Small circuit boards are often assembled several at a time as part of one big panel. This strategy boosts throughput, but assemblers are still left with the tricky task of separating the now highly valuable boards without damaging them.
Several technologies are available for "depaneling" circuit boards. Depaneling machines can be manual, semiautomatic or fully automatic. They separate boards, singly or en masse, by bending, pinching, punching, routing, sawing or shearing. Which technology to use depends on production volume and variety, on the design of the board and its components, and on how the boards are connected.
One method isn’t necessarily better than another, argues John O’Hara, applications engineering manager for Circuit Technology Systems, a div. of Cox Automation Systems (West Chicago, IL). The key is to pick the method that puts the least amount of stress on that particular panel.
"With today’s small component sizes, solder joints and tracers are very small," he says. "Too much stress and vibration during singulation can break those joints, and strain-induced failures are the most difficult to find during testing. If a lead breaks, it can be in contact with the board during test, but separate in the field."
Circuit boards are linked in a panel by tabs or scored lines. Scoring is preferred for square or rectangular boards, while tabs are reserved for irregularly shaped boards.
The bending method is used to break off an edge strip from scored or tabbed panels. The strip is placed inside a slot. Then, through a lever action, the strip is rotated around a fulcrum blade, which gently separates it from the panel. The board can be rotated manually or pneumatically. Of the six singulation methods, bending puts the most stress on the board.
Pinching is a two-blade method for separating scored boards. A circular blade is paired with a second circular blade or a linear blade. To separate the boards, the panel is passed between the blades along the score line. This can be done manually or automatically.
"The blades don’t cut the board as much as they push it apart. This puts very little stress on the board," says Joe Komus, president of Cab Technology Inc. (Tyngsboro, MA).
The gap between the blades is adjustable to the thickness of the board. The larger the clearance between the blades, the lower the stress exerted on the boards during separation.
Blade design varies with the application. For example, a thin blade that is flat on one side is particularly suited to boards with components located close to the score line. Multiple blades can be placed along one axis to separate more than one strip of boards at a time.
Aligning the score line with the lower blade is critical, warns Komus. "If the blades are not 100 percent vertical, the upper blade may hit some components on the board, especially if they are near the edge," he says.
The punching process is for tabbed boards, says Steve Hoover, sales manager for Fancort Industries Inc. (West Caldwell, NJ). A tab is placed over a support die and beneath a fixed cutting blade. The blade can be flat, L-shaped or T-shaped. When the machine is actuated, the blade comes down past the die, cleanly removing the tab. To prevent the blade from getting stuck, it should be 0.15 millimeter thinner than the groove between the boards.
As with pinching equipment, punching machines can be built with multiblade arrangements to remove several tabs at once. This boosts throughput, but tooling costs and changeover time can be an issue.
Another option is to mount the punch above the board, says O’Hara. In this case, the blade is flat, and the board is placed in a custom support die mounted to a X-Y-Z table. Boards can be loaded manually or automatically. "The punch rarely needs to be changed from board to board, so it’s good for a high-mix environment," he says.
An alternative to punching is routing. In this process, a routing bit mounted on a Cartesian gantry turns each tab into dust. This method is ideal for thick substrates and high-mix production. A vacuum device extracts the dust, which could be harmful to operators and the board. "Blowing ionized air at the routing point will keep static charges down and help the vacuum do its job," adds Hoover.
Depaneling saws are miniature versions of the carpenter’s table saw. Equipped with diamond blades, these devices are particularly good for cutting difficult substrates, such as ceramics, and for singulating individual packages, such as ball grid arrays, chip-scale packages and memory modules. Panels can be cut from the top or the bottom. Like routers, depaneling saws include a vacuum device to extract dust.
Shearing singulates both tabbed and scored boards. It can be done manually with scissors, but it’s usually done automatically with a press. Though effective, this method can stress boards more than other methods, and the length of the cut is limited by the length of the blade.
Regardless of method, the blades for most depaneling operations are made from carbon steel. Blade life varies with the application and production volume. A punching blade typically lasts 200,000 operations before it needs sharpening, and it can be sharpened eight to 10 Arial. A handy feature is a counter that tracks the number of punches and notifies the operator when sharpening is required, says O’Hara.
Depaneling is usually performed off-line. If a contract manufacturer assembles the panels, the OEM usually separates them—unless the contractor also handles final assembly. Manufacturers that depanel more than 1,000 boards per shift should consider fully automatic equipment.
With any depaneling method, electronics assemblers can ensure success by designing the panels to facilitate separation. For example, the pinching method cannot be used if components, such as connectors, reach over the edge of a board. High-profile components, such as filter capacitors, may cause access problems for some depaneling machines.
Ideally, all components should be located at least 1 millimeter from the edge of a board. Sensitive components, such as ceramic chip capacitors, resistors and diodes, should be located at least 2 millimeters from the edge.
"Most of the time, the engineer designs the board and then realizes that it has to be separated," says Komus. "It’s a good idea for manufacturers to ask us for advice early in the design process."
To reduce cycle time in punching operations, assemblers should pay attention to the size and location of the tabs. "Make sure all the tabs are the same size, so one set of tools can do the whole job" advises O’Hara. "Also, try to keep the tabs close together. That will minimize the amount of time the machine needs to move."
"Putting tabs in corners makes it difficult for depaneling equipment to reach them," adds Hoover.
Suppliers ListCab Technology Inc.
Circuit Technology Systems
Div. of Cox Automation Systems
West Chicago, IL
Fancort Industries Inc.
West Caldwell, NJ
FKN Systek Inc.
Industrial Tools Inc.
Integrated Production & Test Engineering
Jot Automation Inc.
Wand Singulation Systems Inc.