A last-time-buy plan can contain enough electronic components for the remaining product life and still leave production short next month. The missing detail is often timing: the final shipment arrives after material is needed, or stock counted in the calculation belongs to another program.
Effective last-time-buy planning combines a remaining-demand calculation with a dated inventory balance. Define which builds and repairs the purchase must cover, reconcile the stock available to that scope, and test each period through the end of support. The final quantity should come from that shared plan.
Establish the final-order window and the coverage horizon
First confirm that the manufacturer has actually announced a final-order opportunity for the complete orderable part number. A lifecycle label alone needs interpretation. For example, Texas Instruments distinguishes “not recommended for new designs,” “last time buy,” and “obsolete” in its product lifecycle definitions.
Record the applicable notice revision, affected ordering codes, last-order date, and final-shipment date. These dates serve different purposes: one controls when purchasing must act; the other constrains incoming supply. Analog Devices lists both last-time-buy and last-time-ship dates among the contents of its product discontinuance notices. Use the actual notice and supplier confirmation for your order.
The existing component notice review checklist covers ownership and affected-BOM checks. The quantity calculation begins once the affected requirement is established.
Then agree on the coverage horizon. A lifetime purchase may need to support production and later field repairs. A bridge purchase covers a defined transition to an approved alternative or redesign. State which approach you are funding, including what happens if qualification takes longer than planned.
Put production and service demand on separate lines
Build production demand from the remaining assembly schedule and the number of affected components per assembly. Include every product variant and manufacturing site using the same approved device. Work in component pieces throughout; mixing board quantities with component quantities can distort the result.
Keep the service horizon separate from the end of manufacturing. A product can stop shipping while its installed population still needs support. Ask the service team which units remain supported, how repairs are performed, and how many components those repairs are expected to consume over time.
If service replaces whole boards, translate planned replacement-board builds through the service BOM. If existing finished spare boards already cover part of that demand, reflect their contribution before adding raw-component requirements. Avoid counting the same repair once as a replacement board and again as a component-level repair.
Add production losses, destructive-test samples, or other consumption only where justified. Identify whether the build forecast already includes them. An allowance copied from a previous program can conceal both missing demand and duplicate demand.
Reconcile stock against the same demand scope
Choose one inventory snapshot date and reconcile physical stock, material at contract manufacturers, and confirmed incoming orders. Record identity, quantity, location, release status, ownership, and expected availability date. Quarantined or unresolved material should remain outside committed usable supply until its disposition is established.
Reservations need careful treatment. Stock allocated to builds already included in this forecast still supplies those builds. Exclude reservations for demand outside the plan. Subtracting all allocated stock while keeping the corresponding build demand can create an artificial shortage.
Likewise, count an in-transit shipment once. When it becomes on-hand stock, replace its incoming entry rather than keeping both. A market listing or unaccepted quotation belongs in the sourcing options, not the confirmed-receipts column.
Last-time-buy calculation: a timing gap hidden by the total
Hypothetical example: an OEM has 1,500 usable pieces of one approved IC at the planning snapshot. Its remaining plan consumes 2,100 pieces in production and 300 for service. These figures already include the team's approved consumption allowances; they are not actual customer forecasts or supplier inventory.
The additional lifetime requirement is 2,400 minus 1,500, or 900 pieces. Assume the supplier confirms a 1,000-piece ordering increment, so the proposed final order is 1,000 pieces. That produces a projected 100-piece ending surplus.
However, the order is expected at the beginning of Month 3. The following ledger assumes receipts arrive at the start of each period and demand occurs during it:
| Period | Confirmed receipts | Production consumption | Service consumption | Projected closing balance |
|---|---|---|---|---|
| Month 1 | 0 | 900 | 50 | 550 |
| Month 2 | 0 | 700 | 50 | −200 |
| Month 3 | 1,000 | 500 | 50 | 250 |
| Remaining service period | 0 | 0 | 150 | 100 |
The negative Month 2 balance identifies 200 pieces of unmet requirement. It does not represent physical negative inventory, and carrying the deficit forward does not authorize late builds. The 100-piece final surplus cannot prevent that earlier shortage.
One possible resolution is a confirmed split release: 200 pieces at the start of Month 2 and the remaining 800 at the start of Month 3. That removes the modeled deficit, but leaves no Month 2 margin. The team must still assess whether this schedule is acceptable.
If the final order cannot be split, a separately approved 200-piece bridge lot would increase total purchases to 1,200 and the projected ending surplus to 300. Show that consequence explicitly. Adding 200 pieces to the Month 3 shipment alone would increase stock without fixing the Month 2 gap.
Test the assumptions that could change the decision
Run the ledger with a base forecast and a few specific alternatives. Useful cases include a delayed final shipment, an additional production release, higher service consumption, or a later redesign approval. Change the relevant quantities and dates together.
In the example, a redesign delay that adds 250 component uses increases the unrounded additional requirement from 900 to 1,150. The proposed 1,000-piece final order would then be 150 pieces short over the full horizon. Its timing still needs a separate check.
Keep forecast uncertainty distinct from purchase rounding. The original 100-piece surplus arose from the ordering increment; it was not a statistically established service reserve. State what any additional contingency covers and who accepts the remaining exposure.
A proposed replacement also needs a realistic approval date. NXP's discontinuance terminology explicitly treats replacement references as information requiring customer qualification. A suggested cross-reference should therefore remain outside the approved supply plan until the necessary evaluation is complete.
Check whether the inventory can remain usable
A long coverage horizon creates a storage responsibility. Ask quality to define the packaging, handling, storage, inspection, and release arrangements for the actual component. Retain the associated lot records so stored material can be identified when it is eventually issued.
TI's product shelf-life guidance distinguishes its controlled internal storage from customer storage after delivery, where package materials, moisture sensitivity, protective packaging, and conditions matter. Its findings should not become a blanket claim that any warehouse can hold any component indefinitely.
Include storage and future verification costs when comparing a lifetime buy with a shorter bridge purchase and redesign. The preferred option depends on the actual support horizon, engineering schedule, supplier commitment, and consequences of excess or insufficient stock.
Approve a quantity together with its delivery plan
The decision record should identify the notice, exact part, demand scope, inventory snapshot, dated receipts, base-case quantity, alternative scenarios, and storage owner. Record the supplier's accepted quantities and shipment schedule alongside the internal approval. Confirm cancellation, rescheduling, minimum-order, and packing terms before committing.
Cplus Electronics lists EOL component replacement services, which can support the search for candidates when a longer-term change is being evaluated. Keep sourcing proposals and engineering approval visible as separate stages.
When you submit the component sourcing requirement, distinguish the urgent bridge quantity from the later coverage quantity and state their respective need dates. Include the exact ordering code, condition and documentation requirements, and whether alternatives are permitted. That gives a sourcing partner a precise purchasing task while preserving the assumptions behind your final buy.
