ISSUE 115 MARCH 2025 ULTRAFAST LASERS


THE LASER USER


HOW USP LASER SETTINGS DRIVE


APPLICATIONS IN EV PRODUCTION JIM BOVATSEK Ramping up vehicle electrification plays


a major role in decarbonising mobility worldwide, in order to reach the global net zero goals by 2050 at the latest. Further enhancing battery technology and power electronics, as well as the related production processes, are prerequisites to driving that change.


The past few years have seen rapid advances in electric vehicle production. Manufacturers globally have invested heavily to optimise both their products and production processes, with lasers playing a pivotal role. While high power CW lasers are, for example, used in busbar or contact welding, ultrafast lasers are a key driver when it comes to further enhancing cutting or scribing processes. Due to the high precision and quality needed when cutting lithium (Li) ion battery foils or processing silicon carbide (SiC) substrates used in electric vehicle (EV) power electronics circuits, laser sources must be carefully selected and optimised for the specific application. MKS Instruments conducted some technology deep-dives in their Spectra-Physics industrial laser applications lab, demonstrating how laser pulse settings can enhance or enable applications in EV production processes.


Fast cutting with high-power femtosecond pulses


Lithium-ion batteries are composed of layers of coated metal foils (electrodes). Processing those foils requires high speed, single pass cutting and good edge quality. Femtosecond lasers, such as the Spectra-Physics® IceFyre® FS IR200, are ideally suited to improve cutting results for anode


and cathode Li-ion battery foils. With capabilities such as TimeShift™ pulse tailoring, sophisticated temporal pulse-intensity manipulation is possible, such as burst mode operation with envelope shaping.


To compare cutting processes using TimeShift in burst mode versus conventional single-pulse processing, the maximum cutting speed and the coating “pull back” (how much the coating has receded from the cut edge) have been evaluated. For burst processing, the PRF (pulse repetition frequency) was fixed at 200 kHz and burst pulse counts from 10 to 80 were used. For single pulse processing, a range of PRFs was tested to find a single optimised cutting speed. Figure 1 shows the cutting speeds achieved with various pulse bursts, along with those for optimised single pulse processes (dashed lines).


The data shows that burst mode cutting speeds quickly surpass those with a single pulse, achieving 57% and 75% improvements for the anode and cathode foils, respectively. It is noteworthy that higher total energies are available in a burst envelope of pulses compared to just a single pulse. For example, while the maximum single-pulse energy is ~200 μJ, using bursts of 5, 10, and 20 pulses results in burst envelope energies of up to ~550, ~750, and ~900 μJ. Such large “packets” of energy are evidently beneficial to improve processing speeds.


To assess cut quality, the coating pull back for each condition was measured (Figure 2) and SEM (scanning electron microscope) images were taken to inspect for melting and smearing of the inner metal foil (Figure 3). Less pull


back at the cut edge is preferred and is an indicator of better cut quality.


For both anode and cathode foils, coating pull back initially increases for a 10-pulse burst, but then improves with larger bursts to be nearly equal to (anode) – or less than (cathode) – that with a single pulse. The SEM images for the anode foil show that there is very little smearing at any condition, with the cut looking particularly clean at the 40-pulse condition. While the inner foil of the cathode is less discernable in the images, there appears to be a general trend of thinner and smoother foil edge with increased burst count, which implies reduced melting.


Electrode cutting in burst mode leads to substantial throughput advantages as well as superior or equal quality compared to single- pulse processing. Additionally, the single-pass cutting speeds in excess of 2 m/s are sufficient to keep pace with the reel-to-reel systems used throughout Li-ion battery manufacturing.


SiC scribing with high power picosecond lasers


SiC has generated intense interest amongst electric vehicle (EV) power electronics manufacturers, offering many advantages over traditional silicon electronics for fast, high- current and -voltage devices. However, many fabrication processes are not transferable to SiC due to its higher hardness. For wafer saw dicing singulation, difficulties include chipped die edges, rapid wearing of expensive diamond blades, excessive heat generation, and reduced throughput. To overcome these challenges manufacturers are looking to advanced laser


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Figure 1: Data plot showing the throughput advantage when cutting with pulse bursts compared to a single pulse.


Figure 2: Electrode coating pull back data for processes using single pulses (far left data points) and pulse bursts.


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