---
id: KB-IU-009
url: https://app.codecontract.io/help/manufacturing/electronics-and-component-substitution
idioma: en
categoria: sector-industria
subcategoria: electronica
audiencia: usuario
nivel: avanzado
actualizado: 2026-08-13
tambienEn: [es]
relacionados: [KB-IU-008, KB-NO-007]
citadoPor: [KB-IU-012, KB-NO-025, KB-IU-020]
---

# Electronics and component substitution

_A component goes end-of-life and must be swapped. Documentation does not travel with the function: it travels with the part number._

**Responde a:** replacing an obsolete component · material declarations for electronic components · part number change in a bill of materials · documented component equivalence

In electronics, obsolescence is not an exception: it is the calendar. A component is discontinued, an equivalent has to be found, and the product stays the same for the customer. On paper, however, it has changed — and that is where problems pile up.

## What moves when a part number changes

| Document | Still valid? | Why |
| --- | --- | --- |
| Manufacturer material declarations | No | They were issued for the previous part number |
| Component conformity certificates | No | The same: they follow the part number, not the function |
| The product's bill of materials | Must be updated | And the previous version kept, for what was already built |
| Technical documentation of the finished product | It depends on the change | If it affects safety or what was declared, it is reviewed |

> [!IMPORTANT]
> The key is the first row and it is what gets underestimated most: frameworks such as RoHS or REACH are answered with declarations the manufacturer issues **for a specific part number**. An "equivalent" component from another maker does not inherit those declarations even if it does exactly the same job. If you do not request the new ones, your finished product has quietly lost its documentary backing.

## How to make a substitution that survives an audit

1. **Document the equivalence, not just the decision** — What was compared and against what criteria, not "it's the same".
2. **Request the new component's documentation before fitting it** — Material declarations and certificates, for that part number.
3. **Record from which serial or batch it applies** — It is what lets you answer years later what each unit contained.
4. **And keep the previous bill of materials** — What was built before is supported by that one, not the new one.

> [!WARNING]
> Point three separates an orderly substitution from a silent problem. Without the marker "from here the new part is fitted", two years on you will have units in the field with two configurations and a single bill of materials describing only one. When a claim arrives about a specific unit, you will not know which it carried.

## The awkward case: buying outside the usual channel

**En corto**

- If a component is scarce, offers from unfamiliar distributors will appear.
- There documentation matters more, not less: batch traceability and the original manufacturer's declarations.
- And record where each purchase came from, not only what it cost.

Counterfeit components exist, and their first symptom is not an electrical failure: it is incomplete or generic documentation that does not refer to a specific batch.

> [!NOTE]
> The specific substance frameworks and their scope vary by product and market, and they get updated. This describes how to organise the documentary response; **what applies to you and from when is worth confirming with your adviser** or the manufacturer, not inferring from a distributor's listing.

**Is the distributor's declaration enough?**

As a reference yes; what holds up is the manufacturer's, for that part number.

**Do product tests have to be redone?**

It depends whether the change affects what was tested; that assessment is documented too.

**What if only the package changed?**

It is still another part number, so it still needs its own documentation.

## Ejemplos

**A manufacturer replaces a discontinued component with an equivalent and carries on producing.**

- Requests the new component's declarations before fitting it
- Marks the serial number it applies from and keeps the old bill of materials

→ Facing a claim on a two-year-old unit, it can say exactly what that unit contained.

**A component is discontinued and must be substituted.**

- Checks that version's design file

→ The substitution starts from what was decided.

**It is substituted and the documentation still describes the old one.**

- Updates the file with the new component

→ The paper describes what is made.

**Units with the old and new component coexist.**

- Records from which batch the change applies

→ Each unit has its documentation.

**The new component's supplier provides no documentation.**

- Requests it before starting to use it

→ The change leaves no gap.

**A client asks what one specific unit carried.**

- Checks that batch's file

→ You answer per unit.