Component Obsolescence Management for PCB Assembly
Components disappear. A part that was available in volume last year can be allocated, last time buy or obsolete this year, and the way a product is designed decides how much that costs when it happens. Obsolescence is predictable in principle and ignored in practice.
Why Components Disappear
A manufacturer stops a part when the demand falls below what the process can support, when the die or the package is replaced by a newer generation, or when a material is withdrawn for regulatory reasons.
The withdrawal notice usually arrives with a last time buy window rather than with a replacement. The window is the point at which the design has to be re-qualified or the stock bought, and both cost money that could have been avoided by choosing a part with a longer outlook.
Lifecycle Screening
Every part on the bill of materials should carry a lifecycle status before the design is released, not after the first shortage. The status can be read from the manufacturer, from a distributor, or from a risk service.
The screening is a risk filter rather than a guarantee. A part flagged as active can still be withdrawn, but a part already marked as not recommended for new designs should never enter a product with a multi-year production life. Our component selection notes describe how the check fits the design flow.
Last Time Buys
A last time buy converts a supply risk into an inventory risk. The quantity must cover the remaining production plus the expected service demand, and it must be stored under conditions that keep the parts usable for the whole period.
Storage life is not unlimited. Solderability, moisture sensitivity and the finishes on the terminations all change with time and with the environment, and the stock should be checked and re-baked where the specification allows.
Form, Fit and Function Replacements
A replacement that keeps the footprint, the outline and the electrical behaviour is the cheapest answer, because the board does not change. The trap is that a part matching the description may not match the behaviour at the corners.
Timing, start-up behaviour, leakage and thermal performance are the parameters that usually differ. Each difference must be tested rather than read from a datasheet, and the test should reproduce the corners at which the original part was relied on. Our tolerance notes describe how the corners are defined.
Redesign and Requalification
Where no replacement fits, the board is revised. The revision disturbs the layout, the thermal behaviour and the test program, so the requalification is rarely limited to the component that changed.
The extent of the requalification should be decided by what the change affects, not by the size of the change. A different package can alter the solder joint, the inspection coverage and the reflow profile at once.
Contracts and the Bill of Materials
The supply agreement should say who carries the obsolescence risk and for how long. Without a clause, the cost of the last time buy or the redesign falls on whoever holds the product at the time.
Where the customer controls the bill of materials, the same conversation has to happen with them, and it should happen when the product is designed rather than when the part runs out. Our design release notes cover the record that makes this traceable.
Counterfeit Risk
Obsolete parts available on the open market are the classic counterfeit target. A part that no authorised distributor stocks should be treated as unverified until the provenance and the identity are established.
The verification steps are incoming inspection, marking checks, X-ray of the die, and electrical test. Where these cannot be performed convincingly, the part should not enter production stock, however urgent the shortage.
Records
The lifecycle status, the date of the check, the replacement studied and the decision taken should be recorded with the design. The record is what lets a later change be evaluated without repeating the whole analysis.
It also shows an auditor or a customer that the risk was managed rather than discovered, which is usually the difference between a controlled transition and a line stop.
Process Control and Verification
On a design of this kind, requalification is the item that decides how the rest of the board is arranged. Documenting the assumption is part of the design work, and a short note on the drawing prevents a question that would otherwise arrive a day later and cost a day of schedule. The process window is set by the narrowest step in the flow, so an improvement anywhere else shows up as margin rather than as yield until that step is addressed.
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.
Process Control and Verification
On a design of this kind, requalification is the item that decides how the rest of the board is arranged. Documenting the assumption is part of the design work, and a short note on the drawing prevents a question that would otherwise arrive a day later and cost a day of schedule. The process window is set by the narrowest step in the flow, so an improvement anywhere else shows up as margin rather than as yield until that step is addressed.
A short note on the drawing about handling, storage or packaging is often worth more than an extra decimal place on a tolerance.
Process Control and Verification
On a design of this kind, requalification is the item that decides how the rest of the board is arranged. Documenting the assumption is part of the design work, and a short note on the drawing prevents a question that would otherwise arrive a day later and cost a day of schedule. The process window is set by the narrowest step in the flow, so an improvement anywhere else shows up as margin rather than as yield until that step is addressed.
A first article check confirms that the process and the drawing agree on the points listed above, and that the coupon data supports the values used in the design.
Where a measurement falls outside the expected window, the sample is retained so that the cause can be established before the balance of the batch is released.
FAQ
When should obsolescence be reviewed? At design release, at every significant change, and at least once a year during production. A review carried out only when a shortage appears is a recovery action, not a plan.
Is a last time buy always the answer? No. It is right when the remaining volume is small and the certification cost of a replacement is high. It is wrong when the production life is long, because the stock may not survive it.
What does gopcb provide for obsolescence? We provide lifecycle screening of the bill of materials, alternative part studies with form, fit and function testing, redesign and requalification when no alternative fits, storage and re-bake procedures for stocked parts, and records that tie each decision to the design.
