Punching/die cutting. This process needs a different die for each and every new circuit board, which is 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 needs to be taken up maintain sharp die edges.
V-scoring. Usually the panel is scored on both sides to your depth of approximately 30% of your board thickness. After assembly the boards might be manually broken from the panel. This puts bending strain on the boards which can be damaging to several of the components, particularly those near the board edge.
Wheel cutting/pizza cutter. Another method to manually breaking the net after V-scoring is to use a “pizza cutter” to reduce the remainder web. This involves careful alignment between the V-score along with the cutter wheels. Furthermore, it induces stresses inside the board which may affect some components.
Sawing. Typically machines that are employed to saw boards away from a panel make use of a single rotating saw blade that cuts the panel from either the best or even the bottom.
Each of these methods is restricted to straight line operations, thus only for rectangular boards, and all of them to some degree crushes or cuts the board edge. Other methods tend to be more expansive and include the next:
Water jet. Some say this technology can be achieved; however, the authors are finding no actual users than it. Cutting is conducted with a high-speed stream of slurry, which can be water with the abrasive. We expect it should take careful cleaning once the fact to get rid of the abrasive part of the slurry.
Routing ( nibbling). Usually boards are partially routed just before assembly. The rest of the attaching points are drilled having a small drill size, making it easier to interrupt the boards out of your panel after assembly, leaving the so-called mouse bites. A disadvantage can be quite a significant reduction in panel area towards the routing space, as the kerf width often takes around 1.5 to 3mm (1/16 to 1/8″) plus some additional space for inaccuracies. This means a significant amount of panel space will be necessary for the routed traces.
Laser routing. Laser routing supplies a space advantage, as the kerf width is just a few micrometers. For example, the tiny boards in FIGURE 2 were initially laid out in anticipation how the panel can be routed. This way the panel yielded 124 boards. After designing the design for laser depaneling, the amount of boards per panel increased to 368. So for every single 368 boards needed, merely one panel should be produced instead of three.
Routing may also reduce panel stiffness to the point which a pallet may be needed for support in the earlier steps inside the assembly process. But unlike the previous methods, routing is not really limited to cutting straight line paths only.
Many of these methods exert some extent of mechanical stress on the board edges, which can cause delamination or cause space to formulate around the glass fibers. This can lead to moisture ingress, which can reduce the long-term reliability of the circuitry.
Additionally, when finishing placement of components about the board and after soldering, the ultimate connections involving the boards and panel must 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 can be damaging to components placed close to areas that ought to be broken as a way to eliminate the board in the panel. It is therefore imperative to take the production methods into consideration during board layout and also for panelization to ensure certain parts and traces are certainly not positioned in areas known to be at the mercy of stress when depaneling.
Room is also required to permit the precision (or lack thereof) that the tool path may be put and to take into consideration any non-precision inside the board pattern.
Laser cutting. By far the most recently added tool to PCB Depaneling Router and rigid boards is actually a laser. From the SMT industry various kinds of lasers are employed. CO2 lasers (~10µm wavelength) provides very high power levels and cut through thick steel sheets and also 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 might be called “hot” lasers as they burn or melt the material being cut. (Being an aside, these are the laser types, specially the Nd:Yag lasers, typically utilized to produce stainless steel stencils for solder paste printing.)
UV lasers (typical wavelength ~355nm), on the flip side, are widely used to ablate the material. A localized short pulse of high energy enters the most notable layer from the material being processed and essentially vaporizes and removes this top layer explosively, turning it to dust (FIGURE 3).
Deciding on a a 355nm laser is based on the compromise between performance and cost. To ensure ablation to occur, the laser light must be absorbed through the materials to get cut. In the circuit board industry these are typically mainly FR-4, glass fibers and copper. When looking at the absorption rates for these 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 includes a tapered shape, since it is focused from your relatively wide beam with an extremely narrow beam then continuous in a reverse taper to widen again. This small area the location where the beam is at its most narrow is known as the throat. The perfect ablation takes place when the energy density put on the fabric is maximized, which takes place when the throat in the beam is simply inside of the material being cut. By repeatedly groing through exactly the same cutting track, thin layers of the material will be removed before the beam has cut right through.
In thicker material it could be essential to adjust the target in the beam, since the ablation occurs deeper in the kerf being cut in to the material. The ablation process causes some heating from the material but could be optimized to leave no burned or carbonized residue. Because cutting is performed gradually, heating is minimized.
The earliest versions of UV laser systems had enough power to depanel flex circuit panels. Present machines acquire more power and may also be used to depanel circuit boards around 1.6mm (63 mils) in thickness.
Temperature. The temperature boost in the information being cut depends upon the beam power, beam speed, focus, laser pulse rate and repetition rate. The repetition rate (how fast the beam returns towards the same location) depends on the way length, beam speed and whether a pause is added between passes.
A knowledgeable and experienced system operator will be able to pick the optimum mixture of settings to make certain a clean cut clear of burn marks. There is absolutely no straightforward formula to find out machine settings; they may be influenced by material type, thickness and condition. Dependant upon the board and its application, the operator can decide fast depaneling by permitting some discoloring as well as 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 just what a PCB experiences during soldering (FIGURE 6).
Expelled material. In the laser useful for these tests, an airflow goes over the panel being cut and removes many of the expelled dust into an exhaust and filtering system (FIGURE 7).
To check the impact for any remaining expelled material, a slot was cut in a four-up pattern on FR-4 material using a thickness of 800µm (31.5 mils) (FIGURE 8). Only few particles remained and consisted of powdery epoxy and glass particles. Their size ranged from typically 10µm to some high of 20µm, and some could have was comprised of burned or carbonized material. Their size and number were extremely small, with out conduction was expected between traces and components about the board. If so desired, a basic cleaning process might be put into remove any remaining particles. Such a process could contain the use 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 high priced one.
Surface resistance. After cutting a path over these test boards (Figure 7, slot in the midst of the exam 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 inside the material more than a small area, 50x50mm (2×2″). Using this type of scanner permits the beam to be moved at the extremely high speed over the cutting path, in the plethora of approx. 100 to 1000mm/sec. This ensures the beam is within the same location merely a very short period of time, which minimizes local heating.
A pattern recognition technique is employed, which can use fiducials or another panel or board feature to precisely obtain the location where cut should be placed. High precision x and y movement systems are used for large movements in combination with a galvo scanner for local movements.
In these types of machines, the cutting tool will be the laser beam, and features a diameter of approximately 20µm. This implies the kerf cut by the laser is about 20µm wide, and the laser system can locate that cut within 25µm when it comes to either panel or board fiducials or other board feature. The boards can therefore be put very close together in a panel. For a panel with a lot of small circuit boards, additional boards can therefore be placed, leading to financial savings.
As being the laser beam might be freely and rapidly moved in the x and y directions, cutting out irregularly shaped boards is straightforward. This contrasts with some of the other described methods, which can be restricted to straight line cuts. This becomes advantageous with flex boards, which can be very irregularly shaped and sometimes require extremely precise cuts, by way of example when conductors are close together or when ZIF connectors should be cut out (FIGURE 10). These connectors require precise cuts on both ends of your connector fingers, even though the fingers are perfectly centered in between the two cuts.
A potential problem to think about will be the precision from the board images around the panel. The authors have not found a marketplace standard indicating an expectation for board image precision. The closest they have got come is “as needed by drawing.” This concern can be overcome by adding more 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 outside of the copper edge ring.
Even if ignoring this potential problem, the minimum space between boards in the panel can be as little as the cutting kerf plus 10 to 30µm, dependant upon the thickness of 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 sizable collimating lens is commonly used, toward the edges from the area the beam features a slight angle. Consequently based on the height of the components near to the cutting path, some shadowing might occur. Because this is completely predictable, the distance some components should stay taken off the cutting path could be calculated. Alternatively, the scan area can be reduced to side step this issue.
Stress. Because there is no mechanical connection with the panel during cutting, sometimes every one of the FPC Laser Depaneling can be carried out after assembly and soldering (Figure 11). What this means is the boards become completely separated in the panel in this last process step, and there is not any desire for any bending or pulling around the board. Therefore, no stress is exerted about the board, and components near the fringe of the board will not be at the mercy of damage.
In your tests stress measurements were performed. During mechanical depaneling a significant snap was observed (FIGURES 12 and 13). This also means that during earlier process steps, for example paste printing and component placement, the panel can maintain its full rigidity without any pallets are needed.