The PCB Supply Chain
Printed boards (PCBs) and printed assemblies (PCAs) are often the most technically complex components that are purchased for electronic assemblies and products. This complexity leads to several challenges for a supply chain management (SCM) team that may be significantly different when compared with the other and commodities that the team manages.
Examples Of Printed Supply Chain Issues
PCBs and PCAs are custom-designed and therefore cannot simply be purchased from a catalog. There are many suppliers, but their capabilities and performance vary widely, requiring more attention to supplier selection and qualification.
A wide variety of manufacturing processes are used to create PCBs and PCAs, ranging from precise photoimaging and component placement, mechanical presses for lamination and ovens for solder reflow, wet chemical plating and etching, and high-speed drilling and routing.
PCBs and PCAs are required to perform as part of an electrical and that performance is critical to the success of the final product. The PCB obviously provides interconnections between components attached to the board, but in some cases, it operates as an component in its own right. It may not be possible to determine whether the PCA works correctly until your design team has evaluated it as part of the final product.
Although components on a PCA can be replaced, traces cut, and jumpers added, PCBs and PCAs cannot be easily reworked, returned, or recycled if the product requirements change, which can lead to additional cost and unwanted inventory.
Basics Of The PCB Supply Chain
It All Starts With the Design: Once a product is defined and engineering starts to work, it is the design of the and selection of components that will start a Value Chain of Events. The layout of the printed is the first physical representation of that product. Design for Manufacturability is required as a way of optimizing performance and cost. The challenge of managing the information, documentation, and transfer in order to specify the design requirements and other expectations for the suppliers.
Printed Supply Chain Management: Unless an OEM is one of the few that is vertically endowed with manufacturing, the general considerations for PCB and PCA sourcing decisions, and the criteria that should be used to evaluate and select suppliers is turned over to purchasing.
Supplier Selection and Qualification: Others are involved in the business considerations and selection criteria described to evaluate and qualify suppliers, including processes to perform technical assessments of samples provided by the supplier.
Process Control, Monitoring, and Incoming Inspection: Ongoing for the Supply Chain is the monitoring of quality assurance methodology based on six sigma principles, with specific recommendations for process control, testing, and inspection of PCBs and PCAs at the supplier.
Product Acceptance and Feedback: Finally, management for design qualification, lot acceptance, and ongoing inspection of received PCBs and PCAs. It also includes recommendations for long-term supplier management that minimize the internal management cost while maintaining a high level of performance.
PCB Value Delivery Chain
VALUE is defined as “Benefits Minus the Costs”. To have a successful product for a market, in each step of the Supply Chain, each segment must perceive value! As seen in Figure 1, each segment has the next segment as a customer. Thus, each segment contributes to the value chain.
FIGURE 1: The PCB Value Delivery Chain is generally called the Supply Chain but depends on establishing value at each step.
The choice of a specific supplier depends on the relative importance of several different dimensions of supplier performance (see Table 1). Suppliers have inherent capabilities and strengths that are based on their own strategic decisions about how they choose to compete. Those capabilities will determine how well they fit the sourcing strategy and how they are likely to perform as an ongoing business partner. Understanding what is most important to the business will guide initial supplier selection and determine whether the supplier’s performance continues to meet your requirements.
Table 1 PCB Supplier Performance Criteria
When a new product is conceived, one of the first activities is to break the product down into components or partitions that will allow it to be designed, manufactured, sold and supported. This is extremely important since a mistake here may result in a product without the right features, or that may cost too much, or that may be on the market too late.
The bulk of product creation and design involved the logic design, simulation, component selection, custom integrated circuits, and mechanical designs. HDIS offers advantages in electrical and thermal performance. The key to value here is the ability to simulate the improved electrical and thermal characteristics of the many design options.
PCB Design and PCB Layout:
Many challenges must be faced when designing a new board. The wiring models are important to know in order to select proper design rules and constructions. With blind and buried vias, the new structures are more varied and complicated than conventional boards. Knowing what is cost-effective from a design-for-manufacturing perspective is essential.
Special design rules must be considered with complex structures. Each manufacturing process may have special considerations and limits. Design tools, pad stacks, and auto-routers are all used differently in complex designs. The customization of the design process is not an activity yet. The newer CAD systems also have expert systems available that provide much-needed advice. Manufacturability Audit software concludes the layout process with a thorough check for any mistakes or errors.
Of the entire value delivery chain, fabrication has become the most established. Currently, over two hundred companies worldwide are using at least twenty different processes to make essentially the same HDI/SLP structures. For example, making the microvia is the easy part, since lasers, etchers and photo-dielectrics have been rapidly improving over the years. The challenges are the basics: registration, fine line lithography, metallization and plating. On complex HDI/SLP, all of these must perform at a superior level. While this is certainly taxing, it benefits all printed wiring board manufacturing processes.
Assembly has a new value to deliver with complex-fine-pitch components. Components can be closer together, which can change reflow profiles and repair. As the topside fills up, the opposite side also must take more components including many ones. This also will alter the assembly process and reflow profiles. With newer smaller and denser area array components like chip scale packages or flips chip, the total number of connections per square centimeter increases dramatically. These newer smaller components with underfill or very high surface connection densities may have a reliability interaction with complex structures. Thin structures are more likely to flex during thermal cycles and this introduces new mechanisms and opportunities for failure, which must be thoroughly evaluated and tested.
The final stage of the PCB value chain is assembly level testing. This presents very new issues with the new smaller area array components. If via-in-pads are used with the area array components, after assembly there are no breakout vias to use to test probes. Design-for-Test becomes a major ingredient for system partitioning. Testing from the perimeter, boundary scan or built-in-self-test becomes a major design factor. Components may be so close now that test pads are either too large or there is no room to get a test pin into the area. Adding test pads to the surface after the board is designed can severely add to its complexity and cost, as well as add detrimental parasitics. Newer assembly level verification schemes will probably be developed that do not require the classical bed of nails fixtures, replacing them with faster non-contact test techniques.
In all, the PCB Value Delivery Chain will be a challenge for all of us. Working together and realizing that each part of the delivery will depend on the other links of the chain, we can provide solutions to the OEM allowing them to deliver superior products. Understanding these interactions is the first step in harnessing the power and opportunity for the Supply Chain.