Punching/die cutting. This method demands a different die for each and every new circuit board, which can be not just a practical solution for small production runs. The action could be PCB Depaneling, but either can leave the board edges somewhat deformed. To lessen damage care should be taken to maintain sharp die edges.
V-scoring. Usually the panel is scored on both sides to your depth of around 30% of your board thickness. After assembly the boards can be manually broken out from the panel. This puts bending strain on the boards that can be damaging to several of the components, specially those next to the board edge.
Wheel cutting/pizza cutter. A different approach to manually breaking the internet after V-scoring is to use a “pizza cutter” to cut the other web. This requires careful alignment in between the V-score and also the cutter wheels. Furthermore, it induces stresses inside the board which might affect some components.
Sawing. Typically machines that are utilized to saw boards out of a panel work with a single rotating saw blade that cuts the panel from either the best or the bottom.
Each of these methods is restricted to straight line operations, thus just for rectangular boards, and all of them to some degree crushes and/or cuts the board edge. Other methods tend to be more expansive and can include the subsequent:
Water jet. Some say this technology can be achieved; however, the authors are finding no actual users of this. Cutting is carried out having a high-speed stream of slurry, which is water by having an abrasive. We expect it may need careful cleaning after the fact to remove the abrasive part of the slurry.
Routing ( nibbling). More often than not boards are partially routed just before assembly. The rest of the attaching points are drilled with a small drill size, making it easier to interrupt the boards from the panel after assembly, leaving the so-called mouse bites. A disadvantage could be a significant loss in panel area to the routing space, since the kerf width normally takes approximately 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 needed for the routed traces.
Laser routing. Laser routing offers a space advantage, because the kerf width is simply a few micrometers. By way of example, the small boards in FIGURE 2 were initially organized in anticipation the panel could be routed. In this fashion the panel yielded 124 boards. After designing the layout for laser depaneling, the quantity of boards per panel increased to 368. So for each and every 368 boards needed, only one panel has to be produced as an alternative to three.
Routing also can reduce panel stiffness to the level that a pallet may be required for support during the earlier steps within the assembly process. But unlike the earlier methods, routing is not really restricted to cutting straight line paths only.
Many of these methods exert some degree of mechanical stress on the board edges, which can lead to delamination or cause space to build up around the glass fibers. This may lead to moisture ingress, which actually is effective in reducing the long-term longevity of the circuitry.
Additionally, when finishing placement of components in the board and after soldering, the very last connections between your boards and panel have to be removed. Often this really 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 need to be broken as a way to get rid of the board in the panel. It really is therefore imperative to take the production methods into account during board layout as well as for panelization in order that certain parts and traces will not be placed into areas known to be subject to stress when depaneling.
Room is also required to permit the precision (or lack thereof) that the tool path may be placed and to take into consideration any non-precision from the board pattern.
Laser cutting. By far the most recently added tool to PCB Routing Machine and rigid boards can be a laser. In the SMT industry various kinds of lasers are now being employed. CO2 lasers (~10µm wavelength) offers quite high power levels and cut through thick steel sheets and in addition 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 might be called “hot” lasers because they burn or melt the fabric being cut. (As 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), however, are used to ablate the information. A localized short pulse of high energy enters the most notable layer of your material being processed and essentially vaporizes and removes this top layer explosively, turning it to dust (FIGURE 3).
Choosing a 355nm laser will depend on the compromise between performance and expense. For ablation to occur, the laser light needs to be absorbed through the materials to get cut. In the circuit board industry these are typically mainly FR-4, glass fibers and copper. When examining the absorption rates for such 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 features a tapered shape, since it is focused coming from a relatively wide beam with an extremely narrow beam then continuous in the reverse taper to widen again. This small area the location where the beam are at its most narrow is named the throat. The optimal ablation happens when the energy density placed on the fabric is maximized, which happens when the throat of the beam is simply inside of the material being cut. By repeatedly exceeding exactly the same cutting track, thin layers of your material will probably be removed up until the beam has cut all the way through.
In thicker material it might be needed to adjust the main focus of the beam, because the ablation occurs deeper to the kerf being cut into the material. The ablation process causes some heating from the material but will be optimized to have 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 may also be used to depanel circuit boards as much as 1.6mm (63 mils) in thickness.
Temperature. The temperature increase in the fabric being cut depends upon the beam power, beam speed, focus, laser pulse rate and repetition rate. The repetition rate (how quickly the beam returns on the same location) depends upon the way length, beam speed and whether a pause is added between passes.
An informed and experienced system operator should be able to find the optimum blend of settings to make certain a clean cut without any burn marks. There is absolutely no straightforward formula to determine machine settings; these are relying on material type, thickness and condition. Depending on the board and its particular application, the operator can choose 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 lower than 100°C, way below exactly what a PCB experiences during soldering (FIGURE 6).
Expelled material. In the laser utilized for these tests, an airflow goes all over the panel being cut and removes a lot of the expelled dust into an exhaust and filtration system (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 consisted of powdery epoxy and glass particles. Their size ranged from around 10µm to your high of 20µm, and some may have consisted 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, an easy cleaning process could be included in remove any remaining particles. Such a process could consist of using any sort of wiping with a smooth dry or wet tissue, using compressed air or brushes. One could also employ any kind of cleaning liquids or cleaning baths without or with ultrasound, but normally would avoid any sort of additional cleaning process, especially a costly one.
Surface resistance. After cutting a path during these test boards (Figure 7, slot in the midst of the test pattern), the boards were put through 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 uses a galvanometer scanner (or galvo scanner) to trace the cutting path from the material across a small area, 50x50mm (2×2″). Using this type of scanner permits the beam to be moved with a extremely high speed across the cutting path, in the plethora of approx. 100 to 1000mm/sec. This ensures the beam is within the same location only a very short period of time, which minimizes local heating.
A pattern recognition product is employed, which could use fiducials or another panel or board feature to precisely get the location in which the cut must be placed. High precision x and y movement systems can be used for large movements in conjunction with a galvo scanner for local movements.
In most of these 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 about 20µm wide, as well as the laser system can locate that cut within 25µm with respect to either panel or board fiducials or some other board feature. The boards can therefore be placed very close together in a panel. For any panel with lots of small circuit boards, additional boards can therefore be placed, resulting in saving money.
As being the laser beam might be freely and rapidly moved within both the x and y directions, cutting out irregularly shaped boards is not difficult. This contrasts with several of the other described methods, which is often limited to straight line cuts. This becomes advantageous with flex boards, which can be very irregularly shaped and in some circumstances require extremely precise cuts, as an example when conductors are close together or when ZIF connectors have to be cut out (FIGURE 10). These connectors require precise cuts on ends from the connector fingers, even though the fingers are perfectly centered in between the two cuts.
A potential problem to take into consideration will be the precision of the board images on the panel. The authors have not even found a niche standard indicating an expectation for board image precision. The nearest they have got come is “as needed by drawing.” This concern can be overcome with the addition of over three panel fiducials and dividing the cutting operation into smaller sections because of their own area fiducials. FIGURE 11 shows in a sample board eliminate in Figure 2 how the cutline can be placed precisely and closely around the board, in cases like this, next to the beyond the copper edge ring.
Even when ignoring this potential problem, the minimum space between boards about the panel could be as little as the cutting kerf plus 10 to 30µm, according to the thickness of your panel 13dexopky the system accuracy of 25µm.
Inside the area paid by the galvo scanner, the beam comes straight down in the center. Even though a large collimating lens is commonly used, toward the sides of your area the beam features a slight angle. Which means that dependant upon the height from the components close to the cutting path, some shadowing might occur. As this is completely predictable, the distance some components need to stay removed from the cutting path may be calculated. Alternatively, the scan area can be reduced to side step this problem.
Stress. While there is no mechanical exposure to the panel during cutting, in some circumstances each of the FPC Laser Depaneling can be executed after assembly and soldering (Figure 11). What this means is the boards become completely separated from the panel in this particular last process step, and there is no desire for any bending or pulling in the board. Therefore, no stress is exerted in the board, and components near to the side of the board are certainly not at the mercy of damage.
In our tests stress measurements were performed. During mechanical depaneling a significant snap was observed (FIGURES 12 and 13). This implies that during earlier process steps, like paste printing and component placement, the panel can maintain its full rigidity with no pallets will be required.