Medical device manufacturers are facing the challenges of cutting costs without the flexibility of significant redesign efforts. That is, by the time a medical product is outsourced, it has completed its FDA approval cycle, making even simple design for manufacturability or testability (DFM/DFT) changes difficult. The incorporation of lean manufacturing principles as practiced by Epic Technologies, a contract manufacturer of EMS equipment, is an effective means for meeting these challenges.

Analyzing the design

The contractor analyzes each customer data package during the project-launch phase using Advanced Product Quality Planning (APQP) techniques. While APQP was developed by the automotive industry, its basic philosophy makes sense for any lean product launch process. Key points include:

  • Development of customer required processes through dedication of internal Customer Focus Teams (CFT)

  • Utilization of pre-build DFx analysis for manufacturability and testability

  • Reliability laboratory analysis during new product process validation stages

  • Focused product launch process with feedback, assessment, and corrective action mechanisms to ensure product meets customer requirements

The first step in this process is the design review summary. This report lists the recommendations of the DFM evaluation and assigns a point score to each based on level of urgency. That is:

  • If a product has a critical unresolved issue, it receives 5 points, and the product will not be built. This is rare.

  • If there are major design issues, but the product can be built, it receives 4 points, and by the customer's directive is produced.

  • If there are issues that probably should be corrected, though not really major, it receives 3 points. Product can be built.

  • For minor design issues, 2 points are assigned.

  • For design features that would be nice to have, though not critical, 1 point is assigned.

This ranking system helps focus DFM and DFT recommendations in a cost-benefit framework from the start, and it enables the prioritization of discussions on the most critical recommendations. The foundation for the company's internal DFM and DFT guidelines are based on industry-accepted guidelines based on those published by IPC (global trade association for the electronics interconnect industry) and enhanced through production experience and validations. These guidelines are shared with customer design teams early in the process to stimulate open communication.

Key cost drivers

To eliminate non-value added activities as part of its lean initiative, Epic practices the following:

  • Minimize number of process steps and standardize processes to minimize changeover time.

  • Use 100% SMT or 100% through-hole assemblies as they are the most efficient to process.

  • Avoid placing mixed technology on both sides of the board as this can drive extra automated and manual processing time, as well as increase handling or thermal shock related defects.

  • Standardize panelization for reduced PCB cost and minimized set-up and changeover time.

  • Avoid design elements that require manual processing as they increase labor costs and increase the potential for defects.

  • Pay attention to layout details that can drive rework costs.

  • Eliminate improperly sized through-hole pads and holes that can lead to unacceptable solder joints.

  • Avoid poorly placed fiducials as they impact the accuracy of SMT component layout.

  • Pay attention to orientation of bottom-side SMT components as incorrect orientation or incorrect SMT land patterns can cause opens, shorts, and other defects.

  • Consider labor or special processing costs in component specification strategy.

  • Specify stainless steel component fastening hardware, which can be exposed on the bottom side of a PCBA. Conversely, zinc-plated hardware attracts solder and requires masking.

  • Use standardized test platforms to achieve maximum efficiency.

  • Provide automated in-circuit test (ICT), which offers a more robust and lower cost test than a custom functional tester.

  • Design products to IPC guidelines and have good access points.

Integrating a reliability lab team

Epic's Reliability Lab is co-managed by quality and engineering to ensure that there is agreement on support provided. A process engineer, trained in reliability lab processes, runs the lab. Data is collected in production per lab request, appropriate analysis is performed in the lab, reports are generated, appropriate stakeholder reviews are performed and corrective actions are implemented. The lab focuses on three key areas:

  • New process definition and validation
  • Project launch
  • Quality issue resolution.

The Quality issue resolution element is particularly relevant because defects often occur as the result of supplier or customer issues rather than in the contractor's process. Performance issues that a design team wouldn't have seen two or three years ago are becoming commonplace as product becomes smaller and more mobile. The need to understand defect risks driven by final assembly processes or end market applications has become more critical.

For example, as boards become more densely populated, ball grid arrays (BGAs) are in wide use. If the PCBA is flexed too much in the box-build assembly process, stress fractures may occur that ultimately drive hard-to-identify field failures. The faster these issues are identified and corrected, the lower the cost impact to launch product.

The reliability lab originally addressed these issues as defects occurred. As PCBA complexity increased, the group started offering a package of services to better validate process robustness at both their facility and their customers' operations as part of the new product introduction process. Key areas of analysis include:

  • Strain gauge analysis throughout the entire process.

  • Corrective action may include tooling hole changes, reduction in fastener torque or a change in mounting.

  • Drop testing that includes measurement of strain in the BGA as part of the drop.

  • Corrective action may include BGA underfill, epoxy flux or a thicker PCB substrate specification.

  • Placing mixed technology on both sides of the board can drive extra automated and manual processing time, as well as increase handling or thermal shock related defects.

  • Die penetration testing to identify stress fractures.

  • The board is encapsulated with a high viscosity die, cured and destructively tested to determine if the die penetrated solder joint locations.

  • Corrective action focuses on eliminating the root causes of areas of repetitive stress fracture.

Medical product design teams will continue to face greater challenges as PCBA complexity increases and product size decreases. How design teams respond is critical. Early attention to potential manufacturing-cost reductions combined with a robust production validation processes that improve time to market will separate leading lean manufacturers from all the rest.

Those that continue to succeed in this increasingly competitive market will have well-founded strategies and plans in place, and possibly a reputable manufacturing-services provider.