Ten steps for achieving good design for excellence.

Lean manufacturing emphasizes minimizing variation and eliminating waste and inefficiency. Not surprisingly, a Lean approach to design does the same thing. Much of the focus on a Lean design approach is based in old school common sense.

Know what you are doing. The first step in a Lean design process is to develop an optimized agreement on deliverables. This product specification drives the design process, so the development discussions should address customer expectations for form, fit and function; any requirements driven by the end-market environment; cost constraints; and field-life expectations.  

Involve the entire team. Once the product specification is agreed upon, the development process begins. As in Lean manufacturing, throughput is important. A rapid first iteration helps ensure the process will meet its deadlines. A physical sample of the first iteration is the best way to assist the team involved in the design process in fully understanding the design. The peer review process in the first iteration should involve all engineering disciplines, including software development, PCB layout, mechanical, hardware, test engineering and the production team. While not all individuals may have direct involvement in the design at that point, decisions made in that review will have implications that will impact actions further downstream in the commercialization process. Representatives from all disciplines should be involved in that process, as this helps ensure early identification of challenges and tradeoffs. This reduces the number of design spins and the associated non-value-added work that comes with engineering change orders (ECOs) in new product introduction (NPI).

Design and manufacturing should be joined at the hip. Design for manufacturability and test (DfM/DfT) is far more challenging late in the design process. Similarly, field repair or programming update considerations need to be factored into the design. Establishing a collaborative relationship among design, manufacturing and test personnel helps ensure these considerations are carefully monitored throughout the design process. This helps minimize defects, optimizes the design for automation to reduce variation, and ensures test coverage goals are achieved. This collaboration can also help with procurement choices, as the manufacturing team will have a better view into supplier performance, component reliability and availability. Finally, this type of early collaboration
also ensures products that go through agency reviews have proposed changes designed in before third-party testing and verification begins. This saves significant cost and time during the design process, and ensures changes are made. Late-stage DfM recommendations are often ignored when they would necessitate the repeat of a costly product approval cycle.

Maintain a Lean DFx focus. Some of the most common areas in a good Lean DFx focus include:
Ensure the PCB layout tool library includes a DfM layer with the target facility’s equipment limitations built in to identify potential issues as the printed circuit board is laid out.
Minimize process thermal cycles and consider the impact of layout and component types during thermal cycles.

• Ensure the layout minimizes system-generated noise and sensitivity to outside noise.
• Review clearances both in terms of component clearance relative to the rest of the unit and edge clearances on the PCB assembly relative to automated handling.
• Evaluate potting and coating options against the shock and vibration normally found in the product’s application.
• Poke yoke the assembly process to ensure product can only be assembled one way.
• Standardize parts wherever possible.
• Avoid over-specification of or over-processing parts.
• Optimize panelization to minimize waste of substrate material and conform to the target facility’s preferred panel dimensions.
• Use a combination of software simulation tools and physical samples to test all assumptions related to design and processing efficiency.

Common mistakes this approach eliminates. The PCBA design is often the most complex element of the design when the production implications are considered. An automated DfM analysis within the design tool catches these common design issues:

• Inverted part library footprints.
• Collisions of leaded component insertion equipment with nearby SMT devices.
• Device interference in the z-axis with other parts or features in the assembly.
• Wave solder pallet interference issues.
• Solder shadowing issues related to component position.
• Conformal coating “keep out” area masking problems.
• Accuracy of the original bill-of-materials (BoM) translating through the schematic and into the layout.

Unaddressed, these issues would permeate every aspect of NPI from component procurement to PCB fabrication through machine programming and several processes. Correcting them in production would translate to higher scrap levels and missed deadlines.

Today, design teams have access to better, more automated design tools than ever. Fully accessing the Lean design potential of these tools requires an old school approach in terms of a process that defines the product specification, drives team collaboration, ensures design tools are programmed with appropriate design guidelines and constraints, and stages review points strategically throughout the design process. This approach minimizes design iterations, surprise ECOs and defect opportunities, while helping cut time and cost out of the design process.

Jerry Johnson is general manager, appliance & design at SigmaTron International (sigmatronintl.com); jerry.johnson@sigmatronintl.com. 

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