In an era where delays cannot be tolerated, help has to come from the “interface” between layout design and manufacturing.

The expectation for digital innovation in electronics manufacturing is growing significantly. Examples of real-world IoT technology in action – for example, at the Fraunhofer “Future Packaging” line at SMT Nuremberg last month – demonstrate significant momentum toward mass adoption. However, smart factory innovations have a critical dependency on PCB layout design. Issues related to PCB layout have always been the source of unexpected costs and delays, not only during manufacturing and assembly, but throughout the entire product market lifecycle. Many companies have ended up “just living with” multiple, repeated PCB fabrication and assembly issues for years, regarding it as a given. If smart factories are to work, however, this attitude has to change.

The Distribution Chain Evolution

Executive sales team and product managers responsible for marketing and selling electronic products were significantly and adversely affected by decisions to move manufacturing overseas. Their single aim is to plan, schedule and execute new products in the market to maximize profit for the business. Decisions involved in creating new products, whether completely new, variants or upgrades, are based solely on perceived sales potential. Some of the original sophisticated business intelligence tools were created to identify market opportunities for products – that is, to analyze sales trends to discover what would likely be most successful. As electronic technology moves forward rapidly and many companies are competing to do the same thing at the same time, predicting these trends is difficult. Once an idea looks good, converting it into a delivered product needs to be done as quickly and efficiently as possible. A few weeks’ delay could mean significant loss of sales opportunity.

When manufacturing moved to remote locations, the various costs and risks associated with the distribution chain increased. Holding stock between the factory (for example, in China), and the sales outlets (for example, in the US), can be expensive. Apart from the cost of mass logistics, expense includes the investment cost of all the products in transit, especially if by sea, including every possible point-of-sale destination for each specific product and variant globally. A slight miscalculation of expected demand can result in a huge buildup of unsold inventory throughout the distribution chain. Significant quantities of stock in so many locations for such a long time add the inevitable risk of price depreciation, while goods are in transit or in storage, as market forces change over time.

For many higher technology products recently, the combined cost of the distribution chain represents the most significant part of the costs within the product lifecycle. Periods of ramp-up at the time of the product introduction and management at the end-of-life of the product become more significant as the more profitable steady-state period of sales declines. The proportion of product cost from manufacturing has become far less significant. Apple recently claimed the actual manufacturing cost for certain products, excluding materials, is less than 1% of the retail price. In the alternate scenario where the product is produced close to the market, say in the same country or region, the distribution-chain costs are much lower, as seen by many companies who already direct-ship products to customers.

The business case is based on cost saving in the distribution chain, rather than compensating for any increased costs of local manufacturing using a modern-day
computerized and automated Smart Industry 4.0 facility. However, with the much shorter distribution chain, the variation in delivery demand day to day from customers affects the factory directly, rather than being successively buffered throughout the various stock locations. This means the factory has to be highly flexible, appearing to “make to order,” while retaining high levels of productivity that would be associated with mass production, to be productive in line with business-plan requirements.

This is the essence of Industry 4.0. Smart IoT-connected factories are a key requirement in this environment. What is often neglected is that, as part of this requirement, products need to be able to be assigned or reassigned to any available production configuration on short notice, executed with the highest expectation of quality and minimal startup delay.

Figure 1. The smart assembly factory can choose the best configuration of production line for any product at any time, without overhead cost tied to changes.

Effects of PCB Layout Design on Manufacturing

The time available for the preparation of new products in the market is extremely limited. This includes the whole of the design process, a large part of which is centered around the layout of electronic components on PCBs. By far, the greatest pressure on designers is to complete the design “on time” to not delay the market introduction schedule of the product. The product is expected to work reliably, of course.

Design-layout software tools provide the designer with significant support for automated, intelligent, and even multi-user layout, which follows automated design rule checking (DRC). DRC rules are generic in nature, but can be adjusted to suit the nature of the product design, usually a standard set for each company. The layout designer can check all parts of the final PCB layout design for adherence against these rules. Unfortunately, however, generic DRC engines and rule sets are insufficient to guarantee trouble-free PCB fabrication and subsequent PCB assembly. This is because specific production requirements and limitations have not been taken into account, as well as any potential physical variation in electronic components selected in the assembly bill of materials (BoM).

The effect of issues that have fallen through DRC have been felt for many years: unexpectedly low first-pass yields, high defect rates, even cases in assembly where parts just do not fit, causing obstructions, etc.  The same problems can then repeat over and over again as production is stopped, started or the product is moved between line configurations. These obvious failures are actually the least of the problem because they can be quickly seen and countermeasures taken, albeit with an increase in the cost of manufacturing and a delay in the startup time for the processes.

The real consequence of the problem starts with those cases where issues are seen only a portion of the time. They come and go, or they just seem to happen at random. They are design-related issues that are “on the limit” of acceptable or not. These issues take a lot more effort and time to notice, diagnose, and resolve during the course of the manufacturing process, causing disruption. Issues may not appear until the product has left the factory, found as reliability issues in the market, the infamous and dreaded “intermittent fault.”

A perfectly adequate PCB layout by design-rule standards affects the whole of the product cycle, through distribution and to the customer. When such issues go full circle, profitability is affected rapidly because customer experiences on social media can destroy product confidence. Will this prompt the product managers and sales executives to assign more time for the engineering of the next new product? No, because for them it continues to be a race to adopt technologies
and innovation ahead of the competition, which is the primary driving factor.

The result is a difference in the view between product managers and managers responsible for manufacturing, both of whom want, or even need, perfect quality.
For one, however, it is a different priority than the other. Smart factories enable the business of manufacturing to be more flexible and more varied. The reduced distribution chain buffer has created a higher mix of products and work orders, which increases the number of instances where production startups and changes are made. This results in reduced reliability and on-time delivery of products, in an environment where such delays cannot be tolerated. Help has to come from the “interface” between layout design and manufacturing.

State-of-the-Art Design-for- … Technologies

Many processes are involved in creating a physical bare PCB and, from there, creating the full PCB assembly. The bare PCB is built like a lasagna, with different substrates layered on top of each other, each of which is then subject to tortuous physical processes to create or carve out the circuit pattern and to make interconnections between layers, all of which are then pressed and bonded tightly together. Although the technology of each of these stages has been greatly refined over many years, introducing greater precision, fundamental variations still exist. They become more significant as designers take advantage of the ability to make smaller circuits and higher component density.

The common effects of these potential variations are well known to experts in fabrication engineering. In theory, they could tell the designer how to avoid problems that could compromise the integrity of the product. Fabrication experts and layout designers live in different “worlds” of engineering; thus, direct interaction is expensive and unlikely to be effective. However, the know-how from fabrication can be captured in an extensive rule set, which is then applied using any DfX engine to the layout design, checking millions if not billions of potential issues. The designer needs only to call the DfX function before finalizing the design. With recent advances in PCB technology – flex and rigid-flex, for example – new and additional opportunities for issues are created, which in turn have to be part of the DfX analysis.

Creating and analyzing the design of a single-instance circuit layout is quite a challenge, but that is not the end of the story. The basic laminate layers of the PCB come in large, standard sizes. To reduce the waste of the laminate material, many of the same circuit, or indeed different, related circuits, are combined to be made together in a single set of laminates. This panel design stage creates additional issues, where the individual circuits could interfere with each other. Because PCBs are no longer as square as they used to be, trying to fit as many different intricate shapes of PCBs into a panel has become a significant optimization task.
The PCBs can be effectively and reliably cut into assembly panels that fit into the designated assembly machines, and then further cut into individual circuit boards. Potential issues with stress and damage during cut-out need to be avoided.

For assembly analysis, the opportunities for issues keep on coming. Components to be used in actual production will likely vary from the components that were considered in the design process. Even small changes in the size or shape of component packages, including leads, pins and contacts, can cripple the quality of the end product. Purchasing departments in assembly factories are motivated to choose materials that are the most cost-effective, while satisfying the engineering and quality requirements of the product, and these parts are usually purchased locally.

Alternate choices for each component, packed closely together on a PCB, can result in issues related to physical spacing, the ability to place components reliably and efficiently, and access to test them. For electrical contacts of the components to the PCB, the shape and size of the leads, pins, or contacts can be critical for the solderability of the joints. The state-of-the-art DfX engine creates composite component shapes that will find issues should any combination of materials be used. Avoiding issues highlighted by DfX means the product can then be made reliably anywhere, with any of the approved materials, while avoiding many reliability and quality issues in the end product that would otherwise occur.

‘Close to Perfect’

With the extensive digital analysis that DfX provides, a PCB layout can be completed by the designer by just taking a few extra minutes to run DfX analysis and implement the recommended adjustments to the layout. This small addition to the flow results in reducing the instances of these issues by an order of magnitude. The realization of value from this is felt throughout the whole of the manufacturing and market cycle of the product. PCB fabrication processes can be done confidently with few minor issues to resolve, resulting in a much faster turnaround time for the creation of volume production-ready PCBs. In assembly, the BoM cost can be reduced because lower-cost alternate materials have been checked for physical compatibility in the specific design layout. PCB assembly also can start on any line configuration with a minimum of online issues to resolve, creating shorter startup times.

Starting and stopping smaller production lots and moving to different line configurations with different material combinations now no longer prevents flexibility in the factory, nor causes a significant reduction of productivity. The testing process is more effective, with increased first-pass yield. Failures are genuine manufacturing process defects that can be effectively and immediately managed by industrial engineers. In the market, the result of all of these changes manifested in manufacturing is a step-change increase in the reliability and dependability of products, as well as an accelerated time to market.

Without state-of-the-art DfX, no matter how much effort is put into PCB fabrication and assembly, how close products can get to being “perfect” is limited in reliability and dependability at all stages of the manufacturing processes. Time spent to resolve issues delays the product launch and denies flexibility for the assembly factory. The risk of creating a smart factory is high, whether on-shored, re-shored or even remote, when these product design-based issues have not been addressed. Once the design layout is finalized, the only thing that can be done is to live with the issues.

On the other hand, with DfX, the smart factory has no flexibility issue related to design layout and has only rare unexpected delays for getting new products into the market. The smart assembly factory can choose the best configuration of production line for any product at any time, without the significant cost overhead of change. This is essential if the factory is to meet a daily variable demand for a greater number of products and variants in line with customer demand.

Michael Ford is marketing development manager, Mentor (mentor.com); michael_ford@mentor.com.