Arlon 85NT PCB: Polyimide Aramid Thermal Design

Use the product sheet instead of mixing older family summaries

The official 85NT sheet describes a pure polyimide system with Tg 250°C and nonwoven aramid reinforcement. It lists in-plane CTE of 7–9 ppm/°C and Td of 426°C. Some older overview tables use a different Tg headline, so retain the controlled product revision used for the actual decision.

These typical values do not define every finished stackup. Copper, direction and temperature range affect the composite response. A low in-plane value also does not substitute for the through-thickness data needed to review plated interconnects.

Evidence and construction decision

Define the package interface and the thermal sequence

Record the package material, footprint, attachment geometry, supports and operating excursion. Identify whether the concern is edge displacement, solder-joint loading, registration or another measurable requirement. Use a length that corresponds to that physical question.

Separately list lamination, finishing, assembly and rework exposures. An assembly can have modest operating temperature variation but severe manufacturing excursions. Those histories may require different evidence from the material and board suppliers.

Interpret the free-mismatch tool correctly

The worksheet calculates the difference in unconstrained expansion of two materials over a common length. With hypothetical coefficients of 15 and 5 ppm/°C, a 50 mm length and a 100°C rise, it gives 50 µm differential movement. No 85NT property is preselected as a design default.

The model does not solve the constrained assembly. It excludes bending, joint compliance, creep and fatigue. A smaller free mismatch can motivate further investigation, but cannot establish a quantified service-life improvement without an appropriate assembly model and test basis.

Free differential thermal expansion

Optional cost comparison from your own allowances

Use a quotation or a clearly labeled internal assumption for each input. Keep the quantity, construction and inspection scope the same when comparing alternatives. This uncalibrated planning model adds entered values; it contains no current market rates and does not issue a RAYPCB quotation. You can contact the team without completing it.

Compare epoxy and polyimide aramid routes deliberately

55NT uses epoxy with nonwoven aramid, while 45NK uses woven aramid. Preserve both resin and reinforcement architecture in the comparison. A similar CTE range does not make the products interchangeable under the same press or assembly process.

For a glass-reinforced polyimide route, 35N owns a different construction review. Choose the comparison according to the actual failure mechanism and controlled requirements, not a universal ranking of material names.

Include drilling, moisture and registration in the proposal

Low in-plane expansion does not eliminate process risks. The manufacturing team needs the layer structure, copper pattern, critical holes and dimensional tolerances. Material-specific handling and qualified processing remain necessary.

The public 85NT sheet contains an availability table whose 85N-prefixed entries and a drill-unit presentation need clarification before procurement or machine setup. Use controlled documents for the supplied material, and do not transform a website summary into a production recipe.

Ask for a construction and evidence plan

Provide exact 85NT callout, source revision, stackup, package interface, thermal range, assembly history and acceptance requirements. Include quantity and permitted alternatives. Identify which dimensional or reliability evidence is needed for the customer decision.

The optional budget worksheet adds only entered allowances and cannot establish current material pricing. Keep the approved construction, assumptions and verification boundary with the drawing. The useful outcome is a reviewable proposal; the online mismatch result is supporting arithmetic, not qualification of the finished board or assembly.

Review the package, board and attachment together

The finished board combines a dielectric, copper patterns, holes, surface coatings and a manufacturing history. Its behavior cannot be inferred from a family name alone. State the supplied grade, reinforcement, thickness, copper and processing conditions that matter to the intended application.

Keep handling and assembly requirements with the fabrication drawing. A thin panel, punched outline or unusual support condition can change the production route even when the electrical circuit is simple. Ask the fabricator to review the actual features and panel format rather than assuming a dimensional example represents a production capability.

For cost comparison, hold the drawing, quantity, test scope and acceptance requirements constant. Record one-time tooling separately from recurring work, and distinguish raw material utilization from accepted-board yield. Any calculator on this page uses supplied assumptions; an actual quotation requires the files and an agreed scope.

A source-qualified table should be read alongside the exclusions and footnotes, not separated from them. If the supplier limits an application, identify whether that limitation affects the current design before requesting a price. A familiar family classification does not override an explicit restriction, and a positive calculator result cannot remove it.

For a repeat build, compare the newly proposed supply with the previously approved material record. Exact grade, manufacturing site where relevant, foil treatment, reinforcement and dimensional basis can matter. Define which changes require notification and which need technical approval. This avoids turning a purchasing substitution into an unnoticed design change.

Receiving records should support the agreed identity and traceability requirement. A certificate for a raw material, a finished-board inspection report and an assembly test result cover different boundaries. Request the records that actually answer the project questions rather than collecting unrelated certificates.

When a source contains conflicting values, keep the discrepancy visible until a controlled revision or written supplier response resolves it. Do not create a new table by combining the most favorable entries from several sources. The released drawing, material list and quotation should all describe the same accepted construction.

Compare in-plane expansion along the same direction and temperature interval. A package body, ceramic carrier, copper pattern and reinforced board need not move equally. The free differential-expansion result identifies a dimensional mismatch; it does not calculate solder-joint strain because joint geometry, distance from the neutral point, constraints and temperature cycling are excluded.

Record woven or nonwoven reinforcement explicitly. The fiber architecture can affect drilling, dimensional behavior and moisture response independently of the resin family. Do not choose a replacement solely because its nominal expansion is close to a package value. The finished construction and attachment must be reviewed together, including any permitted assembly repair.