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12 SMT007 MAGAZINE I NOVEMBER 2026 Part Numbering Schemes: Small Choices With Large Outcomes Each BOM is unique to the customer and must be modeled one-to-one in the contract manufacturer's system. In EMS, that includes approved alternates for the customer's design: functionally identical compo- nents differentiated by manufacturer or packaging. Modeling raw components by manufacturer part number (MPN) usually provides the most flex- ibility. The temptation is to use customer-specific or internal numbers so material purchased for a job "sticks" to that demand. Further, alternate parts can also be received under the same number, providing a rough solution for functionally identical alternate parts. However, linking inventory to a single BOM means material can sit idle on one job while another build is short of the same part. MPN-based inventory reveals common demand for customers, supporting larger, more cost-effective purchases. That flexibility requires two controls: tracking valid alternates for each BOM position and reserving material for a specific customer or job. These controls are difficult enough that many EMS compa- nies fall back on customer part numbers. However, solutions are available for companies with suffi- ciently developed processes. Modeling Components: Tracking Alternate Parts Across Shared Inventory Tracking valid alternates requires a defined group of approved MPNs for each BOM component. These groups need to be flexible enough to be specific to a customer or BOM, yet selectively reusable to reduce maintenance. Cetec ERP's Part Spec Groups provide that struc- ture. Each BOM position links to a group of approved MPNs, named with the customer part number or an internal part number (IPN). This preserves the Figure 1: A BOM line linked to its approved parts management capabilities. The line is short on its stocked MPN, and the group holds the approved alternates for that customer's position.