Laser depaneling can be executed with extremely high precision. It is then extremely valuable in situations where areas of the board outline demand close tolerances. It also becomes appropriate when really small boards are involved. As the cutting path is very narrow and will be located very precisely, individual boards can be placed closely together on the panel.
The reduced thermal effects suggest 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 is certainly less possibility of component failures or future reliability issues. Finally, the positioning of the Inline PCB Router is software-controlled, which suggests changes in boards can be handled quickly.
To check the impact for 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 was comprised of powdery epoxy and glass particles. Their size ranged from around 10µm to your high of 20µm, and some might have was comprised of burned or carbonized material. Their size and number were extremely small, with no conduction was expected between traces and components on the board. If you have desired, an easy cleaning process might be added to remove any remaining particles. This kind of process could consist of using just about any wiping with a smooth dry or wet tissue, using compressed air or brushes. One could also employ just about any cleaning liquids or cleaning baths without or with 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 (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., as well as the SIR values exceeded 10E11 Ohm, indicating no conductive material is
Cutting path location. The laser beam typically works with a galvanometer scanner (or galvo scanner) to trace the cutting path inside the material over a small area, 50x50mm (2×2″). Using such a scanner permits the beam to be moved with a very high speed along the cutting path, in the range of 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 in which the cut must be placed. High precision x and y movement systems are used for large movements together with a galvo scanner for local movements.
In these sorts of machines, the cutting tool will be the laser beam, and features a diameter of around 20µm. What this means is the kerf cut through the laser is approximately 20µm wide, and also 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. For any panel with many small circuit boards, additional boards can therefore be placed, ultimately causing financial savings.
As the Desktop PCB Router can be freely and rapidly moved within both the x and y directions, cutting out irregularly shaped boards is easy. This contrasts with a few of the other described methods, which is often limited to straight line cuts. This becomes advantageous with flex boards, which are often very irregularly shaped and occasionally require extremely precise cuts, for instance when conductors are close together or when ZIF connectors must be eliminate . These connectors require precise cuts for both ends from the connector fingers, as the fingers are perfectly centered between the two cuts.
A potential problem to consider will be the precision in the board images on the panel. The authors have not yet found a business standard indicating an expectation for board image precision. The nearest they lsgmjm come is “as required by drawing.” This issue may be overcome with the addition of greater than three panel fiducials and dividing the cutting operation into smaller sections making use of their own area fiducials. Shows in a sample board reduce in Figure 2 that the cutline may be placed precisely and closely round the board, in this case, near 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 in the panel as well as the system accuracy of 25µm.
In the area protected by the galvo scanner, the beam comes straight down in the middle. Despite the fact that a sizable collimating lens is used, toward the sides of the area the beam has a slight angle. Which means that depending on the height of the components close to the cutting path, some shadowing might occur. As this is completely predictable, the distance some components need to stay removed from the cutting path may be calculated. Alternatively, the scan area can be reduced to side step this challenge.
Stress. While there is no mechanical contact with the panel during cutting, in some circumstances all of the depaneling can be performed after assembly and soldering. This means the boards become completely separated from your panel within this last process step, and there is no requirement for any bending or pulling on the board. Therefore, no stress is exerted on the board, and components near the side of the board usually are not susceptible to damage.
Inside our tests stress measurements were performed. During mechanical depaneling an important snap was observed. This too means that during earlier process steps, like paste printing and component placement, the panel can maintain its full rigidity with no pallets are required.
A standard production strategy 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 quantity of the breakout tabs. The final PCB Separator step will generate even less debris, and through this method laser cutting time is reduced.
After many tests it is now clear the sidewall from the cut path can be very neat and smooth, no matter the layers within the FR-4 boards or polyimide flex circuits. If the requirement for a clean cut is not really high, as in tab cutting of the pre-routed board, the cutting speed could be increased, leading to 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 noticed in Figure 3 as well as in the electron microscope picture.
As noted, it is actually essential to keep the material to get cut through the laser as flat as possible for maximum cutting. In particular instances, as in cutting flex circuits, it could be as basic as placing the flex on the downdraft honeycomb or an open cell foam plastic sheet. For circuit boards it could be more difficult, specifically for boards with components on both sides. In those instances it still could be desirable to prepare a fixture that can accommodate odd shapes and components.