The balloon catheter is one of the principal instruments of non-invasive vascular surgery. It is used most commonly for angioplasty (and in recent years for delivering stents) at a multitude of different sites in the body from small arteries in the heart to the bilary duct. It is composed of a polymer balloon that is attached to a polymer shaft at two points called the distal and proximal bonds. The diverse utility of balloon catheters means a large range of component sizes and materials are used during production; this leads to a complexity of bonding methods and technology. The proximal and distal bonds have been conventionally made using cyanoacrylate or UV curing glue, however with performance requirements of bond strength, flexibility, profile, and manufacturing costs these bonds are increasingly being made by welding using laser, RF, and Hot Jaw methods. This paper describes laser welding of distal and proximal balloon bonds and details beam delivery, bonding mechanisms, bond shaping, laser types, and wavelength choice.
The small focused spot size and localized heating possible with laser soldering makes it an attractive alternative technique for bonding surface mount devices with small lead pitch onto a printed wiring board. Using a Nd:YAG laser, we have applied this technique to reflow soldering of a test device-a 224-pin quad ceramic chip (lead spacing 25 mil)-onto pretinned substrates. The soldering step was incorporated into a larger workcell, in which an Adept robot was used to place the component in position and also to scan the laser beam, delivered via a fiber, over the leads to be soldered. The mobile laser head was modified to accept a miniature CCD camera coupled to a Cognex vision system, which allowed coincident viewing of the soldering process and postsoldering inspection of the joints.
The drive towards miniaturization in electronics assembly has produced new devices with small lead pitch and high lead count which are difficult to bond reliably to substrates using conventional mass soldering technology. Micro-soldering using lasers has the potential to solve many of the problems involved. The results of Nd:YAG laser soldering trials on a ceramic chip with Kovar leads spaced at 0.025 in. are described. The results are compared with the predictions of a detailed finite-element thermal model of the systems and also with real-time thermocouple measurements of the temperature reached at specific locations during the soldering step. Implications for future work in this area are discussed.
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