding technology and for process development in several other optical material welding applications (e.g. glass to silicon; glass to ceramic, Nd:YAG to metal, etc.).
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