Repair Strategy: Levels of Repair and Spares Planning
How far a repair goes depends on where it is performed and on what the repaired unit must subsequently be trusted to do. A repair at the production line and a repair in a service centre are different operations with different requirements.
Levels of Repair
A board level repair replaces or reworks a component on the board. It requires the equipment to reflow a joint and the skills to work on a fine pitch assembly.
A module level repair replaces a subassembly. It is faster, it requires no soldering, and it produces a unit whose history is partly unknown because the parts come from different sources.
A unit level repair replaces the whole product, which restores the function but discards the evidence of what failed. Where the failure is not understood, the replaced unit may fail in the same way. Our design release checklist notes where the repair strategy is recorded.
Where the Repair Is Performed
A repair at the production line is performed by the operators, with the same equipment and the same procedures that built the unit. The result is close to a new build.
A repair in a field service location is performed with limited equipment and without the ability to test to the original specification. The result is a unit that works and whose margin is unknown.
A repair at a depot sits between the two. It justifies the equipment and the procedures if the volume is sufficient, and it is where the analysis of the failures should be concentrated.
What a Repair Restores
The repaired unit should meet the same specification as a new one, or the customer should know that it does not. The distinction must be explicit, because a repaired unit sold as new is a liability.
Where a repair cannot restore the full specification, the limitation should be recorded and the unit’s subsequent use constrained.
The repair must also restore any protection that was disturbed, such as a conformal coating, and this is where many repairs fall short. Our quality notes describe the verification of the repaired unit.
<img src="https://www.gopcba.com/wp-content/uploads/2026/06/AI-Hardware-Manufacturing.jpg" alt="Repaired unit undergoing screening before return” />
Spares Planning
The spares needed follow from the failure rates and the repair level. A board level repair needs the components that fail; a module level repair needs the modules.
Where a component is obsolete, the spares plan requires either a stock of the part or a redesign. Buying a lifetime stock is a decision that should be made before the part disappears rather than after.
The spares holding should be reviewed against the actual repair data, since a part that is never used occupies capital and a part that runs out stops the repair. Our component reliability notes describe how the failure rate is estimated.
Screening Repaired Units
A repaired unit should be tested at least as thoroughly as a new one, and preferably with an additional screening step, because the repair process introduces its own risks.
A thermal cycle or a burn in after the repair reveals a joint that was not properly formed and a component that was damaged by the heat.
The screening is particularly important where the repair involved a large component or a thermal pad, since the heat required can affect the surrounding joints.
Traceability of Repairs
The repair should be recorded against the unit, with the failure, the parts used, the work performed and the test result.
The record allows a repaired unit’s subsequent failure to be assessed against the repair, which is otherwise impossible.
Where the same repair appears repeatedly on the same product, the record shows a design or process problem rather than a series of individual faults. Our industrial assembly notes describe how such records are structured.
Practical Rules
Choose the repair level from the economics and from the confidence required, and make the choice explicit in the documentation.
Restore the full specification where possible and record the limitation where not. Screen every repaired unit beyond what a new unit receives.
Feed the repair records into the spares plan and into the design review, so that the repair process improves the product rather than only returning it to service.
Additional Considerations for This Build
Practical attention to depot repair pays for itself here, because it decides whether the finished board behaves as the drawing intended. Where the requirement is not stated on the fabrication drawing or in the assembly notes, the shop has to assume a default, and that default is rarely the value the design was simulated with. Stating depot repair explicitly, together with the tolerance that applies, removes the assumption and keeps the result predictable from batch to batch.
Process Control and Verification
On a design of this kind, traceability is the item that decides how the rest of the board is arranged. A short note on the drawing about handling, storage or packaging is often worth more than an extra decimal place on a tolerance. Where a value sits close to a process limit, the drawing should say so, since the shop can then open the process window rather than working to a nominal figure that carries no tolerance.
A stack-up that is drawn rather than described removes most of the ambiguity from a quotation, and it lets the fabricator price the board against the dielectric and copper weights that will actually be used. Where the requirement is not written down, the shop supplies its own default, and the default is chosen for the process rather than for the design.
The measurements that matter are the repeatable ones: conductor width and spacing, annular ring, finished hole size, plating thickness and surface finish are all verifiable on a coupon that travels with the panel. Running a first article through the same checks as the production panel confirms that the two agree, and that comparison is the cheapest form of process control available at prototype stage.
Process Control and Verification
On a design of this kind, traceability is the item that decides how the rest of the board is arranged. A short note on the drawing about handling, storage or packaging is often worth more than an extra decimal place on a tolerance. Where a value sits close to a process limit, the drawing should say so, since the shop can then open the process window rather than working to a nominal figure that carries no tolerance.
Process Control and Verification
On a design of this kind, traceability is the item that decides how the rest of the board is arranged. A short note on the drawing about handling, storage or packaging is often worth more than an extra decimal place on a tolerance. Where a value sits close to a process limit, the drawing should say so, since the shop can then open the process window rather than working to a nominal figure that carries no tolerance.
FAQ
Is a repaired unit as good as a new one? Where the repair restores the specification and is screened, it is close. The residual risk is why the record and the screening matter.
Should repairs be performed at the field location? Where the equipment and the test allow, yes. Otherwise the unit should go to a depot rather than being repaired to an unknown standard.
What does gopcb provide for repair strategy? We provide repair level definitions with their test and screening requirements, procedures for board level rework including coating restoration, screening after repair, repair records tied to the unit, and spares recommendations based on the failure data.
