Patient-connected electronics under IEC 60601-1
Where the isolation barrier is drawn decides the whole architecture — and the documentation is a deliverable, not an afterthought.
Outcome An architecture whose isolation strategy and design records were settled before layout, rather than negotiated after a review.
Diagram: isolation-barrier block drawing showing patient-connected, applied-part and mains-side domains. Original vector artwork, no client hardware.
Medical electronics differ from industrial electronics less in the circuit than in what counts as finished. A board that works is half the deliverable; the other half is being able to show why every decision was made, to someone who was not there.
The decision that shapes everything
On a patient-connected device the first architectural question is where the isolation barriers go — and everything downstream follows from the answer.
IEC 60601-1 does not ask “is it isolated.” It asks how many means of protection stand between the patient and a hazard, whether the device stays safe under a single fault, and whether you can demonstrate both. That determines the power architecture, the communications topology, which signals may cross which boundary, and how large the board has to be before a single track is drawn.
Get it wrong and it is not a component change. It is a different board.
What that means in practice
Creepage and clearance are layout constraints, not clearances to check later. The required distances depend on working voltage, pollution degree, insulation material group and the number of means of protection. They consume board area, dictate connector selection, and rule out routing that would otherwise be obvious. They belong in the design rule set before layout starts.
Isolation crossings are budgeted. Every signal that has to cross a barrier costs an isolator, board area and a power domain. Counting them early usually changes the architecture — often by moving a function to the other side of the barrier so it does not need to cross at all.
Single-fault thinking runs through the schematic. For each protective measure, what happens when it fails? That question drives component derating, redundancy where it is genuinely required, and the failure modes that have to be detectable rather than silent.
| Constraint | What it decides |
|---|---|
| Means of patient protection | Isolation ratings, barrier count, test voltages |
| Creepage and clearance | Board area, connector choice, routing keep-outs |
| Pollution degree and material group | Achievable distances for a given voltage |
| Single-fault condition | Derating, redundancy, detectability of failures |
| Assembly class (IPC-A-610 Class 3) | Process window, acceptance criteria, rework limits |
Documentation as a deliverable
In most sectors design records are a courtesy. Here they are part of the product.
Requirements traceability tables, written rationale for the decisions that carry safety weight, and review packages structured so an auditor can follow the reasoning without a guided tour. Scoped and priced as work, because that is what it is — and because retrofitting a design history file to a finished board is far more expensive than keeping it as you go.
What we do not do
We do not certify. Certification runs through a notified body, and any design house implying otherwise is overselling. Nor do we write the risk management file — that is the manufacturer’s, under ISO 14971.
What we do is make sure the electronics do not make certification harder than it needs to be: isolation and clearance correct from the schematic, component choices you can defend, and records that answer an auditor’s question rather than provoking three more.
Further images to produce
These slots are laid out and waiting for assets. Each carries its own
brief — see shotList in this project’s source file.
Layout detail: creepage and clearance across an isolation barrier, annotated with the distances. Generic illustration rather than the client board.
Optional: the traceability table format, cropped. Shows the documentation discipline without showing content.