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A trade name such as oil, coolant or cleaner is not a complete exposure specification. Additives, absorbed water, oxidation state, contaminants and temperature can change how a liquid interacts with conductors, resistors, overglaze, contacts, terminals and seals. This guide owns selection of the chemical and temperature states that belong in a project matrix. The separate exposure-timing owner defines removal, drying and measurement chronology after a medium is selected. Neither page declares universal chemical resistance or infers service life from a short soak.
Key design decisions
- Identify real formulations, concentration ranges, contamination and aging states instead of using generic fluid families.
- Separate immersion, splash, vapor, condensation, residue and recovery because they load the card differently.
- Treat temperature acceleration as empirical unless one unchanged degradation mechanism and its model parameters are established.
Inventory every exposed material and interface
Map the path from external medium to each functional surface. Record substrate, fired resistor, conductor, protective glass overglaze where present, exposed contact path, terminal finish, solder or attachment, polymer carrier, adhesive, seal and connector. A coating that protects one resistor region may end at the sliding track, leaving an edge or conductor transition exposed. The material name alone is insufficient; identify drawing revision, supplier grade when controlled, cure or firing state and any post-process cleaning relevant to the interface.
Distinguish direct exposure from secondary transfer. A sealed card can still encounter vapor, permeation, condensate or fluid carried along a shaft. A terminal outside the nominal wet zone may see residue during maintenance. Mark contact-motion regions separately because wiping can remove films, transport debris or expose fresh surface. Unknown materials and hidden interfaces remain open inputs; they must not be filled with a generic statement that ceramic is chemically inert.
Replace media names with chemical states
For each medium, record product identifier or composition, base chemistry, additive package when known, concentration, pH where relevant, water content, dissolved ions, particulate contamination and oxidation or aging state. A new service fluid can differ from drained field fluid. Cleaning agents may be diluted incorrectly or mixed with process residue. If the exact formulation is confidential, the system owner can provide bounded constituent classes or arrange testing with supplied samples while preserving the uncertainty in public claims.
Create separate entries for credible worst states rather than blending them into an average. Examples include fresh fluid, water-contaminated fluid, thermally aged fluid, a mixed maintenance residue and a specified cleaner. The selection should come from the real application and service procedure. Do not import a competitor's compatibility table or one polymer vendor's immersion rating as proof for a complete printed-card assembly.
Define how the medium reaches the card
Describe exposure mode, wetted area, orientation, pressure, flow, replenishment, aeration and duration. Continuous immersion maintains contact differently from periodic splash. Vapor may condense at a cooler surface. A small droplet at a conductor-overglaze edge can create a concentrated local condition after evaporation. Flow across a wiper path can transport debris, while static immersion may not reproduce that motion. Map each exposure to operating, storage, cleaning, assembly or fault state.
Use a time history rather than one total duration when cycling matters. Record wet time, dry time, drain orientation and recovery period before electrical reading. If the product moves while wet, include stroke, contact load and electrical bias; if it remains stationary, state that. A compatibility conclusion from static coupons cannot automatically cover a loaded sliding contact. Likewise, an assembled-device result may confound card, seal and connector effects unless observations separate them.
Couple chemistry to measured temperature
Assign fluid and specimen temperatures to every exposure state, including ramp, dwell and gradients where relevant. Ambient oven setting is not proof of interface temperature. Heating can change viscosity, evaporation, reaction rate, dissolved gas and concentration at a drying edge. Cooling can create condensation or phase separation. Use sensors and locations suited to the question, and record whether the medium is replenished or allowed to age during the test.
An Arrhenius expression k=A exp[-E_a/(RT)] is usable only when one degradation mechanism remains dominant and A and E_a are established for the relevant material system. Without that evidence, tests at 25, 60 and 90 degrees Celsius are three empirical conditions, not a universal acceleration ladder. For example, an observed twofold change cannot be extrapolated across temperatures if evaporation creates a different exposure or a seal opens another ingress path. Preserve temperature-time combinations separately until mechanism equivalence is demonstrated.
| Dimension | Required record | Why the distinction matters |
|---|---|---|
| Chemistry | Formulation, concentration, contamination and age | Generic names hide active constituents |
| Contact mode | Immersion, splash, vapor, residue or condensation | Wetting and transport differ |
| Temperature-time | Fluid and specimen histories | Reaction, viscosity and evaporation change |
| Functional state | Motion, load, bias and recovery | The exposed interface may change during use |
Select a small matrix that separates chemical questions
Choose rows because they test different formulation or temperature hypotheses, not because a long list appears comprehensive. A useful minimum might pair fresh and aged fluid at the normal upper temperature, then add a water-contaminated or cleaner-residue state when the service history supports it. If two commercial formulations share a base fluid but use different additive packages, keep them separate. Every row must identify why it could change an exposed material interface and what decision its comparison supports.
Use controls to distinguish media selection from other causes. A thermal control experiences the same time and temperature without the test medium. A stationary exposed specimen can be compared with a moving exposed specimen when wiper interaction matters. A protected witness can reveal whether change concentrates at a coating boundary. Detailed removal and recovery chronology belongs to the measurement-timing owner; this selection record only requires that candidate rows use one comparable controlled method.
Interpret location-specific compatibility signatures
A change confined to the wetting line can indicate concentration during evaporation or repeated meniscus motion. Discoloration beside an overglaze edge points to an interface location but does not identify the chemical mechanism. Increased intermittent output only while moving wet suggests contact-film or debris transport effects. A stable card measurement with connector drift directs attention outside the printed track. Cracking or loss near an attachment may involve differential swelling or mechanical stress rather than direct resistor attack.
Pair signatures with microscopy or other appropriate analysis only where supported. Avoid naming corrosion, dissolution, swelling or leaching solely from color. Record the affected material, coordinates, exposure phase and whether the condition persists after controlled recovery. If several materials changed together, use additional controls or cross-sections approved for the project. The public conclusion should remain bounded to observed conditions and must not become an all-chemicals resistance claim.
Set a rule for adding or removing matrix rows
Define what makes one chemistry-temperature row necessary: a distinct additive, contamination route, phase state, evaporation concentration, material interface or service excursion. Conversely, do not treat two nominal labels as separate rows when composition and exposure bounds are demonstrably equivalent for the question. Retain the rationale and uncertainty. Selection is complete when credible application states are bracketed and every row has a decision purpose, not when an arbitrary media count has been reached.
Separate screening from qualification. A short comparison can eliminate clearly unsuitable combinations but cannot establish a service interval. A component exposure can examine the card under bounded conditions but may not cover seals, wiring and replenishment. An assembled system test can address those interfaces yet needs diagnostics to assign cause. Identify the evidence level before testing so selection of one representative medium is not later presented as qualification of every formulation in its commercial family.
Release a controlled media-compatibility matrix
The released matrix should list each medium state, supplier or composition reference, concentration, contamination, aging, exposure mode, wetted regions, orientation, temperature-time history, motion, electrical bias, recovery and criterion. Link specimen material-stack and drawing revisions. Retain actual fluid lot or sample traceability where appropriate. Changes to formulation, cleaner, seal, card coating boundary, terminal, contact material or service temperature reopen the affected assessment.
For an engineering review, provide safety information through the proper channel, representative media samples where permitted, material stack, drawings, exposed areas, service and cleaning sequences, temperature histories, motion and load, electrical state, expected lifetime usage, functional limits and prior signatures. The review can propose a bounded specimen matrix and observations by application review. Handling, disposal and hazardous testing require the customer's safety requirements and suitable facilities; no unsupported chemical-processing capability is implied.
Define a resistor-card media compatibility program
Send the actual chemistry, exposure history and functional boundaries so the review addresses your service condition rather than a generic fluid name.
- Media identifiers, composition ranges and safety information
- Fresh, aged, contaminated and mixed states of concern
- Card material stack, coating boundaries and exposed interfaces
- Immersion, splash, vapor, residue and recovery sequences
- Fluid and specimen temperature-time histories
- Contact motion, load, electrical state and measurement method
- Functional criteria, service interval and required evidence level
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