Punching/die cutting. This method takes a different die for each and every new circuit board, which happens to be not a practical solution for small production runs. The action can be PCB Depaneling, but either can leave the board edges somewhat deformed. To lessen damage care must be taken up maintain sharp die edges.
V-scoring. Often the panel is scored on sides into a depth of approximately 30% of your board thickness. After assembly the boards might be manually broken out of your panel. This puts bending strain on the boards that can be damaging to several of the components, specially those near the board edge.
Wheel cutting/pizza cutter. Another strategy to manually breaking the web after V-scoring is to use a “pizza cutter” to slice the other web. This involves careful alignment involving the V-score along with the cutter wheels. Furthermore, it induces stresses inside the board which can affect some components.
Sawing. Typically machines that are employed to saw boards from a panel work with a single rotating saw blade that cuts the panel from either the best or even the bottom.
Every one of these methods has limitations to straight line operations, thus just for rectangular boards, and every one of them to a few degree crushes and cuts the board edge. Other methods are definitely more expansive and can include these:
Water jet. Some say this technology can be accomplished; however, the authors are finding no actual users from it. Cutting is conducted with a high-speed stream of slurry, which is water with the abrasive. We expect it will need careful cleaning following the fact to get rid of the abrasive portion of the slurry.
Routing ( nibbling). Most of the time boards are partially routed ahead of assembly. The remainder attaching points are drilled with a small drill size, making it easier to interrupt the boards out from the panel after assembly, leaving the so-called mouse bites. A disadvantage might be a significant lack of panel area towards the routing space, as the kerf width normally takes around 1.5 to 3mm (1/16 to 1/8″) plus some additional space for inaccuracies. This implies a lot of panel space will likely be needed for the routed traces.
Laser routing. Laser routing provides a space advantage, as being the kerf width is just a few micrometers. By way of example, the little boards in FIGURE 2 were initially outlined in anticipation how the panel could be routed. In this manner the panel yielded 124 boards. After designing the layout for laser depaneling, the number of boards per panel increased to 368. So for each and every 368 boards needed, merely one panel has to be produced as opposed to three.
Routing also can reduce panel stiffness to the point which a pallet may be required for support in the earlier steps in the assembly process. But unlike the previous methods, routing will not be confined to cutting straight line paths only.
Many of these methods exert some extent of mechanical stress around the board edges, which can cause delamination or cause space to build up around the glass fibers. This can lead to moisture ingress, which helps to reduce the long term reliability of the circuitry.
Additionally, when finishing placement of components in the board and after soldering, the ultimate connections between the boards and panel have to be removed. Often this can be accomplished by breaking these final bridges, causing some mechanical and bending stress around the boards. Again, such bending stress could be damaging to components placed close to areas that should be broken to be able to get rid of the board from the panel. It really is therefore imperative to accept production methods into consideration during board layout and for panelization in order that certain parts and traces usually are not positioned in areas known to be at the mercy of stress when depaneling.
Room can also be necessary to permit the precision (or lack thereof) in which the tool path may be placed and to look at any non-precision inside the board pattern.
Laser cutting. The most recently added tool to PCB Router and rigid boards is actually a laser. Within the SMT industry several kinds of lasers are being employed. CO2 lasers (~10µm wavelength) can provide extremely high power levels and cut through thick steel sheets as well as through circuit boards. Neodymium:Yag lasers and fiber lasers (~1µm wavelength) typically provide lower power levels at smaller beam sizes. These two laser types produce infrared light and can be called “hot” lasers since they burn or melt the information being cut. (As an aside, these are the laser types, specially the Nd:Yag lasers, typically used to produce stainless stencils for solder paste printing.)
UV lasers (typical wavelength ~355nm), however, are employed to ablate the information. A localized short pulse of high energy enters the most notable layer of your material being processed and essentially vaporizes and removes this top layer explosively, turning it to dust (FIGURE 3).
The option of a 355nm laser is based on the compromise between performance and expense. For ablation to take place, the laser light needs to be absorbed through the materials to get cut. In the circuit board industry these are generally mainly FR-4, glass fibers and copper. When examining the absorption rates for these particular materials (FIGURE 4), the shorter wavelength lasers are the most appropriate ones for that ablation process. However, the laser cost increases very rapidly for models with wavelengths shorter than 355nm.
The laser beam includes a tapered shape, as it is focused from a relatively wide beam for an extremely narrow beam and then continuous in the reverse taper to widen again. This small area in which the beam is at its most narrow is named the throat. The optimal ablation occurs when the energy density put on the fabric is maximized, which happens when the throat in the beam is simply in the material being cut. By repeatedly exceeding the identical cutting track, thin layers in the material will probably be removed up until the beam has cut right through.
In thicker material it could be necessary to adjust the focus from the beam, because the ablation occurs deeper in the kerf being cut in to the material. The ablation process causes some heating of your material but could be optimized to depart no burned or carbonized residue. Because cutting is done gradually, heating is minimized.
The earliest versions of UV laser systems had enough ability to depanel flex circuit panels. Present machines acquire more power and could also be used to depanel circuit boards up to 1.6mm (63 mils) in thickness.
Temperature. The temperature boost in the content being cut depends upon the beam power, beam speed, focus, laser pulse rate and repetition rate. The repetition rate (how quickly the beam returns towards the same location) depends on the way length, beam speed and whether a pause is added between passes.
An informed and experienced system operator will be able to pick the optimum mix of settings to guarantee a clean cut free of burn marks. There is not any straightforward formula to determine machine settings; they are affected by material type, thickness and condition. Based on the board along with its application, the operator can decide fast depaneling by permitting some discoloring or perhaps some carbonization, versus a somewhat slower but completely “clean” cut.
Careful testing has shown that under most conditions the temperature rise within 1.5mm from the cutting path is lower than 100°C, way below exactly what a PCB experiences during soldering (FIGURE 6).
Expelled material. From the laser useful for these tests, an airflow goes throughout the panel being cut and removes a lot of the expelled dust into an exhaust and filtering system (FIGURE 7).
To check the impact of the remaining expelled material, a slot was cut inside a four-up pattern on FR-4 material using a thickness of 800µm (31.5 mils) (FIGURE 8). Only few particles remained and was comprised of powdery epoxy and glass particles. Their size ranged from typically 10µm to some high of 20µm, plus some could have was made up of burned or carbonized material. Their size and number were extremely small, with out conduction was expected between traces and components around the board. In that case desired, a simple cleaning process could be included in remove any remaining particles. Such a process could contain the application of any type of wiping having a smooth dry or wet tissue, using compressed air or brushes. You could also employ any type of cleaning liquids or cleaning baths with or without ultrasound, but normally would avoid any sort of additional cleaning process, especially a costly one.
Surface resistance. After cutting a path in these test boards (Figure 7, slot in the middle of the exam pattern), the boards were exposed to a climate test (40°C, RH=93%, no condensation) for 170 hr., and also the SIR values exceeded 10E11 Ohm, indicating no conductive material is present.
Cutting path location. The laser beam typically uses a galvanometer scanner (or galvo scanner) to trace the cutting path in the material spanning a small area, 50x50mm (2×2″). Using this kind of scanner permits the beam to get moved with a quite high speed along the cutting path, in the range of approx. 100 to 1000mm/sec. This ensures the beam is with the same location merely a very limited time, which minimizes local heating.
A pattern recognition technique is employed, that may use fiducials or any other panel or board feature to precisely find the location in which the cut has to be placed. High precision x and y movement systems can be used for large movements together with a galvo scanner for local movements.
In most of these machines, the cutting tool may be the laser beam, and it has a diameter of approximately 20µm. This simply means the kerf cut from the laser is all about 20µm wide, along with the laser system can locate that cut within 25µm with respect to either panel or board fiducials or another board feature. The boards can therefore be put very close together inside a panel. For the panel with many different small circuit boards, additional boards can therefore be placed, ultimately causing cost benefits.
As the laser beam might be freely and rapidly moved in the x and y directions, getting rid of irregularly shaped boards is straightforward. This contrasts with a number of the other described methods, that may be limited to straight line cuts. This becomes advantageous with flex boards, which can be very irregularly shaped and in some instances require extremely precise cuts, as an example when conductors are close together or when ZIF connectors should be reduce (FIGURE 10). These connectors require precise cuts on both ends in the connector fingers, as the fingers are perfectly centered involving the two cuts.
A prospective problem to consider may be the precision of the board images on the panel. The authors have not really found an industry standard indicating an expectation for board image precision. The nearest they may have come is “as required by drawing.” This challenge could be overcome with the help of a lot more than three panel fiducials and dividing the cutting operation into smaller sections making use of their own area fiducials. FIGURE 11 shows within a sample board eliminate in Figure 2 the cutline may be put precisely and closely throughout the board, in this instance, next to the away from the copper edge ring.
Even if ignoring this potential problem, the minimum space between boards in the panel may be as low as the cutting kerf plus 10 to 30µm, according to the thickness from the panel 13dexopky the device accuracy of 25µm.
Within the area covered by the galvo scanner, the beam comes straight down in the center. Though a big collimating lens can be used, toward the sides from the area the beam includes a slight angle. Which means that based on the height of the components near to the cutting path, some shadowing might occur. As this is completely predictable, the space some components have to stay taken from the cutting path might be calculated. Alternatively, the scan area might be reduced to side step this challenge.
Stress. While there is no mechanical contact with the panel during cutting, sometimes all the FPC Laser Depaneling can be executed after assembly and soldering (Figure 11). This implies the boards become completely separated from the panel in this particular last process step, and there is absolutely no requirement for any bending or pulling about the board. Therefore, no stress is exerted in the board, and components nearby the side of the board are certainly not at the mercy of damage.
Within our tests stress measurements were performed. During mechanical depaneling an important snap was observed (FIGURES 12 and 13). This also ensures that during earlier process steps, for example paste printing and component placement, the panel can maintain its full rigidity without any pallets will be required.