When you’re ready to move your design to the manufacturing and assembly stage, there are several important pieces of documentation you’ll need to prepare for your manufacturer. Panelization drawings, assembly drawings, manufacturing bills of materials, design files, and testing requirements should all be prepared as you consult with a CM to begin a manufacturing run.
Perhaps the most important is your bill of materials. Assembly cannot begin without this important piece of documentation. This document details component quantities, their reference designators on your board, sourcing information, and any critical notes your manufacturer needs to know when working with your components. An experienced CM will perform a bill of materials analysis before beginning manufacturing to ensure your next product can be produced and assembled successfully.
Scrubbing in a Bill of Materials Analysis
When your CM begins a bill of materials analysis, one of the first tasks is to perform a bill of materials scrub. The bill of materials is scanned manually or automatically to identify any inconsistencies or errors. The goal is to eliminate any confusion for assemblers and ensure the design data matches the component data in the bill of materials.
What Is Checked During Scrubbing?
What types of mistakes can appear in a bill of materials? A key error check is to compare the component description against the customer-supplied manufacturer’s part number in the bill of materials. Similarly, reference designators listed in the bill of materials must be compared with the designators in the schematic and the layout, which are then matched against their nets. This is why it is important to provide an IPC-D-356 netlist because this can be used to compare a schematic netlist to your board’s Gerber data and component reference designators.
Mismatches between reference designators in a bill of materials and a schematic are quite common in new designs where multiple team members are collaborating and changes are made frequently. It is common for low-grade design to lack tools for bill of materials analysis and synchronization. Choosing the right design software with supply chain visibility and design synchronization can help you avoid a redesign and errors in your documentation. The best CMs will use this type of design software to examine your design files during an initial review.
One great way to assist your CM during a design review and bill of materials analysis is to list acceptable alternative part numbers in your bill of materials. This helps your manufacturer cut down design review time to quickly solve sourcing problems.
Anyone who has experience managing the supply chain for components, both during design and before assembly, knows the headaches and delays caused by a lack of visibility. Sourcing components for an initial prototype or high-volume production run may seem as simple as searching for components on Google, but your design is at risk of delays or failure if components are not properly sourced.
Specialized Components vs. Wholesale Components
If you have supply chain visibility and management tools available during design time, you can consider sourcing components yourself. Specialized components like powerful PLDs, unique SoCs or SoMs, and other rare components can be quickly located by a designer simply by going directly to the component manufacturer. The manufacturer will typically list verified distributors from which you can source these components. This allows designers to determine whether a design can be produced at scale with the desired component, or whether replacements need to be chosen. Ideally, this should be done as early as possible in the design process.
For other components that need to be procured at high volume, you can take advantage of a CM’s relationship with component vendors. Your CM may have relationships with large distributors and can buy large stocks of components at wholesale prices, and they often pass those savings onto their customers. The best CMs will perform a bill of materials analysis and will identify whether they can help a customer save money on components by leveraging the CM’s relationships with major distributors.
When a component required for a new board goes EOL, often the only place to procure these components is through brokers or resellers. Going through a reseller is risky because these components could be counterfeit. A reliable CM will have relationships with reputable brokers who are experienced in filtering out counterfeits. Larger CMs may even keep these components in stock, allowing you to get a board spin completed while you redesign your board with newer components.