Punching/die cutting. This process needs a different die for every new circuit board, which happens to be not much of 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 delivered to maintain sharp die edges.
V-scoring. Often the panel is scored on sides to a depth of approximately 30% of your board thickness. After assembly the boards may be manually broken out of the panel. This puts bending strain on the boards that can be damaging to some of the components, in particular those near the board edge.
Wheel cutting/pizza cutter. An alternate method to manually breaking the world wide web after V-scoring is to try using a “pizza cutter” to cut the other web. This calls for careful alignment involving the V-score and also the cutter wheels. It also induces stresses inside the board which may affect some components.
Sawing. Typically machines that are employed to saw boards away from a panel use a single rotating saw blade that cuts the panel from either the very best or maybe the bottom.
All these methods is limited to straight line operations, thus simply for rectangular boards, and each one for some degree crushes and cuts the board edge. Other methods tend to be more expansive and will include the next:
Water jet. Some say this technology can be carried out; 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 may need careful cleaning following the fact to get rid of the abrasive part of the slurry.
Routing ( nibbling). Most of the time boards are partially routed ahead of assembly. The remaining attaching points are drilled with a small drill size, making it simpler to get rid of the boards out from the panel after assembly, leaving the so-called mouse bites. A disadvantage can be a significant loss in panel area to the routing space, as the kerf width often takes as much as 1.5 to 3mm (1/16 to 1/8″) plus some additional space for inaccuracies. This implies a lot of panel space will likely be necessary for the routed traces.
Laser routing. Laser routing provides a space advantage, since the kerf width is just a few micrometers. As an example, the tiny boards in FIGURE 2 were initially presented in anticipation how the panel could be routed. This way the panel yielded 124 boards. After designing the layout for laser depaneling, the amount of boards per panel increased to 368. So for every 368 boards needed, just one single panel must be produced instead of three.
Routing could also reduce panel stiffness to the stage which a pallet may be required for support throughout the earlier steps within the assembly process. But unlike the prior methods, routing is not really confined to cutting straight line paths only.
Many of these methods exert some extent of mechanical stress about the board edges, which can lead to delamination or cause space to build up across the glass fibers. This may lead to moisture ingress, which is able to reduce the long-term longevity of the circuitry.
Additionally, when finishing placement of components on the board and after soldering, the ultimate connections between your boards and panel must 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 can be damaging to components placed near areas that ought to be broken as a way to remove the board from the panel. It is actually therefore imperative to accept the production methods into consideration during board layout and also for panelization so that certain parts and traces are certainly not positioned in areas regarded as subject to stress when depaneling.
Room can also be necessary to permit the precision (or lack thereof) with which the tool path may be placed and to take into account any non-precision inside the board pattern.
Laser cutting. One of the most recently added tool to PCB Routing Machine and rigid boards is actually a laser. Inside the SMT industry various kinds of lasers are employed. CO2 lasers (~10µm wavelength) can offer 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 might be called “hot” lasers because they burn or melt the fabric being cut. (As being an aside, these are the laser types, particularly the Nd:Yag lasers, typically accustomed to produce steel stencils for solder paste printing.)
UV lasers (typical wavelength ~355nm), on the other hand, are used to ablate the information. A localized short pulse of high energy enters the very best 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 will depend on the compromise between performance and expense. For ablation to happen, the laser light should be absorbed from the materials to get cut. Within the circuit board industry they are mainly FR-4, glass fibers and copper. When looking at the absorption rates for these materials (FIGURE 4), the shorter wavelength lasers are the most appropriate 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, as it is focused from a relatively wide beam to an extremely narrow beam after which continuous inside a reverse taper to widen again. This small area in which the beam reaches its most narrow is referred to as the throat. The ideal ablation occurs when the energy density placed on the material is maximized, which takes place when the throat of the beam is merely inside the material being cut. By repeatedly groing through exactly the same cutting track, thin layers of your material is going to be removed before the beam has cut right through.
In thicker material it can be required to adjust the focus from the beam, as being the ablation occurs deeper into the kerf being cut to 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 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 around 1.6mm (63 mils) in thickness.
Temperature. The temperature boost 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 to the same location) is determined by the road length, beam speed and whether a pause is added between passes.
An experienced and experienced system operator can pick the optimum mix of settings to ensure a clean cut without any burn marks. There is no straightforward formula to determine machine settings; they are influenced by material type, thickness and condition. Dependant upon the board along with its application, the operator can pick 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 in the cutting path is less than 100°C, way below such a PCB experiences during soldering (FIGURE 6).
Expelled material. Inside the laser useful for these tests, an airflow goes across the panel being cut and removes most of the expelled dust into an exhaust and filtering method (FIGURE 7).
To test the impact associated with a 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 about 10µm into a high of 20µm, and a few may have was made up 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 you have desired, a basic cleaning process could be included with remove any remaining particles. This sort of process could consist of the usage of any type 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 any type of additional cleaning process, especially a pricey one.
Surface resistance. After cutting a path over these test boards (Figure 7, slot in the midst of the test pattern), the boards were exposed 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 uses a galvanometer scanner (or galvo scanner) to trace the cutting path within the material more than a small area, 50x50mm (2×2″). Using such a scanner permits the beam to be moved in a quite high speed across the cutting path, in the range of approx. 100 to 1000mm/sec. This ensures the beam is in the same location only a very small amount of time, which minimizes local heating.
A pattern recognition technique is employed, which could use fiducials or other panel or board feature to precisely get the location where cut has to be placed. High precision x and y movement systems are used for large movements in combination with a galvo scanner for local movements.
In most of these machines, the cutting tool will be the laser beam, and contains a diameter of around 20µm. This means the kerf cut from the laser is approximately 20µm wide, along with the laser system can locate that cut within 25µm regarding either panel or board fiducials or some other board feature. The boards can therefore be put very close together within a panel. For the panel with many small circuit boards, additional boards can therefore be put, leading to cost benefits.
Since the laser beam could be freely and rapidly moved within both the x and y directions, removing irregularly shaped boards is easy. This contrasts with a few of the other described methods, which may be limited by straight line cuts. This becomes advantageous with flex boards, which are often very irregularly shaped and in some instances require extremely precise cuts, for instance when conductors are close together or when ZIF connectors need to be cut out (FIGURE 10). These connectors require precise cuts for both ends of the connector fingers, even though the fingers are perfectly centered between your two cuts.
A potential problem to consider is definitely the precision of your board images about the panel. The authors have not really found an industry standard indicating an expectation for board image precision. The closest they have got come is “as required by drawing.” This challenge could be overcome by adding more than three panel fiducials and dividing the cutting operation into smaller sections because of their own area fiducials. FIGURE 11 shows within a sample board reduce in Figure 2 the cutline can be placed precisely and closely around the board, in cases like this, next to the outside of the copper edge ring.
Regardless if ignoring this potential problem, the minimum space between boards around the panel can be as low as the cutting kerf plus 10 to 30µm, according to the thickness of the panel 13dexopky the program accuracy of 25µm.
Throughout the area covered by the galvo scanner, the beam comes straight down in between. Despite the fact that a huge collimating lens can be used, toward the edges of the area the beam has a slight angle. Consequently based on the height in the components near the cutting path, some shadowing might occur. Because this is completely predictable, the space some components should 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 experience of the panel during cutting, in some circumstances every one of the FPC Laser Depaneling can be carried out after assembly and soldering (Figure 11). This simply means the boards become completely separated from the panel in this particular last process step, and there is not any requirement for any bending or pulling around the board. Therefore, no stress is exerted in the board, and components nearby the edge of the board will not be subjected to damage.
In your tests stress measurements were performed. During mechanical depaneling a significant snap was observed (FIGURES 12 and 13). This means 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.