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V-Groove Panelization Method with V-cut PCB Separator Machine
Generally speaking, this calls for cutting 1/3 the thickness of the board from the top and 1/3 the thickness from the bottom, collinear with the top cut, with a 30- to 45-degree circular cutting blade. A machine is needed to depanel it, as the remaining 1/3 of the board thickness left intact is surprisingly strong, and breaking it off by hand would put severe stress on the PCB.
2. V-grooves tend to cause a wide variety of problems in board design and PCB manufacturability.
Many prefer the V-groove method (Fig. 2) where possible (in which no components hang over the edge), because it’s more efficient and produces less surface stress when using a properly designed machine known as a “pizza cutter.” Also, the pizza-cutter-type depaneling machines for V-grooves are inexpensive, last forever, and require very little adjustment and maintenance. Furthermore, they’re portable—you can mount the depaneling machines on a small cart and easily move them around the shop wherever they’re needed.
However, this is the most restrictive method of panelization. For example, you can’t use a V-groove breakout method where components are hanging over the edge. Even if they’re too close to the edge of the board, you can’t use this method unless you’re cutting a straight line all the way through the PCB array.
To clear the circular cutting blade, you must maintain 0.05-in. clearance from components to the center of the V-groove score, taking into consideration component size and mounting variations. Tall components, such as radial capacitors, radial inductors, and power-dissipating radial ceramic resistors, would have to be spaced greater than 0.05 in. (nominal) because of position variation, whereas connectors and other low-profile parts may be placed at 0.05-in. clearance.
Surface-mount multilayer ceramic chip capacitors (MLCCs) must be oriented with the long side parallel to the V-groove cut if less than 0.25 in. (6.35 mm) away from the score line and kept 0.119 in. (3 mm) away regardless. This becomes more important with the larger-size caps and with certain cap dielectrics. The surface stress, caused by forcing the depaneling blade into the V-groove, transfers through the board surface to the rigid solder joints, and then to the component bodies. This can fracture them if they're too close to the V-groove. Orienting the long edge of the capacitor body parallel to the edge minimizes the risk of body fracture (Fig. 2, again).
V-grooves can also weaken a PCB array, which is very undesirable when the array must go through a wave-solder machine. The surface tension of the solder wave, pulling down on the preheated PCB material, is exacerbated by V-grooves in the array. When the board is pulled down, the protruding leads tend to run into, and sometimes get hung up, on the wave-solder baffle.
3. In the case of a rectangular PCB, strengthen the array by â€œjump scoringâ€ on the shorter, or leading and trailing, edges.
In the case of a rectangular PCB, you would strengthen the array by “jump scoring” on the shorter, or leading and trailing, edges (Fig. 3). Since the V-groove blade is circular, you must cut beyond the edge of the board to achieve a full-depth V-groove at the edge of the board. Running the cut 1/4 in. past the edge of the PCB, halfway through a 1/2-in. breakaway edge, will leave enough of the leading and trailing edges to strengthen the array and minimize the pulling down effect of the wave, while achieving the desired full depth V-groove cut on the board.
When jump scoring is used, the depaneling operators must be instructed to remove the leading and trailing edges before trying to separate the boards. You may get some push back from the PCB fabricator, but it gives you a stronger array. Give the fabricator a break by not dimensioning the end of the jump score. It’s hard to control, and you don’t know the V-groove cutting-blade diameter. So you don’t know exactly where the cut will end.
Note: The V-groove method is undesirable if a “clean,” smooth board edge is required, but this is rarely the case.
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