Lean Manufacturing for Rigid Flex PCB


Many companies are familiar with lean manufacturing concepts and have successfully used these techniques to improve manufacturing processes. Lean techniques, while most often used in printed circuit board fabrication and assembly operations, can also be applied to nonmanufacturing processes. One such process is new part number introduction (NPIP). The main thrust of lean manufacturing is to reduce or eliminate waste. There are typically seven wastes (mudas), as defined by Toyota executive Taiicho Ohno, when he developed Toyota's Production System (TPS) [1] (" Muda" is a Japanese word meaning uselessness, idleness or other synonyms of waste.) The seven mudas are: - Transport
- Inventory
- Motion
- Waiting
- Over-processing
- Over-production
- Defects

The common part number startup for Rigid flex PCB often can suffer from a number of those wastes. Certain waste items are specific to a part number (customer out of office, conflicts in documentation, iterative design discussions, etc.) or be ingrained as accepted gaps in a supplier's product launch system. As part of a continuous enhancement mentality, wastes should be recognized for reduction through a documented and monitored part number introduction process.

Some of the more common waste elements are:

Transport: In a new part number introduction process (NPIP), transport is the movement of documentation (electronic or paper) from one department to another requiring successive reviews and sign-offs. Excess transport is a symptom of a departmentalized approach to part number start-up rather than a process flow approach. A cross-functional design review team with one leader can help and remove departmental barriers assure that reviews and inputs are done in parallel rather than serially. Transport can also include sending out info requests and approvals to customers and providers. These demands need to be challenged regarding their effectiveness and necessity.

Waiting: New part number start-up needs information flow. Oftentimes the process becomes stalled at various steps when someone is waiting for information. This can happen from within the company, the customer, or the supplier. A good NPIP system includes checklists so the needed documentation is quickly identified and missing parts can be requested instantly. Team members are focused on quick communication so that there is as little waiting time as possible. Customers, internal team members, and suppliers all need to be intimately included to foster good communication. Again, parallel processing is an important notification. Sometimes a decision followed by a course correction, is a quicker journey to the destination than waiting for all the information to become available.

Over-processing: In the design and kick off start-up system, the equivalent of over-processing is over-specification. It is appealing to indicate a tighter tolerance than required because designers believe it provides them a bigger safety margin. While this is sometimes the case, other times a tighter tolerance will push a supplier to make compromise that reduce producing yields, require additional tooling, and add time to the processing sequence. Additional delays occur when acceptance criteria are defined in absolute phrases. Criteria specifying "no stains" or "no foreign material" can create an inspection struggle until a meeting of the minds occurs between the customer and supplier. Having a well-documented design and design guide, as well as having knowledgeable manufacturing technicians on the startup team, will assist assure that a new part number kick off with reasonable production yields and fulfills the customer's requirements.

Over-production: The equivalent of overproduction in a part number startup system is over-design. As in the case described in overprocessing, developing in "safety margins" might be desirable, but it can also backfire. An example in the world of flexible circuits might be specifying thicker copper to allow much higher amperage capability, but thicker copper can also degrade flexibility. Over-design may also add cost, so one needs to understand if the added cost truly yields a more reliable product.

Defects: The outcome of a poorly performed part number introduction may result in low production yields triggering high scrap rates, late deliveries and potentially malfunctioning product delivered to the customer. A startup procedure should be rigorous enough to avoid pitfalls seen on previous part numbers. It's not possible to have everyone review each part number prior to product launch, but utilizing multiple subject matter experts to preview design layouts is a good first step. Capturing the cooperative wisdom of the organization is the objective as this can help recognize "gotchas" that can be prevented. This review should be regarded a proactive step but in the world of custom made flex PCB and heaters even the best plans may result in surprises. A team focused on quick response is critical when this happens. The best NPIP system is a combination of pre-launch proactive review and a reactive team ready to respond quickly when the demons inevitably are revealed.
It is a continuous improvement effort plan to supply magnified customer support during initial part number design and delivery. It is an approach customized to an organization that provides custom engineered products. Similar techniques and practices can help reduce the mudas encountered during part number startup.