Laser depaneling can be performed with extremely high precision. It is then extremely beneficial in situations where areas of the board outline demand close tolerances. It also becomes appropriate when very small boards are involved. Since the cutting path is quite narrow and may be located very precisely, individual boards can be put closely together on the panel.
The low thermal effects imply that although a laser is involved, minimal temperature increases occur, and thus 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 alterations in boards could be handled quickly.
To check the impact of the 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 around 10µm to a high of 20µm, and a few may 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. In that case desired, a simple cleaning process may be added to remove any remaining particles. Such a process could contain the usage of just about any wiping having a smooth dry or wet tissue, using compressed air or brushes. You can also use any kind of 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 during these test boards (slot in the midst of the test 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 utilizes a galvanometer scanner (or galvo scanner) to trace the cutting path inside the material more than a small area, 50x50mm (2×2″). Using this kind of scanner permits the beam to be moved in a high speed along the cutting path, in the plethora of approx. 100 to 1000mm/sec. This ensures the beam is in the same location only a very short time, which minimizes local heating.
A pattern recognition system is employed, which can use fiducials or any other panel or board feature to precisely find the location where cut must be placed. High precision x and y movement systems can be used as large movements in conjunction with a galvo scanner for local movements.
In these sorts of machines, the cutting tool is the laser beam, and contains a diameter of approximately 20µm. This means the kerf cut from the laser is approximately 20µm wide, and also the laser system can locate that cut within 25µm regarding 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 a lot of small circuit boards, additional boards can therefore be placed, leading to cost savings.
Since the LED PCB Depanelizer can be freely and rapidly moved both in the x and y directions, eliminating irregularly shaped boards is simple. This contrasts with a few of the other described methods, which may be limited to straight line cuts. This becomes advantageous with flex boards, which can be very irregularly shaped and in some circumstances require extremely precise cuts, for instance when conductors are close together or when ZIF connectors have to be eliminate . These connectors require precise cuts for both ends of the connector fingers, while the fingers are perfectly centered involving the two cuts.
A possible problem to think about will be the precision of the board images on the panel. The authors have not yet found a niche standard indicating an expectation for board image precision. The closest they lsgmjm come is “as necessary for drawing.” This issue could be overcome by adding greater than three panel fiducials and dividing the cutting operation into smaller sections using their own area fiducials. Shows in a sample board eliminate in Figure 2 the cutline may be placed precisely and closely across the board, in cases like this, near the outside the copper edge ring.
Even if ignoring this potential problem, the minimum space between boards on the panel can 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 center. Although a big collimating lens is utilized, toward the edges in the area the beam features a slight angle. Which 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 have to stay removed from the cutting path may be calculated. Alternatively, the scan area could be reduced to side step this issue.
Stress. Because there is no mechanical exposure to the panel during cutting, in some circumstances all of the depaneling can be carried out after assembly and soldering. This means the boards become completely separated from your panel in 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 fringe of the board usually are not susceptible to damage.
Inside our tests stress measurements were performed. During mechanical depaneling a significant snap was observed. This also means that during earlier process steps, like paste printing and component placement, the panel can maintain its full rigidity and no pallets are needed.
A common production method is to pre-route the panel before assembly (mechanical routing, employing a ~2 to 3mm routing tool). Rigidity will be dependant on the dimensions and volume of the breakout tabs. The ultimate PCB Depanel step will generate much 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 quite neat and smooth, regardless of the layers inside the FR-4 boards or polyimide flex circuits. If the requirement for a clean cut will not be extremely high, like tab cutting of a pre-routed board, the cutting speed may 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 will permit moisture ingress over time . Polyimide, as found in flex circuits, cuts well and permits for extremely clean cuts, as observed in Figure 3 and then in the electron microscope picture.
As noted, it is actually required to maintain the material to get cut through the laser as flat as possible for maximum cutting. In particular instances, as in 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 may be more challenging, especially for boards with components on both sides. In those instances it still might be desirable to make a fixture that can accommodate odd shapes and components.