Greater traceability and complex builds means more staff. Or does it?

OEMs increasingly want to see greater levels of value-added support from their EMS providers, regardless of size. This is particularly true of highly regulated industries such as medical, automotive, avionics, homeland security and defense where field failure analysis activities may require information related to assembly process parameters. Furthermore, the transition to RoHS-compliant manufacturing is driving a need for better process traceability to support OEM studies of the impact of new processes on long-term product reliability.

For the regional EMS provider, this presents an interesting challenge. How can technologically complex customer requirements be met while maintaining an overhead structure commensurate with a smaller business footprint? For Clover Electronics, the answer has been to develop a strategy that uses a combination of factory automation and strategic supplier alliances to address customer requirements without significantly adding to overhead cost.

The fact that most OEMs have fully embraced the idea that all their EMS providers should be full partners in manufacturing is actually a positive development that enables all levels of EMS firms to increase the percentage of value-add contributed to a project and contribute to improved product manufacturability and quality. Also, greater codependency drives longer-term relationships, which can be cost-effective for both parties. Meeting these customer needs for competitive cost, high quality and excellent traceability requires both technological expertise and a business strategy that focuses on reducing hidden costs and leveraging outside resources.

The Technology Strategy

At Clover Electronics, the technology strategy needed to address three areas:

• Minimize the need for unique engineering overhead requirements.
  
  
• Meet customer requirements for specific services such as detailed traceability and quality reporting.
  
  
• Rapidly address any manufacturing issues that arose on the floor.

As mentioned, regional EMS providers must offer a full range of service and expertise without creating excessive overhead expense. At regional revenue levels, it can be cost-prohibitive to have a full-time process engineering staff capable of providing all the answers in paste deposition or thermal profiling that may be required by that company’s 30 or more customers.

One way to address this issue is to supplement internal staff with strategic alliances that fill the gaps. Second, automating key points in process monitoring permits fast development of robust processes and makes it easy for technicians and production operators to handle a portion of what has traditionally been an engineering workload.

For example, in this EMS provider’s SMT production area, solder paste deposition is monitored using a DEK Hawkeye 2-D in-process vision system followed by an offline 3-D laser measurement system for key characteristics of first-article inspection and statistical process control (Figure 1). Reflow soldering is optimized with a KIC system for precise profile development and continuous monitoring of the thermal profile. Each product has a documented list of key inspection points and a sample size. Setting parameters correctly from the project start ensures consistent quality.


A key area where engineering workload can be reduced through automation is thermal profiling. Determining ideal thermal profiles can be a challenge even for large EMS providers because profiling can be fairly subjective. Five engineers may give five different recommendations. Use of thermal profiling software can automate the rapid development of thermal profiles.

In this example, the system supports three areas of the reflow process: profiling, process optimization and process monitoring/traceability.

The OEM customer initially defines the process window typically by determining the intersection among solder specifications, the substrate specifications and component tolerances. An engineer at the contractor then attaches thermocouples to a sample product and runs a manual profile to compare against the process window. Time vs. temperature, peak temp or whatever data the customer requires can be collected.

The software generates a Process Window Index: a single number that indicates how the process fits the defined process window. The lower the number, the closer the process is toward the center of the process window. The size of the process window and capabilities of the reflow oven determine how low the number can be and facilitate development of robust thermal profiles in tighter process windows. For instance, RoHS has tighter process windows and use of this type of mathematical modeling can help in rapid determination of the best profile option.

To establish PWI options, the process optimization software monitors oven set points such as conveyor speed and temperature in each zone, and will select the optimum combination within a few seconds. The definition of the optimum profile can vary by project. In some cases, a profile in the center of the process window is most desirable. In another situation, the optimum profile may be the process with the highest conveyor speed deep in spec. Another option may be the process that consumes the least amount of energy within spec. Once the appropriate PWI is selected, the oven is ready for production.

Most EMS companies run a manual profile at set intervals. The challenge is this methodology establishes whether the reflow process is within specifications during the spot check, but doesn’t necessarily demonstrate whether it is in spec during the entire production run. Plus, there are many opportunities where a machine is stable but the process is out of specification. For example, if the exhaust changes, the profile may go out of spec even though the oven appears stable. If an operator loads the wrong recipe, it processes the wrong recipe. It’s to the manufacturer’s advantage to be able to measure the profile for each and every board processed through the reflow oven, including the PWI for each assembly. If the PWI goes over 100, it throws up an alarm that stops production. However, waiting until that point for corrective action would result in some scrap. As a result, the system also calculates CpK, and users can designate a lower limit. Once the CpK number drops below the user-established limit, a warning alerts to the need for corrective action while the process is still in spec.

Addressing Traceability

Customers value robust traceability mechanisms for several reasons:

• Regulatory agencies specific to their industry may require it.
  
  
• It can make it easier to analyze field failures and identify the magnitude of the issue.
  
  
• It provides valuable data for refurbishment or large-scale upgrade processes on longer lifecycle product.
  
  
• It supports efficient management of products with limited shelf life.

As illustrated above, drivers for traceability support are not limited to large-scale projects. Manual data collection can be time-consuming and costly. When a technology strategy also addresses likely customer traceability needs, data collection for even the most unique customer needs can be collected and stored automatically. At Clover Electronics, most customers only request lot traceability when necessary for a specific product, although internal systems support both lot and component date code traceability. Each product is serialized.

A key enhancement in this contractor’s traceability process is that not only do stored data include standard information such as date produced, revision level and the process specification in force at the time, they also include details on solder paste deposition and thermal profiles for that assembly (Figure 2). Questions such as “Was the process in control when this assembly was in the reflow oven?” are easily answered. For example, the last part of the barcode unique to assembly will indicate the profile used for the specific assembly with a date and time stamp. Time/temp profile, PWI number and peak temperature used are also logged for each assembly.


Rapidly Addressing Manufacturing Issues

Domestic EMS providers continue to remain competitive with solutions because speed, service and flexibility reduce customers’ total cost of outsourcing. The best way to illustrate the benefits derived from a strong manufacturing technology strategy and strategic alliances with key suppliers is by discussing manufacturing issues and ways they were resolved.

Example 1: NPI issues. A customer added a new product with a different board finish from other products in that family. The board finish deviation had been coordinated between the customer and PWB fabricator as the result of a tight design cycle. When production started, there were electrical test failures. The Clover team checked the stencil and called the paste and stencil manufacturers. The stencil supplier was able to identify a change in stencil thickness and amount of paste applied was the best solution for eliminating the electrical test failures. The solder paste deposition measurement system enabled the team to monitor paste height precisely on each board, and availability of those metrics reduced the time it took to troubleshoot the problem. Through the team effort, the issue was resolved in 2.5 days.

Example 2: RoHS challenges. A customer with leaded boards that were not cost-effective to redesign now has to accept some RoHS components because leaded components are no longer available. This particular customer had received several recommendations by other suppliers for optimum processing of these mixed-technology assemblies. These recommendations included processing at Pb-free temperatures or running the assemblies at a temperature in between typical leaded and RoHS specifications.

Clover was able to tap strategic alliances with its suppliers, which included outside consultants. The result: A paste expert, profiling expert and manufacturing expert were able to discuss potential options. The recommended solution was to either convert to 100% RoHS because the leaded BGA was obsolete, or manually place an RoHS-compliant BGA using a BGA reflow station. In response to the team’s queries, the customer indicated it was experiencing higher field failures on assemblies reflowed at RoHS temperatures because the higher temperatures were overstressing the leaded components. The customer was able to initiate corrective action across the entire supply base.

Example 3: Product quality issues on complex assemblies. A customer wished to cut costs on an older product. The original design included a number of wire harnesses soldered directly to the board. The redesign used connectors, which created more potential heat sinks during reflow. The process optimization software helped address this issue in the thermal profiling stage.

The EMS industry has done an excellent job of demonstrating its value in the product realization cycle. As a result, OEM customers have high expectations for service and support. Teaming with materials and equipment suppliers and engineering consulting firms is one way to cost-effectively increase breadth of expertise.

Developing repeatable, consistent processes with automatic monitoring at key points is another way to eliminate hidden costs and better leverage existing production resources. Strategies that combine these elements enhance quality and ensure complex customer requirements are met.

Bibliography

1. Jeff Roberts, “Teaming for Increased Process Visibility,” SMTA International Conference, August 2008.

Jeff Roberts is president of Clover Electronics (cloverelectronics.com); jroberts@cloverelectronics.com.