Punching/die cutting. This procedure takes a different die for each and every new circuit board, which happens to be not really a practical solution for small production runs. The action could be PCB Depaneling, but either can leave the board edges somewhat deformed. To minimize damage care must be taken to maintain sharp die edges.
V-scoring. Usually the panel is scored on sides to your depth around 30% from the board thickness. After assembly the boards can be manually broken out from the panel. This puts bending stress on the boards that can be damaging to several of the components, especially those near the board edge.
Wheel cutting/pizza cutter. A different method to manually breaking the net after V-scoring is to apply a “pizza cutter” to cut the other web. This requires careful alignment between the V-score along with the cutter wheels. Additionally, it induces stresses in the board which could affect some components.
Sawing. Typically machines that are widely used to saw boards out of a panel use a single rotating saw blade that cuts the panel from either the very best or the bottom.
Each one of these methods is restricted to straight line operations, thus simply for rectangular boards, and all of them to many degree crushes or cuts the board edge. Other methods are definitely more expansive and include the following:
Water jet. Some say this technology can be done; however, the authors have found no actual users of it. Cutting is performed by using a high-speed stream of slurry, that is water having an abrasive. We expect it should take careful cleaning once the fact to eliminate the abrasive portion of the slurry.
Routing ( nibbling). More often than not boards are partially routed just before assembly. The remaining attaching points are drilled using a small drill size, making it simpler to break the boards from the panel after assembly, leaving the so-called mouse bites. A disadvantage might be a significant loss of panel area on the routing space, as being the kerf width normally takes up to 1.5 to 3mm (1/16 to 1/8″) plus some additional space for inaccuracies. This implies lots of panel space will be essential for the routed traces.
Laser routing. Laser routing supplies a space advantage, because the kerf width is only a few micrometers. By way of example, the little boards in FIGURE 2 were initially laid out in anticipation that the panel will be routed. In this fashion the panel yielded 124 boards. After designing the layout for laser depaneling, the volume of boards per panel increased to 368. So for each and every 368 boards needed, merely one panel has to be produced as an alternative to three.
Routing could also reduce panel stiffness to the level that the pallet may be needed for support through the earlier steps from the assembly process. But unlike the previous methods, routing is just not confined to cutting straight line paths only.
Most of these methods exert some degree of mechanical stress about the board edges, which can cause 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 on the board and after soldering, the ultimate 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 on the boards. Again, such bending stress could be damaging to components placed in close proximity to areas that must be broken so that you can eliminate the board through the panel. It is therefore imperative to take the production methods into mind during board layout and also for panelization to ensure certain parts and traces are not positioned in areas regarded as susceptible to stress when depaneling.
Room is likewise necessary to permit the precision (or lack thereof) which the tool path can be put and to look at any non-precision inside the board pattern.
Laser cutting. The most recently added tool to PCB Routing Machine and rigid boards is a laser. In the SMT industry various kinds of lasers are now 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. Both these laser types produce infrared light and can be called “hot” lasers as they burn or melt the material being cut. (As being an aside, these represent the laser types, specially the Nd:Yag lasers, typically utilized to produce stainless steel stencils for solder paste printing.)
UV lasers (typical wavelength ~355nm), on the flip side, are used to ablate the information. A localized short pulse of high energy enters the most notable 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 is dependant on the compromise between performance and expense. To ensure that ablation to occur, the laser light should be absorbed through the materials being cut. Within the circuit board industry these are typically mainly FR-4, glass fibers and copper. When looking at the absorption rates for these particular materials (FIGURE 4), the shorter wavelength lasers are the most suitable ones for your ablation process. However, the laser cost increases very rapidly for models with wavelengths shorter than 355nm.
The laser beam features a tapered shape, because it is focused from a relatively wide beam with an extremely narrow beam and then continuous inside a reverse taper to widen again. This small area the location where the beam is in its most narrow is known as the throat. The perfect ablation occurs when the energy density put on the content is maximized, which takes place when the throat from the beam is simply inside of the material being cut. By repeatedly exceeding the same cutting track, thin layers in the material is going to be removed up until the beam has cut all the way through.
In thicker material it can be necessary to adjust the main objective of your beam, because the ablation occurs deeper into the kerf being cut to the material. The ablation process causes some heating of your material but may be optimized to leave no burned or carbonized residue. Because cutting is completed gradually, heating is minimized.
The earliest versions of UV laser systems had enough capability to depanel flex circuit panels. Present machines have 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 is determined by the beam power, beam speed, focus, laser pulse rate and repetition rate. The repetition rate (how quickly the beam returns towards the same location) is dependent upon the road length, beam speed and whether a pause is added between passes.
An informed and experienced system operator are able to choose the optimum blend of settings to ensure a clean cut free of burn marks. There is no straightforward formula to find out machine settings; they may be influenced by material type, thickness and condition. Based on the board and its application, the operator can decide fast depaneling by permitting some discoloring or perhaps some carbonization, versus a somewhat slower but completely “clean” cut.
Careful testing indicates that under most conditions the temperature rise within 1.5mm through the cutting path is lower than 100°C, way below such a PCB experiences during soldering (FIGURE 6).
Expelled material. Inside the laser utilized 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 check the impact of any remaining expelled material, a slot was cut within a four-up pattern on FR-4 material having 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 an average of 10µm into a high of 20µm, and several could possibly have was made up of burned or carbonized material. Their size and number were extremely small, with no conduction was expected between traces and components in the board. If you have desired, an easy cleaning process may be added to remove any remaining particles. This kind of process could contain 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 pricey one.
Surface resistance. After cutting a path in 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 also the SIR values exceeded 10E11 Ohm, indicating no conductive material is present.
Cutting path location. The laser beam typically works with a galvanometer scanner (or galvo scanner) to trace the cutting path from the material over a small area, 50x50mm (2×2″). Using this sort of scanner permits the beam being moved at the quite high speed down the cutting path, in the plethora of approx. 100 to 1000mm/sec. This ensures the beam is in the same location just a very short period of time, which minimizes local heating.
A pattern recognition method is employed, which can use fiducials or some other panel or board feature to precisely find the location where 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 most of these machines, the cutting tool may be the laser beam, and contains a diameter of around 20µm. This simply means the kerf cut by the laser is around 20µm wide, and the laser system can locate that cut within 25µm when it comes to either panel or board fiducials or another board feature. The boards can therefore be put very close together within a panel. For the panel with many different small circuit boards, additional boards can therefore be put, ultimately causing cost benefits.
Since the laser beam could be freely and rapidly moved in both the x and y directions, removing irregularly shaped boards is not difficult. This contrasts with a few of the other described methods, which can be limited by straight line cuts. This becomes advantageous with flex boards, which are generally very irregularly shaped and in some instances 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, while the fingers are perfectly centered involving the two cuts.
A potential problem to take into account will be the precision of your board images on the panel. The authors have not found a marketplace standard indicating an expectation for board image precision. The nearest they have come is “as essental to drawing.” This challenge might be overcome with the addition of a lot more than three panel fiducials and dividing the cutting operation into smaller sections using their own area fiducials. FIGURE 11 shows in the sample board eliminate in Figure 2 that the cutline may be placed precisely and closely across the board, in this case, near the outside the copper edge ring.
Even if ignoring this potential problem, the minimum space between boards around the panel is often as little as the cutting kerf plus 10 to 30µm, based on the thickness of the panel 13dexopky the program accuracy of 25µm.
In the area covered by the galvo scanner, the beam comes straight down in the center. Even though a large collimating lens can be used, toward the sides of the area the beam includes a slight angle. Consequently according to the height of the components nearby the cutting path, some shadowing might occur. As this is completely predictable, the distance some components should stay removed from the cutting path might be calculated. Alternatively, the scan area can be reduced to side step this concern.
Stress. Because there is no mechanical contact with the panel during cutting, occasionally every one of the FPC Laser Depaneling can be executed after assembly and soldering (Figure 11). This simply means the boards become completely separated through the panel in this 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 the edge of the board will not be subject to damage.
Inside our tests stress measurements were performed. During mechanical depaneling a substantial snap was observed (FIGURES 12 and 13). This too means that during earlier process steps, such as paste printing and component placement, the panel can maintain its full rigidity and no pallets are needed.