Punching/die cutting. This technique takes a different die for each and every new circuit board, which can be not much of a practical solution for small production runs. The action may be PCB Depaneling, but either can leave the board edges somewhat deformed. To lower damage care needs to be delivered to maintain sharp die edges.
V-scoring. Often the panel is scored for both sides to some depth of approximately 30% from the board thickness. After assembly the boards may be manually broken from the panel. This puts bending force on the boards that may be damaging to a number of the components, in particular those near the board edge.
Wheel cutting/pizza cutter. An alternate approach to manually breaking the internet after V-scoring is by using a “pizza cutter” to cut the rest of the web. This requires careful alignment in between the V-score along with the cutter wheels. Furthermore, it induces stresses within the board which could affect some components.
Sawing. Typically machines that are utilized to saw boards out of a panel utilize a single rotating saw blade that cuts the panel from either the top or perhaps the bottom.
All these methods has limitations to straight line operations, thus just for rectangular boards, and each of them for some degree crushes and cuts the board edge. Other methods are definitely more expansive and will include the following:
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 is water with an abrasive. We expect it will need careful cleaning following the fact to get rid of the abrasive area of the slurry.
Routing ( nibbling). Usually boards are partially routed prior to assembly. The other 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 could be a significant loss in panel area on 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. What this means is a significant amount of panel space will be needed for the routed traces.
Laser routing. Laser routing gives a space advantage, as the kerf width is only a few micrometers. For example, the little boards in FIGURE 2 were initially laid out in anticipation how the panel could be routed. In this manner 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, just one panel should be produced as an alternative to three.
Routing may also reduce panel stiffness to the level that the pallet is usually necessary for support during the earlier steps in the assembly process. But unlike the prior methods, routing is not really limited to cutting straight line paths only.
Many of these 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 can reduce the long-term longevity of the circuitry.
Additionally, when finishing placement of components in the board and after soldering, the final connections in between the 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 may be damaging to components placed near areas that need to be broken so that you can eliminate the board through the panel. It is therefore imperative to accept the production methods under consideration during board layout as well as for panelization to ensure certain parts and traces are not placed into areas considered subjected to stress when depaneling.
Room is additionally expected to permit the precision (or lack thereof) that the tool path can be placed and to consider any non-precision within the board pattern.
Laser cutting. One of the most recently added tool to PCB Router and rigid boards can be a laser. Within the SMT industry several kinds of lasers are employed. CO2 lasers (~10µm wavelength) can offer quite 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 while they burn or melt the fabric being cut. (For an aside, these are the basic laser types, specially the Nd:Yag lasers, typically employed to produce stainless stencils for solder paste printing.)
UV lasers (typical wavelength ~355nm), alternatively, are used to ablate the material. A localized short pulse of high energy enters the 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 expense. To ensure that ablation to occur, the laser light has to be absorbed through the materials to be cut. Within the circuit board industry they are mainly FR-4, glass fibers and copper. When looking at 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 has a tapered shape, since it is focused from a relatively wide beam to a extremely narrow beam and after that continuous in the reverse taper to widen again. This small area in which the beam is at its most narrow is known as the throat. The optimal ablation happens when the energy density used on the information is maximized, which happens when the throat of your beam is merely inside the material being cut. By repeatedly exceeding the same cutting track, thin layers in the material is going to be removed up until the beam has cut right through.
In thicker material it may be required to adjust the focus in the beam, since the ablation occurs deeper in the kerf being cut in to the material. The ablation process causes some heating in the material but can be optimized to leave 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 acquire more power and could also be used to depanel circuit boards up to 1.6mm (63 mils) in thickness.
Temperature. The temperature boost 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 on the same location) is dependent upon the road length, beam speed and whether a pause is added between passes.
An informed and experienced system operator are able to choose the optimum mix of settings to guarantee a clean cut free of burn marks. There is no straightforward formula to find out machine settings; they are affected by material type, thickness and condition. According to the board and its application, the operator can decide fast depaneling by permitting some discoloring or perhaps 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 what a PCB experiences during soldering (FIGURE 6).
Expelled material. Inside the laser used for these tests, an airflow goes across the panel being cut and removes the majority of the expelled dust into an exhaust and filtering method (FIGURE 7).
To check 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 typically 10µm to a high of 20µm, and some could have consisted of 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 basic cleaning process might be put into remove any remaining particles. This kind of process could comprise of the use of any sort 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 with or without ultrasound, but normally would avoid any kind of additional cleaning process, especially a pricey one.
Surface resistance. After cutting a path in these test boards (Figure 7, slot in the center of the test pattern), the boards were exposed to a climate test (40°C, RH=93%, no condensation) for 170 hr., and also 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 within the material spanning a small area, 50x50mm (2×2″). Using this sort of scanner permits the beam to be moved with a very high speed over the cutting path, in all the different approx. 100 to 1000mm/sec. This ensures the beam is incorporated in the same location simply a very limited time, which minimizes local heating.
A pattern recognition system is employed, which could use fiducials or any other panel or board feature to precisely obtain the location where the cut has to 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 may be the laser beam, and contains a diameter of around 20µm. This simply means the kerf cut by the laser is around 20µm wide, and the laser system can locate that cut within 25µm with regards to either panel or board fiducials or other board feature. The boards can therefore be put very close together within a panel. For a panel with lots of small circuit boards, additional boards can therefore be put, leading to saving money.
Since the laser beam might be freely and rapidly moved within both the x and y directions, cutting out irregularly shaped boards is easy. This contrasts with a few of the other described methods, which 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 instance when conductors are close together or when ZIF connectors must be cut out (FIGURE 10). These connectors require precise cuts on both ends in the connector fingers, even though the fingers are perfectly centered in between the two cuts.
A possible problem to take into consideration may be the precision in the board images about the panel. The authors have not yet found a business standard indicating an expectation for board image precision. The nearest they already have come is “as necessary for drawing.” This problem may be overcome with the help of 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 the cutline can be put precisely and closely around the board, in cases like this, next to the away from the copper edge ring.
Even when ignoring this potential problem, the minimum space between boards in the panel could be as little as the cutting kerf plus 10 to 30µm, according to the thickness of the panel 13dexopky the machine accuracy of 25µm.
In the area paid by the galvo scanner, the beam comes straight down in the center. Despite the fact that a big collimating lens is utilized, toward the sides of your area the beam has a slight angle. Because of this based on the height of the components near the cutting path, some shadowing might occur. Since this is completely predictable, the distance some components need to stay taken from the cutting path might be calculated. Alternatively, the scan area may be reduced to side step this concern.
Stress. As there is no mechanical connection with the panel during cutting, in some instances every one of the FPC Cutting Machine can be performed after assembly and soldering (Figure 11). This simply means the boards become completely separated from your panel within this last process step, and there is not any requirement for any bending or pulling on the board. Therefore, no stress is exerted around the board, and components near the fringe of the board are certainly not subjected to damage.
In our tests stress measurements were performed. During mechanical depaneling a substantial snap was observed (FIGURES 12 and 13). This too signifies that during earlier process steps, for example paste printing and component placement, the panel can maintain its full rigidity without any pallets are essential.