Engineering resources
Polyimide versus epoxy for a thermally cycled assembly
Choosing between a polyimide and an epoxy PCB begins with the assembly’s temperature history. Two designs described as high temperature may present very different problems: one experiences brief soldering excursions, while another spends thousands of hours warm and repeatedly returns to a cold environment. A resin family name does not resolve that difference.
Write the exposure before comparing the materials
Record minimum and maximum board temperatures, dwell durations, ramp rates, expected cycle count and whether the assembly is powered. Identify the measurement location. Chamber air, a component case and a plated through-hole region are different locations; use the location relevant to the requirement. Keep assembly exposure separate from service exposure so neither disappears inside a single maximum-temperature entry.
Arlon identifies 85N as a polyimide laminate and prepreg system and 45N as a multifunctional epoxy system. Their data sheets offer material-specific evidence, but a comparison must retain the measurement methods and conditions. A higher listed transition temperature is not a guaranteed lifetime for your assembled board.
Build a decision table around failure consequences
| Design concern | Information to supply | Evidence to request |
|---|---|---|
| Through-hole integrity | Board thickness, hole structures, cycling profile | Representative interconnect test plan |
| Component attachment | Package geometry and soldering sequence | Assembly-level assessment |
| Dimensional fit | Mounting constraints and connector positions | Measured fit across the operating range |
| Material substitution | Exact candidate grades and constructions | Documented comparison and approval |
A useful comparison experiment
Hypothetical project. A controller team is considering two material systems for a six-layer board. Comparing two samples made with different hole sizes, copper weights and stack thicknesses would mix material effects with geometry effects. Instead, define which variables are held constant and which must change because the materials require different constructions. Record both the proposed changes and why they are necessary.
Agree on measurements before testing: baseline continuity, the electrical monitoring approach during cycling, dimensional checks and the post-test inspection needed to resolve suspect results. A board that still powers on may leave intermittent interconnect behavior unexplored. Conversely, a failed test needs failure analysis before it is attributed to the resin family.
Make the selection reviewable
Use a candidate matrix with columns for supported requirements, open questions and evidence. A blank field is an unresolved item, not a pass. Where service data are unavailable, state the uncertainty and assign the next qualification action. Purchasing should receive the approved material designation and substitution rule, rather than a generic instruction to buy the higher-Tg option.
Compare the exact grades in the material directory, then attach the thermal profile to the manufacturing review. This connects material selection to the physical board and its intended life.
Project review
Send your drawing and project requirements for a fabrication review. Identify the board revision, intended material and any acceptance requirements with your attachments.
Sources and scope
References checked 9 October 2026. The worksheets and hypothetical examples are original editorial guidance. They do not establish production settings, material availability or approval of a particular construction.