Using Asynchronous Process Manufacturing for Product Development

Medical Device & Diagnostic Industry Magazine
MDDI Article Index

An MD&DI  January 1998 Column

MANUFACTURING

A nonlinear, high-mix, high-speed manufacturing process can reduce new product development costs and improve quality.

Medical devices place unique demands on electronics manufacturers. Electromedical products generally entail small or midsize production runs, employ a high mix of circuit cards to achieve equipment functionality, and require real-time configuration flexibility to meet fluctuating customer demands. Device manufacturers also expect a rapid time to market to help offset the time spent seeking FDA approval.

A process known as asynchronous process manufacturing (APM) has been developed to meet these stringent requirements. The APM methodology allows high-mix/high-speed manufacture in Class II and Class III environments.

APM is a nonlinear continuous-flow manufacturing process whereby small, highly trained teams perform setup off-line. Moving a product into production is like putting a module into place. That module then moves through the assembly line to the next available station, not necessarily in the same line, according to a specialized execution system, with all sequences controlled by a sophisticated information system. The process can lead to a significant reduction in production time as well as cost, compared to larger, more typical assembly systems. This article examines the components of an APM system, drawing on examples from a program implemented by an electronics manufacturing service provider.

HIGH MIX AND HIGH SPEED

While high mix/high speed may seem redundant, APM provides high-mix medical OEMs with fast processes on high-speed surface-mount technology (SMT) systems. However, the decision to adopt APM cannot be approached casually. Using APM usually entails redrawing the facility layout, reconfiguring high-speed SMT systems, designing and implementing a highly sophisticated information technology system, and completely reorganizing the employee structure.

The facility that serves as the model, for example, installed three Fuji SMT lines, each equipped with MPM AP27 screen printers, Fuji CPIV high-speed chip placers, Fuji IPII flexible placement systems, and BTU or Heller convection reflow ovens. After SMT processing, the boards proceed through a variety of automatic insertion equipment, including Universal radial-lead inserters, Universal IC inserters, and Dynapert VCD axial inserters. The boards continue through one of eight manual load lines and one of three Electrovert wave-solder systems. At the end are burn-in chambers, functional test systems, and networked in-circuit test systems. All processes are certified to IPC-610A Class III.

HOW IT WORKS

In conventional continuous-flow manufacturing (CFM) facilities, Fuji SMT systems are generally used for high volume/low-mix runs and can effectively produce approximately 1000 boards per shift (Figure 1). A card proceeds synchronously through SMT, load, wave solder, secondary add, and final test. Each in-line process is dependent on the previous process and must wait for its completion before beginning. Consequently, product changes cause increasing amounts of downtime in each successive process.

Figure 1. Using the conventional flow manufacturing process, the build time is about 90 to 210 minutes per kit.

In APM, however, all of the process equipment on every line is separated into individual process points. Equipment in the process is standardized to a minimum number of recipes, thus making all like-process systems uniform. This standardization enables a batch of cards to move asynchronously from the first SMT line, for example, to the second load and wave area, back to the first secondary component area, before finishing in the third test area (Figure 2).

Figure 2. Using asynchronous process manufacturing, a company achieved approximately 50% faster throughput compared with that of conventional flow manufacturing.

OFF-LINE SETUP

In typical high-volume/low-mix manufacturing environments, each SMT line employs dedicated feeders. In order to change a product, manufacturers must also change the parts in the feeders, resulting in expensive downtime while the kit is pulled and parts are loaded. To keep lines up and running in a high-mix environment, manufacturers must invest a significant amount of money in extra feeders, which are kept off-line in the stockroom. When a kit is pulled, reels are loaded on stockroom feeders. When a work order is scheduled to run, the full feeder cart is rolled up to the SMT line, eliminating downtime between product changes and optimizing line usage.

After the surface-mount or automatic insertion process, the circuit cards are put onto rolling racks, pushed to the loading area, and matched up with the through-hole components, which are assembled into kits ahead of time, again reducing downtime. Two or three loading teams with approximately seven people per team are prepared to work on the next board that comes down the line. The cards are finished in the secondary-add department by one of several hand solder teams before proceeding to the testing station, where networked HP3065 and HP3070 instruments perform in-circuit tests along with functional and burn-in tests as required.

By dividing the lines into process points, wide pipelines are created and bottlenecks are avoided. Because all processes are standardized and not configured to specific customer jobs, operators never have to wait for a line to clear before running another customer's job. The difference in throughput is like rush-hour traffic on a two-lane highway versus a six-lane freeway. At any given time, any of the eight manual loading lines can receive materials from any one of three different SMT lines, and boards can move onto any of three wave-solder areas and six component secondary-add areas.

DOCUMENTATION

Jumping from one process point to the next with a high mix of products is possible only if processes are standardized and applications remain consistent. Every process must be done the same way, every time, by every operator. Consequently, manufacturing documentation must be very detailed. Using APM, hundreds of different assemblies can be on the floor at the same time. In this model, each assembly is accompanied by documentation ranging in length from 30 to more than 100 pages, including flowcharts, accepted deviations, solder chemistries, a complete customer revision history, SMT data, autoinsertion and loading information, program names, label placement, bin tags, part numbers, wave-solder procedures, add-in components, hand-solder instructions, and inspection protocols. In addition, every document is written in an internal specification language implicitly understood by all team specialists. This standard documentation clearly states when IPC-610A Class III workmanship standards must be maintained and when device history records are needed for lot traceability.

Standardization also extends to equipment calibrations. Maintenance technicians calibrate and maintain all duplicate equipment to the same standards so that when the recipe for a particular board is called up, that board can go to any system with the same results. Consequently, all SMT lines operate consistently, regardless of the product being run, and all reflow ovens produce the same process characteristics, even if the SMT lines consist of different oven models from various manufacturers.

INFORMATION ON DEMAND

APM cannot succeed without a sophisticated information system for workflow management. The facility in the model developed a proprietary system, known as the assembly execution system (AES), that tracks the status of each job throughout the entire manufacturing process, from kit picking through packaging. Because all production lines are certified to produce Class III products, it is not necessary for the AES to send a work order through a uniquely configured or dedicated line.

APM is, by nature, a highly random scheme. The job of the AES is essentially to forecast the work load at a given process point in order to route each job to the next available station.

RULES FOR KIT PULLING

The immediate availability of components and other materials is essential for high-mix APM. High speed is dictated by two essential production rules. First, the size of a kit is determined by how long it takes to get through the manufacturing operation, from pulling the kit through packaging; no kit takes more than one 16-hour day (two 8-hour shifts) to go through any process. Second, no kit is accepted for manufacturing until complete.

To ensure that all kits are complete, unique parts for each job are handled by a planner/buyer, part of a three-person program management team assigned to each customer. Along with the team engineer, who provides technical support, and the program manager, who is ultimately responsible for managing the account, the planner/buyer responds to any material issues. Because the entire team is in constant communication with the customer, the planner/buyer can ensure that all kits are clean and ready by the start date. Two-day delivery on standard commodity parts is accomplished by means of a just-in-time (JIT)/bulletin-board system that provides suppliers with material requirements up to 52 weeks in advance.

TRAINED PERSONNEL

Just as the AES/manufacturing resource planning (MRP) information systems are the glue that holds APM together, employee teams keep the systems working. In the model system, every employee is assigned to a team of three to seven operators responsible for one function only. For example, a loading team works exclusively at loading circuit cards and is responsible for error-free loading procedures. The SMT team is responsible for line work load and quality. Hand-solder teams must be highly skilled in all aspects of their job.

With APM, the goal is to move product, not people. Consequently, if a team has time before the next project, members are not shuffled from process to process, but go to just-in-time training (JITT) to improve specialized skills. Available for any team member on as little as five minutes' notice, JITT trains loaders in component recognition, teaches adders different solder techniques and workmanship standards, and helps SMT teams learn machine theory and solder-paste compositions. All training is performed to IPC Class III standards.

A bonus program based on team quality and accuracy presents an incentive to work to maximum potential with minimum errors. In the model setup, 60% of a team's bonus is calculated on quality and 40% on reducing cycle time. In addition, a team can lose up to 10% of its quarterly bonus for transaction errors resulting from entering incorrect data into the AES. Consequently, teams stay focused on providing accurate data, which are essential to APM success.

QUALITY AND SPEED

In a lot size of 50 boards traveling through an APM facility, if one board has a problem, the entire lot stops to wait for it. The production line, along with its engineers, have a 16-hour window to repair the board and move the lot. If the supervisor or engineer determines that the board cannot be repaired, the work order proceeds as 49 boards and the customer is notified. Thus there are no partial shipments and no "bone piles."

High product quality is made possible by extremely accurate SMT lines. These expensive systems can handle 15,000 part placements per hour. Combined with other APM advantages, these systems offer a dramatic reduction in cycle time regardless of work order sizes. For example, before APM was instituted in the model facility, the average cycle time from kit pull to packaging was 21 days—standard for a high-mix operation.

In less than six months using the APM system, cycle time was reduced to an average of under five days—well below what many larger low-mix, high-speed manufacturers can achieve.

STRINGENT REQUIREMENTS

APM relies on several crucial factors for proper implementation, including world-class production equipment with at least a 25—35% excess capacity, consistent application of documented processes, and sophisticated information systems that make accurate data immediately available to all personnel as well as the medical customer. Facilities must be compliant with FDA's quality system regulation and meet the requirements set forth by IPC 610A Class III.

Using APM, a new assembly can be introduced into production every day without losing momentum. To assist customers with new product development, the model facility introduced a prototype service, providing 5- and 10-day turnaround on prototype boards. Customers can get rapid prototypes and valuable feedback to support design-for-manufacturability. With APM, they can also move their product through manufacturing qualification on a greatly reduced schedule, resulting in faster time to market.

APM enables electronic manufacturers to help medical OEMs in their competitive marketplace by providing the high-mix, high-speed manufacturing services they need to reduce new product development costs while improving quality and market response.

Ty Griffin is medical marketing manager for EFTC (Greeley, CO), a provider of electronic manufacturing services for high-mix OEM customers.

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