Michael Ford


Designers, take note: A good DfM process can require just a few mouse clicks.

In electronics assembly manufacturing the principles of Lean are most often thought of in context with the optimization of specific processes on the shop-floor. Lean thinking can be applied far more widely, however, extending to the very earliest part of the manufacturing operation, an area responsible for a great deal of fixed product-related waste and costs that assembly manufacturing ends up having to live with during a product cycle. The application of Lean thinking to new product introduction can turn a multi-process nightmare into a slick Lean flow, where costly mistakes and surprises are eliminated, and the need for almost all the work and lead-time are removed.

A reasonable expectation from the assembly engineering team is that each PCB layout should be designed so that the product can be manufactured without issues, risk or compromise. The reality is the potential for a multitude of issues, however, because the designer cannot be expected to know every detail about assembly engineering, including the needs, capabilities, and requirements of the various processes. Traditionally, at best, the layout engineer is given summarized guidelines to follow. Any issues for assembly left unresolved at this point represent a potential waste of the designer’s time because there may be comebacks from fabrication or assembly engineering teams, with the need for additional work to create layout revision(s) necessary to resolve potential manufacturing problems.

The solution for the designer is to have an automated mechanism whereby the layout of the PCB can be checked against a defined and maintained set of rules that represent specific manufacturing requirements. This design for manufacturing (DfM) process can qualify designs ready for production with just a few mouse clicks. DfM tools perform thousands of checks across all aspects of the layout. The vast majority of needed re-spins caused by layout issues can be resolved using DfM software. The designer gains by spending less time answering questions and complaints about the design. In most cases, the effort of many layout re-spins is also saved, permitting the product to move much faster into the remainder of the production process and allowing the designer to focus on the next layout design.

Removal of waste from the NPI process has only just begun. Even at a simplistic level, the effect of comprehensive DfM will remove significant waste from the manufacturing process, repeated for every PCB produced. Without adequate DfM, compromises and countermeasures spanning the course of production have to be made: for example, limitations in the choice of setup and optimization of SMT equipment, and compromised testability of the PCB caused by limited or unreliable accessibility and solderability issues. Significant quality hotspots on the product can be completely avoided, reducing flow disruption, repair times, and material spoilage and enhancing overall quality.

From the perspective of the assembly process engineers, yet more waste can be removed. Receiving a complete and fully qualified design for manufacturing in a single package would eliminate a great deal of time as they process the data to define and set up all the various assembly manufacturing processes, including SMT programming. The traditional way in which design data are issued to assembly causes the engineering team to spend significant time reconstructing the information from the many different formats in which different aspects of the product model data are defined. This is often comprised of simple lists and drawings, information not specific enough to understand the assembly requirements without significant work. The reason this is commonly done in such a poor way is mainly historical, carrying significant operational momentum.

However, via DfM tools and support by professional design layout packages, the fully qualified product model can be contained in a detailed and comprehensive form within a single file. Using this file then removes the need for data reconstruction, which reduces needless workload and the lead-time for the product to hit the market, as well as eliminating the wide scope of opportunity for mistakes to be made during the process.

Concern has been raised by some that such files provide a potential source of leakage of intellectual property about designs, especially where manufacturing is performed in a different country or by a different company. The reality is that the assembler will inevitably see the physical PCBs, the materials used, and will know all about the mapping of interconnections to produce the PCB and complete the required testing and repairs. The IP of value is mainly related to the design intent, specification and standard, which does not need to be shared with manufacturing and is not a part of the transferred data package. Because of the nature of manufacturing, there is ultimately the need to have trust and/or a good non-disclosure agreement between the design and manufacturing entities. The Lean solution to the data transfer problem is only to provide exactly what is needed to a full level of detail without ambiguity, which only a standard, managed and complete data format can provide.

Benefits of the Lean approach to NPI, including the use of intelligent data transfer, extend further into the factory operation. The complete design layout data include shape information of the materials that the designer has selected. The purchasing team at the local factory will also have received this information because they are responsible for ordering the required materials for production. However, the purchasing team is continuously challenged to source reliable quality materials at the lowest possible prices, which may differ from the ones specified, so long as they continue to meet the design specification. It can be difficult for the purchasing team, even with support from the local assembly engineering team, to assess whether alternative materials found can potentially be used without compromise to the product quality or assembly cost. Electrical specification, performance and tolerances are relatively simple to check, whereas subtle but critical differences in the parts’ shapes and connection specifications are much more difficult to assess. Poor choices easily can be made that can introduce errors and unreliability on SMT placement machines related to variations in the physical packaging of the materials.

The DfM tools as used during the design layout process can also be a key solution for the factory, permitting any combination of proposed alternative materials to be assessed for manufacturability. This is easy for the assembly engineers in the factory to perform, as they have received the single-file qualified product model from design, giving them the exact same environment for the DfM analysis with modified materials. Using DfM tools in design, the layout can be altered to accommodate the material choices, whereas in the case of assembly, the material selection can be altered to accommodate the fixed physical design layout.
The Lean element of this activity comes from the upfront qualification of locally sourced materials, avoiding issues that would otherwise need countermeasures once the alternative materials ordered had physically arrived at the factory and were in use. This effectively ensures their commitment for use, bringing waste related to quality, productivity, rework and on-time delivery.

The next phase of the Lean flow in the factory may come as a surprise. Rather than traditionally going straight to a tool where all the individual manufacturing processes such as SMT are programmed, the Lean next step is to consider the production plan. How the exchange in the order of these two engineering processes can be more Lean will be explained in our next installment.

Michael Ford is marketing development manager, Mentor Graphics (mentor.com); michael_ford@mentor.com. His column runs bimonthly.

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