Laser depaneling can be carried out with very high precision. This makes it extremely useful in situations where parts of the board outline demand close tolerances. It also becomes appropriate when tiny boards are participating. Since the cutting path is extremely narrow and can be located very precisely, PCB Depanelizer can be placed closely together on the panel.
The reduced thermal effects imply that despite the fact that a laser is involved, minimal temperature increases occur, and therefore essentially no carbonization results. Depaneling occurs without physical contact with the panel and without bending or pressing; therefore there exists less possibility of component failures or future reliability issues. Finally, the position of the cutting path is software-controlled, meaning alterations in boards may be handled quickly.
To test the impact of the remaining expelled material, a slot was cut in a four-up pattern on FR-4 material using a thickness of 800µm (31.5 mils). Only few particles remained and consisted of powdery epoxy and glass particles. Their size ranged from typically 10µm to a high of 20µm, and some may have was comprised of burned or carbonized material. Their size and number were extremely small, without any conduction was expected between traces and components on the board. If so desired, an easy cleaning process could be put into remove any remaining particles. This kind of process could consist of using any kind of wiping having a smooth dry or wet tissue, using compressed air or brushes. One could also use just about any cleaning liquids or cleaning baths without or with ultrasound, but normally would avoid any kind of additional cleaning process, especially an expensive one.
Surface resistance. After cutting a path in these test boards (slot in the center of the exam pattern), the boards were exposed to a climate test (40?C, RH=93%, no condensation) for 170 hr., as well as the SIR values exceeded 10E11 Ohm, indicating no conductive material is
Cutting path location. The laser beam typically uses a galvanometer scanner (or galvo scanner) to trace the cutting path in the material more than a small area, 50x50mm (2×2″). Using such a scanner permits the beam to become moved in a extremely high speed across the cutting path, in all the different approx. 100 to 1000mm/sec. This ensures the beam is incorporated in the same location only a very limited time, which minimizes local heating.
A pattern recognition method is employed, which could use fiducials or any other panel or board feature to precisely discover the location in which the cut has to be placed. High precision x and y movement systems can be used as large movements in combination with Motorized PCB Depanelizer for local movements.
In these kinds of machines, the cutting tool will be the laser beam, and features a diameter of approximately 20µm. This implies the kerf cut by the laser is all about 20µm wide, as well as the laser system can locate that cut within 25µm with regards to either panel or board fiducials or any other board feature. The boards can therefore be placed very close together in a panel. To get a panel with many small circuit boards, additional boards can therefore be placed, leading to financial savings.
Because the laser beam could be freely and rapidly moved in both the x and y directions, cutting out irregularly shaped boards is straightforward. This contrasts with a few of the other described methods, which can 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 need to be eliminate . These connectors require precise cuts on both ends from the connector fingers, while the fingers are perfectly centered in between the two cuts.
A potential problem to consider will be the precision of the board images on the panel. The authors have not found a business standard indicating an expectation for board image precision. The nearest they have got come is “as necessary for drawing.” This challenge may be overcome with the addition of greater than three panel fiducials and dividing the cutting operation into smaller sections using their own area fiducials. Shows in a sample board cut out in Figure 2 the cutline can be put precisely and closely lmuteg the board, in this instance, next to the outside of the copper edge ring.
Even 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 in the panel in addition to the system accuracy of 25µm.
Within the area protected by the galvo scanner, the beam comes straight down in the center. Despite the fact that a big collimating lens can be used, toward the sides from the area the beam includes a slight angle. This means that depending on the height of the components near the cutting path, some shadowing might occur. Since this is completely predictable, the space some components must stay taken from the cutting path may be calculated. Alternatively, the scan area could be reduced to side step this challenge.
Stress. Because there is no mechanical exposure to the panel during cutting, in some instances all of the depaneling can be performed after assembly and soldering. This means the boards become completely separated from the panel in this particular last process step, and there is absolutely no necessity for any bending or pulling on the board. Therefore, no stress is exerted on the board, and components nearby the edge of the board are certainly not subject to damage.
In our tests stress measurements were performed. During mechanical depaneling a significant snap was observed. This implies that during earlier process steps, such as paste printing and component placement, the panel can maintain its full rigidity with no pallets are needed.
A common production technique is to pre-route the panel before assembly (mechanical routing, employing a ~2 to 3mm routing tool). Rigidity is then determined by the size and style and volume of the breakout tabs. The final depaneling step will generate even less debris, and making use of this method laser cutting time is reduced.
After many tests it is clear the sidewall in the cut path can be quite neat and smooth, regardless of the layers within the FR-4 boards or Laser Depaneling. If the necessity for a clean cut will not be very high, as in tab cutting of the pre-routed board, the cutting speed can be increased, leading to some discoloration .
When cutting through epoxy and glass fibers, you will find no protruding fibers or rough edges, nor exist gaps or delamination that will permit moisture ingress with time . Polyimide, as utilized in flex circuits, cuts well and permits for extremely clean cuts, as noticed in Figure 3 and in the electron microscope picture.
As noted, it really is essential to keep the material to get cut through the laser as flat as you can for maximum cutting. In particular instances, as with cutting flex circuits, it can be as easy as placing the flex on the downdraft honeycomb or an open cell foam plastic sheet. For circuit boards it might be more difficult, especially for boards with components on both sides. In those instances still it could be desirable to prepare a fixture that may accommodate odd shapes and components.