Punching/die cutting. This process demands a different die for every single new circuit board, which can be not really a practical solution for small production runs. The action might be PCB Depaneling, but either can leave the board edges somewhat deformed. To reduce damage care has to be come to maintain sharp die edges.
V-scoring. Often the panel is scored on both sides to your depth of about 30% of the board thickness. After assembly the boards could be manually broken from the panel. This puts bending stress on the boards that can be damaging to several of the components, particularly those next 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 slice the remainder web. This calls for careful alignment in between the V-score and the cutter wheels. In addition, it induces stresses in the board which can 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 very best or the bottom.
All these methods has limitations to straight line operations, thus only for rectangular boards, and each one to a few degree crushes and/or cuts the board edge. Other methods will be more expansive and will include the subsequent:
Water jet. Some say this technology can be achieved; however, the authors have realized no actual users of this. Cutting is conducted by using a high-speed stream of slurry, which is water by having an abrasive. We expect it will need careful cleaning once the fact to eliminate the abrasive portion of the slurry.
Routing ( nibbling). Usually boards are partially routed before assembly. The rest of the attaching points are drilled with a small drill size, making it easier to destroy the boards out from the panel after assembly, leaving the so-called mouse bites. A disadvantage can be a significant reduction in panel area to the routing space, as the kerf width normally takes around 1.5 to 3mm (1/16 to 1/8″) plus some additional space for inaccuracies. This means a significant amount of panel space is going to be required for the routed traces.
Laser routing. Laser routing provides a space advantage, because the kerf width is only a few micrometers. For instance, the small boards in FIGURE 2 were initially presented in anticipation the panel would be routed. In this fashion the panel yielded 124 boards. After designing the layout for laser depaneling, the amount of boards per panel increased to 368. So for each and every 368 boards needed, just one single panel should be produced rather than three.
Routing also can reduce panel stiffness to the point that the pallet may be needed for support during the earlier steps from the assembly process. But unlike the prior methods, routing is just not limited by cutting straight line paths only.
The majority of these methods exert some degree of mechanical stress in the board edges, which can cause delamination or cause space to build up around the glass fibers. This may lead to moisture ingress, which is effective in reducing the long-term longevity of the circuitry.
Additionally, when finishing placement of components about the board and after soldering, the very last connections involving the boards and panel really need to be removed. Often this can be accomplished by breaking these final bridges, causing some mechanical and bending stress around the boards. Again, such bending stress could be damaging to components placed close to areas that need to be broken in order to take away the board from the panel. It really is therefore imperative to accept production methods into consideration during board layout as well as for panelization to ensure that certain parts and traces will not be put into areas known to be subjected to stress when depaneling.
Room is likewise expected to permit the precision (or lack thereof) that the tool path can be placed and to take into account any non-precision from the board pattern.
Laser cutting. Probably the most recently added tool to PCB Router and rigid boards is actually a laser. In the SMT industry various kinds lasers are now being employed. CO2 lasers (~10µm wavelength) can provide 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 may be called “hot” lasers while they burn or melt the content being cut. (Being an aside, these are the laser types, specially the Nd:Yag lasers, typically utilized to produce stainless-steel stencils for solder paste printing.)
UV lasers (typical wavelength ~355nm), however, are widely 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).
The option 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 from the materials to be cut. Inside the circuit board industry these are typically mainly FR-4, glass fibers and copper. When thinking about the absorption rates for these particular 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 includes a tapered shape, because it is focused coming from a relatively wide beam for an extremely narrow beam after which continuous inside a reverse taper to widen again. This small area where the beam reaches its most narrow is known as the throat. The optimal ablation happens when the energy density used on the content is maximized, which happens when the throat in the beam is simply in the material being cut. By repeatedly going over exactly the same cutting track, thin layers of your material will be removed up until the beam has cut right through.
In thicker material it might be required to adjust the focus from the beam, because the ablation occurs deeper in the kerf being cut into 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 done 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 may also be used to depanel circuit boards up to 1.6mm (63 mils) in thickness.
Temperature. The temperature rise in the information being cut depends on the beam power, beam speed, focus, laser pulse rate and repetition rate. The repetition rate (how quickly the beam returns for the same location) depends on the way length, beam speed and whether a pause is added between passes.
An experienced and experienced system operator will be able to choose the optimum mixture of settings to make certain a clean cut free from burn marks. There is absolutely no straightforward formula to determine machine settings; they are influenced by material type, thickness and condition. Dependant upon the board and its application, the operator can pick fast depaneling by permitting some discoloring and 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 just what a PCB experiences during soldering (FIGURE 6).
Expelled material. Within the laser utilized for these tests, an airflow goes over the panel being cut and removes many 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 in the 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 typically 10µm to your high of 20µm, and several may have contained burned or carbonized material. Their size and number were extremely small, with no conduction was expected between traces and components in the board. In that case desired, a basic cleaning process could be included in remove any remaining particles. This kind of process could consist of the usage of any sort of wiping using a smooth dry or wet tissue, using compressed air or brushes. One could also use 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 in 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 across a small area, 50x50mm (2×2″). Using this kind of scanner permits the beam to become moved with a high speed across the cutting path, in the plethora of approx. 100 to 1000mm/sec. This ensures the beam is with the same location simply a very small amount of time, which minimizes local heating.
A pattern recognition product is employed, which can use fiducials or some other panel or board feature to precisely discover the location where the cut must be placed. High precision x and y movement systems are used for large movements along with a galvo scanner for local movements.
In most of these machines, the cutting tool is definitely the laser beam, and possesses a diameter of approximately 20µm. This means the kerf cut from the laser is approximately 20µm wide, and also the laser system can locate that cut within 25µm when it comes to either panel or board fiducials or other board feature. The boards can therefore be put very close together in a panel. For any panel with a lot of small circuit boards, additional boards can therefore be put, creating cost savings.
Because the laser beam could be freely and rapidly moved within both the x and y directions, cutting out irregularly shaped boards is simple. This contrasts with a few of the other described methods, that may be limited to straight line cuts. This becomes advantageous with flex boards, which can be very irregularly shaped and in some instances require extremely precise cuts, for instance when conductors are close together or when ZIF connectors have to be eliminate (FIGURE 10). These connectors require precise cuts on both ends from the connector fingers, whilst the fingers are perfectly centered between the two cuts.
A prospective problem to take into account will 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 closest they have got come is “as necessary for drawing.” This challenge could be overcome by adding over three panel fiducials and dividing the cutting operation into smaller sections making use of their own area fiducials. FIGURE 11 shows inside a sample board reduce in Figure 2 how the cutline may be placed precisely and closely throughout the board, in cases like this, near the beyond the copper edge ring.
Even though ignoring this potential problem, the minimum space between boards around the panel can be as little as the cutting kerf plus 10 to 30µm, dependant upon the thickness in the panel 13dexopky the machine accuracy of 25µm.
Throughout the area protected by the galvo scanner, the beam comes straight down in the center. Despite the fact that a sizable collimating lens is commonly used, toward the sides in the area the beam carries a slight angle. Which means that according to the height in the components nearby the cutting path, some shadowing might occur. As this is completely predictable, the space some components have to stay taken from the cutting path can be calculated. Alternatively, the scan area can be reduced to side step this issue.
Stress. As there is no mechanical experience of the panel during cutting, in some instances every one of the FPC Depaneling Machine 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 not any necessity for any bending or pulling around the board. Therefore, no stress is exerted about the board, and components near to the fringe of the board are not subjected to damage.
In your tests stress measurements were performed. During mechanical depaneling a tremendous snap was observed (FIGURES 12 and 13). This also ensures that during earlier process steps, such as paste printing and component placement, the panel can maintain its full rigidity and no pallets are essential.