FEATURED ARTICLE Introduction to Laser Micromanufacturing BY RONALD D. SCHAEFFER


Laser micromanufacturing is just like traditional manufacturing except that we use photons (light!) instead of, for instance, drill bits and saw blades. Lasers are used for machining, marking, welding and surface treatment. This article provides a brief summary of how lasers are used in several exemplary situations. In conclusion, a discussion is made concerning the use of Contract Manufacturers with respect to owning                    involves lasers for material removal, addition or alteration and furthermore, the feature sizes on target are less than 1 mm (and usually much less) and the material thickness is also less than 1 mm (and again, usually much less).


          some unique properties that make it attractive for machining purposes. So, why use lasers for materials processing? First, they are non-contact meaning that there is less chance of damage to the part and no tool wear. Second, they can be very selective in the material removal or joining process. By choosing the right laser wavelength and energy density on target, we can, in many cases, remove one material selectively over another or weld dissimilar materials. A third reason is that lasers can be very  manufacturing of a part might be more affordable using custom, hard tooling, but this is very expensive and cannot usually be done for prototypes. Lasers make exceptional prototyping devices         other technologies that have their own inherent disadvantages.


Because lasers are available from the infrared portion of the electromagnetic spectrum through the ultraviolet, we have a lot of choices concerning just which laser to use. In general, IR lasers (like CO2


depending on the material, etc. In any case, the key to clean and low taper processing seems to be Peak Power Intensity. High PPI is achieved by any combination of short pulse length, high energy per pulse and focusing to a small spot size. Fortunately, new lasers have been commercialized over the past few years which now allow us to go down into the picosecond (10-12


seconds) and even femtosecond (10-15 seconds) pulse


length regime, which turns out to be extremely valuable for micromachining applications especially.


For joining and deposition, longer wavelengths and longer pulse lengths (or cw = continuous wave) are used since the purpose is to precisely deliver heat to a certain point. Longer wavelength lasers inherently introduce heat into the system by exciting the vibration-rotation bonds. Figure 1 shows a graph depicting laser wavelength plotted against pulse length. It can be seen that in the upper right hand corner the IR lasers with long pulse lengths are used for joining applications, while machining is carried out in most other quadrants. There are no big manufacturing applications currently for UV lasers with long pulse or CW output.


CW ms μs ns ps fs


and Nd:YAG for instance) are infrared lasers and  lasers on the other hand can, in principle, have enough photon energy to break chemical bonds without heating the material  ‘cold’ process. Even for UV lasers though, longer pulse lengths can increase the thermal component of the laser processing, so for material removal we typically like to work with the shortest pulses possible, given cost and reliability requirements. As a general statement, pulse lengths over 1 ns (10-9


seconds) show thermal side effects and pulse lengths below 1 ns may not, 14 LIATODAY FOCUS: SCIENCE & RESEARCH SEPTEMBER/OCTOBER 2014 UV Visible Wavelength Figure 1. Laser Pulse Duration vs Wavelength


The most important thing in material removal applications is that there is strong absorption of the incident photons – at least 50 percent absorption is needed and the closer to 100 percent the better. Absorption depth is a function of the material, the incident energy density and also the laser wavelength – as a


IR Welding


CW or Long Pulse Purely Thermal Input


Micromachining - Ablation -<30ns, typically UV


-5-10 ps, greater range of materials -fs less than the thermal diffusion timescale


Pulse Duration


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