Why common metrics fail to root out the causes, and actually add cost in the process.
Many companies adopt a reactive approach to measuring the cost of (poor) quality that focuses on defects and nonconformities. Most companies measure scrap, rework and customer returns, and often “fix” the problem through increased inspection or process adjustments. However, those fixes often fail to eliminate the root cause of the problem.
We try to take a more proactive approach by educating customers on ways to reduce the cost of poor quality through upfront planning. This month, we look at the top five areas where a proactive approach saves money and capitalizes on the efficiencies inherent in a Lean manufacturing philosophy.
1. Failure to adopt DfM recommendations. Lean manufacturing is most efficient when consistent processes are in place. Comprehensive DfM guidelines are part of ensuring repeatable, consistent processes. Optimizing designs for Lean manufacturing requires designers to balance goals for functionality, material cost and long-term product enhancement flexibility against throughput cost and logistics efficiency.
Poor pad geometry and component layout location contribute most to poor quality. In addition to increasing the potential defects, poorly designed PCBs add processing cost.
For example, improperly sized through-hole pads and holes will result in unacceptable solder joints, which drive added inspection and touchup. Lack of fiducials, improperly placed fiducials, or fiducials in the wrong shape or size affect the accuracy of SMT component placement.
Incorrect orientation of bottom-side SMT components can increase the frequency of opens and shorts, resulting in a reduction of quality and increased inspection and touchup. Incorrect SMT land patterns can cause opens, shorts, tombstoning, etc., resulting in a reduction in quality and added inspection.
2. Design that drives manual processing. Hand insertion vs. automatic placement triples the labor cost. Hand soldering vs. wave or reflow soldering results in triple the cost of automated soldering multiplied by the number of leads being hand soldered.
3. Component selection. Component sourcing decisions can impact quality, process efficiency, schedule flexibility and product delivery. Consider materials compatibility, thermal characteristics and the component’s ability to anticipate heat cycles, availability and supplier quality track record.
Sole sourcing components adds additional complexity and potential cost, since it limits options in the event of quality or availability issues. When a Lean manufacturing process is involved, another consideration is whether the component supplier will support Lean supply chain principles.
4. Design for test and testability. Lean test strategies often use standardized test platforms. Efficient in-circuit test requires a PCB designed to industry standards and with good access points. And, a robust test process can detect both workmanship and non-process-related defects. According to an Agilent study, analysis of manufacturing defect root causes suggests 10-15% of defects are actually attributable to nonfunctioning parts or defective materials, rather than being assembly process related. EPIC has seen similar statistics in its internal defects analysis.
Test point access also can be a significant cost driver. If a design doesn’t have test point access sufficient to permit automated ICT, AOI or x-ray inspection or flying probe test are higher-cost alternatives. Those tools have longer test times, are less effective in testing the product, and require greater operator interface time. Custom functional test systems alone may not provide as robust a test process and typically increase test time and overall test cost.
Functional test is another area. In many cases, customers consign less-than-optimal functional testers. Inefficiencies inherent in a poorly designed functional tester are only part of the potential cost driver. Maintaining multiple unique customer-supplied testers carries a cost. When possible, use a standardized proprietary functional test platform. When customers insist on using a poorly designed functional tester, provide a report on risks and added cost.
Stress and strain are also potential areas of concern. Design an assembly process that minimizes the potential for overstressing PCBs and a robust testing process to catch issues that may arise in this area.
5. Test correlation. With typical product cost models, it is not realistic to say that zero defects are consistently attainable. Achieving near “zero” levels attainable in a robust process requires detailed upfront planning to ensure all variables and controls are well-defined, implemented and monitored.
Test correlation between a contractor and its customers’ testing can be a challenge. The amount of non-value-added activities surrounding differences in test coverage from contractor to customer is huge when this issue is not addressed proactively. Although full test correlation is not always attainable because customers may be running tests they choose not to outsource, based on time considerations such as burn-in, all other elements of test correlation should be considered.
The key to driving down cost and eliminating costs of poor quality is all based on one thing: the contractor’s and customer’s willingness to truly work together and plan for success. The more robust the front-end planning, the more robust the process and overall product quality.