Avoiding Mistakes in SMT Manufacturing Via MOS


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Jason Spera, Aegis Software

Conversations surrounding quality management in electronics assembly often focus on data collection, repair and test management, and mining the results of these activities through reporting, dashboards, etc. Certainly these functions comprise important elements of a quality system. However, to actually improve quality, the factory must avoid mistakes that result in nonconformances, not simply report on them after they occur. To maximize yield and minimize waste, a total quality system should provide controls to eliminate as many mistakes as possible, as well as capture and analyze the few nonconformances that do arise. Both control and visibility are required. Without both ends of this quality equation, the only visibility the manufacturing enterprise might enjoy is a comprehensive view of how poorly a process has executed. This is certainly not the goal of any quality system. A holistic approach to both proactive and reactive quality can be achieved through manufacturing operations systems (MOS). Such solutions offer a means to increase yield and reduce waste, while gaining traceability to a greater scope of the factors affecting quality.

Opportunities for Error in Electronics ManufacturingMany daily events in a manufacturing enterprise, beginning in the process engineering lab or even program management, can lead to nonconformances downstream in the process. In the EMS scope, opportunities for errors exist along the flow from new product introduction (NPI) through process execution and even to the final packing and shipping of product. In high-mix environments, and when the issue of running multiple chemistries and RoHS is introduced, these opportunities for error increase significantly. This article explores common errors along the flow from receipt of design data through final products shipment.

When a product design is released to the factory, either from the PLM system or from a customer, the opportunity for mistakes emerges promptly. CAD and part list (BOM) data often contain well-hidden errors. These errors include CAD part mismatches to BOM content and intra-BOM problems such as quantity discrepancies to the list of reference designators. Other common errors involve AML and AVL version issues, or part master synchronization with ERP and the corporate or customer part numbering systems. Such issues are difficult for personnel to find manually, and the ramifications of their escape from the engineering office are significant. They propagate through all subsequent documentation, process designs, machine programs, and into the final product. Results include scrap, excessive rework, delivery delays and potentially damaged customer relationships. The risks continue when process engineers begin their data preparation. When visual aids for the factory operators and the machine programs for placement, AOI, AXI, dispensing, printers, etc, are created manually, opportunities exist for minor errors that lead to repeated manufacturing mistakes.

All of these errors occur before production begins. When the job hits the line, the risk continues. The first risk usually involves materials and process set ups. In an uncontrolled environment, operators easily choose the wrong paste chemistry, squeegee, stencil, or even spatula and unknowingly contaminate a product or build it improperly. Yet another risk includes operators inadequately certified to execute a process. Cart, feeder, and machine set ups are more obvious opportunities for set-up errors. A less obvious error involves the actual machine program loaded when a unit reaches the machine; an error leads to the production of many incorrect products. Setup risk continues through to hand stations where the wrong soldering equipment, torque wrenches, or even cleaning chemicals may be used if not controlled. The opportunities for operators to inadvertently cause rework through small errors in the set up or changeover between jobs are numerous along the process flow.

When the process begins, new risk factors appear. Assuming every route station is set up properly, and the machines are executing the right programs, and all operators are where they should be and properly certified, the risk shifts to trapping process mistakes in real time. The first mistake is usually revision control. Is the station presenting the operator the right documentation at the right station and revision for the product before the operator? Other risks involve route sequence enforcement, such as stopping a unit that has skipped a station or an entire process. Similarly, units with defects can accidentally escape a work cell and move ahead in the process without actually being reworked. Worse, units may escape final test or configuration areas into the shipment areas with known test failures. These units arrive at the customer nonfunctional, a particularly embarrassing situation for any manufacturer.

Even if one assumes that the afore-mentioned risks are not of concern, and execution will be perfect, consider the reality of ECNs and process deviations. A system is required to ensure that changes can be introduced rapidly and directly into an executing process without delay or error. This is perhaps the greatest risk in daily production in a high-mix world, and the greatest challenge to overcome.

Manufacturing Operations Systems to Control Mistakes and RiskUnfortunately, a modern electronics manufacturing factory is a complex engine that must be both fast and controlled without the luxury of any consistency in what it is producing or how it is to produce it. This leads to MOS at the manufacturing facility. When one considers the scope of even the limited selection of risks discussed in this article, a collection of point solutions to control this risk is not adequate. The effort to configure each point tool for every production job wastes excessive time and overhead, and in itself introduces risk. Furthermore, a total solution requires synergy among its elements. Awareness of the design data is critical to virtually every other control point in the process. Awareness of the route, version control, machine data streams, and process materials is critical throughout the process; point solutions create redundant configurations and data sets, and compromise the control capabilities of the solution.

The MOS concept is to connect the product design data to process planning and launch processes and then use results to fully control every aspect of the executing process reducing or eliminating risk. MOS delivers both halves of the quality equation of proactively preventing errors and reporting upon quality results in real-time and historically. To achieve this, the system must span the entire factory floor and office operations. An MOS system gives manufacturers a single solution for importing design CAD and BOM data from their customers or R&D department and helps create an entire process flow including visual documentation, machine programs, and materials and certification requirements for each station. The risks identified in these preparation processes are eliminated up-front through automation, the use of one data set per product, and through automated workflows.

MOS systems use a golden definition of a perfectly executed and documented process to run the factory floor in real time, but enable controlled engineering change management as circumstances demand. More importantly, it enforces the process. Upon the scan of a product at any conveyor or workstation, the process plan is used to launch the right revision of the right visual aid, present the guided and enforced materials verification environment, confirm appropriate operator presence and machine programs, and redirect the product to another line if necessary. The operators are prevented from making mistakes because the system either locks conveyors or, in non-conveyorized situations, it alarms via dashboards, informs managers, and halts scanning of that unit at any forward station. Multiple layers of protection prevent cascading errors that would otherwise propagate and worsen downstream.

While controlling production, the system gathers information from operators and machines on performance and quality, and every process and product event. Materials consumed, quality indictments, machine events, or product movement events are mapped to the design-awareness and BOM intelligence created in the system's planning engine. Each step in the process adds to the data set mapped to a unit and increases the systems' ability to control risk and stop errors from propagating.

As a unit moves through the process, indictments and test errors drive automatic reroutes and notifications. Units with nonconformances cannot proceed unless engineers intentionally allow it. As units enter upper-level assembly, they add intelligence to the product. The system can enforce the process through a nested awareness of all subassemblies. At the very end of the process, such systems conduct a final total check that all risk was eliminated before packaging into a box or pallet.

Upon product completion, a total traceability dataset accompanies it, with product, process, and materials content. A benefit of MOS technology is that while the goal of the system is control and quality a default result of these benefits is visibility in real-time dashboards, reports, and traceability.

ConclusionManufacturers are increasingly seeking holistic solutions to prevent errors in their process. The proliferation of point systems is being reversed by system consolidation. The MOS model is more cost effective and capable of actually reducing errors and improving product quality. As an added benefit, the manufacturer exploiting a MOS system obtains traceability and visibility as result of implementing what is primarily a quality improvement and risk control system.

Jason Spera, CEO, Aegis Software, may be contacted at NEED INFO.

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