Continuing with our discussion on the Original Equipment Manufacturer-Contract Manufacturer (OEM-CM) relationship, it is important to note that, while many contractor operations are similar, they may have very different procedures and methods for mapping workflow.
The OEM can help by anticipating potential problems and segmenting the workflow to ensure a minimum number of line-down incidents. (See: Talking Points in OEM-Contractor Negotiation
Most top-level electronic products share some commonality when it comes to the structuring of bills of materials (BOM). This structure is referred to as a "BOM tree," and, depending on the selected manufacturing resource planning (MRP) output format, the entire BOM can be represented as "nested" or "indented."
The lowest level of the assembly is the component level and the unpopulated printed circuit board (PCB). The next level has the stuffed or populated boards, with or without programmed parts. Next level up is the electromechanical assemblies that include mounting hardware, fan brackets, programmed parts, shields, heat sinks, air dams, on-board wire harnesses, and the assembled PCBs.
The top or final assembly usually includes some kind of mechanical housing or enclosure, complete with power supply, wire harnesses, interconnects for points of connections to the outside world, and miscellaneous hardware.
For the purpose of this article, let's assume your model of working with the CM is the consignment version and you are building up to the top level of your product. To facilitate kit and build management, identify and assign a group numbering scheme to the unique assembly structures mentioned above. These groupings are subject to the CM's review -- it may already have an established workflow that involves dedicated work centers with bench inventory determined by each work station's function.
The goal is to segregate major stand-alone assemblies to help identify potential build authorizations and to accommodate time-phased inventory awareness. Instead of identifying particular shortages at the piece-part level, potentially stopping the entire product from moving forward in the linear assembly process, it may be sufficient for the CM to say, "Kit group level 1.3 is not complete." It will then be your call to begin the build knowing that groups 1.1 and 1.2 can proceed as "material complete" while anticipating the timing to fill the shortages for group 1.3.
This will allow time-critical phone conversations without delaying the gathering of detailed knowledge about particular part shortages. The particulars may be determined at a later time and acted upon without incurring unnecessary line-down situations. Below is a suggested breakdown for easy identification of both materials-based issues and also functions or services-based concerns.
- Group level 1.1: PCB sub-assembly. Each board has its own group identifier, 1.1, 1.2, 1.3, etc., including:
- Printed circuit card (PCB) -- 1.1 (Motherboard)
- PCB components
- Printed circuit card (PCB) -- 1.2 (Daughterboard)
- PCB components
- Printed circuit card (PCB) -- 1.3 (Power supply controller)
- PCB components
Group level 2.1: Electromechanical assembly. Each electromechanical sub-assembly has its own group identifier, 2.1, 2.2, 2.3, etc., including:
- All sheet metal and machined parts
- Power supply
- Fans and blowers
- All wire harnesses
- All fastener hardware
- All cable tie-downs
- Loctite adhesive other assembly substances
Group level 3.1: Packaging materials and components. These include:
- Installation Kit (assembled and part number label attached)
- Outer shipping carton
- Set of end-caps (Left, Right)
- Box labels without serial number label attached
Group level 4.1: In-circuit test (ICT), functional test, and burn-in issues. This call-out is further identified with the assembly to which it applies, including the following:
- Parts won't program
- Ovens non-operational
- Test equipment malfunctions
- Software problems
- Failed ICT
Examples of service- or function-related call-outs might be:
- 4.1a/1.1 = Part-programing problem on the motherboard
- 4.1e/1.3 = Power supply controller failed ICT
By using this method, the entire top-level product is moving via a parallel assembly operation as opposed to a linear, step-by-step arrangement. If there are any shortages detected at the kit audit stage or during assembly due to a high scrap fallout rate, then the unaffected assemblies keep moving forward.
Now your company has a much better system for meeting your delivery schedules as forecasted. There will always be fire drills, but this process of grouping the assembly operations and materials makes the management of those emergencies less harrowing and on-time deliveries more likely.