Laser depaneling can be performed with very high precision. This will make it extremely beneficial in situations where elements of the board outline demand close tolerances. In addition, it becomes appropriate when really small boards are involved. Because the cutting path is extremely narrow and can be located very precisely, PCB Depanelizer can be placed closely together on the panel.
The low thermal effects imply that even though a laser is involved, minimal temperature increases occur, and for that reason essentially no carbonization results. Depaneling occurs without physical exposure to the panel and without bending or pressing; therefore there is less probability of component failures or future reliability issues. Finally, the position of the cutting path is software-controlled, which means modifications in boards can be handled quickly.
To test the impact of any remaining expelled material, a slot was cut in a four-up pattern on FR-4 material having 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 some high of 20µm, and a few could have consisted of burned or carbonized material. Their size and number were extremely small, and no conduction was expected between traces and components on the board. If you have desired, a basic cleaning process might be included in remove any remaining particles. This kind of process could consist of using just about any wiping using a smooth dry or wet tissue, using compressed air or brushes. One could also have any kind of cleaning liquids or cleaning baths with or without ultrasound, but normally would avoid any type of additional cleaning process, especially a high priced one.
Surface resistance. After cutting a path during these test boards (slot in the center of the exam pattern), the boards were put through 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 within the material over a small area, 50x50mm (2×2″). Using such a scanner permits the beam to get moved with a extremely high speed over the cutting path, in all the different approx. 100 to 1000mm/sec. This ensures the beam is incorporated in the same location merely a very limited time, which minimizes local heating.
A pattern recognition method is employed, which could use fiducials or other panel or board feature to precisely find the location where cut needs to be placed. High precision x and y movement systems are used for large movements in conjunction with Pneumatic PCB Depanelizer for local movements.
In these sorts of machines, the cutting tool will be the laser beam, and contains a diameter of approximately 20µm. What this means is the kerf cut from the laser is all about 20µm wide, and also the laser system can locate that cut within 25µm regarding either panel or board fiducials or other board feature. The boards can therefore be put very close together in a panel. To get a panel with lots of small circuit boards, additional boards can therefore be put, leading to cost savings.
Because the laser beam could be freely and rapidly moved within both the x and y directions, eliminating irregularly shaped boards is straightforward. This contrasts with a number of the other described methods, which can be confined to straight line cuts. This becomes advantageous with flex boards, which are generally very irregularly shaped and occasionally require extremely precise cuts, for example 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 between the two cuts.
A prospective problem to think about is definitely the precision of the board images on the panel. The authors have not even found an industry standard indicating an expectation for board image precision. The closest they have got come is “as essental to drawing.” This problem can be overcome by adding more than three panel fiducials and dividing the cutting operation into smaller sections using their own area fiducials. Shows in a sample board reduce in Figure 2 that this cutline can be placed precisely and closely lmuteg the board, in this case, next to the outside of the copper edge ring.
Even when ignoring this potential problem, the minimum space between boards on the panel may be as little as the cutting kerf plus 10 to 30µm, depending on the thickness of the panel plus the system accuracy of 25µm.
Inside the area protected by the galvo scanner, the beam comes straight down in the middle. Although a sizable collimating lens is utilized, toward the sides of 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. Because this is completely predictable, the space some components must stay taken off the cutting path may be calculated. Alternatively, the scan area can be reduced to side step this issue.
Stress. Because there is no mechanical exposure to the panel during cutting, in some circumstances all the depaneling can be carried out after assembly and soldering. What this means is the boards become completely separated through the panel in this last process step, and there is absolutely no need for any bending or pulling on the board. Therefore, no stress is exerted on the board, and components near the side of the board are certainly not subjected to damage.
Inside our tests stress measurements were performed. During mechanical depaneling an important snap was observed. This means that during earlier process steps, like paste printing and component placement, the panel can maintain its full rigidity and no pallets are required.
A standard production method is to pre-route the panel before assembly (mechanical routing, using a ~2 to 3mm routing tool). Rigidity is then dependant on the size and volume of the breakout tabs. The ultimate depaneling step will generate even less debris, and making use of this method laser cutting time is reduced.
After many tests it has become remove the sidewall in the cut path can be extremely neat and smooth, regardless of the layers within the FR-4 boards or Laser Depaneling. If the need for a clean cut is not really high, as in tab cutting of a pre-routed board, the cutting speed could be increased, resulting in some discoloration .
When cutting through epoxy and glass fibers, there are no protruding fibers or rough edges, nor are there gaps or delamination that would permit moisture ingress over time . Polyimide, as found in flex circuits, cuts well and permits for extremely clean cuts, as seen in Figure 3 as well as in the electron microscope picture.
As noted, it really is necessary to keep your material to get cut through the laser as flat as is possible for maximum cutting. In particular instances, like cutting flex circuits, it can be as basic as placing the flex on the downdraft honeycomb or an open cell foam plastic sheet. For circuit boards it might be more challenging, particularly for boards with components on both sides. In those instances still it may be desirable to get ready a fixture that may accommodate odd shapes and components.
