-
- News
- Books
Featured Books
- smt007 Magazine
Latest Issues
Current IssueComing to Terms With AI
In this issue, we examine the profound effect artificial intelligence and machine learning are having on manufacturing and business processes. We follow technology, innovation, and money as automation becomes the new key indicator of growth in our industry.
Box Build
One trend is to add box build and final assembly to your product offering. In this issue, we explore the opportunities and risks of adding system assembly to your service portfolio.
IPC APEX EXPO 2024 Pre-show
This month’s issue devotes its pages to a comprehensive preview of the IPC APEX EXPO 2024 event. Whether your role is technical or business, if you're new-to-the-industry or seasoned veteran, you'll find value throughout this program.
- Articles
- Columns
Search Console
- Links
- Events
||| MENU - smt007 Magazine
STEP 6: Component Placement
December 31, 1969 |Estimated reading time: 11 minutes
Component placement needs have undergone significant changes in the past few years. Component sizes have been reduced, while the need for placement speed continues to increase. This article offers an overview of the challenges and potential solutions available to meet changing placement requirements.
By Larry Groves, Dynatech/Samsung
Component placement requirements have undergone significant changes in the past few years. Component sizes have consistently been reduced, while the need for placement speed has increased to keep the cost-per-placement under control. Placement systems must be able to handle a wider variety of parts and maintain an accurate record of parts placed on boards. It is not enough to be able to place components. The system has to work with extraordinarily low defect rates and high pick reliability to keep production and materials costs under control. This must be part of the basic machine design, and ingrained into an assembler’s corporate culture.
Designers are faced with the daily task of creating smaller products with more intricate circuitry. Passive components get smaller, while active components become more complex and move toward 3-D packages (Figure 1). Placement systems are faced with the prospect of handling components from 01005s up to odd-form connectors - and everything in between. Machines that regularly placed 0402s are challenged when package sizes shrink to 0201, and such systems are usually incapable of placing 01005s. Mechanical and software updates have limited ability to improve the situation, due to the requirements of this package.
What is the best way to meet assembly challenges? First, placement systems are designed to pick parts from a feeding device and place them at the correct location on a substrate. The basic principle is simple; it is how placement systems are designed that makes the difference. A few key issues affect the capability to place small components at high speeds. Achieving higher speeds can be accomplished with faster motors and more accurate drive mechanisms. Centering smaller components requires higher-resolution vision capabilities. But feeders also must be able to move faster, presenting the parts consistently - even with smaller, lower-mass components.
Components and Feeding Systems
How can legacy placement systems based, on original designs meant for larger components and slower speeds, meet today’s goals? Let’s look at the major challenge presented by placing smaller parts. With typical 01005 components measuring about 60% smaller than traditional 0201s, the delivery method of choice is either paper or embossed tape carriers. Pocket size is critical when picking the part from the tape. Standard packaging supplies these components on 8-mm paper - pressed or punched - tape in pockets on 2-mm pitch. Paper-fiber build-up in the feeders or pockets can trap components in the tape, causing mis-picks. Controlling the presentation height of the part is critical because of its reduced thickness. Static electricity characteristics, especially of the cover tape, also factor into chip presentation. This is crucial because components are so light that they could be pulled out of the tape pocket as the feeder advances; it has nothing to do with preventing potential electrical damage. Feeders designed to handle EIA-481-compliant tape address static issues; however, unless the feeder is designed specifically for 01005s, reliability can fall to low levels. This can affect materials and, ultimately, product cost.
Figure 1. Passive components continue to shrink, ranging from 1206 to 01005 package sizes. Photo courtesy of Samsung Techwin, Ltd.
Many legacy feeders - pneumatic, mechanical, and electronic - limit the ability to advance tape-fed 01005s and 0201s successfully. Instead, they provide a platform ripe with opportunities for errors by causing chips to be positioned incorrectly, and, at times, missing from their pickup pockets.
Nozzle design is crucial in parts handling. Critical dynamics are aperture size and nozzle-tip diameter. Best results usually are obtained by using a nozzle designed specifically for 01005s. While 0201 nozzles may pick up 01005s repeatedly, the OD of the nozzle hangs over the edge of the chip, creating a spacing issue on the board during placement. The ID can allow the component to be ingested by the machine, causing service problems by clogging nozzles and filters. Nozzles designed to handle 01005s allow them to be placed with minimal spacing to the next chip.
Centering and Placement Accuracy
When working with small packages, systems on the machine are interrelated. Pick-up reliability is affected dramatically by the mechanical accuracy of the machine. While we tend to think of machine accuracy in terms of placements, a 100-µm offset at pick-up can place the nozzle 50% off of the 01005 component, causing vacuum leaks and mis-picks. Additionally, Z-control on the machine becomes extremely critical with these small packages. We no longer have the luxury of overdriving the nozzle into the pickup pocket to get the part. Even a small overdrive can flex the tape and cause the part directly behind the picked part to be shifted out of the pocket or inverted. Once the chip is positioned properly in the feeder and picked up by the nozzle, it is time to center the component before placement. Several types of centering systems are used on placement machines, but all perform the same function - identify the coordinate center of the device relative to that of the spindle.
Figure 2. Placement system designs are based on the need to track every step of the assembly process. Image courtesy of Samsung Techwin, Ltd.
Traditional laser-based chip centering uses the body outline to calculate the physical center of the component. This method requires that component thickness be positioned exactly in the laser stripe for accurate centering data. Laser-centering machines face an extraordinary challenge ensuring that the component is positioned correctly for imaging. Camera-based systems look at the underside of the chip, providing a larger area with which to locate the four corners and calculate the physical center of the component. They also are less sensitive to the Z-height for imaging. In either case, the alignment system must have sufficient resolution to see and identify components within their respective tolerance values. Given that the pad geometry is nominally 0.007" × 0.008", incorrectly identifying the center of a 01005 can result in chip misplacement and a poor solder joint. With 01005s, the critical dimension appears to be the X dimension. This is due to pad spacing and soldering mechanics. A small offset across the Y-axis of the part will self-center somewhat, but an offset in X often results in an unsoldered termination due to the small amount of solder present on the pads and the stack-up tolerance of the screen printer. Realistically, placement accuracy should be about 50 µm for prototyping, and substantially less for production equipment. Based on solder paste deposition, any centering error can cause the chip to be placed at the edge of the error margin, potentially yielding an opportunity for post-reflow errors.
The advent of fine-pitch devices such as QFPs, SSOPs, and TSSOPs has accelerated the learning curve for placement accuracy. Flip-chip and chip-scale packages (CSPs) serve to underscore the issue of vision-system resolution and placement accuracy. Most current-generation systems can place these larger devices, regardless of the package style, due to overall dimensions. Camera resolution allows the inspection of up to 0.012" lead pitches, reporting back adjustments to the placement routine or flagging unacceptable parts. However, this inherent placement accuracy does not necessarily affect the ability to place 01005s and 0201s at current production speeds, with the resulting need for higher resolutions to capture the 0.016" × 0.008" body.
Traceability and Accountability
The pick-and-place requirement of the process has expanded over the years to additional goals normally reserved for IT/MIS departments. We now are asked to keep track of on- and off-machine component inventory and provide a high level of traceability for boards built. But how can manufacturers attain these goals when legacy systems lack the necessary hardware and hooks in operating software to permit tracking to this level? The industry has answered this call by offering a number of third-party products that can be added to legacy systems. These designs include a combination of mechanical adaptations of RFID and data collection/analysis software that monitor placement-system operation and report results to a management program. Some third-party suppliers work directly with legacy OEMs to take advantage of embedded hooks within a machine’s operating software. Alliances using this collaborative effort can provide better results than a vendor working alone to develop a stand-alone third-party add-on.
Legacy assembly systems’ usefulness can be expanded by implementing this type of solution. But there are a number of issues to consider before making this investment. Placement-system vendors are designing newer products with the capability to handle advanced tracking requirements, along with handling smaller components placed at higher speeds. Rather than adapting existing hooks within legacy software, newer designs are based on an inherent need to provide tracking at every step of the process (Figure 2). For some OEMs, that means stepping outside the basic comfort zone and embracing the IT/MIS functions that surround the PCB assembly process.
The ultimate solution for traceability is built into the fundamental concepts of assembler hardware and software, and extends to feeders. In some circumstances, the solution embraces the IT/MIS department’s need to track boards and components from the receiving dock to the shipping dock.
PCBs and components are tracked as they arrive at the facility, move to the stock room, and finally at the assembly line. But that’s where many systems end. Tracking information is lost at this stage with a legacy placement system, unless a company implements an add-on offered by the manufacturer or a third-party vendor. With newer placement systems, tracking PCBs and components continues with software integrated into the existing factory-side MIS/MRP by design. Inventory information is shared between the PCB assembly line and the MRP system using a standard Ethernet connection to the line-management system. As components leave the stockroom and MRP control, they are added to the line-manufacturing lot-tracking system. Intelligent feeders are assigned to each part number where lot, value, and reel capacity - actual inventory - are logged into the tracking system to provide real-time inventory status and traceability. In turn, when intelligent feeders are placed onto the assembler, inventory information is shared with placement system software automatically.
Tracking individual PCBs requires the addition of bar codes or other serialized information per board. The line-management system reads the information as it enters the production line. Complete inventory information for components placed on each board becomes part of the build record, enabling cradle-to-grave traceability for every PCB built. Once the assembly process is complete, inventory and lot-tracking information is shared upstream with the MRP, allowing factory-wide visibility and ensuring the capability to improve overall quality throughout the assembly process.
Legacy System or New Design?
Upgrading an existing legacy system is questionable. Unless the system is only a couple of years old, it likely will not have the capabilities to meet the challenge of centering an 01005. The most viable solution is a placement system designed to handle 01005s at faster speeds from the onset, not as an afterthought or reaction to newer industry requirements. Some key questions to consider when choosing to upgrade a legacy placement system or buy a new one include:
- What is the useful life of the legacy system?
- Did design specifications for placement accuracy meet 01005 requirements?
- What is the fastest placement speed of the legacy system (preferably using the IPC 9850 specifications)?
- Was the legacy system maintained according to manufacturer guidelines?
- How many upgrades, updates, and modifications would be needed to adapt the legacy system to handle 01005s at current production speeds?
- Does the legacy system offer necessary hooks to manage on-machine inventory effectively?
- How many add-on subsystems are required to implement line-level lot tracking?
- Will the available traceability upgrade/add-on interface with my MRP system?
The answers to these questions bring the art and science of assembly and business decision-making into play. Technology and the marketplace are in constant flux, and analysis of the facts force managers to consider an equal number of “what-if’s?”
Conclusion
In the final analysis, manufacturers are faced with the ongoing reality of placing smaller components at faster speeds that do not compromise the quality of PCBs produced. Demands on tracking components to specific PCBs continue to play a role in improving the quality of boards produced by SMT assembly lines. Placement systems continue to age as profit margins shrink, draining pools of funds for capital investment in replacement assemblers. These issues force manufacturers to make some difficult decisions on how to reach lofty goals within available budgets.
Upgrading an existing legacy placement system or complete line only prolongs the inevitable need for replacement. This delay can, in fact, inhibit the ability to reach the next plateau of product quality and speed because the difference in machine performance is so great that a new machine is the better investment. Traceability suffers because afterthought add-ons often provide incomplete data collection that yields only a partial solution for increasing quality. Choosing the most appropriate, successful growth path is more limited, and requires a perspective encompassing forward-thinking design concepts to meet current and future assembly challenges.
REFERENCES
- “Process Characterization of the 01005 (English) Component Package,” Borkes & Groves; From the proceedings of SMTA International, September 2006.
Larry Groves, technical services manager, Dynatech/Samsung, may be contacted at (215) 675-3566; larry.groves@dynatechSMT.com.