ORIGINAL ARTICLE -- Automated Depaneling System Cuts Scrap, Boosts Board Output

Estimated reading time: 7 minutes

Printed circuit board (PCB) manufacturers are feeling the pressures of a new century. These pressures come from different sources -- higher density assemblies, narrowing profit margins and tougher international competition, to name a few. But they are all pushing manufacturers in the same direction: toward more automated PCB production.

Thanks to automation, PCB manufacturers have already reaped impressive gains at the front end of their production processes. But the benefits from expensive front-end assembly equipment -- lower costs, higher throughput, better product quality -- can be lost at the other end of the production line, where outdated manual processes are still far too common.

One of these manual end-of-line (EOL) processes is depaneling, the separation of multiple boards from a panel. Manual depaneling is a time-consuming process that slows down production lines. Worse, it subjects PCBs to bending stresses that can damage the boards and their delicate components. Often, this damage results in latent field failures.

To replace troublesome manual processes, manufacturers need an automated EOL depaneling system that is fast enough for a production line and gentle enough to handle fragile PCBs. The system must also be flexible enough to handle different board sizes, shapes, and spacings.

Designed to meet these requirements, a new technology* offers two different depaneling approaches in one fully automated machine. The technology reportedly improves depaneling quality, while reducing labor costs and cycle times. It also minimizes stresses on PCB assemblies, slashing the high scrap rates characteristic of manual depaneling operations.

Problematic OptionsToday, PCB manufacturers employ a variety of depaneling techniques. The most common include:

Manual depaneling. In traditional manual depaneling operations, gloved plant personnel use pliers or other implements to break the boards apart. This technique, which requires no tooling changes or software setups, appeals to some PCB manufacturers because of its simplicity and low investment costs.

But manual depaneling has many disadvantages. Among them:

• The process is labor-intensive and inaccurate, resulting in longer cycle times and higher process costs.
• Because it is best suited to straight-line breaks, manual depaneling is not ideal for sophisticated contours.
• Depaneling technicians may not be grounded, so the boards they handle can be damaged by static electricity.
• Repetitive motion can lead to carpal tunnel injuries to operators.

Perhaps most serious, manual breakout can overstress PCBs, cracking the component joints. As a result, scrap rates soar, threatening the profitability of the entire production process. In addition, field failures are more likely and failure-related costs rise exponentially.

Punching. In punching processes, a press with a dedicated die stamps PCBs out of a panel. Boards can be separated from a panel in one blow, which makes punching a fast depaneling method.

On the downside, manufacturers who choose punching must pay high tooling costs. To prevent downtime during tool maintenance, the process normally requires two die sets per product. That means 10 different products would require 20 die sets, with total tooling costs in the hundreds of thousands of dollars.

In addition, the impact of the die can shock the PCB, resulting in cracks, delamination, and other types of board damage. The process is also semi-manual, with operators needed to load and unload the press.

Laser cutting. This relatively new technique offers speed and allows inline processing. But laser cutting can produce charred, jagged, and electrically conductive depaneled edges. A laser is an expensive item to add to a production line and users must monitor changes in circuit composition in order to prevent laser failure and burned board edges.

The drawbacks of these depaneling methods led to the development of this technology, which is said to boost depaneling flexibility by providing both circular saw and router technology. The saw cuts straight lines, while the router can cut curving board edges and tabs. The programmable router is ideal for sophisticated board geometries, quickly and accurately depaneling PCBs with complex contours.

Able to keep up with automated production lines, the technology offers a maximum saw speed of 8"/second and a top router speed of 3"/second. Despite its speed, this technology makes cuts with excellent edge definition. It is also accurate, with servo repeatability of plus or minus 0.0005".

Measuring 18" sq, the routing window can accommodate large panel sizes. For smaller panels or higher throughput, the system allows dual-lane product flow. Thanks to these features and others, the system can process nearly 50 percent more PCB designs than comparable machines. The bidirectional technology also handles both left-to-right and right-to-left product flow.

In most routing systems, a gripper mechanism holds the PCB in place from the top, while the board is routed from below. By contrast, this technology is a "top-side" depaneling approach, with the router on top and the board-holding fixture below. Besides reducing fixturing costs, this arrangement increases the rigidity of the fixture, which improves cutting speed and accuracy. The fixture also features a patent-pending clamping device and bottom-side vacuum extraction tooling; as a result, the boards are held securely in place and maintain a dust-free environment.

For boards with straight edges, this technology includes a servo-driven z-axis saw blade that can accommodate various component heights and clearances. This unique blade can rotate as much as 270 degrees to make angular cuts.Most other depaneling saws are powered by a router spindle that limits them to high-speed operation. Since these motors tend to stall at speeds below 10,000 rpm, they cannot provide much low-end torque. As a result, the saws cannot slice through hard-to-cut materials such as ceramics and copper, which are used for the backing of high-powered ball grid arrays.

So the designers of this technology decided against a router spindle, opting instead for a special servomotor. This servomotor can spin the belt-driven saw blade at speeds of 500 to 2,500 rpm, which are better suited for high cutting loads. For precise speed control, the system also includes an encoder that can hold rotational speed to accuracies of plus or minus 1 rpm.

The system's modular design lets users choose the configuration that is right for them -- saw only, router only, saw and router, single lane, dual lane, etc. In addition, quick-change tooling and intuitive software make it easy to reconfigure for product changeovers.

For easier programming, the technology includes a camera system that lets users "teach" the machine the cut path, as well as circuit entry and exit points. Once the teach points are automatically saved, the depaneling program can be tested in either a camera-only mode or a test-cycle mode that requires a manual check of each program step.

The technology includes Windows-based control software that allows rapid configuration of the routing path. The software features an enhanced routine program editor that integrates the video-assisted camera image. The editor also simplifies the testing of routing programs and provides a real-time synchronous editing mechanism.

Comparative AdvantagesUnlike manual methods, the technology does not rely on technicians to perform depaneling tasks. It also eliminates stress and board damage caused by manual depaneling. This can greatly increase the profitability of manufacturing operations. Consider an automobile manufacturing facility, which makes millions of PCBs a year. Even a depaneling scrap rate of less than 1 percent can cost the facility hundreds of thousands of dollars a year. In facilities like this, the technology quickly pays for itself by slashing the amount of scrap generated by PCB production.

As for punching, it's an adequate option for depaneling low-cost single-sided PCBs. But punching can cause costly damage to high-value double-sided boards. By switching to the technology, manufacturers can greatly reduce the board damage and scrap produced by punching operations, saving thousands of dollars a year and increasing confidence in the integrity of the delivered product. The switch will also lower tooling costs and eliminate manual parts of the depaneling process.

In IndustryOffering both saw and router options, the depaneling technology is the first suitable for both standard panel layouts and closely spaced PCBs. In the cell phone industry, standard panel layouts include "prerouts" cut between the boards, which are held to the panels by tabs. The boards come in a variety of shapes that allow them to fit into different handsets. During depaneling operations, the S/R Flex router moves along the curved board edges and cuts the tabs.

The situation is different in the automotive industry, where square panels contain closely spaced boards separated by V-scored grooves. In manual depaneling operations, technicians bend the panels along the scored lines until they break. This bending puts a great deal of stress on the boards, which are multi-layered and crammed with components. In some cases, depaneling stresses delaminate the boards and produce cracks at the component/board interface.

This technology eliminates the bending loads and edge stresses placed on the boards. In the S/R Flex machine, panels are fixtured to prevent bending during the depaneling process. The spaces between the boards are too long and narrow for a router, which would greatly decrease spindle life in automotive depaneling. So the technology cuts out the boards with a gentle sawing process, which separates complex, multi-layered PCBs without damaging them.

ConclusionCombining saw and router technology, this technology offers PCB manufacturers a unique, flexible depaneling option. The technology boosts yields by eliminating bending loads and edge stresses that can damage boards during manual depaneling procedures. It also offers much faster throughput rates than conventional depaneling techniques. By slashing scrap rates and increasing output, the technology quickly pays for itself, making it a valuable and cost-effective addition to the end of an automated production line.

*Saw/Router Flex (S/R Flex) Technology from Cencorp LLC of Longmont, Colo.