Punching/die cutting. This technique requires a different die for each new circuit board, which happens to be not much of 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 needs to be come to maintain sharp die edges.
V-scoring. Often the panel is scored on sides to some depth of approximately 30% in the board thickness. After assembly the boards might be manually broken from the panel. This puts bending stress on the boards which can be damaging to several of the components, specially those close to the board edge.
Wheel cutting/pizza cutter. A different technique to manually breaking the internet after V-scoring is to use a “pizza cutter” to reduce the rest of the web. This requires careful alignment between your V-score and the cutter wheels. Furthermore, it induces stresses within the board which may affect some components.
Sawing. Typically machines that are widely used to saw boards from a panel work with a single rotating saw blade that cuts the panel from either the top or even the bottom.
Every one of these methods is restricted to straight line operations, thus just for rectangular boards, and each one to many degree crushes and cuts the board edge. Other methods are more expansive and will include these:
Water jet. Some say this technology can be accomplished; however, the authors have found no actual users from it. Cutting is conducted with a high-speed stream of slurry, which happens to be water with the abrasive. We expect it should take careful cleaning after the fact to remove the abrasive portion of the slurry.
Routing ( nibbling). More often than not boards are partially routed ahead of assembly. The remaining attaching points are drilled with a small drill size, making it easier to break the boards out of your panel after assembly, leaving the so-called mouse bites. A disadvantage might be a significant loss of panel area on the routing space, because the kerf width often takes as much as 1.5 to 3mm (1/16 to 1/8″) plus some additional space for inaccuracies. This simply means a lot of panel space is going to be essential for the routed traces.
Laser routing. Laser routing supplies a space advantage, as the kerf width is only a few micrometers. As an example, the small boards in FIGURE 2 were initially organized in anticipation the panel will be routed. In 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 368 boards needed, only one panel has to be produced as an alternative to three.
Routing can also reduce panel stiffness to the point a pallet may be needed for support throughout the earlier steps from the assembly process. But unlike the prior methods, routing will not be limited by cutting straight line paths only.
The majority of these methods exert some degree of mechanical stress around the board edges, which can lead to delamination or cause space to formulate throughout the glass fibers. This can lead to moisture ingress, which often helps to reduce the long-term reliability of the circuitry.
Additionally, when finishing placement of components around the board and after soldering, the very last connections involving the boards and panel really need to be removed. Often this is accomplished by breaking these final bridges, causing some mechanical and bending stress around the boards. Again, such bending stress might be damaging to components placed near areas that should be broken as a way to take away the board through the panel. It can be therefore imperative to accept production methods into mind during board layout as well as for panelization to ensure that certain parts and traces usually are not positioned in areas considered to be at the mercy of stress when depaneling.
Room is also necessary to permit the precision (or lack thereof) that the tool path may be put and to take into consideration any non-precision inside the board pattern.
Laser cutting. By far the most recently added tool to PCB Routing Machine and rigid boards is really a laser. In the SMT industry various kinds lasers are employed. CO2 lasers (~10µm wavelength) offers 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. Both these laser types produce infrared light and could be called “hot” lasers as they burn or melt the content being cut. (As being an aside, these are the laser types, especially the Nd:Yag lasers, typically used to produce stainless steel stencils for solder paste printing.)
UV lasers (typical wavelength ~355nm), alternatively, are used to ablate the fabric. A localized short pulse of high energy enters the most notable layer from the material being processed and essentially vaporizes and removes this top layer explosively, turning it to dust (FIGURE 3).
The choice of a 355nm laser is based on the compromise between performance and price. In order for ablation to take place, the laser light should be absorbed by the materials to be cut. Within the circuit board industry these are generally mainly FR-4, glass fibers and copper. When thinking about the absorption rates for such materials (FIGURE 4), the shorter wavelength lasers are the most appropriate ones for the ablation process. However, the laser cost increases very rapidly for models with wavelengths shorter than 355nm.
The laser beam features a tapered shape, since it is focused coming from a relatively wide beam for an extremely narrow beam and then continuous within a reverse taper to widen again. This small area where the beam is in its most narrow is referred to as the throat. The optimal ablation happens when the energy density used on the content is maximized, which occurs when the throat of the beam is merely in the material being cut. By repeatedly going over a similar cutting track, thin layers of your material is going to be removed till the beam has cut right through.
In thicker material it might be required to adjust the focus of your beam, as the ablation occurs deeper in to the kerf being cut in the material. The ablation process causes some heating from the material but will 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 power to depanel flex circuit panels. Present machines convey more power and may also be used to depanel circuit boards as much as 1.6mm (63 mils) in thickness.
Temperature. The temperature surge in the material being cut is dependent 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 dependent upon the road length, beam speed and whether a pause is added between passes.
A knowledgeable and experienced system operator are able to select the optimum mixture of settings to make certain a clean cut free of burn marks. There is absolutely no straightforward formula to determine machine settings; these are relying on material type, thickness and condition. According to the board as well as its application, the operator can select fast depaneling by permitting some discoloring or 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 through the cutting path is under 100°C, way below such a PCB experiences during soldering (FIGURE 6).
Expelled material. Within the laser used 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 check the impact for any remaining expelled material, a slot was cut in the four-up pattern on FR-4 material with 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, and several may have consisted of burned or carbonized material. Their size and number were extremely small, and no conduction was expected between traces and components around the board. Then desired, a simple cleaning process could possibly be included with remove any remaining particles. This sort of process could contain the application of any type of wiping having a smooth dry or wet tissue, using compressed air or brushes. You can also have any sort of cleaning liquids or cleaning baths with or without ultrasound, but normally would avoid just about any additional cleaning process, especially an expensive one.
Surface resistance. After cutting a path during 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., as well as 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 from the material spanning a small area, 50x50mm (2×2″). Using this type of scanner permits the beam to get moved with a extremely high speed over the cutting path, in all the different approx. 100 to 1000mm/sec. This ensures the beam is within the same location simply a very limited time, which minimizes local heating.
A pattern recognition product is employed, that may use fiducials or other panel or board feature to precisely discover the location where cut needs to be placed. High precision x and y movement systems can be used as large movements along with a galvo scanner for local movements.
In these types of machines, the cutting tool will be the laser beam, and possesses a diameter of approximately 20µm. This means the kerf cut by the laser is approximately 20µm wide, along with the laser system can locate that cut within 25µm with regards to either panel or board fiducials or some other board feature. The boards can therefore be placed very close together inside a panel. For a panel with a lot of small circuit boards, additional boards can therefore be put, creating cost savings.
As the laser beam may be freely and rapidly moved in the x and y directions, removing irregularly shaped boards is easy. This contrasts with a number of the other described methods, which may be restricted to straight line cuts. This becomes advantageous with flex boards, which are often very irregularly shaped and occasionally require extremely precise cuts, for example when conductors are close together or when ZIF connectors have to be reduce (FIGURE 10). These connectors require precise cuts on ends in the connector fingers, while the fingers are perfectly centered between your two cuts.
A prospective problem to think about may be the precision from the board images around the panel. The authors have not found a marketplace standard indicating an expectation for board image precision. The nearest they already have come is “as required by drawing.” This issue may be overcome by adding greater than three panel fiducials and dividing the cutting operation into smaller sections because of their own area fiducials. FIGURE 11 shows within a sample board eliminate in Figure 2 that this cutline can be put precisely and closely around the board, in such a case, near the outside of the copper edge ring.
Even though ignoring this potential problem, the minimum space between boards in the panel may be as little as the cutting kerf plus 10 to 30µm, dependant upon the thickness of the panel 13dexopky the device accuracy of 25µm.
In the area covered by the galvo scanner, the beam comes straight down in between. Despite the fact that a sizable collimating lens is used, toward the sides in the area the beam carries a slight angle. Because of this according to the height from the components close to the cutting path, some shadowing might occur. Since this is completely predictable, the space some components have to stay taken from the cutting path could be calculated. Alternatively, the scan area might be reduced to side step this concern.
Stress. As there is no mechanical exposure to the panel during cutting, occasionally all the FPC Depaneling Machine can be performed after assembly and soldering (Figure 11). This means the boards become completely separated from the panel within this last process step, and there is not any need for any bending or pulling about the board. Therefore, no stress is exerted around the board, and components close to the fringe of the board will not be subject to damage.
In your tests stress measurements were performed. During mechanical depaneling an important snap was observed (FIGURES 12 and 13). This ensures that during earlier process steps, like paste printing and component placement, the panel can maintain its full rigidity with no pallets are required.