Laser depaneling can be performed with high precision. This will make it extremely useful in situations where elements of the board outline demand close tolerances. In addition, it becomes appropriate when tiny boards are involved. Since the cutting path is extremely narrow and may be located very precisely, individual boards can be put closely together on the panel.
The low thermal effects mean that despite the fact that a laser is involved, minimal temperature increases occur, and for that reason 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 position of the Inline PCB Router is software-controlled, which means modifications in boards could be handled quickly.
To test the impact for any remaining expelled material, a slot was cut in a four-up pattern on FR-4 material with a thickness of 800µm (31.5 mils). Only few particles remained and was comprised of powdery epoxy and glass particles. Their size ranged from typically 10µm to your high of 20µm, plus some could 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. In that case desired, a basic cleaning process could be put into remove any remaining particles. This kind of process could contain using any type of wiping with a smooth dry or wet tissue, using compressed air or brushes. One could 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 costly one.
Surface resistance. After cutting a path during these test boards (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 the SIR values exceeded 10E11 Ohm, indicating no conductive material is
Cutting path location. The laser beam typically utilizes a galvanometer scanner (or galvo scanner) to trace the cutting path inside the material over a small area, 50x50mm (2×2″). Using this kind of scanner permits the beam to become moved with a high speed over 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 time, which minimizes local heating.
A pattern recognition system is employed, which may use fiducials or some other panel or board feature to precisely find the location in which the cut needs to be placed. High precision x and y movement systems can be used for large movements together with a galvo scanner for local movements.
In these sorts of machines, the cutting tool is definitely the laser beam, and it has a diameter of approximately 20µm. This implies the kerf cut from the laser is about 20µm wide, and also the laser system can locate that cut within 25µm with regards to either panel or board fiducials or other board feature. The boards can therefore be put very close together in a panel. For a panel with a lot of small circuit boards, additional boards can therefore be placed, leading to cost savings.
Since the PCB Depaneling Router may be freely and rapidly moved in both the x and y directions, eliminating irregularly shaped boards is simple. This contrasts with a number of the other described methods, which may be limited to straight line cuts. This becomes advantageous with flex boards, which are generally very irregularly shaped and in some instances require extremely precise cuts, for example when conductors are close together or when ZIF connectors must be eliminate . These connectors require precise cuts on ends from the connector fingers, while the fingers are perfectly centered between the two cuts.
A possible problem to take into consideration is the precision of the board images on the panel. The authors have not even found a niche standard indicating an expectation for board image precision. The nearest they lsgmjm come is “as essental to drawing.” This challenge can be overcome with the addition of greater than three panel fiducials and dividing the cutting operation into smaller sections with their own area fiducials. Shows in 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 away from the copper edge ring.
Even if ignoring this potential problem, the minimum space between boards on the panel could be as little 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 covered 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 edges of the area the beam has a slight angle. Which means that depending on the height in the components nearby the cutting path, some shadowing might occur. As this is completely predictable, the space some components have to stay taken off the cutting path can be calculated. Alternatively, the scan area can be reduced to side step this challenge.
Stress. As there is no mechanical connection with the panel during cutting, occasionally all of the depaneling can be executed after assembly and soldering. This means the boards become completely separated through the panel in this last process step, and there is not any need for any bending or pulling on the board. Therefore, no stress is exerted on the board, and components nearby the side of the board are not subject to damage.
In our tests stress measurements were performed. During mechanical depaneling an important snap was observed. This too means that during earlier process steps, such as paste printing and component placement, the panel can maintain its full rigidity without any pallets are required.
A typical production technique is to pre-route the panel before assembly (mechanical routing, employing a ~2 to 3mm routing tool). Rigidity will be determined by the size and quantity of the breakout tabs. The last PCB Separator step will generate even less debris, and through 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 polyimide flex circuits. If the requirement for a clean cut is not really extremely high, like tab cutting of the pre-routed board, the cutting speed could be increased, causing 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 as time passes . Polyimide, as utilized in flex circuits, cuts well and permits for extremely clean cuts, as seen in Figure 3 and in the electron microscope picture.
As noted, it is required to maintain the material to be cut through the laser as flat as possible for optimum cutting. In some instances, as with cutting flex circuits, it can be as basic as placing the flex over a downdraft honeycomb or an open cell foam plastic sheet. For circuit boards it might be more challenging, especially for boards with components on sides. In those instances it still may be desirable to prepare a fixture that may accommodate odd shapes and components.