The capability extract shows in thirty seconds what runs as standard and what carries a surcharge.
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To the data check →Sensor front ends work with signals small enough that the board itself becomes part of the measurement. Leakage across a contaminated surface, a dielectric that drifts, a thickness that varies between lots — each one shows up as measurement error rather than as a failure.
What sensor work needs from a PCB is unusual: not the finest structures or the highest layer count, but consistency. A capacitive front end reading femtofarads cares that the dielectric thickness is the same this month as last; a high-impedance amplifier input cares that flux residue is not quietly providing a leakage path across the guard ring.
That pushes the specification in directions that look conservative on paper. Class 3 acceptance, controlled ionic contamination, tightened thickness tolerance, and often ceramic rather than an organic laminate where the temperature coefficient of the substrate would otherwise dominate the error budget. Fine structures matter far less here than reproducibility does.
Ionic contamination is measured rather than assumed. On a high-impedance input, residue is a leakage path and leakage is measurement error.
Thickness and dielectric consistency held lot to lot, so a sensor calibrated against one batch still reads correctly against the next.
FR-4 where it suffices, ceramic where the substrate's own temperature behaviour would otherwise dominate the error budget.
The parameters that matter for a sensor front end, and how they are verified.
| Parameter | Control | Verification |
|---|---|---|
| Ionic contamination | Cleaning process controlled | ROSE or ion chromatography on request |
| Surface insulation resistance | Material and cleaning | SIR testing on request |
| Dielectric thickness | Tightened tolerance available | Microsection per lot |
| Dielectric constant | Material batch consistency | Laminate certification |
| Acceptance class | IPC-A-600 Class 3 | Documented inspection |
| Solder mask | Class H available | IPC-SM-840 |
| Guard ring geometry | As designed, mask pulled back | AOI and visual |
| Lot traceability | To laminate batch | Standard |
Guide values for pre-selection. Binding values are confirmed per project against your data.
The points below are what most often comes back as a query after data review. Settling them before layout freeze saves a loop.
A high-impedance input needs a driven guard on every layer it appears on, with solder mask pulled back so that no residue bridges the gap. Half a guard ring is often worse than none.
Standard cleaning is adequate for most work and inadequate for femtoamp inputs. If leakage matters, say so — it changes the process, not just the inspection.
Where the substrate's own dielectric drift with temperature enters the error budget, an organic laminate may be the limiting component. Ceramic removes that term entirely.
Sensors are calibrated against a specific build. A laminate substitution that would be invisible on a digital board can shift a calibration — treat the material as part of the design, not a purchasing variable.
For medical and safety-related sensing, usually yes. For industrial sensing it depends on what the acceptance criteria actually protect — Class 3 tightens annular ring and barrel copper, which may or may not be what limits your reliability.
When the substrate's temperature coefficient or its moisture uptake enters your error budget, or when the operating temperature is beyond what an organic laminate tolerates. Otherwise FR-4 with tightened tolerances is far more economical.
On request, yes, along with ionic contamination testing. Both are worth specifying up front on high-impedance designs rather than investigating after a yield problem.
Standard tolerance is what the laminate supplier certifies; tightened tolerance is available and verified by microsection. If your calibration depends on it, specify it — otherwise you get the standard band.
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