Punching/die cutting. This procedure demands a different die for every new circuit board, that is not much of 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 has to be come to maintain sharp die edges.
V-scoring. Typically the panel is scored on both sides to some depth of around 30% from the board thickness. After assembly the boards might be manually broken from the panel. This puts bending force on the boards that could be damaging to a few of the components, in particular those close to the board edge.
Wheel cutting/pizza cutter. An alternate method to manually breaking the net after V-scoring is to apply a “pizza cutter” to reduce the other web. This requires careful alignment between the V-score and also the cutter wheels. Furthermore, it induces stresses from the board which may affect some components.
Sawing. Typically machines that are utilized to saw boards from a panel work with a single rotating saw blade that cuts the panel from either the top or maybe the bottom.
Each one of these methods is restricted to straight line operations, thus exclusively for rectangular boards, and each one to some degree crushes or cuts the board edge. Other methods will be more expansive and will include the next:
Water jet. Some say this technology can be carried out; however, the authors have realized no actual users of it. Cutting is performed with a high-speed stream of slurry, that is water having an abrasive. We expect it may need careful cleaning once the fact to eliminate the abrasive part of the slurry.
Routing ( nibbling). Quite often boards are partially routed just before assembly. The remaining attaching points are drilled by using a small drill size, making it simpler to break the boards out of the panel after assembly, leaving the so-called mouse bites. A disadvantage might be a significant loss of panel area towards the routing space, as being the kerf width normally takes up to 1.5 to 3mm (1/16 to 1/8″) plus some additional space for inaccuracies. This implies a significant amount of panel space will be required for the routed traces.
Laser routing. Laser routing gives a space advantage, as the kerf width is only a few micrometers. As an example, the small boards in FIGURE 2 were initially laid out in anticipation how the panel will be routed. In this way the panel yielded 124 boards. After designing the layout for laser depaneling, the number of boards per panel increased to 368. So for each 368 boards needed, merely one panel should be produced instead of three.
Routing may also reduce panel stiffness to the stage that the pallet may be required for support during the earlier steps within the assembly process. But unlike the previous methods, routing is not limited by cutting straight line paths only.
A large number of methods exert some extent of mechanical stress about the board edges, which can cause delamination or cause space to produce around the glass fibers. This might lead to moisture ingress, which often is able to reduce the long term reliability of the circuitry.
Additionally, when finishing placement of components around the board and after soldering, the final connections between the boards and panel must be removed. Often this can be accomplished by breaking these final bridges, causing some mechanical and bending stress on the boards. Again, such bending stress might be damaging to components placed close to areas that need to be broken so that you can take away the board through the panel. It really is therefore imperative to accept the production methods under consideration during board layout as well as for panelization so that certain parts and traces are certainly not put into areas known to be subjected to stress when depaneling.
Room is likewise expected to permit the precision (or lack thereof) with which the tool path may be placed and to take into account any non-precision in the board pattern.
Laser cutting. The most recently added tool to PCB Routing Machine and rigid boards is really a laser. From the SMT industry several kinds of lasers are 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 as they burn or melt the information being cut. (As being an aside, they are the laser types, particularly the Nd:Yag lasers, typically used to produce stainless steel stencils for solder paste printing.)
UV lasers (typical wavelength ~355nm), on the other hand, are employed to ablate the content. A localized short pulse of high energy enters the top layer from the material being processed and essentially vaporizes and removes this top layer explosively, turning it to dust (FIGURE 3).
Choosing a 355nm laser is based on the compromise between performance and cost. For ablation to occur, the laser light has to be absorbed from the materials to be cut. Within the circuit board industry these are generally mainly FR-4, glass fibers and copper. When examining the absorption rates for such materials (FIGURE 4), the shorter wavelength lasers are the most suitable ones for the ablation process. However, the laser cost increases very rapidly for models with wavelengths shorter than 355nm.
The laser beam features a tapered shape, as it is focused from the relatively wide beam for an extremely narrow beam after which continuous inside a reverse taper to widen again. This small area where the beam reaches its most narrow is called the throat. The perfect ablation takes place when the energy density placed on the content is maximized, which occurs when the throat of your beam is definitely in the material being cut. By repeatedly exceeding the same cutting track, thin layers in the material will likely be removed until the beam has cut right through.
In thicker material it may be essential to adjust the focus of your beam, as being the ablation occurs deeper in to the kerf being cut to the material. The ablation process causes some heating of the material but will be optimized to have 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 convey more power and could also be used to depanel circuit boards as much as 1.6mm (63 mils) in thickness.
Temperature. The temperature rise in the material being cut depends on the beam power, beam speed, focus, laser pulse rate and repetition rate. The repetition rate (how rapidly the beam returns towards the same location) depends on the road length, beam speed and whether a pause is added between passes.
A knowledgeable and experienced system operator should be able to select the optimum mix of settings to make certain a clean cut clear of burn marks. There is absolutely no straightforward formula to ascertain machine settings; they can be relying on material type, thickness and condition. Depending on the board and its particular application, the operator can select fast depaneling by permitting some discoloring or 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 less than 100°C, way below exactly what a PCB experiences during soldering (FIGURE 6).
Expelled material. Within the laser employed for these tests, an airflow goes throughout the panel being cut and removes most of the expelled dust into an exhaust and filtering system (FIGURE 7).
To examine the impact of any remaining expelled material, a slot was cut within a four-up pattern on FR-4 material by using a thickness of 800µm (31.5 mils) (FIGURE 8). Only few particles remained and contained powdery epoxy and glass particles. Their size ranged from about 10µm to your high of 20µm, plus some may have consisted of burned or carbonized material. Their size and number were extremely small, without any conduction was expected between traces and components about the board. If you have desired, a basic cleaning process may be put into remove any remaining particles. This type of process could include using any type of wiping by using a smooth dry or wet tissue, using compressed air or brushes. You can likewise use any type of cleaning liquids or cleaning baths without or with ultrasound, but normally would avoid any kind of additional cleaning process, especially a high priced one.
Surface resistance. After cutting a path within these test boards (Figure 7, slot in the midst of the exam pattern), the boards were subjected to a climate test (40°C, RH=93%, no condensation) for 170 hr., as well as 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 inside the material spanning a small area, 50x50mm (2×2″). Using this sort of scanner permits the beam to get moved at the very high speed over the cutting path, in all the different approx. 100 to 1000mm/sec. This ensures the beam is with the same location merely a very short period of time, which minimizes local heating.
A pattern recognition method is employed, which can use fiducials or another panel or board feature to precisely get the location in which the cut must be placed. High precision x and y movement systems are used for large movements in conjunction with a galvo scanner for local movements.
In these kinds of machines, the cutting tool may be the laser beam, and features a diameter of approximately 20µm. This means the kerf cut from the laser is approximately 20µm wide, and also the laser system can locate that cut within 25µm with respect to either panel or board fiducials or other board feature. The boards can therefore be placed very close together in a panel. For any panel with lots of small circuit boards, additional boards can therefore be put, creating financial savings.
As the laser beam may be freely and rapidly moved in both the x and y directions, getting rid of irregularly shaped boards is simple. This contrasts with a number of the other described methods, which can be limited to straight line cuts. This becomes advantageous with flex boards, which are generally very irregularly shaped and sometimes require extremely precise cuts, as an example when conductors are close together or when ZIF connectors need to be cut out (FIGURE 10). These connectors require precise cuts on both ends from the connector fingers, while the fingers are perfectly centered in between the two cuts.
A possible problem to consider may be the precision from the board images in the panel. The authors have not really found an industry standard indicating an expectation for board image precision. The nearest they have come is “as necessary for drawing.” This problem might be overcome with the addition of a lot more than three panel fiducials and dividing the cutting operation into smaller sections because of their own area fiducials. FIGURE 11 shows in the sample board reduce in Figure 2 that this cutline may be put precisely and closely around the board, in such a case, next to the beyond the copper edge ring.
Regardless if ignoring this potential problem, the minimum space between boards about the panel is often as low as the cutting kerf plus 10 to 30µm, according to the thickness of the panel 13dexopky the machine accuracy of 25µm.
Inside the area paid by the galvo scanner, the beam comes straight down in between. Despite the fact that a large collimating lens can be used, toward the edges of the area the beam features a slight angle. Which means that based on the height from the components near the cutting path, some shadowing might occur. Since this is completely predictable, the space some components need to stay taken from the cutting path could be calculated. Alternatively, the scan area might be reduced to side step this issue.
Stress. While there is no mechanical exposure to the panel during cutting, occasionally each of the FPC Laser Depaneling can be executed after assembly and soldering (Figure 11). What this means is the boards become completely separated from your panel within this last process step, and there is no necessity for any bending or pulling around the board. Therefore, no stress is exerted in the board, and components close to the side of the board will not be subjected to damage.
In your tests stress measurements were performed. During mechanical depaneling a significant snap was observed (FIGURES 12 and 13). This signifies that during earlier process steps, including paste printing and component placement, the panel can maintain its full rigidity and no pallets are essential.