Punching/die cutting. This procedure needs a different die for each and every new circuit board, which happens to be not really a practical solution for small production runs. The action might be PCB Depaneling, but either can leave the board edges somewhat deformed. To lower damage care must be come to maintain sharp die edges.
V-scoring. Usually the panel is scored on sides to your depth of approximately 30% from the board thickness. After assembly the boards might be manually broken out of the panel. This puts bending strain on the boards that could be damaging to some of the components, particularly those near the board edge.
Wheel cutting/pizza cutter. Another technique to manually breaking the world wide web after V-scoring is to try using a “pizza cutter” to slice the other web. This involves careful alignment in between the V-score along with the cutter wheels. Additionally, it induces stresses inside the board which may affect some components.
Sawing. Typically machines that are used to saw boards from a panel utilize a single rotating saw blade that cuts the panel from either the most notable or maybe the bottom.
All these methods is limited to straight line operations, thus simply for rectangular boards, and each one to many degree crushes and cuts the board edge. Other methods are more expansive and may include the following:
Water jet. Some say this technology can be done; however, the authors are finding no actual users of it. Cutting is carried out with a high-speed stream of slurry, which happens to be water with an abrasive. We expect it will require careful cleaning once the fact to remove the abrasive area of the slurry.
Routing ( nibbling). More often than not boards are partially routed ahead of assembly. The other attaching points are drilled by using a small drill size, making it easier to destroy the boards out of your panel after assembly, leaving the so-called mouse bites. A disadvantage might be a significant loss in panel area on the routing space, since the kerf width typically takes up to 1.5 to 3mm (1/16 to 1/8″) plus some additional space for inaccuracies. What this means is lots of panel space will be needed for the routed traces.
Laser routing. Laser routing gives 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 presented in anticipation the panel could be routed. In this fashion the panel yielded 124 boards. After designing the design for laser depaneling, the volume of boards per panel increased to 368. So for each 368 boards needed, merely one panel must be produced as opposed to three.
Routing could also reduce panel stiffness to the point that the pallet is usually necessary for support during the earlier steps within the assembly process. But unlike the earlier methods, routing will not be limited to cutting straight line paths only.
Many of these methods exert some degree of mechanical stress on the board edges, which can cause delamination or cause space to develop round the glass fibers. This might lead to moisture ingress, which actually can reduce the long-term longevity of the circuitry.
Additionally, when finishing placement of components in the board and after soldering, the very last connections involving the boards and panel have to be removed. Often this really is accomplished by breaking these final bridges, causing some mechanical and bending stress about the boards. Again, such bending stress might be damaging to components placed in close proximity to areas that ought to be broken so that you can take away the board from your panel. It is actually therefore imperative to accept the production methods into consideration during board layout and then for panelization to ensure that certain parts and traces are not placed in areas considered to be susceptible to stress when depaneling.
Room can also be necessary to permit the precision (or lack thereof) with which the tool path may be placed and to consider any non-precision in the board pattern.
Laser cutting. By far the most recently added tool to PCB Routing Machine and rigid boards is a laser. Within the SMT industry several kinds of lasers are employed. CO2 lasers (~10µm wavelength) can provide high power levels and cut through thick steel sheets and in addition 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 may be called “hot” lasers since they burn or melt the fabric being cut. (As an aside, these are the basic laser types, specially the Nd:Yag lasers, typically utilized to produce stainless steel stencils for solder paste printing.)
UV lasers (typical wavelength ~355nm), alternatively, are widely used to ablate the information. A localized short pulse of high energy enters the top layer of your material being processed and essentially vaporizes and removes this top layer explosively, turning it to dust (FIGURE 3).
Choosing a 355nm laser is founded on the compromise between performance and cost. To ensure that ablation to occur, the laser light needs to be absorbed with the materials to be cut. Within the circuit board industry they are mainly FR-4, glass fibers and copper. When looking at the absorption rates for these particular materials (FIGURE 4), the shorter wavelength lasers are the most suitable ones for that ablation process. However, the laser cost increases very rapidly for models with wavelengths shorter than 355nm.
The laser beam carries a tapered shape, as it is focused from the relatively wide beam for an extremely narrow beam then continuous in a reverse taper to widen again. This small area where beam is in its most narrow is known as the throat. The perfect ablation takes place when the energy density placed on the material is maximized, which occurs when the throat of the beam is simply inside of the material being cut. By repeatedly exceeding the identical cutting track, thin layers of the material is going to be removed before the beam has cut all the way through.
In thicker material it might be needed to adjust the target in the beam, as being the ablation occurs deeper to the kerf being cut in to the material. The ablation process causes some heating in the material but could be optimized to depart no burned or carbonized residue. Because cutting is completed gradually, heating is minimized.
The earliest versions of UV laser systems had enough ability to depanel flex circuit panels. Present machines get more power and could also be used to depanel circuit boards approximately 1.6mm (63 mils) in thickness.
Temperature. The temperature rise in the fabric being cut depends on the beam power, beam speed, focus, laser pulse rate and repetition rate. The repetition rate (how fast the beam returns for the same location) is dependent upon the road length, beam speed and whether a pause is added between passes.
An informed and experienced system operator can pick the optimum mix of settings to make sure a clean cut without any burn marks. There is no straightforward formula to determine machine settings; they are affected by material type, thickness and condition. Depending on the board and its particular application, the operator can choose fast depaneling by permitting some discoloring and even some carbonization, versus a somewhat slower but completely “clean” cut.
Careful testing indicates that under most conditions the temperature rise within 1.5mm from your cutting path is lower than 100°C, way below such a PCB experiences during soldering (FIGURE 6).
Expelled material. From the laser employed for these tests, an airflow goes over the panel being cut and removes most 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 in the four-up pattern on FR-4 material having a thickness of 800µm (31.5 mils) (FIGURE 8). Only few particles remained and contained powdery epoxy and glass particles. Their size ranged from typically 10µm to your high of 20µm, plus some might have was comprised of burned or carbonized material. Their size and number were extremely small, with out conduction was expected between traces and components on the board. If you have desired, a basic cleaning process could be included with remove any remaining particles. This kind of process could contain the application of just about any wiping using a smooth dry or wet tissue, using compressed air or brushes. You can also use any sort of cleaning liquids or cleaning baths with or without ultrasound, but normally would avoid any sort of additional cleaning process, especially a pricey one.
Surface resistance. After cutting a path over these test boards (Figure 7, slot in the midst of the test pattern), the boards were put through a climate test (40°C, RH=93%, no condensation) for 170 hr., along with the SIR values exceeded 10E11 Ohm, indicating no conductive material is present.
Cutting path location. The laser beam typically utilizes a galvanometer scanner (or galvo scanner) to trace the cutting path in the material spanning a small area, 50x50mm (2×2″). Using such a scanner permits the beam to get moved at a high speed along the cutting path, in the range of approx. 100 to 1000mm/sec. This ensures the beam is incorporated in the same location only a very small amount of time, which minimizes local heating.
A pattern recognition system is employed, which could use fiducials or other panel or board feature to precisely get the location where the cut must be placed. High precision x and y movement systems are used for large movements together with a galvo scanner for local movements.
In these kinds of machines, the cutting tool is definitely the laser beam, and features a diameter of around 20µm. This means the kerf cut from the laser is approximately 20µm wide, along with the laser system can locate that cut within 25µm with regards to either panel or board fiducials or any other board feature. The boards can therefore be put very close together in the panel. For a panel with many small circuit boards, additional boards can therefore be put, creating cost savings.
Since the laser beam can be freely and rapidly moved within both the x and y directions, cutting out irregularly shaped boards is straightforward. This contrasts with a few of the other described methods, which can be confined to straight line cuts. This becomes advantageous with flex boards, which are often very irregularly shaped and sometimes require extremely precise cuts, as an example when conductors are close together or when ZIF connectors must be cut out (FIGURE 10). These connectors require precise cuts on both ends of the connector fingers, as the fingers are perfectly centered between your two cuts.
A prospective problem to take into consideration is definitely the precision from the board images around the panel. The authors have not even found a business standard indicating an expectation for board image precision. The closest they have got come is “as essental to drawing.” This issue may be overcome with the help of greater than three panel fiducials and dividing the cutting operation into smaller sections with their own area fiducials. FIGURE 11 shows in the sample board cut out in Figure 2 that the cutline can be placed precisely and closely round the board, in this instance, near the away from the copper edge ring.
Even when ignoring this potential problem, the minimum space between boards in the panel could be as little as the cutting kerf plus 10 to 30µm, according to the thickness from the panel 13dexopky the program accuracy of 25µm.
In the area covered by the galvo scanner, the beam comes straight down in the middle. Though a sizable collimating lens can be used, toward the sides of the area the beam includes a slight angle. Which means that dependant upon the height of the components near to the cutting path, some shadowing might occur. Because this is completely predictable, the space some components should stay removed from the cutting path may be calculated. Alternatively, the scan area can be reduced to side step this problem.
Stress. As there is no mechanical connection with the panel during cutting, in some instances every one of the FPC Depaneling Machine 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 necessity for any bending or pulling around the board. Therefore, no stress is exerted on the board, and components nearby the side of the board are not susceptible to damage.
In our tests stress measurements were performed. During mechanical depaneling a tremendous snap was observed (FIGURES 12 and 13). This too ensures that during earlier process steps, such as paste printing and component placement, the panel can maintain its full rigidity and no pallets will be required.