SMT Material Handling Support Systems

Estimated reading time: 7 minutes

Modular storage and transport equipment can maximize production line efficiency and provide flexibility to support future work-flow changes.

Mick Cronin

It can be said that the global electronics production industry "practices what it preaches." In the same way that new and advanced technologies are introduced for industrial and consumer use, the industry has successfully adopted new production technologies to increase profits and yields. One of the most significant developments in electronics assembly has been the adoption of SMT, which has provided the platform for assemblers to automate the assembly process, maximize the real estate on printed circuit boards (PCB) and increase yields. As a result, OEMs and contract manufacturers (CM) that were the first to adopt SMT have gained a significant competitive advantage.

A modular SMT storage and transport platform can enhance assembly line efficiency and further complement this competitive technology. SMT material handling systems are designed to support all process aspects and can be easily reconfigured to support production requirements.

Stencil Frame Handling

Valuable stencil frames are secured safely in specially designed racks (Figure 1). Typically, a central storage area will have stationary units built to accommodate a large quantity of frames. A modular system affords the flexibility to select the size and number of storage levels that best fit within the space constraints. Research confirms that a 24" wide by 42" long unit offers an acceptable balance between high-capacity storage and a sensible footprint. Overall design should accommodate stencil frames up to 1 5/8" thick, which is more than adequate for the majority of frames. Optional stop bars are recommended and should be positioned at the back of each storage level to prevent the frames from sliding out of the unit.

Engineers often request that casters be put on these racks to provide frame mobility. In some situations, key stencil frames can be stored in a mobile stencil storage unit adjacent to the SMT line for quick and easy access, minimizing downtime.

Whatever the system employed, it needs to be electrostatic discharge (ESD) safe and the construction must be free of debris or contaminants that could potentially clog critical screens. Wood or plywood construction should be avoided. ESD accessories that can enhance the system include: label holders for easy frame identification, non-marking conductive casters that provide a "soft" and ESD-safe ride, and a grounding cable that provides an additional point of contact.

Component Reel and Feeder Arm Handling

For optimum results, component reel and feeder arm storage should be based on a modular-style platform (Figure 2). With a modular-based system, individual storage levels can be interchanged and built according to production requirements.

For example, bulk reel or feeder storage may be required in a stockroom area. Stationary or mobile units with multiple levels of storage provide a high-density storage solution appropriate for this application. Conductive label holders can provide an effective reel identification system and, in the case of reel storage, removable dividers can facilitate customized reel compartments.

On the production floor, mobile units can be built to transport reels, feeders or both. Reels or feeders required to support a particular run can be positioned next to the SMT line, minimizing any potential equipment downtime. In the case of a combination unit, it can act as a dedicated job cart, equipped to support a particular pick-and-place machine. The feeders and reels can be staged next to the machine, permitting quick feeder changeover. Machine downtime can be minimal, ensuring maximum production-line efficiencies.

When specifying the appropriate casters, care should be taken. Casters should exhibit superior vibration dampening characteristics, minimizing any potential damage to reels and feeders, as well as a braking system that is easy to lock if the cart is moved to an uneven floor. If conductive casters are preferred, non-marking conductive casters are recommended to avoid carbon sloughing on ESD floors.

PCB Handling

Tray carts have become the preferred method for storing and transporting PCBs and other electronics assemblies. The tray-based system is inherently flexible and offers one of the safest PCB handling options available. Consider some of the benefits:

- Tray carts can transport PCBs to and from any point on the SMT line - to an off-line through-hole process, to manual board stuffing stations, to inspection stations or to a rework area.

- Because the whole premise of the system is tray-based, the tray is handled - not the PCB. This reduces handling damage rates.

- 18 x 26" ESD trays can easily handle PCBs in a variety of sizes, and several PCBs can be placed on one tray. Additionally, no cart or panel adjustments are required.

- As PCBs continue to become ever-more populated with little or no edge clearance, traditional PCB handling methods such as totes and horizontal-hold PCB trucks will become obsolete. Also, tray carts are perfectly positioned to transport flexible circuitry, which is becoming more common.

When specifying a tray-cart system, make sure at least two brake casters, locking bars (front and back), push handles (front and back) and a grounding cable are included on the unit to guarantee optimum cart performance. Also keep in mind weight considerations. Wire cart designs are lighter than steel fabricated designs when fully loaded.

Finally, a dual-layer tray inlay is recommended over either a conductive or a static-dissipative mat. A dual-layer type mat, featuring a static-dissipative material on top and a conductive material on the bottom, offers the safest controlled charge-dissipation solution. Conductive mats can potentially cause an arching situation when exposed to a charged device and a static-dissipative mat may leave residue charges that could come in contact with other components placed on the mat. The dual-layer mat dissipates a charge at a controlled rate through the static- dissipative layer and, once in contact with the conductive layer, is bled rapidly and safely out of the danger area.

Totes and PCB Accessories

Tote boxes offer efficient storage of items in bulk or compartmentalized fashion with the use of dividers and covers. Snap-on covers, offering a more secure fit, and insert covers, which provide easy access to tote contents, are available. Typically, these rigid totes are injection molded from polypropylene and are stackable with or without snap-on or insert-type covers. Snap-on cardholders that mount on the front of the tote box provide an efficient content identification system. Predominately, conductive totes and bins are preferred for part and component storage because of the permanent nature of this ESD material. However, as electronics production components have become more sensitive to ESD events, some have switched to static-dissipative materials for added ESD safety.

Totes can quickly and easily be converted to an effective PCB handling system with the addition of some basic PCB accessories. Placed inside standard totes, grid boards provide a pattern of slots where boards can be captured by the bottom edge (Figure 3). PCB holders that integrate into standard totes to provide positive capture of PCBs on opposite ends are also available. Slotted on both sides for use as an end or common center panel, PCB holders are available in both conductive and static-dissipative materials.

Inspection/Rework Stations

Assembly and inspection stations should be ergonomically designed and easy to reconfigure to support different tasks. As manufacturing needs change, the work flow and facility layout may also need modification. Workbench systems that feature task-specific, easy-to-adjust accessories are recommended.

Ergonomic bench systems typically include accessories that effectively support the task being performed, are easy to access and ultimately aid in worker productivity. Examples of ergonomic accessories include swing-arm bin holders, swing-arm monitor/keyboard holders, retractable power tool holders, cantilever shelves (wire and laminate), tool holders, solder spool holders and general utility racks. To promote maximum employee productivity and enhance worker well being, choose a bench system that features these accessories.

Conclusion

As the trend toward multiple global manufacturing facilities continues to evolve, more companies are specifying the same production equipment worldwide. Typically, once a production line material handling solution is developed at a facility in the United States, that same solution is often specified for overseas manufacturing locations. For this reason, it is smart to identify storage and material handling manufacturers that can provide uniform SMT material handling products globally. A supplier who can provide the type of global product support discussed in this article will ultimately be a valuable business resource.

SMT will be a constant in electronics production for some time. Material handling support systems are essential and critical to the success of any electronics production environment. They contribute to increased manufacturing yields, reduced handling damage and provide the flexibility required should production needs change. SMT material handling support systems ultimately maximize production-line efficiencies.

MICK CRONIN is product manager with InterMetro Industries Corp., 651 N. Washington Street, Wilkes-Barre, PA 18705; (570) 825-2741; Fax: (570) 824-2704; E-mail: mick. cronin@intermetro.com; Web site: www. metro.com.

Figure 1. Stencil frame handling system.

Figure 2. Modular reel and feeder arm handling system.

Figure 3. Grid boards capture PCBs by the bottom edge.