Engineers often create PCB assembly variants to cover alternative customer needs, regional power differences, optional features, or future upgrade provisions. However, overly complex and fragmented variants complicate manufacturing, raising costs through excess tooling, changeover, and inventory demands.
This guide covers techniques to effectively prepare assembly variants for economical high-volume production. Consolidate using universal parts, master configurations, and flexible PCB designs where possible to simplify manufacturing. Target consistent processes and components across variants whenever viable.
Challenge of PCB Variants
Manufacturing problems arise when variants diverge across too many attributes:
PCBs
- Different board sizes and layer counts
- Mounting holes/keepouts changing locations
- Component spacing/routing variations
BOMs & Parts
- Alternate parts for simple substitution flexibility
- Region specific component variants
- Upgraded next generation parts
Test & Programming
- Separate test coverage due to functionality differences
- Unique product calibration values required
Such differences drive extensive part proliferation, complex tooling, prolonged changeovers, and inventory waves. Costs and lead times suffer as a result.
Planning consolidated PCB variants reduces overheads.
Strategy 1: Leverage Common PCBs
Share common PCB designs across variants whenever possible by carefully planning partitioning.
Figure 1. Single base PCB supporting four headset variants through selective device stuffing and con- figuration
Maintain Same External Interfaces
Retain consistent external dimensions, mounting points, connector locations and styles across PCB variants even when internal circuitry changes.
Standardize Cutouts/Keepouts
Fix locations of major tooling holes, fiducials, component voids, and wire ingress paths across all PCB variants to enable use of same panels, jigs and testing shields.
Ensure Layouts Support Multiple Configurations
Plan layouts with provisions for alternate stuffing options, disable jumpers,configuration pins/pads, and placeholders for substituted components.
Accommodate all planned spice, upgrade, and regional substitutions within same board outline.
Strategy 2: Reduce Part Variants
Minimize differences in bill of material (BOM) parts used across assemblies through standardization and universal components.
Figure 2. Part substitution using compatible alternates with same footprints minimizes BOM variations
Choose Packages Supporting Multiple Parts
Select surface mount component packages capable of supporting the full range of voltage, temperature, and other variants required. Allows same PCB stuffing and pick and place programs.
Qualify Broadly Suitable Parts
Validate parts meeting all application needs such as wider temperature or higher voltage ratings usable across assemblies without substitutions.
Specify Widely Available Parts
Choose commodity resistors, capacitors, and semiconductors used globally to avoid country specific components. Confirm with procurement and vendors.
Reducing part variants, even marginally, across builds lowers materials complexity substantially.
Strategy 3: Develop Master Configurations
For more extensive feature differences, create master PCB configurations covering the superset of any assembly through selective population.
Figure 3. Master PCB configuration supporting three product variants through selective on-board component stuffing
Layout Single Universal PCB
Board layout supports installing all optional components with provisions for depopulation as needed. Contains union of features across build variants.
Assign Unique Locators for Optional Parts
Use distinct part numbers for optional components at same locations across master configuration to identify parts not stuffed for specific production variants.
Build Complete Components and Programing Data
BOMs, pick-and-place and assembly drawings cover full master configuration options. Manufacturing selectively enables/disables based on build.
This reduces the need for boards unique to each variant.
Strategy 4: Utilize Flexible PCB Technology
When physical layout differs substantially between variants, flexible PCB technology allows variants consolidated onto common panels.
Figure 4. Multilayer flexible PCB manufacturing combining three rigid and two flexible circuit variants onto same panel
Understand Trading Flex Boards
Flexible boards interconnect separate rigid PCB modules allowing stacked modules. Enables volume consolidation.
Check Capabilities
Discuss merging rigid-flex board combinations with flex PCB manufacturers. Assess capabilities to manufacture combination board panel.
Restrain Layer Counts
Avoid excessive rigid-flex layer counts as yield rapidly decreases. Carefully allocate layers.
Leveraging flexible boards provides integration while limiting layers.
Summary Checklist
In summary, simplify PCB assembly variants using these key steps:
Commonality
- Maintain same PCB size and interfaces
- Standardize mounting, tooling holes and cutouts
- Support alternate configurations in base layout
Convergence
- Substitute components from standard packages
- Specify parts operable across environment conditions
- Choose globally available commodity parts
Consolidation
- Design master configuration PCB supporting full superset build options
- Assign unique locators for optional components
- Provide complete assembly data for master population
Combination
- Verify manufacturer capability to fabricate rigid-flex layers needed
- Limit rigid-flex layer counts to maintain yield
- [ ]igrate distinct PCB modules into common flexible assembly
Carefully applying these best practices primes very diverse PCB assemblies for economical high volume manufacturing. Manufacturing is engaged early to assess proposed consolidation approaches for feasibility.
Frequently Asked Questions
What are recommended limits on the number of PCB assembly variants?
As rule of thumb, aim to keep PCB assemblies below five variants, ideally three or less. Up to seven can work if variants well aligned. Over seven rapidly increases manufacturing complexity costs, degrading economies of scale.
What component substitutions cause the biggest issues in PCB manufacturing?
Semiconductor changes require modifications across most production and test areas and represent one of the highest impact component substitutions. Other problematic substitutes include connectors affecting mechanical tooling or density changes forcing layout adjustments.
Should PCB assembly variants eliminate use of flexible circuits altogether?
On the contrary, flexible PCB technology, including rigid-flex, provides one of the best ways to consolidate physically disparate variants when layout differences are unavoidable. The technology affords enhanced flexibility in integrating modules with high variability into common panels for volume production.
How can manufacturers identify and selectively populate PCB assembly variants?
Use clear labeling in assembly drawings matching configured part locators. Barcode individual reels of variant components by part number for automated pick and place processing per unique builds. Further customize testing fixtures with build identification for variant test program loading.
At what threshold of added layers should rigid-flex PCB technology be avoided?
The cost and yield reduction tradeoff for rigid-flex boards typically warrants avoiding flex layers if total layer counts exceed 12-14 layers for most applications. However, high layer counts exceeding this threshold may justify rigid-flex for small form factors or extreme complexity consolidation.
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