Punching/die cutting. This procedure takes a different die for each and every new circuit board, which is not just 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 taken up maintain sharp die edges.
V-scoring. Often the panel is scored for both sides to your depth around 30% of your board thickness. After assembly the boards might be manually broken from the panel. This puts bending strain on the boards that can be damaging to a few of the components, especially those next 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 cut the remaining web. This calls for careful alignment in between the V-score as well as the cutter wheels. In addition, it induces stresses within the board which might 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 top or perhaps the bottom.
Every one of these methods has limitations to straight line operations, thus just for rectangular boards, and all of them to a few degree crushes and/or cuts the board edge. Other methods tend to be more expansive and can include these:
Water jet. Some say this technology can be achieved; however, the authors are finding no actual users than it. Cutting is carried out using a high-speed stream of slurry, which happens to be water with the abrasive. We expect it will need careful cleaning right after the fact to take out the abrasive part of the slurry.
Routing ( nibbling). More often than not boards are partially routed just before assembly. The remainder attaching points are drilled by using a small drill size, making it easier to break the boards out of the panel after assembly, leaving the so-called mouse bites. A disadvantage can be quite a significant loss of panel area towards the routing space, as the kerf width often takes as much as 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 necessary for the routed traces.
Laser routing. Laser routing supplies a space advantage, because the kerf width is only a few micrometers. By way of example, the small boards in FIGURE 2 were initially laid out in anticipation the panel can be routed. 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 and every 368 boards needed, merely one panel must be produced as an alternative to three.
Routing could also reduce panel stiffness to the level a pallet may be needed for support through the earlier steps from the assembly process. But unlike the previous methods, routing is not really restricted to cutting straight line paths only.
Many of these methods exert some degree of mechanical stress in the board edges, which can cause delamination or cause space to produce across the glass fibers. This may lead to moisture ingress, which in turn can reduce the long term reliability of the circuitry.
Additionally, when finishing placement of components around the board and after soldering, the ultimate connections in between the boards and panel need to be removed. Often this can be 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 close to areas that ought to be broken in order to get rid of the board from the panel. It is actually therefore imperative to accept production methods into mind during board layout and for panelization in order that certain parts and traces will not be placed into areas considered subject to stress when depaneling.
Room can also be necessary to permit the precision (or lack thereof) which the tool path can be placed and to take into consideration any non-precision within the board pattern.
Laser cutting. By far the most recently added tool to PCB Router and rigid boards is actually a laser. From the SMT industry several kinds of lasers are being employed. CO2 lasers (~10µm wavelength) can offer quite 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 while they burn or melt the information being cut. (As an aside, these represent the 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 used to ablate the content. A localized short pulse of high energy enters the top layer of the 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 cost. To ensure ablation to take place, the laser light needs to be absorbed with the materials to be cut. Inside the circuit board industry these are mainly FR-4, glass fibers and copper. When viewing the absorption rates for these particular materials (FIGURE 4), the shorter wavelength lasers are the best 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 the relatively wide beam to a extremely narrow beam after which continuous in a reverse taper to widen again. This small area the location where the beam is in its most narrow is called the throat. The ideal ablation occurs when the energy density put on the fabric is maximized, which takes place when the throat of the beam is merely in the material being cut. By repeatedly groing through the identical cutting track, thin layers of your material is going to be removed up until the beam has cut all the way through.
In thicker material it may be required to adjust the target of the beam, because the ablation occurs deeper to the kerf being cut in to the material. The ablation process causes some heating from the material but may be optimized to depart no burned or carbonized residue. Because cutting is completed gradually, heating is minimized.
The earliest versions of UV laser systems had enough capacity to depanel flex circuit panels. Present machines acquire more power and can also be used to depanel circuit boards approximately 1.6mm (63 mils) in thickness.
Temperature. The temperature increase in the material being cut depends upon the beam power, beam speed, focus, laser pulse rate and repetition rate. The repetition rate (how quick the beam returns for the same location) depends upon the path length, beam speed and whether a pause is added between passes.
An informed and experienced system operator should be able to find the optimum mixture of settings to guarantee a clean cut without any burn marks. There is not any straightforward formula to find out machine settings; they can be relying on material type, thickness and condition. According to the board and its particular application, the operator can decide fast depaneling by permitting some discoloring as well as 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 below 100°C, way below such a PCB experiences during soldering (FIGURE 6).
Expelled material. From the laser employed for these tests, an airflow goes over the panel being cut and removes the majority of the expelled dust into an exhaust and filtering system (FIGURE 7).
To test the impact associated with a remaining expelled material, a slot was cut in the four-up pattern on FR-4 material 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 some high of 20µm, and some might 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 about the board. If you have desired, a basic cleaning process may be added to remove any remaining particles. This kind of process could include the use of any type of wiping with a smooth dry or wet tissue, using compressed air or brushes. You could likewise use any type 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 over these test boards (Figure 7, slot in the center of the exam pattern), the boards were put through 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 relies on a galvanometer scanner (or galvo scanner) to trace the cutting path in the material over a small area, 50x50mm (2×2″). Using this kind of scanner permits the beam being moved in a high speed along the cutting path, in the range of approx. 100 to 1000mm/sec. This ensures the beam is within the same location only 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 get the location where 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 kinds of machines, the cutting tool may be the laser beam, and features a diameter of around 20µm. This implies the kerf cut with the laser is all about 20µm wide, and the laser system can locate that cut within 25µm when it comes to either panel or board fiducials or another board feature. The boards can therefore be put very close together within a panel. For the panel with many different small circuit boards, additional boards can therefore be placed, creating cost savings.
Since the laser beam might be freely and rapidly moved both in the x and y directions, cutting out irregularly shaped boards is simple. This contrasts with some of the other described methods, which can be limited by straight line cuts. This becomes advantageous with flex boards, which are often very irregularly shaped and occasionally require extremely precise cuts, by way of example when conductors are close together or when ZIF connectors should be reduce (FIGURE 10). These connectors require precise cuts on both ends of the connector fingers, whilst the fingers are perfectly centered in between the two cuts.
A possible problem to think about will be the precision of your board images around the panel. The authors have not even found a niche standard indicating an expectation for board image precision. The closest they have come is “as essental to drawing.” This concern could be overcome with the addition of more than three panel fiducials and dividing the cutting operation into smaller sections because of their own area fiducials. FIGURE 11 shows inside a sample board eliminate in Figure 2 that the cutline may be placed precisely and closely across the board, in this case, next to the away from the copper edge ring.
Regardless if ignoring this potential problem, the minimum space between boards on the panel could be as little as the cutting kerf plus 10 to 30µm, depending on the thickness in the panel 13dexopky the machine accuracy of 25µm.
Throughout the area covered by the galvo scanner, the beam comes straight down in the middle. Although a large collimating lens can be used, toward the edges of your area the beam includes a slight angle. This means that dependant upon the height in the components close to the cutting path, some shadowing might occur. As this is completely predictable, the space some components have to stay taken off the cutting path can be calculated. Alternatively, the scan area could be reduced to side step this concern.
Stress. Because there is no mechanical exposure to the panel during cutting, in some circumstances all of the FPC Cutting Machine can be executed after assembly and soldering (Figure 11). What this means is the boards become completely separated from your panel with this last process step, and there is absolutely no need for any bending or pulling about the board. Therefore, no stress is exerted around the board, and components near the edge of the board are not susceptible to damage.
Inside our tests stress measurements were performed. During mechanical depaneling a significant snap was observed (FIGURES 12 and 13). This also signifies that during earlier process steps, like paste printing and component placement, the panel can maintain its full rigidity with out pallets are required.