Reading time ( words)
With increasing demands placed on component structure, finding methods to improve automated odd-form component placement is paramount.
John A. Kukowski
John G. Ricci
Frank L. Carollo
In electronic printed circuit board (PCB) assembly, "odd-form" generally refers to through-hole or surface mount components whose height, weight or shape traditionally would not allow them to be placed automatically using standard pick-and-place machines.
While most of the processes in PCB assembly have enjoyed great advances in automation over the years, until recently, odd-form component placement has seen somewhat less progress toward automation. For the most part, odd-form placement has remained a manual process. One reason for this is a continuing acceptance of current methods of hand assembly, primarily caused by a perceived lack of suitable odd-form component packaging, feeding and placement equipment. However, that thinking has started to change. A number of factors have combined to lead electronic manufacturers to take a new look at automating odd-form component assembly. The key drivers behind this new push are manufacturers` increasing needs for higher production volumes, improved product quality, reduced time-to-market, lower assembly cost and increased global competitiveness.
As a result, all the players in the odd-form arena - electronics product manufacturers, component and packaging suppliers, and assembly equipment producers - now have more incentive to develop automated odd-form solutions that can be integrated into standard production processes.
Responding to Market Needs
Odd-form components are suitable for a broad range of applications, including automotive, communications and computer/ peripheral. In electronics manufacturing in general, and in these fields in particular, the critical advantages of automation are potentially significant gains in quality and productivity. These gains result from the consistent, reliable, high-speed component placement and positional accuracy of automatic equipment, compared to the variability of manual assembly.
Board real estate is shrinking and passive and active components are dwindling in size. This impacts odd-form assembly in a number of ways. First, as components grow closer in proximity, the board designer faces the challenge of planning for automated tooling requirements. Odd-form components such as headers, jacks and switches must be positioned so that adjacent components are spaced at a safe distance, allowing adequate tooling clearances to place or clinch odd-form components.
Second, smaller electronic products most likely contain surface mount packages, driving process engineers to include the odd-form components in the same assembly and reflow operation. This can be accomplished by using intrusive reflow technology, where through-hole leads of odd-form components are also reflowed using stenciled solder paste rather than wave solder.
For example, high-density PCBs are often double-sided. With the market demanding high-speed switching circuits with signal conditioning, process engineers are seeing the introduction of high-lead-count straddle-mount connectors that contain fine-pitch surface mount leads that straddle the top and bottom sides of the PCB, and have high-force ground pins inserted into the board`s edge.
With the availability of the intrusive reflow process and use of straddle-mount connectors, equipment manufacturers must now offer automated placement machines that provide the flexibility to place fine-pitch and standard surface mount devices (SMD), odd-form components and straddle-mount connectors - all in one machine. At a minimum, such a machine must have sophisticated software, supplemental data I/O for added tooling, a highly accurate vision system and high-force insertion capability just to enter the odd-form marketplace.
These capabilities are critical in today`s increasingly sophisticated technological environment. With this type of flexible placement equipment, customers can handle multiple component technologies in one operation, subsequently increasing speed and quality, while reducing floor space requirements.
The majority of odd-form components (up to 75 to 80 percent) are connectors. The most common remaining types include transformers, relays, crystal oscillators and electrolytic capacitors. In the past, such components could not withstand the heat of reflow ovens, but the introduction of new high-temperature materials has allowed manufacturers to implement odd-form components into most standard surface mount assembly processes.
Odd-form components cover a wide variety of forms; larger components (e.g., slot-one connectors, Universal Serial Bus [USB] connectors, DIMM connectors, headers, phone jacks and speakers) are most often used in computer motherboards. Miniature components (e.g., surface mount and ball grid array [BGA] connectors, vibrators, shields and miniature speakers) can be found in the latest palm top and cellular phone products.
Until recently, the primary odd-form component technology had been through-hole components that were processed with wave soldering. The challenge designers and assemblers face (to produce products that are faster, more complex and more reliable, at a lower cost) has resulted in a major shift for odd components. This challenge has driven component manufacturers to change or release new odd-form component types, such as:
- Replacing the standard through-hole, odd-form components with surface mount equivalents.
- Changing the component body material of the through-hole components to a high-temperature material that can be processed using reflow ovens.
- Introducing solderless through-hole connectors incorporating compliant pin technology originally developed for backplane applications.
- Supplying straddle-mount connectors that mount to the side of the PCB for miniature and high-speed communication products.
- Adapting the latest BGA technology into connectors.
A key factor contributing to the increased viability of automating odd-form component assembly is component packaging. There are limited standards established by the Electronic Industries Association (EIA). The most common packaging formats are tape-and-reel, radial and axial tape, extruded tube, tray, continuous strip and bulk.
As might be expected, each of these packaging formats has benefits and drawbacks, depending on the circumstances in which they are used.
Tape-and-reel. This form of packaging allows for a higher volume of parts than either tubes or trays. Tapes are available in flat-carrier, deep-pocket and semi-pocket formats. The EIA standard for these tapes is EIA-481. All three tape formats are available in standard configurations and can provide a high volume of on-line parts inventory.
However, components used with tape often require repackaging, which can add to costs. As supplied for surface mount assembly, deep-pocket tape is covered by adhesive tape. In deep pockets, tall or heavy parts may change position or break the cover tape.
Semi-pocket tapes, on the other hand, have shallower pockets and cover tapes that loop over components. In the shallower pockets, the cover tape holds the parts snugly. The packaging of multiple parts per pitch is possible with semi-pocket tape. The advantages of packaging multiple components per pitch are that more inventory is available on-line and feeder space is conserved.
Radial and axial tapes. These types of tape are covered by two different EIA standards: EIA-468-B for radial tapes and EIA-296-E for axial tapes. These packages work for a wide range of components and are generally produced at a low cost. Because of its configuration, radial tape should not be used for components that are tall and can easily be deformed on the tape.
Extruded tubes. Tubes are the most commonly used format and can be a low-cost solution. Components such as D-Sub connectors, phone jacks, transformers, relays and shrouded headers are generally supplied in tube packaging. Recently, component manufacturers have begun to supply long connectors - SIMMs, DIMMs and other connectors with a long aspect ratio - in edge-stacked tubes.
Tubes are a good package format for protecting the component and achieving high-quality automated production. Although tube packaging can be inexpensive to implement, users need to verify that the tube used for shipping is acceptable for automated component feeding. Some tubes constructed with a thin cross section allow the tube to deform easily, resulting in components jamming within the tube. Depending on the component weight, these thin cross-section tubes may not be suitable for stacking in a feeder. Heavy components packaged in thin cross-section tubes will deform adjacent tubes when stacked in an automated multi-tube feeder.
Other potential areas of concern when selecting tube packaging are a specially designed feeder track, a tube design not allowing "shingling" of components and tube orientation when loading the feeder. Equipment manufacturers provide a number of tube feeders from low-cost to quick-change stackable, making tube packaging one of the most widely used formats.
Trays. Component trays are an inexpensive means to supply components. One of the key issues with trays is that components are not packaged for automation. Component leads are not always oriented in the insertion plane and pocket registration of the trays is often not acceptable for reliable automated pickup and insertion.
There are a number of other factors to consider when choosing trays: They lack the rigidity required by many assembly machines; vacuum-form trays provide a limited on-line parts inventory; there are no standards for vacuum-formed trays for use with odd-form components; and tray size may take up a significant amount of feeder space in a placement machine.
Continuous strip. This packaging is designed for high-volume automation applications and is often used for continuous headers, battery clips and motor brushes. In most cases, this packaging technique eliminates the need for a secondary means of component packaging. Generally, the component remains on the carrier strip during the manufacturing process.
Continuous strip packaging provides high levels of on-line parts inventory. However, strips are application-specific and may carry a higher automation cost because of the need for a specially designed feeder mechanism.
Bulk. The bulk format eliminates the expense of individual component pack-aging and reduces environmental issues. A significant number of odd-form components are shipped to assemblers in this format. However, bulk remains one of the most difficult packaging formats to automate with odd-form components.
Generally, bulk components require a specially designed and manufactured bowl feeder, which results in higher cost and longer lead times. The feeders usually take up considerable space and are not easily retooled for product changeover.
Bulk packaging and bowl feeding are a good alternative for high-volume, dedicated assembly cells. Because bulk packaging has a clear price advantage, equipment manufacturers continue to strive to develop a reliable and cost-effective feeder. Over the past year, a number of flexible part feeders have been introduced to the market to meet these objectives. These feeders are in the early technology development phase, but the goal of having a bulk feeder that is cost-effective, reliable and rapidly retooled is coming closer to reality.
As improvements have been made in odd-form component packaging formats in recent years, odd-form assembly machinery has likewise advanced. Unlike SCARA robotic systems of the past, which were designed to perform a single task and were expensive to reconfigure for other uses, modern automatic odd-form assembly systems can be integrated into existing assembly lines. They can now be reconfigured to produce different PCBs and can achieve accurate, high-speed placement at a competitive cost.
Modern odd-form automation systems utilize an overhead gantry-style positioning system with vision to precisely position each component for accurate placement. With the trend toward surface mount odd-form components and pin-in-paste PCB assembly, accuracy is an essential part of a reliable process. As companies eliminate wave soldering and move to pin-in-paste, the component must be placed accurately into the solder paste the first time so the solder paste is not disturbed and solder joint integrity is not compromised.
In recent years, equipment manufacturers have made major advances to automate odd-form assembly. These advances include: enhanced vision systems; specially designed interchangeable grippers and nozzles; the ability to insert straddle-mount connectors with the same machine that places standard surface mount components; and improved component feeding mechanisms. Automated assembly systems can be configured to work with a variety of odd-form component types, feeders and package formats.
Manufacturers are increasingly looking for odd-form assembly equipment that has been enhanced for greater speed and accuracy. These enhancements may include a dual-beam, overhead gantry placement system (with a four-spindle head or servo-gripper head on each beam) for increased speed. Improved accuracy in X, Y and theta rotation may be achieved with more sophisticated vision systems for component inspection and verification.1
Where Does the Industry Go from Here?
The trend to make products that are smaller and more complex - and to do it faster and at lower costs - is driving the need to integrate more functions onto the PCB. This, in turn, drives the demand for odd-form components and the resulting need to automate odd-form component placement.
Over the last few years, the electronics industry has dedicated significant resources to automating odd-form component assembly. Manufacturers have responded by implementing assembly process changes, such as adapting pin-in-paste technology and using more surface mount odd-form components. Component suppliers have begun developing significant changes in component packaging. And equipment vendors are providing automated assembly systems that can be configured to work with a variety of odd-form component types, feeders and package formats.
This is only the beginning. Suppliers of com-ponents, packages and assembly equipment, along with electronics manufacturing companies, are working to establish standards for odd-form assembly processes. The National Electronics Manufacturing Initiative (NEMI) has established a team to identify and meet the challenge of automating odd-form component assembly. The nature of this challenge is two-fold: It depends not only on developing odd-form placement equipment with a clear cost advantage over manual assembly, but also on developing industry standards for packaging those components.
The companies that will survive and prosper in this emerging marketplace will be those offering the end user a product that meets certain key market values: a low-cost assembly cell; flexibility to handle a wide variety of components; ability to perform functions such as lead clinching, screw driving and glue dispensing; high reliability; powerful, user-friendly software; and changeable tooling.
Odd-form component placement automation is a critical step in the ongoing evolution of electronic assembly. The challenges are many but innovative solutions are now being developed.
1 One such odd-form placement machine is the GSM platform elevated gantry assembly cell from Universal Instruments Corp.
JOHN A. KUKOWSKI, JOHN C. RICCI and FRANK L. CAROLLO may be contacted at Universal Instruments Corp., P.O. Box 825, Binghamton, NY 13902-0825; (607) 779-7522; Fax: (607) 772-1878; Web site: www.uic.com.