Laser soldering

Y. Wadia, H. Xie, and M. Kajitani, "Liver repair and hemorrhage control by using laser soldering of liquid albumin in a porcine model," Lasers Surg. Med., 17 319-328,2000. 

The presence of the hot liquid flux during soldering helps to promote thermal uniformity on the board.This is very important in mass reflow and may play an even more crucial role in some solder-in-place processes such as hot-bar laser. In some forms of laser soldering, the flow of hot flux may help to preheat leads and pads, readying them for solder joint formation. In the case of hot-bar soldering, a pool of liquid flux may help to even out thermal disparities over the length of the heated bar. 

When laser soldering is implemented properly, high soldering yields and exceptional bond characteristics are possible. Its use is usually relegated to low-volume soldering applications. 

For successful laser soldering, it is necessary to use tooling to hold the component—or, more specifically, the component leads—down to circuit board pads. 

Laser soldering requires no hot zones to profile or maintain, does not induce substrate warpage, and requires no heated bonding head that can degrade or vary with usage. Components can be spaced exceptionally close to one another—closer than currently permitted for other techniques, especially when one considers rework. 

FIGURE 47.33 Laser soldering (a) through-lead laser soldering (b) through-pad laser soldering (B). 

One of the attractions of working with a laser is the fact that its beam can be split for multiple use within one station or even shared between two or more stations. The split can be accomplished by the use of bifurcated fibers or beam splitting mirrors. The beam of a single laser cavity can be duplexed to solder two sides of a surface-mount component simultaneously. It is entirely possible to share a common beam between two or more laser soldering stations either simultaneously or in a time-shared manner. 

FIGURE 47.35 For laser soldering to be effective, it is necessary to have lead-to-pad, pad-to-pad, and lead-to-pad coplanarity (a) noncoplanar component leads on constant-volume (coplanar) solder pads (b)a coplanar lead array on noncoplanar PWB solder lands. 

Solder requirements are the same as for any other process. There are no ahoy composition requirements specific to laser soldering, as this soldering method is compatible with leaded or lead-free solder alloys. Even high-temperature alloys can be soldered by this technique. When single-point laser reflow is apphed, the board quality and integrity are not compromised if parameters are chosen and adequately controlled. 

Laser soldering is not prone to solder bridges and if component leads are held down to solder-coated PWB lands, then soldering defects are rare. Perhaps the most common characteristic... 

Chang, D. U, Analytical Investigation of Thick Film Ignition Module by Laser Soldering, Proceedings of ICALEO 85,1985, pp.27-38. 

D. Simhon, A. Ravid, M. Halpem, I. Cilesiz, T. Brosh, N. Kariv, A. Leviav and A. Katzir, Laser soldering of rat skin, using fiber optic temperature controlled system ,. Lasers Surg Med, vol. 29(3), pp. 265-273,2001. 

Laser soldering provides very precise heat source for precision work. 

Microdispensing unit 20-axis manipulator Laser soldering system 3D camera system Wafer station 3D placement head... 

Nicolics, J. Musiejovsky, L. Semerad, E. Optimization of process parameters for laser soldering of surface mounted devices. IEEE Trans. Comp., Hybrids, Manuf. Technol. Dec. 1992,15 (6), 1155-1159. Zarrow, P. Lead free don t fight a fact, deal with it. Circuits Assem. Aug. 1999,10,18-20. 

Laser soldering provides an alternative solution to selective joining. The progression of the semiconductor laser has made this method more attractive for soldering. Nevertheless, it only represents a small niche because it requires a direct line of vision and is a rather delicate process. The use of nitrogen is not very common for laser systems because no benefit had been identified. 

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