Punching/die cutting. This technique demands a different die for every single new circuit board, which can be not really a practical solution for small production runs. The action may be PCB Depaneling, but either can leave the board edges somewhat deformed. To minimize damage care needs to be taken to maintain sharp die edges.
V-scoring. Often the panel is scored on sides to a depth of about 30% from 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 a few of the components, in particular those near the board edge.
Wheel cutting/pizza cutter. An alternate method to manually breaking the internet after V-scoring is to try using a “pizza cutter” to slice the other web. This requires careful alignment involving the V-score along with the cutter wheels. Furthermore, it induces stresses in the board which can affect some components.
Sawing. Typically machines that are widely used to saw boards away from a panel work with a single rotating saw blade that cuts the panel from either the very best or perhaps the bottom.
All these methods is restricted to straight line operations, thus simply for rectangular boards, and each one to a few degree crushes and cuts the board edge. Other methods will be more expansive and will include the following:
Water jet. Some say this technology can be achieved; however, the authors have found no actual users from it. Cutting is conducted using a high-speed stream of slurry, which can be water by having an abrasive. We expect it may need careful cleaning following the fact to eliminate the abrasive part of the slurry.
Routing ( nibbling). More often than not boards are partially routed ahead of assembly. The rest of the attaching points are drilled having a small drill size, making it easier to destroy the boards out of the panel after assembly, leaving the so-called mouse bites. A disadvantage can be quite a significant reduction in panel area towards the routing space, because the kerf width normally takes up to 1.5 to 3mm (1/16 to 1/8″) plus some additional space for inaccuracies. This simply means a significant amount of panel space will probably be necessary for the routed traces.
Laser routing. Laser routing gives a space advantage, since the kerf width is simply a few micrometers. For example, the tiny boards in FIGURE 2 were initially organized in anticipation how the panel could be routed. 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 368 boards needed, just one panel has to be produced as opposed to three.
Routing may also reduce panel stiffness to the level a pallet may be required for support throughout the earlier steps from the assembly process. But unlike the last methods, routing is not restricted to cutting straight line paths only.
Most of these methods exert some extent of mechanical stress around the board edges, which can lead to delamination or cause space to produce around the glass fibers. This might lead to moisture ingress, which helps to reduce the long term reliability of the circuitry.
Additionally, when finishing placement of components about the board and after soldering, the final connections involving the boards and panel need to be removed. Often this is certainly accomplished by breaking these final bridges, causing some mechanical and bending stress about the boards. Again, such bending stress might be damaging to components placed in close proximity to areas that should be broken as a way to eliminate the board through the panel. It really is therefore imperative to accept production methods into mind during board layout and also for panelization so that certain parts and traces will not be placed into areas regarded as at the mercy of stress when depaneling.
Room can also be required to permit the precision (or lack thereof) with which the tool path may be put and to take into consideration any non-precision from the board pattern.
Laser cutting. By far the most recently added tool to PCB Router and rigid boards is a laser. Inside the SMT industry various kinds lasers are being employed. CO2 lasers (~10µm wavelength) offers very 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 could be called “hot” lasers because they burn or melt the content being cut. (Being an aside, these are the basic laser types, especially the Nd:Yag lasers, typically accustomed to produce steel stencils for solder paste printing.)
UV lasers (typical wavelength ~355nm), however, are widely used to ablate the content. A localized short pulse of high energy enters the best layer in 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 price. For ablation to occur, the laser light must be absorbed through the materials to get cut. Inside the circuit board industry these are typically mainly FR-4, glass fibers and copper. When viewing 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 has a tapered shape, since it is focused from the relatively wide beam with an extremely narrow beam then continuous in the reverse taper to widen again. This small area in which the beam is at its most narrow is called 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 within the material being cut. By repeatedly exceeding the identical cutting track, thin layers of your material will probably be removed before the beam has cut all the way through.
In thicker material it might be essential to adjust the focus from the beam, as the ablation occurs deeper to the kerf being cut into the material. The ablation process causes some heating of the material but may 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 capability 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 surge in the fabric being cut is determined by the beam power, beam speed, focus, laser pulse rate and repetition rate. The repetition rate (how rapidly the beam returns towards the same location) depends on the path length, beam speed and whether a pause is added between passes.
An informed and experienced system operator are able to pick the optimum mix of settings to make sure a clean cut free from burn marks. There is absolutely no straightforward formula to find out machine settings; they can be 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 demonstrated 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. Within the laser employed for these tests, an airflow goes throughout the panel being cut and removes many of the expelled dust into an exhaust and filtering method (FIGURE 7).
To test the impact of the remaining expelled material, a slot was cut inside 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 typically 10µm to your high of 20µm, and some could have was comprised of burned or carbonized material. Their size and number were extremely small, with out conduction was expected between traces and components in the board. Then desired, a simple cleaning process could be added to remove any remaining particles. This sort of process could consist of the application of any sort of wiping using a smooth dry or wet tissue, using compressed air or brushes. You can also have any type of cleaning liquids or cleaning baths without or with ultrasound, but normally would avoid just about any additional cleaning process, especially a high priced one.
Surface resistance. After cutting a path during these test boards (Figure 7, slot in the middle of the exam 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 uses a galvanometer scanner (or galvo scanner) to trace the cutting path inside the material over a small area, 50x50mm (2×2″). Using such a scanner permits the beam to become moved with a extremely high speed down the cutting path, in the range of approx. 100 to 1000mm/sec. This ensures the beam is in the same location just a very small amount of time, which minimizes local heating.
A pattern recognition method is employed, which may use fiducials or another panel or board feature to precisely discover the location the location where the cut must be placed. High precision x and y movement systems are used for large movements together with a galvo scanner for local movements.
In these kinds of machines, the cutting tool may be the laser beam, and possesses a diameter of approximately 20µm. What this means is the kerf cut through the laser is approximately 20µm wide, and also the laser system can locate that cut within 25µm with respect to either panel or board fiducials or another board feature. The boards can therefore be put very close together inside a panel. For any panel with many different small circuit boards, additional boards can therefore be placed, ultimately causing financial savings.
As being the laser beam may be freely and rapidly moved both in the x and y directions, cutting out irregularly shaped boards is not difficult. This contrasts with a few of the other described methods, which may be confined to straight line cuts. This becomes advantageous with flex boards, which are often very irregularly shaped and occasionally require extremely precise cuts, for instance when conductors are close together or when ZIF connectors should be remove (FIGURE 10). These connectors require precise cuts on ends of the connector fingers, whilst the fingers are perfectly centered in between the two cuts.
A possible problem to consider is the precision of your board images in the panel. The authors have not found a marketplace standard indicating an expectation for board image precision. The closest they already have come is “as required by drawing.” This concern can be overcome by having a lot more than three panel fiducials and dividing the cutting operation into smaller sections with their own area fiducials. FIGURE 11 shows inside a sample board remove in Figure 2 that the cutline can be put precisely and closely around the board, in this instance, near the outside of the copper edge ring.
Regardless if ignoring this potential problem, the minimum space between boards on the panel can be as low as the cutting kerf plus 10 to 30µm, depending on the thickness from the panel 13dexopky the device accuracy of 25µm.
In the area included in the galvo scanner, the beam comes straight down at the center. Though a sizable collimating lens is commonly used, toward the edges from the area the beam has a slight angle. This means that dependant upon the height of the components close to the cutting path, some shadowing might occur. Because this is completely predictable, the space some components have to stay pulled from the cutting path could be calculated. Alternatively, the scan area may be reduced to side step this problem.
Stress. Because there is no mechanical experience of the panel during cutting, in some instances each of the FPC Laser Depaneling can be carried out after assembly and soldering (Figure 11). What this means is the boards become completely separated through the panel with this last process step, and there is no desire for any bending or pulling around the board. Therefore, no stress is exerted on the board, and components nearby the fringe of the board will not be susceptible to damage.
Inside our tests stress measurements were performed. During mechanical depaneling a substantial snap was observed (FIGURES 12 and 13). And also 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.