Punching/die cutting. This method takes a different die for 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 lower damage care should be come to maintain sharp die edges.
V-scoring. Often the panel is scored on both sides into a depth of about 30% of your board thickness. After assembly the boards may be manually broken out of your panel. This puts bending stress 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 internet after V-scoring is by using a “pizza cutter” to slice the remaining web. This calls for careful alignment involving the V-score and also the cutter wheels. Furthermore, it induces stresses within the board which can affect some components.
Sawing. Typically machines that are used to saw boards out of 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 simply for rectangular boards, and each one for some degree crushes and cuts the board edge. Other methods tend to be more expansive and include the next:
Water jet. Some say this technology can be carried out; however, the authors have discovered no actual users of this. Cutting is carried out by using a high-speed stream of slurry, which can be water having an abrasive. We expect it will need careful cleaning once the fact to remove the abrasive part of the slurry.
Routing ( nibbling). Usually boards are partially routed just before assembly. The remaining attaching points are drilled having a small drill size, making it simpler to destroy the boards out from the panel after assembly, leaving the so-called mouse bites. A disadvantage can be a significant lack of panel area for the routing space, as being the kerf width often takes as much as 1.5 to 3mm (1/16 to 1/8″) plus some additional space for inaccuracies. This implies a lot of panel space will probably be required for the routed traces.
Laser routing. Laser routing gives a space advantage, as being the kerf width is only a few micrometers. For instance, the small boards in FIGURE 2 were initially outlined in anticipation that the panel would be routed. In this way the panel yielded 124 boards. After designing the layout for laser depaneling, the quantity of boards per panel increased to 368. So for every 368 boards needed, just one panel has to be produced as an alternative to three.
Routing also can reduce panel stiffness to the level that the pallet is usually necessary for support during the earlier steps from the assembly process. But unlike the previous methods, routing is just not confined to cutting straight line paths only.
Most of these methods exert some extent of mechanical stress on the board edges, which can cause delamination or cause space to build up throughout the glass fibers. This can lead to moisture ingress, which in turn helps to reduce the long-term longevity of the circuitry.
Additionally, when finishing placement of components on the board and after soldering, the very last connections in between the boards and panel have to be removed. Often this 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 near to areas that should be broken in order to take away the board from your panel. It really is therefore imperative to accept production methods into consideration during board layout and then for panelization in order that certain parts and traces usually are not positioned in areas known to be susceptible to stress when depaneling.
Room can also be needed to permit the precision (or lack thereof) which the tool path may be placed and to take into account any non-precision in the board pattern.
Laser cutting. Probably the most recently added tool to PCB Router and rigid boards can be a laser. In the SMT industry several types of lasers are being employed. CO2 lasers (~10µm wavelength) can provide 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. Both these laser types produce infrared light and can be called “hot” lasers as they burn or melt the information being cut. (As an aside, these are the laser types, especially the Nd:Yag lasers, typically utilized to produce stainless stencils for solder paste printing.)
UV lasers (typical wavelength ~355nm), on the flip side, are employed to ablate the fabric. A localized short pulse of high energy enters the very best layer of the material being processed and essentially vaporizes and removes this top layer explosively, turning it to dust (FIGURE 3).
Choosing a 355nm laser is dependant on the compromise between performance and price. In order for ablation to take place, the laser light needs to be absorbed with the materials being cut. Within the circuit board industry these are generally mainly FR-4, glass fibers and copper. When viewing the absorption rates for these particular materials (FIGURE 4), the shorter wavelength lasers are the most suitable ones to the ablation process. However, the laser cost increases very rapidly for models with wavelengths shorter than 355nm.
The laser beam carries a tapered shape, because it is focused from a relatively wide beam to an extremely narrow beam and then continuous in a reverse taper to widen again. This small area where the beam is at its most narrow is known as the throat. The optimal ablation takes place when the energy density used on the information is maximized, which occurs when the throat of the beam is just inside the material being cut. By repeatedly exceeding a similar cutting track, thin layers in the material will be removed till the beam has cut all the way through.
In thicker material it may be required to adjust the main focus in the beam, since the ablation occurs deeper into the kerf being cut in to the material. The ablation process causes some heating from the material but will be optimized to have no burned or carbonized residue. Because cutting is carried out 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 up to 1.6mm (63 mils) in thickness.
Temperature. The temperature rise in the material being cut depends upon the beam power, beam speed, focus, laser pulse rate and repetition rate. The repetition rate (how rapidly the beam returns to the same location) is determined by the way length, beam speed and whether a pause is added between passes.
A knowledgeable and experienced system operator should be able to find the optimum combination of settings to ensure a clean cut without any burn marks. There is absolutely no straightforward formula to ascertain machine settings; these are affected by material type, thickness and condition. Based on the board and its 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 has shown that under most conditions the temperature rise within 1.5mm from your cutting path is under 100°C, way below such a PCB experiences during soldering (FIGURE 6).
Expelled material. In the laser useful for these tests, an airflow goes across the panel being cut and removes most of the expelled dust into an exhaust and filtering system (FIGURE 7).
To test 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 about 10µm to your high of 20µm, and a few may have contained burned or carbonized material. Their size and number were extremely small, without any conduction was expected between traces and components around the board. If so desired, a simple cleaning process could possibly be included with remove any remaining particles. This kind of process could include the use of just about any wiping having a smooth dry or wet tissue, using compressed air or brushes. One could likewise use just about any 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 in these test boards (Figure 7, slot during the test pattern), the boards were exposed to a climate test (40°C, RH=93%, no condensation) for 170 hr., and 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 get moved at a very high speed down 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 short period of time, which minimizes local heating.
A pattern recognition technique is employed, that may use fiducials or any other panel or board feature to precisely get the location where the cut needs 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 these sorts of machines, the cutting tool is the laser beam, and contains a diameter of around 20µm. This simply means the kerf cut by the laser is about 20µm wide, along with the laser system can locate that cut within 25µm with regards to either panel or board fiducials or another board feature. The boards can therefore be put very close together in the panel. To get a panel with lots of small circuit boards, additional boards can therefore be placed, leading to cost benefits.
Because the laser beam might be freely and rapidly moved in the x and y directions, getting rid of irregularly shaped boards is simple. This contrasts with some of the other described methods, that may be limited to straight line cuts. This becomes advantageous with flex boards, which are generally very irregularly shaped and in some circumstances require extremely precise cuts, for example when conductors are close together or when ZIF connectors should be remove (FIGURE 10). These connectors require precise cuts on ends from the connector fingers, even though the fingers are perfectly centered between the two cuts.
A potential problem to take into account is definitely the precision of the board images about the panel. The authors have not even found an industry standard indicating an expectation for board image precision. The nearest they have got come is “as essental to drawing.” This problem might be overcome by having over three panel fiducials and dividing the cutting operation into smaller sections with their own area fiducials. FIGURE 11 shows in the sample board remove in Figure 2 that the cutline may be put precisely and closely throughout the board, in such a case, near the outside the copper edge ring.
Even if ignoring this potential problem, the minimum space between boards on the panel can be as little as the cutting kerf plus 10 to 30µm, according to the thickness from the panel 13dexopky the system accuracy of 25µm.
Throughout the area protected by the galvo scanner, the beam comes straight down in the middle. Even though a sizable collimating lens is commonly used, toward the sides in the area the beam includes a slight angle. Which means that based on the height of your components near the cutting path, some shadowing might occur. As this is completely predictable, the space some components have to stay removed from the cutting path may be calculated. Alternatively, the scan area could be reduced to side step this problem.
Stress. Because there is no mechanical contact 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 means the boards become completely separated in the panel in this particular last process step, and there is no requirement for any bending or pulling about the board. Therefore, no stress is exerted on the board, and components near to the edge of the board usually are not susceptible to damage.
In your tests stress measurements were performed. During mechanical depaneling a substantial snap was observed (FIGURES 12 and 13). This also implies that during earlier process steps, including paste printing and component placement, the panel can maintain its full rigidity without any pallets are essential.
