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60 SMT007 MAGAZINE I OCTOBER 2026 absorption, and production economics must all align to maximize the technology. Still, why is laser soldering getting so much atten- tion? It could be because rising board complexi- ties are making it a requirement. Densely popu- lated boards are more likely to have solder joints that cannot be reached by other well-established methods, such as wave soldering. Complexity also raises the possibility of conflicting heat require- ments across the board. For example, connectors, plastic housings, and heat-sensitive components may make convection reflow a yield-crushing option. If only there were a way to deliver higher soldering temperatures in a precise, no-touch way, just to the spot where it's required. Laser soldering equipment manufacturers will tell you they have the answer. At the heart of the system, naturally, is a laser beam focused on the solder joint, which absorbs the light and converts it into heat until the solder melts and forms the wetted joint. The soldering energy is applied precisely, heating only the solder joint; no other adjacent components experience any significant heat from the process. Typically, near-infrared lasers (808–980 nm) are used as the working laser. 1 Recently, however, some systems have moved to a blue laser in the 450 nm range, as this wavelength often seems to have better absorption efficiency. Occasionally, when jetting solder balls, high-powered Nd:YAG lasers (1064 nm) are employed. Research suggests that selecting the best wave- length is not determined by the solder's specific melting temperature, but by how efficiently the light is absorbed by the joint's solder, pad, lead, and surface finish. This is where blue lasers are gaining traction, as they can reduce the energy required to reflect off metals. Infrared diode lasers, however, remain attractive because they are mature, econom- ical, and widely available. Laser soldering's value, which controls where, when, and how quickly heat enters an assembly, creates a narrower and more demanding process window. In addition, the number of performance parameters to optimize for laser soldering can be significant. This is both a strength and a poten- tial weakness for laser soldering. For example, the amount of energy required may vary between individual solder joints. While this seems an easy requirement to accommodate, compared to, say, wave soldering, the parameters available add to the complexity (though those operators experienced with optimizing convection reflow profiles will see this as familiar territory). Laser absorption parameters include: • Beam diameter, shape, and energy distribu- tion • Focal distance and beam angle • Laser power, ramp rate, and dwell time • Thermal mass of the pad, lead, and connect- ed copper • Solder alloy, flux chemistry, and wire-feed rate • Surface finish, contamination, and oxidation • Part movement and positional tolerance • Cooling rate and resulting intermetallic struc- ture • Use of cameras, pyrometers, and closed-loop power control Keep in mind that the laser applies increasing heat while the beam is on. In contrast, a soldering iron tip applies energy at a steady tempera- ture. Beam exposure time, therefore, becomes a critical parameter. " Research suggests that selecting the best wavelength is not determined by the solder's specific melting temperature, but by how efficiently the light is absorbed by the joint's solder, pad, lead, and surface finish."