Punching/die cutting. This process needs a different die for every new circuit board, which happens to be not a practical solution for small production runs. The action might be PCB Depaneling, but either can leave the board edges somewhat deformed. To minimize damage care needs to be come to maintain sharp die edges.
V-scoring. Usually the panel is scored for both sides to a depth around 30% of your board thickness. After assembly the boards could be manually broken out from the panel. This puts bending strain on the boards that may be damaging to a number of the components, in particular those near to the board edge.
Wheel cutting/pizza cutter. A different approach to manually breaking the net after V-scoring is to try using a “pizza cutter” to slice the remaining web. This calls for careful alignment between your V-score as well as the cutter wheels. It also induces stresses within the board which can affect some components.
Sawing. Typically machines that are employed to saw boards out of a panel work with a single rotating saw blade that cuts the panel from either the very best or the bottom.
Every one of these methods has limitations to straight line operations, thus simply for rectangular boards, and all of them to many degree crushes or cuts the board edge. Other methods are more expansive and can include the following:
Water jet. Some say this technology can be done; however, the authors have realized no actual users than it. Cutting is conducted with a high-speed stream of slurry, that is water having an abrasive. We expect it may need careful cleaning after the fact to remove the abrasive portion of the slurry.
Routing ( nibbling). Quite often boards are partially routed ahead of assembly. The rest of the attaching points are drilled with a small drill size, making it easier to break the boards out from the panel after assembly, leaving the so-called mouse bites. A disadvantage could be a significant reduction in panel area to the routing space, because 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 probably be necessary for the routed traces.
Laser routing. Laser routing offers a space advantage, as the kerf width is simply a few micrometers. As an example, the tiny boards in FIGURE 2 were initially presented in anticipation the panel would be routed. In this manner the panel yielded 124 boards. After designing the design for laser depaneling, the number of boards per panel increased to 368. So for each 368 boards needed, merely one panel needs to be produced instead of three.
Routing could also reduce panel stiffness to the level that the pallet is usually necessary for support through the earlier steps in the assembly process. But unlike the previous methods, routing is not really limited to cutting straight line paths only.
The majority of these methods exert some degree of mechanical stress on the board edges, which can cause delamination or cause space to produce throughout the glass fibers. This may lead to moisture ingress, which actually can reduce the long-term reliability of the circuitry.
Additionally, when finishing placement of components on the board and after soldering, the very last connections between your boards and panel need to be removed. Often this is accomplished by breaking these final bridges, causing some mechanical and bending stress in the boards. Again, such bending stress could be damaging to components placed near to areas that should be broken as a way to eliminate the board from the panel. It really is therefore imperative to take the production methods into account during board layout and for panelization so that certain parts and traces usually are not placed into areas considered to be at the mercy of stress when depaneling.
Room is also necessary to permit the precision (or lack thereof) in which the tool path may be placed and to take into consideration any non-precision in the board pattern.
Laser cutting. Probably the most recently added tool to PCB Router and rigid boards is actually a laser. Within the SMT industry various kinds of lasers are employed. CO2 lasers (~10µm wavelength) can offer high power levels and cut through thick steel sheets plus 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 could be called “hot” lasers because they burn or melt the information being cut. (As being an aside, these are the laser types, particularly the Nd:Yag lasers, typically employed to produce stainless stencils for solder paste printing.)
UV lasers (typical wavelength ~355nm), however, are employed to ablate the content. A localized short pulse of high energy enters the best layer of your material being processed and essentially vaporizes and removes this top layer explosively, turning it to dust (FIGURE 3).
The option of a 355nm laser is based on the compromise between performance and expense. To ensure ablation to take place, the laser light must be absorbed from the materials to become cut. Inside the circuit board industry these are typically mainly FR-4, glass fibers and copper. When viewing the absorption rates of these materials (FIGURE 4), the shorter wavelength lasers are the most suitable ones for your ablation process. However, the laser cost increases very rapidly for models with wavelengths shorter than 355nm.
The laser beam features a tapered shape, because it is focused from a relatively wide beam with an extremely narrow beam then continuous inside a reverse taper to widen again. This small area in which the beam is at its most narrow is referred to as the throat. The ideal ablation takes place when the energy density applied to the fabric is maximized, which occurs when the throat of your beam is just inside the material being cut. By repeatedly going over the same cutting track, thin layers of your material will probably be removed until the beam has cut all the way through.
In thicker material it might be essential to adjust the focus of the beam, as the ablation occurs deeper into the kerf being cut in the material. The ablation process causes some heating from the material but could be optimized to go out of no burned or carbonized residue. Because cutting is carried out gradually, heating is minimized.
The earliest versions of UV laser systems had enough ability to depanel flex circuit panels. Present machines convey more power and can also be used to depanel circuit boards as much as 1.6mm (63 mils) in thickness.
Temperature. The temperature boost in the content being cut depends on the beam power, beam speed, focus, laser pulse rate and repetition rate. The repetition rate (how rapidly the beam returns on the same location) is dependent upon the way length, beam speed and whether a pause is added between passes.
An educated and experienced system operator should be able to find the optimum blend of settings to make certain a clean cut clear of burn marks. There is absolutely no straightforward formula to figure out machine settings; they may be relying on material type, thickness and condition. According to the board along with its application, the operator can choose 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 the cutting path is under 100°C, way below just what a PCB experiences during soldering (FIGURE 6).
Expelled material. Within the laser useful for these tests, an airflow goes throughout the panel being cut and removes the majority of the expelled dust into an exhaust and filtration 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 was made up of powdery epoxy and glass particles. Their size ranged from around 10µm to a high of 20µm, plus some could possibly have was made up of burned or carbonized material. Their size and number were extremely small, with no conduction was expected between traces and components in the board. In that case desired, a simple cleaning process might be included with remove any remaining particles. This type of process could consist of the application of any sort of wiping having a smooth dry or wet tissue, using compressed air or brushes. You can also use any type of cleaning liquids or cleaning baths with or without ultrasound, but normally would avoid just about any additional cleaning process, especially a high priced one.
Surface resistance. After cutting a path during these test boards (Figure 7, slot in the middle 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 uses 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 to get moved at the extremely high speed over the cutting path, in the plethora of approx. 100 to 1000mm/sec. This ensures the beam is incorporated in the same location just a very small amount of time, which minimizes local heating.
A pattern recognition technique is employed, which may use fiducials or another panel or board feature to precisely find the location the location where the cut should be placed. High precision x and y movement systems can be used as large movements in combination with a galvo scanner for local movements.
In most of these machines, the cutting tool is the laser beam, and contains a diameter of approximately 20µm. This simply means the kerf cut by the laser is approximately 20µm wide, and the laser system can locate that cut within 25µm with respect to either panel or board fiducials or another 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, ultimately causing cost benefits.
Because the laser beam could be freely and rapidly moved both in the x and y directions, getting rid of irregularly shaped boards is easy. This contrasts with a few of the other described methods, which is often limited to straight line cuts. This becomes advantageous with flex boards, which are often very irregularly shaped and sometimes require extremely precise cuts, by way of example when conductors are close together or when ZIF connectors should be remove (FIGURE 10). These connectors require precise cuts on both ends of your connector fingers, while the fingers are perfectly centered involving the two cuts.
A prospective problem to take into account is definitely the precision in the board images about the panel. The authors have not found a business standard indicating an expectation for board image precision. The nearest they have got come is “as essental to drawing.” This challenge might be overcome with the addition of a lot more than three panel fiducials and dividing the cutting operation into smaller sections with their own area fiducials. FIGURE 11 shows within a sample board reduce in Figure 2 that the cutline can be placed precisely and closely throughout the board, in cases like this, next to the outside of the copper edge ring.
Even though ignoring this potential problem, the minimum space between boards around the panel can be as low as the cutting kerf plus 10 to 30µm, based on the thickness of your panel 13dexopky the program accuracy of 25µm.
Throughout the area paid by the galvo scanner, the beam comes straight down at the center. Even though a big collimating lens is used, toward the sides of your area the beam has a slight angle. Which means that based on the height in the components near the cutting path, some shadowing might occur. Since this is completely predictable, the space some components need to stay taken off the cutting path could be calculated. Alternatively, the scan area could be reduced to side step this issue.
Stress. Because there is no mechanical experience of the panel during cutting, sometimes all the FPC Laser Depaneling can be executed after assembly and soldering (Figure 11). This means the boards become completely separated from your panel in this last process step, and there is absolutely no requirement for any bending or pulling in the board. Therefore, no stress is exerted around the board, and components near the fringe of the board are certainly not susceptible to damage.
In our tests stress measurements were performed. During mechanical depaneling a substantial snap was observed (FIGURES 12 and 13). This also means that during earlier process steps, including paste printing and component placement, the panel can maintain its full rigidity without any pallets are essential.