Punching/die cutting. This process requires a different die for every single new circuit board, which can be not a practical solution for small production runs. The action may be PCB Depaneling, but either can leave the board edges somewhat deformed. To lower damage care needs to be taken to maintain sharp die edges.
V-scoring. Usually the panel is scored for both sides into a depth around 30% from the board thickness. After assembly the boards can be manually broken out of your panel. This puts bending stress on the boards that can be damaging to a number of the components, in particular those near the board edge.
Wheel cutting/pizza cutter. An alternate strategy to manually breaking the internet after V-scoring is to try using a “pizza cutter” to cut the remainder web. This involves careful alignment between your V-score and also the cutter wheels. Furthermore, it induces stresses in the board which can affect some components.
Sawing. Typically machines that are employed to saw boards out from a panel utilize 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 exclusively for rectangular boards, and each of them to some degree crushes and cuts the board edge. Other methods tend to be more expansive and can include the subsequent:
Water jet. Some say this technology can be done; however, the authors have discovered no actual users from it. Cutting is carried out with a high-speed stream of slurry, which can be water with an abrasive. We expect it will need careful cleaning right after the fact to get rid of the abrasive part of the slurry.
Routing ( nibbling). Quite often boards are partially routed before assembly. The remainder attaching points are drilled using a small drill size, making it simpler to get rid of the boards from the panel after assembly, leaving the so-called mouse bites. A disadvantage could be a significant loss of panel area for the routing space, as being the kerf width normally takes around 1.5 to 3mm (1/16 to 1/8″) plus some additional space for inaccuracies. This simply means a lot of panel space will be necessary for the routed traces.
Laser routing. Laser routing provides a space advantage, because the kerf width is only a few micrometers. For example, the tiny boards in FIGURE 2 were initially presented in anticipation how the panel can be routed. In this way the panel yielded 124 boards. After designing the design for laser depaneling, the amount of boards per panel increased to 368. So for every single 368 boards needed, just one panel must be produced as an alternative to three.
Routing could also reduce panel stiffness to the level that the pallet may be required for support during the earlier steps inside the assembly process. But unlike the earlier methods, routing is not restricted to cutting straight line paths only.
The majority of these methods exert some extent of mechanical stress around the board edges, which can cause delamination or cause space to produce round 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 in the board and after soldering, the final connections in between the boards and panel need to be removed. Often this really is accomplished by breaking these final bridges, causing some mechanical and bending stress in the boards. Again, such bending stress might be damaging to components placed near to areas that need to be broken so that you can remove the board in the panel. It is therefore imperative to accept production methods into account during board layout and for panelization to ensure that certain parts and traces are certainly not put into areas regarded as susceptible to stress when depaneling.
Room can also be expected to permit the precision (or lack thereof) which the tool path may be put and to take into consideration any non-precision in the board pattern.
Laser cutting. Probably the most recently added tool to PCB Router and rigid boards is a laser. Within the SMT industry several kinds of lasers are increasingly being employed. CO2 lasers (~10µm wavelength) provides 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. Both these laser types produce infrared light and can be called “hot” lasers as they burn or melt the fabric being cut. (As being an aside, they are the laser types, particularly the Nd:Yag lasers, typically employed to produce stainless stencils for solder paste printing.)
UV lasers (typical wavelength ~355nm), on the other hand, are employed to ablate the information. A localized short pulse of high energy enters the very best layer from 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 will depend on the compromise between performance and expense. To ensure ablation to take place, the laser light must be absorbed through the materials to be cut. Inside the circuit board industry these are mainly FR-4, glass fibers and copper. When examining the absorption rates for these materials (FIGURE 4), the shorter wavelength lasers are the best 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 from the relatively wide beam with an extremely narrow beam and after that continuous inside a reverse taper to widen again. This small area where the beam is at its most narrow is called the throat. The perfect ablation takes place when the energy density put on the content is maximized, which occurs when the throat in the beam is definitely in the material being cut. By repeatedly exceeding a similar cutting track, thin layers of the material will likely be removed before the beam has cut right through.
In thicker material it may be necessary to adjust the main objective from the beam, because the ablation occurs deeper to the kerf being cut in the material. The ablation process causes some heating in the material but could 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 up to 1.6mm (63 mils) in thickness.
Temperature. The temperature rise in the fabric 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 determined by the way length, beam speed and whether a pause is added between passes.
An educated and experienced system operator will be able to choose the optimum blend of settings to ensure a clean cut without any burn marks. There is no straightforward formula to ascertain machine settings; they may be affected by material type, thickness and condition. Depending on the board and its particular application, the operator can decide fast depaneling by permitting some discoloring as well as some carbonization, versus a somewhat slower but completely “clean” cut.
Careful testing has demonstrated that under most conditions the temperature rise within 1.5mm in the cutting path is below 100°C, way below such a PCB experiences during soldering (FIGURE 6).
Expelled material. Within the laser useful for these tests, an airflow goes across the panel being cut and removes the majority of the expelled dust into an exhaust and filtration system (FIGURE 7).
To test the impact of the remaining expelled material, a slot was cut within a four-up pattern on FR-4 material using a thickness of 800µm (31.5 mils) (FIGURE 8). Only few particles remained and contained powdery epoxy and glass particles. Their size ranged from typically 10µm into a high of 20µm, and several might have consisted of burned or carbonized material. Their size and number were extremely small, and no conduction was expected between traces and components about the board. If so desired, a basic cleaning process could be added to remove any remaining particles. Such a process could comprise of the use of any kind of wiping using a smooth dry or wet tissue, using compressed air or brushes. You could also have just about any 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 in the midst of the test pattern), the boards were put through a climate test (40°C, RH=93%, no condensation) for 170 hr., along with the SIR values exceeded 10E11 Ohm, indicating no conductive material is present.
Cutting path location. The laser beam typically relies on a galvanometer scanner (or galvo scanner) to trace the cutting path in the material more than a small area, 50x50mm (2×2″). Using this kind of scanner permits the beam to get moved in a high speed down the cutting path, in the plethora of approx. 100 to 1000mm/sec. This ensures the beam is incorporated in the same location simply a very limited time, which minimizes local heating.
A pattern recognition method is employed, which can use fiducials or 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 for large movements together with a galvo scanner for local movements.
In these kinds of machines, the cutting tool is the laser beam, and it has a diameter of around 20µm. This simply means the kerf cut by the laser is about 20µm wide, and also the laser system can locate that cut within 25µm with regards to either panel or board fiducials or other board feature. The boards can therefore be placed very close together in a panel. For the panel with many different small circuit boards, additional boards can therefore be put, ultimately causing financial savings.
Since the laser beam could be freely and rapidly moved in the x and y directions, cutting out irregularly shaped boards is straightforward. This contrasts with a few 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 sometimes require extremely precise cuts, for example when conductors are close together or when ZIF connectors should be eliminate (FIGURE 10). These connectors require precise cuts on ends from the connector fingers, as the fingers are perfectly centered between your two cuts.
A potential problem to think about may be the precision from the board images about the panel. The authors have not found an industry standard indicating an expectation for board image precision. The closest they have got come is “as needed by drawing.” This problem may be overcome with the addition of a lot more than three panel fiducials and dividing the cutting operation into smaller sections with their own area fiducials. FIGURE 11 shows in the sample board cut out in Figure 2 the cutline can be placed precisely and closely across the board, in such a case, near the away from the copper edge ring.
Even though ignoring this potential problem, the minimum space between boards about the panel may be as low as the cutting kerf plus 10 to 30µm, based on the thickness of your panel 13dexopky the device accuracy of 25µm.
Within the area covered by the galvo scanner, the beam comes straight down in the center. Even though a big collimating lens is utilized, toward the edges in the area the beam includes a slight angle. This means that dependant upon the height in the components nearby the cutting path, some shadowing might occur. As this is completely predictable, the distance some components should stay pulled from the cutting path can be calculated. Alternatively, the scan area can be reduced to side step this problem.
Stress. While there is no mechanical experience of the panel during cutting, sometimes all the FPC Cutting Machine can be executed after assembly and soldering (Figure 11). This implies the boards become completely separated in the panel within this last process step, and there is no necessity for any bending or pulling in the board. Therefore, no stress is exerted on the board, and components nearby the edge of the board usually are not subject to damage.
Inside our tests stress measurements were performed. During mechanical depaneling a tremendous snap was observed (FIGURES 12 and 13). This signifies that during earlier process steps, for example paste printing and component placement, the panel can maintain its full rigidity and no pallets will be required.