The issue, whether to automate or not to automate the depanelling process, is a question that every surface mount assembler in the electronics manufacturing industry faces when determining how to optimise the production processes and to enhance productivity. Juha Hanninen reports.

While the concept of automated depanelling has already been developed for years, it has only recently been the trend that both - OEMs as well as contract manufacturers - have embraced the technology as a viable approach to board singulating.
The desired manufacturing automation level in general is determined by labour costs and process phases suitability to manual work. However, direct cost-based calculation does not always lead to optimal solutions. When compared with manual work, automated processes allow obvious benefits: increased product and process quality, reduced waste and speed-up of production. Automation also allows detailed control of processes and their impacts on the overall production flow. Process machine uptimes may become higher and the number of process-related quality flaws may diminish. The incentive to automate certain tasks may also be due to ergonomics reasons.
The trend to automate the depanelling process is clearly noticeable. Depanelling automation is more and more taken into consideration when excess labour is being used to depanel printed circuit boards by hand.
For many companies, excess labour may be as little as two or three dedicated workers doing nothing but manually separating boards from framed arrays. Cutting tabs by hand with dikes or nibblers is a tedious task, which quickly becomes tiresome for a worker. The additional handling during the depanelling process inevitably leads to increased scrap levels late in the process, on higher value-added assemblies.
In most cases, electronic manufacturers and especially EMS providers, tend to automate the depanelling process in order to satisfy customer edge quality requirements and also to preserve dimensional tolerances.
Depanelling solutions based on routing as technology offers better flexibility, speed, accuracy and the edge quality realised is superior compared to alternative methods.
The cutting force does not harm single PCBs and the number of rejected PCBs is kept very low. Also the initial costs of a routing system are moderate and product-specific parts represent a small ongoing expense. Due to the advantages, routing is generally preferred for depanelling of high-tech, commercial, and industrial production. Other, more technical points, which must be taken into consideration when using routers are fixturing (product-specific parts), dust removal, vibration, static charge, and tab cutting versus full profile routing.

Fixturing

Due to the forces imparted during the routing process, the individual boards within the panel must each be held securely in place by a fixture or gripper. The simplest and least expensive way to do this is by pinning internally to at least two non-plated holes on each panel.
When pinning is not an option, a vision system to verify panel location before routing could also be used. In this way the routing process is not related to typically product-specific holes and the machine can be run without changes between production batches.

Dust removal

Dust removal is also one of the most important issues in today's depanelling process. On most routers the router-bit is surrounded by a vacuum foot, which usually holds a bit-concentric router brush.
An up or down cutting chip breaker routing-bit is most commonly used to draw the cuttings into the vacuum airflow. In most tab cutting or even full profile applications this configuration is sufficient to remove all dust and is also one part of the whole dust evacuation system.
When talking about the dust evacuation normally all, including many router manufacturers, are thinking only the vacuum pump and its capability to create a strong vacuum level. But this is only half of the truth.
The critical point of a vacuum pump is the maintenance of a sufficient or maximum airflow - not depending on how long the pump had been used or how much dust is in the container. With normal dust bag systems it is not possible to realise continuous vacuum levels, as it is a fact that the airflow level will drop dramatically when the dust bag is filled with dust and filters become dirty.
Full ESD control is even more important when thinking of damage to components and final products. Static charge, generated by the router-bits' cutting material and vacuum airflow, is a very localised phenomenon.
Therefore this is usually managed by the use of conductive materials, ionised air and by adding a braided copper ground cable to the inside of the vacuum hose. But even more troublesome is the attraction of dust particles when a static charge is present. This will cause malfunctions of final products or additional cleaning process will be needed in the production line. It is obvious that this cannot be a solution in today's manufacturing line so integrated ESD control is vital in the whole production line.
Dust evacuation should be understood as a single process, which includes components like the routing bit, ESD control, vacuum pump and routing parameters. If one of these components is not working, it is impossible to get the maximum performance out of the dust evacuation process. The result will be as poor as the weakest link allows.
A much less common consideration is the vibration effect of routing on sensitive or delicate components. All kind of vibration will also directly affect the life-time of a routing bit. This is not an issue at an economic point of view but rapid wear of the routing bit will decrease the routing quality dramatically. And the quality of final products is a big issue.
Most vibration can be avoided by using rigid fixturing as gripping, or lastly the usage of different style of router bits as well as altering spindle speeds and feed rates may enable a shifting of router resonant frequencies "out of phase" with component resonant frequencies.

Stand-alone vs in-line routing

Once the electronic manufacturer (OEM or contract) has chosen routing as the best and most suitable depanelling method, the next step is to determine how the anticipated future requirements will be satisfied in the best way. Options are a standalone, manually loaded router or automated in-line routing system.
In the recent past, the choice was relatively straightforward. Standalone manually loaded routers were most commonly used in medium volume, high product mix applications. Product changeover could be accomplished within seconds by simply lifting out the fixture, placing a new fixture into the machine, and accessing the new routing program from a menu previously stored in memory. By comparison, automated in-line routing systems were used in high volume, low or no mix applications. For the most part this pattern will continue, although recent advances in material handling automation will certainly allow greater flexibility to implement an in-line solution in even higher mix applications.
Customers in the global market place are demanding flexible automation and robotic devices that can enhance their own manufacturing productivity. Their specific needs includes speed, flexibility, ease of use, reliability, availability and affordability of production automation. Based on our experience many customers prefer practical, affordable automation solutions as opposed to highly complex, expensive systems that require constant maintenance and attention by technicians.
JOT Automation's approach to depanelling is targeted to fulfill the current and future requirements toward depanelling. Its depanelling equipment consists of standardised products, which provide reliability, cost-effectivity and short ramp-ups secured by tested technology and solutions. JOT Automation's product portfolio is providing answers for all level of automation. As flexibility is a built-in feature in all of our equipment it has the capability to provide customer-specific optimised solutions utilising all the advantages of standard products.
To guarantee efficient automatic production, many standardised options are available in JOT Automation's routers. They can be equipped with several grippers (eg, a programmable servo gripper and pneumatic multi gripper), and also a gripper magazine is available for larger cells. To be able to operate within tolerances and verify routing positions on the board correctly, routers can be equipped with a vision-system. Additionally, a graphical user interface, video aided programming, automatic tool change and motorised width adjustment are also available options.

Summary

As with any other technology base where many choices exist, every process engineer and production manager must determine what is the most appropriate relative to their own depanelling needs.
While the older automated techniques may offer an initial cost advantage over routing, the issues of edge quality, speed, flexibility, and overall reliability continue to drive to the routing process in the market today. As OEMs and contract manufacturers continue to increase the sophistication level of the circuit boards they produce, these considerations become vitally important. Whatever the application is, however, the choice for depanelling equipment must first take into account the key issues of quality, cost, and productivity, before the best method can be determined. u

ENQUIRY No 28

Juha Hanninen is with JOT Automation Group Plc, Oulunsalo, Finland. www.jotautomation.com