Optimizing Legacy Products
Respinning a board to eliminate PTH parts can pay off in production.
When an electronics manufacturing services (EMS) provider is involved in developing a new product, it is easy to provide design for excellence (DfX) recommendations that align with Lean manufacturing philosophy.
Addressing manufacturability or testability issues associated with legacy products is much more challenging, however. The reasons printed circuit board layout or product design choices may not be optimal are many. Design cycles have been compressed and design resources have been cut at many OEMs. When layout or product development is outsourced to a third-party design team without manufacturing familiarity, the result may be a PCB assembly (PCBA) that meets form, fit, function and cost recommendations, but ignores industry standard design rules, sole sources much of the bill of materials (BoM) or requires unnecessary processing.
SigmaTron’s new product introduction (NPI) process evaluates these issues as new projects are onboarded through a combination of an engineering team review and automated checks through a third-party design tool. When improvement opportunities are identified, the team can provide redesign or PCB layout services to correct the issues.
How does this align with Lean manufacturing philosophy? One recent through-hole to SMT conversion is a good illustration. A legacy, mixed-technology PCBA was experiencing material cost and availability issues because it had many through-hole parts that were either going end-of-life (EOL) or sustaining manufacturer price hikes. The OEM was open to converting the bulk of the through-hole parts to SMT. Connectors and a sensor needed to remain unchanged for the PCBA to function within its larger product and remain compatible with the existing test fixture, but the bulk of the layout could be optimized for manufacturability.
The design for manufacturability (DfM) analysis showed several issues:
- Due to tight clearances, through-hole components required manual placement, increasing assembly costs and creating defect opportunities
- SMT components had been placed on both sides of the PCBA with tight edge and component clearances, creating defect opportunities and requiring selective solder pallets in wave solder
- Top- and bottom-side components required two passes through the SMT line to place all parts, increasing the number of thermal cycles the PCBAs were exposed to.
The PCBA was redesigned to replace the problematic through-hole parts with SMT packages. The new layout placed all SMT parts on the top side, eliminating the need for a bottom-side placement pass and the concomitant thermal cycle in reflow. It also enabled automated placement of the bulk of the components, eliminating much of the variation present in manual processes. This improved yields significantly. The single-sided design also eliminated the need for selective solder pallets in wave soldering, which lowered tooling costs and eliminated the pallet load and unload steps. Additionally, the SMT part replacements were cheaper and more widely available than their through-hole counterparts.
With product sizes shrinking, it is not uncommon to see edge clearance and component spacing design rules violated, particularly when a third-part design team performs the layout without equipment constraint information set up in their design tools. As shown in the example, that can impact the ability to automate production processes and create defect opportunities.
Companies stick with legacy designs that are not optimized for Lean environments for many reasons. Insufficient volume or regulatory issues may not justify the redesign cost. The design may have been appropriate at the originally specified volumes, and no analysis over whether the volumes have grown to justify redesign to better automate production has taken place. Product managers may not understand design issues’ cost or quality impact on the PCBAs they manage. As this example illustrates, however, assembly costs and defect drivers in designs that don’t incorporate Lean principles to enhance manufacturability can be significant.
The adage, “What costs a dollar in design, costs $10 in production and $100 in the field,” illustrates the cost escalation driven by the failure to correct design issues. Considering the cost and quality benefits of a PCBA optimized for Lean manufacturing can be valuable in assessing whether the redesign of a legacy product is justified. When products are outsourced, collaborating with an EMS provider’s engineering team is a good way to achieve the lowest total cost of ownership.
is a senior design engineer with SigmaTron International (sigmatronintl.com); mark.bellot@sigmatronintl.com.
