Punching/die cutting. This procedure demands a different die for each new circuit board, which can 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 lessen damage care has to be taken to maintain sharp die edges.
V-scoring. Often the panel is scored on both sides into a depth of about 30% of your board thickness. After assembly the boards can be manually broken out of the panel. This puts bending strain on the boards that may be damaging to several of the components, especially those near to the board edge.
Wheel cutting/pizza cutter. A different method to manually breaking the net after V-scoring is to try using a “pizza cutter” to cut the remainder web. This involves careful alignment between your V-score and the cutter wheels. It also induces stresses inside the board which could affect some components.
Sawing. Typically machines that are used to saw boards from a panel use a single rotating saw blade that cuts the panel from either the top or the bottom.
All these methods is limited to straight line operations, thus only for rectangular boards, and each one to some degree crushes 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 found no actual users from it. Cutting is conducted having a high-speed stream of slurry, which happens to be water by having an abrasive. We expect it will require careful cleaning right after the fact to remove the abrasive portion of the slurry.
Routing ( nibbling). Most of the time boards are partially routed ahead of assembly. The remaining attaching points are drilled with a small drill size, making it simpler to destroy the boards out of the panel after assembly, leaving the so-called mouse bites. A disadvantage can be a significant loss of panel area to the routing space, because the kerf width normally takes approximately 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 probably be essential for the routed traces.
Laser routing. Laser routing gives a space advantage, as the kerf width is only a few micrometers. For instance, the small boards in FIGURE 2 were initially presented in anticipation that the panel could be routed. In this way the panel yielded 124 boards. After designing the design for laser depaneling, the quantity of boards per panel increased to 368. So for every single 368 boards needed, merely one panel should be produced rather than three.
Routing also can reduce panel stiffness to the stage that a pallet may be needed for support in the earlier steps within the assembly process. But unlike the earlier methods, routing is just not confined to cutting straight line paths only.
A large number of methods exert some degree of mechanical stress on 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 longevity of the circuitry.
Additionally, when finishing placement of components on the board and after soldering, the very last connections between your boards and panel really need to be removed. Often this is accomplished by breaking these final bridges, causing some mechanical and bending stress about the boards. Again, such bending stress may be damaging to components placed close to areas that must be broken to be able to remove the board through the panel. It is therefore imperative to take the production methods into account during board layout and for panelization in order that certain parts and traces are certainly not placed in areas known to be susceptible to stress when depaneling.
Room is additionally required to permit the precision (or lack thereof) in which the tool path can be put and to take into account any non-precision from the board pattern.
Laser cutting. One of the most recently added tool to PCB Routing Machine and rigid boards is a laser. In the SMT industry various kinds lasers are being employed. CO2 lasers (~10µm wavelength) offers 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. These two laser types produce infrared light and can be called “hot” lasers because they burn or melt the information being cut. (Being an aside, these represent the laser types, specially the Nd:Yag lasers, typically used to produce stainless steel stencils for solder paste printing.)
UV lasers (typical wavelength ~355nm), on the other hand, are utilized 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).
The option of a 355nm laser is dependant on the compromise between performance and price. For ablation to take place, the laser light needs to be absorbed by the materials being cut. In the circuit board industry these are typically mainly FR-4, glass fibers and copper. When looking at the absorption rates for these materials (FIGURE 4), the shorter wavelength lasers are the most suitable ones for the ablation process. However, the laser cost increases very rapidly for models with wavelengths shorter than 355nm.
The laser beam carries a tapered shape, because it is focused from a relatively wide beam to a extremely narrow beam and then continuous within a reverse taper to widen again. This small area where beam are at its most narrow is known as the throat. The perfect ablation happens when the energy density placed on the information is maximized, which occurs when the throat in the beam is simply inside the material being cut. By repeatedly exceeding the same cutting track, thin layers of your material will likely be removed until the beam has cut all the way through.
In thicker material it can be necessary to adjust the focus of your beam, as the ablation occurs deeper in to the kerf being cut to the material. The ablation process causes some heating from the material but can be optimized to have 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 approximately 1.6mm (63 mils) in thickness.
Temperature. The temperature increase in the content being cut depends upon the beam power, beam speed, focus, laser pulse rate and repetition rate. The repetition rate (how quickly the beam returns to the same location) is determined by the path length, beam speed and whether a pause is added between passes.
An informed and experienced system operator should be able to pick the optimum mix of settings to make certain a clean cut free from burn marks. There is absolutely no straightforward formula to figure out machine settings; they may be affected by material type, thickness and condition. Dependant upon the board as well as its application, the operator can choose fast depaneling by permitting some discoloring and even some carbonization, versus a somewhat slower but completely “clean” cut.
Careful testing has revealed that under most conditions the temperature rise within 1.5mm through the cutting path is less than 100°C, way below what a PCB experiences during soldering (FIGURE 6).
Expelled material. Inside the laser employed for these tests, an airflow goes across the panel being cut and removes a lot of the expelled dust into an exhaust and filtering method (FIGURE 7).
To evaluate the impact of any remaining expelled material, a slot was cut within a four-up pattern on FR-4 material with a thickness of 800µm (31.5 mils) (FIGURE 8). Only few particles remained and consisted of powdery epoxy and glass particles. Their size ranged from about 10µm to a high of 20µm, and a few could have was made up of burned or carbonized material. Their size and number were extremely small, and no conduction was expected between traces and components around the board. In that case desired, an easy cleaning process could possibly be included with remove any remaining particles. This sort of process could include using any type of wiping having a smooth dry or wet tissue, using compressed air or brushes. You could also use any kind of cleaning liquids or cleaning baths without or with ultrasound, but normally would avoid any type of additional cleaning process, especially a high priced one.
Surface resistance. After cutting a path during 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., and 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 from the material over a small area, 50x50mm (2×2″). Using this type of scanner permits the beam to get moved in a very high speed along the cutting path, in all the different approx. 100 to 1000mm/sec. This ensures the beam is in the same location merely a very short time, which minimizes local heating.
A pattern recognition product is employed, which may use fiducials or any other panel or board feature to precisely discover the location the location where the cut should be placed. High precision x and y movement systems can be used as large movements in conjunction with a galvo scanner for local movements.
In these kinds of machines, the cutting tool may be the laser beam, and contains a diameter of around 20µm. This means the kerf cut by the laser is all about 20µm wide, as well as 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 within a panel. For a panel with a lot of small circuit boards, additional boards can therefore be placed, creating saving money.
Because the laser beam might be freely and rapidly moved in the x and y directions, eliminating irregularly shaped boards is easy. This contrasts with several of the other described methods, that may be limited to straight line cuts. This becomes advantageous with flex boards, which are often very irregularly shaped and in some instances 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 from the connector fingers, even though the fingers are perfectly centered between your two cuts.
A possible problem to consider may be the precision in the board images in the panel. The authors have not found an industry standard indicating an expectation for board image precision. The closest they have come is “as necessary for drawing.” This challenge could be overcome by adding a lot more than three panel fiducials and dividing the cutting operation into smaller sections making use of their own area fiducials. FIGURE 11 shows in a sample board cut out in Figure 2 how the cutline may be placed precisely and closely around the board, in such a case, near the outside the copper edge ring.
Even when ignoring this potential problem, the minimum space between boards in the panel could be as low 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 between. Though a sizable collimating lens is utilized, toward the edges of your area the beam features a slight angle. Which means that depending on the height of the components nearby the cutting path, some shadowing might occur. As this is completely predictable, the space some components need to stay removed from the cutting path might be calculated. Alternatively, the scan area can be reduced to side step this concern.
Stress. As there is no mechanical experience of the panel during cutting, in some circumstances all the FPC Laser Depaneling can be carried out after assembly and soldering (Figure 11). This means the boards become completely separated in the panel with this last process step, and there is no requirement for any bending or pulling about the board. Therefore, no stress is exerted about the board, and components nearby the fringe of the board are certainly not subject to damage.
In our tests stress measurements were performed. During mechanical depaneling a tremendous snap was observed (FIGURES 12 and 13). This also implies that during earlier process steps, such as paste printing and component placement, the panel can maintain its full rigidity and no pallets are essential.