Punching/die cutting. This method takes a different die for each and every new circuit board, that 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 minimize damage care should be taken up maintain sharp die edges.
V-scoring. Often the panel is scored on both sides to your depth of around 30% from the board thickness. After assembly the boards could be manually broken out of the panel. This puts bending force on the boards that can be damaging to some of the components, in particular those next to the board edge.
Wheel cutting/pizza cutter. A different method to manually breaking the web after V-scoring is to use a “pizza cutter” to cut the remaining web. This involves careful alignment between your V-score along with the cutter wheels. Furthermore, it induces stresses in the board which can affect some components.
Sawing. Typically machines that are utilized to saw boards away from a panel work with a single rotating saw blade that cuts the panel from either the very best or perhaps the bottom.
Each of these methods is restricted to straight line operations, thus simply for rectangular boards, and all of them to many degree crushes and/or cuts the board edge. Other methods are definitely more expansive and can include these:
Water jet. Some say this technology can be carried out; however, the authors have discovered no actual users of this. Cutting is carried out having a high-speed stream of slurry, which is water with the abrasive. We expect it will need careful cleaning following the fact to eliminate the abrasive part of the slurry.
Routing ( nibbling). Most of the time boards are partially routed before assembly. The remaining attaching points are drilled by using a small drill size, making it easier to destroy the boards out of the panel after assembly, leaving the so-called mouse bites. A disadvantage might be a significant lack of panel area for the routing space, since the kerf width often takes up to 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 required for the routed traces.
Laser routing. Laser routing gives a space advantage, because the kerf width is simply a few micrometers. As an example, the tiny boards in FIGURE 2 were initially organized in anticipation how the panel can be routed. In this fashion the panel yielded 124 boards. After designing the layout for laser depaneling, the amount of boards per panel increased to 368. So for every single 368 boards needed, merely one panel must be produced rather than three.
Routing may also reduce panel stiffness to the stage a pallet is usually necessary for support through the earlier steps in the assembly process. But unlike the last methods, routing will not be limited by cutting straight line paths only.
Many of these methods exert some degree of mechanical stress about the board edges, which can cause delamination or cause space to build up throughout the glass fibers. This can lead to moisture ingress, which is able to reduce the long term longevity of the circuitry.
Additionally, when finishing placement of components on the board and after soldering, the last connections between your boards and panel really need to be removed. Often this is certainly accomplished by breaking these final bridges, causing some mechanical and bending stress on the boards. Again, such bending stress could be damaging to components placed in close proximity to areas that need to be broken in order to remove the board from your panel. It can be therefore imperative to accept the production methods into consideration during board layout and then for panelization to ensure certain parts and traces are not placed into areas considered subjected to stress when depaneling.
Room is also necessary to permit the precision (or lack thereof) that the tool path may be placed and to look at any non-precision within the board pattern.
Laser cutting. One of the most recently added tool to PCB Routing Machine and rigid boards is a laser. Within the SMT industry various kinds lasers are being employed. CO2 lasers (~10µm wavelength) provides 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 can be called “hot” lasers because they burn or melt the content being cut. (For 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 employed to ablate the information. A localized short pulse of high energy enters the best layer in 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 founded on the compromise between performance and price. To ensure ablation to occur, the laser light must be absorbed by the materials being cut. In the circuit board industry these are mainly FR-4, glass fibers and copper. When viewing the absorption rates for such 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 has a tapered shape, as it is focused from your relatively wide beam to a extremely narrow beam after which continuous in a reverse taper to widen again. This small area where beam is in its most narrow is referred to as the throat. The optimal ablation occurs when the energy density used on the information is maximized, which happens when the throat in the beam is merely within the material being cut. By repeatedly going over the same cutting track, thin layers in the material will probably be removed until the beam has cut all the way through.
In thicker material it may be necessary to adjust the main focus from the beam, as the ablation occurs deeper in the kerf being cut into the material. The ablation process causes some heating of your material but will be optimized to go out of 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 can also be used to depanel circuit boards as much as 1.6mm (63 mils) in thickness.
Temperature. The temperature rise in the content being cut is dependent upon the beam power, beam speed, focus, laser pulse rate and repetition rate. The repetition rate (how fast the beam returns for the same location) depends on the way length, beam speed and whether a pause is added between passes.
A knowledgeable and experienced system operator should be able to choose the optimum blend of settings to make sure a clean cut free of burn marks. There is absolutely no straightforward formula to figure out machine settings; these are relying on material type, thickness and condition. Dependant upon the board and its particular application, the operator can choose fast depaneling by permitting some discoloring or perhaps some carbonization, versus a somewhat slower but completely “clean” cut.
Careful testing has revealed 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. Inside the laser utilized 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 examine the impact of 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 was comprised of powdery epoxy and glass particles. Their size ranged from about 10µm to some high of 20µm, plus some could possibly 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 in the board. Then desired, a straightforward cleaning process could be put into remove any remaining particles. This kind of process could comprise of the application of any type of wiping by using a smooth dry or wet tissue, using compressed air or brushes. You could 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 costly one.
Surface resistance. After cutting a path within these test boards (Figure 7, slot in the center of the test 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 utilizes a galvanometer scanner (or galvo scanner) to trace the cutting path in the material across a small area, 50x50mm (2×2″). Using this sort of scanner permits the beam being moved at a extremely high speed down the cutting path, in all the different approx. 100 to 1000mm/sec. This ensures the beam is in the same location merely a very limited time, which minimizes local heating.
A pattern recognition system is employed, which may use fiducials or another panel or board feature to precisely get the location in which the 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 sorts of machines, the cutting tool is definitely the laser beam, and possesses a diameter of around 20µm. What this means is the kerf cut from the laser is about 20µm wide, along with the laser system can locate that cut within 25µm regarding either panel or board fiducials or any other board feature. The boards can therefore be placed very close together in a panel. For any panel with many small circuit boards, additional boards can therefore be placed, resulting in financial savings.
Because the laser beam could be freely and rapidly moved in both the x and y directions, removing irregularly shaped boards is not difficult. This contrasts with a number of the other described methods, that may be restricted to straight line cuts. This becomes advantageous with flex boards, which can be very irregularly shaped and occasionally require extremely precise cuts, by way of example when conductors are close together or when ZIF connectors must be remove (FIGURE 10). These connectors require precise cuts on ends of the connector fingers, as the fingers are perfectly centered between your two cuts.
A prospective problem to take into consideration is the precision of the board images around the panel. The authors have not really found a business standard indicating an expectation for board image precision. The nearest they have come is “as needed by drawing.” This challenge can be overcome by adding over 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 cut out in Figure 2 the cutline may be placed precisely and closely throughout the board, in this case, near the away from the copper edge ring.
Regardless if ignoring this potential problem, the minimum space between boards about the panel can be as low as the cutting kerf plus 10 to 30µm, dependant upon the thickness from the panel 13dexopky the system accuracy of 25µm.
Inside the area protected by the galvo scanner, the beam comes straight down in the center. Although a big collimating lens is used, toward the sides of your area the beam includes a slight angle. Because of this dependant upon the height of the components near to the cutting path, some shadowing might occur. Since this is completely predictable, the distance some components have to stay taken off the cutting path can be calculated. Alternatively, the scan area might be reduced to side step this concern.
Stress. While there is no mechanical contact with the panel during cutting, sometimes all the FPC Cutting Machine can be carried out after assembly and soldering (Figure 11). This implies the boards become completely separated through the panel in this particular last process step, and there is absolutely no desire for any bending or pulling in the board. Therefore, no stress is exerted about the board, and components near the edge of the board are certainly not subjected to damage.
Within our tests stress measurements were performed. During mechanical depaneling a significant snap was observed (FIGURES 12 and 13). This too ensures that during earlier process steps, for example paste printing and component placement, the panel can maintain its full rigidity with out pallets will be required.