Part of the rigid-flex circuit board resource.
A rigid-flex PCB can connect the electrode interface, sensing electronics, and battery region of an ECG patch while accommodating a curved package. The useful question is where the assembly should bend and where it must remain supported. Making every region flexible is not a substitute for defining those boundaries. Our rigid-flex PCB engineering resources explain the construction; this article develops a packaging review specifically for a chest-worn patch.
The following is an engineering planning framework, not a clinical design, a qualified medical device, or a claim that a particular commercial monitor uses rigid-flex. Electrode selection, electrical safety, skin-contact materials, and clinical performance require their own product-level verification.
Begin with three mechanical interfaces
Before routing, draw three interfaces separately: the electrode-to-skin contact, the board-to-enclosure support, and the battery-to-electronics connection. Mark which parts are disposable, which can be reused, and which must be disconnected. A continuous circuit can simplify an internal connection but can also make replacement more difficult.
For example, consider a conceptual reusable electronics pod on a disposable electrode patch. An integral flex tail may suit an internal connection inside the pod. It does not automatically solve the detachable interface to the disposable patch. Compare that boundary against a suitable connector or contact system before integrating both sides into one assembly.
Write down the intended wear and handling conditions as requirements to investigate: body movement, attachment and removal, transport, storage, and any permitted cleaning. Avoid describing the board merely as “flexible.” The manufacturing drawing needs to distinguish an assembly fold from a region expected to move repeatedly.
Separate electrode movement from component support
Analog Devices explains that electrode contact characteristics affect ECG signal quality, and that movement of the electrodes and the electronics can introduce artifacts. That is a reason to review mechanical behavior alongside the analog front end, rather than evaluating the circuit only while it sits still on a bench. See its wearable ECG design discussion.
For a candidate rigid-flex layout, identify a supported region for the sensing IC and its nearby circuitry. Then trace the load path from each electrode attachment to that region. Ask whether pulling the adhesive carrier, pressing the pod, or opening the enclosure could load a solder joint or sharply bend a transition. The goal of this review is to identify risks for prototype testing; a drawing alone cannot establish artifact performance.
Keep a separate list of electrical and mechanical failures. Intermittent electrode contact, conductor damage, and analog interference may produce superficially similar symptoms but demand different corrections. Measure the signal while observing the assembly so the investigation does not default to changing filters for every motion-related problem.
Compare the packaging architectures
| Candidate | Question it can address | Tradeoff to review |
|---|---|---|
| Rigid sensing board with separate interconnect | Can a replaceable connection meet the package envelope? | Connector space, assembly access, retention, and contact reliability. |
| Flex circuit with local reinforcement | Does the product need a thin routing carrier with supported attachment points? | Component support, handling fixtures, and the boundary of each reinforced area. |
| Integrated rigid-flex with multiple rigid regions | Must component regions occupy different orientations inside one package? | Fabrication complexity, transition geometry, assembly sequence, and replacement scope. |
Use the same enclosure and service requirements when comparing these candidates. Comparing a bare rigid-flex board against a fully packaged alternative hides important differences. Include the battery holder, mechanical supports, electrode attachment, seals, and test access in each concept. The broader rigid-flex applications overview provides context for other product types.
Let the battery choice influence the outline early
TI’s TIDA-010280 Holter reference platform combines ECG acquisition with wireless communication and documents alternative battery arrangements. Its relevance here is architectural: the power source and conversion circuitry belong in the system definition before the enclosure outline is frozen. It is not evidence that an arbitrary patch will achieve the reference platform’s performance.
Create an assembly sketch showing how the cell enters the product and what takes the insertion force. If replacement is allowed, reserve the access route and define what the user can touch. If replacement is not allowed, document the manufacturing connection and the inspection step before enclosure closure. In both cases, decide how the circuit is supported during battery installation.
Place the battery envelope in the mechanical model, including its attachment hardware and applicable tolerances. Review whether a displaced cell or a compressed enclosure can contact the flex span. A nominally clear drawing should become a set of measurable assembly checks, not an assumption of clearance under every condition.
Describe the flex region as a controlled part of the assembly
Altium’s rigid-flex documentation distinguishes static and dynamic use, supports different regional stacks, and describes folded-state inspection. Use those modeling capabilities to communicate geometry. They do not replace mechanical qualification of the finished patch.
For each flexible region, specify its endpoints, available free length, intended direction of motion, enclosure restraints, and whether it bends during assembly or service. Ask the fabricator to review the proposed material stack and transition details against those requirements. Do not transfer a generic minimum bend-radius ratio into a product lifetime claim.
Our regional stackup planning tool can help organize the discussion. Treat its output as a concept to review, and use the rigid-flex design guidelines when preparing the fabrication notes. Include both the flat manufacturing view and the intended assembled position.
Prototype the interfaces before optimizing the board area
A useful early prototype answers a small set of packaging questions. Can the assembly be installed without forcing the flexible section? Does the enclosure support the intended rigid regions? Can the electrode interface be attached and removed as intended? Is there access to inspect the battery connection before sealing?
Build a test matrix that separates mechanical handling, electrical acquisition, and environmental exposure. Start with controlled bench signals and defined motions, then use the product team’s approved verification approach for subsequent evaluations. Record configuration changes so an improvement is attributable to a specific revision. Neither a continuity check nor a clean stationary trace establishes complete device suitability.
- Identify the exact prototype stack, enclosure revision, electrode interface, and battery assembly.
- Record the applied movement or handling sequence rather than using “normal use” as the test description.
- Inspect transition regions and connection points before and after testing.
- Compare signal behavior with wireless and power functions in the intended operating states.
- Define acceptance criteria and responsible reviewers before interpreting the results.
Questions to settle before requesting fabrication
Does an ECG patch require rigid-flex?
No. Choose it when the regional geometry and integration benefits justify the construction. A supported rigid board or reinforced flex may fit the requirements. Compare complete assemblies before selecting the board technology.
Can the flex section serve as a battery hinge?
Only treat it that way if the design explicitly addresses the resulting motion and loading. A connection intended to fold during assembly should not silently become a repeated service hinge.
What belongs in the initial RFQ?
Provide the regional stack concept, flat outline, assembled geometry, supported areas, expected motion, electrode connection concept, battery installation sequence, and inspection requirements. Mark unresolved assumptions. Request a project-specific review with that information so the discussion starts with the actual assembly constraints.