T260 and T288 describe time-to-delamination results obtained at specified test temperatures of 260 °C and 288 °C. They help compare how laminate or board specimens respond to a defined thermal test. The numbers are not a count of permitted reflow cycles or a guarantee that a finished board will survive assembly.
For example, a reported T288 >30 min means the result exceeded 30 minutes under the stated test conditions. It does not mean that every finished board made from the material can remain at 288 °C for 30 minutes without damage. Before using the number, identify the specimen, method, conditioning and reporting limit, then consider the entire board construction and thermal history.
If you are diagnosing a board that already shows separation or blistering, start with PCB delamination and blistering. This page focuses on reading the time-to-delamination result before a material or build is released.
What do T260 and T288 measure?
In a thermomechanical analysis (TMA) test, an instrument monitors specimen movement in the thickness direction during a specified temperature program. The reported time is measured from the temperature or hold reference defined by the applicable test procedure to the detected endpoint. A thickness change can have several causes, so interpretation may require examining the specimen and the recorded curve.
- T260 identifies a result for a test at 260 °C.
- T288 identifies a result for a test at 288 °C.
- The number of minutes belongs to the specimen and procedure used, including the test endpoint and reporting limit.
IPC-TM-650 method 2.4.24.1 describes a TMA approach to time-to-delamination testing. Ask for the applicable revision and the laboratory report when a purchase specification or qualification requires the result; do not assume every product sheet supplies all test details.
How is time to delamination different from Tg and Td?
These properties answer different questions and cannot be used interchangeably.
| Property | What the result describes | How to read it |
|---|---|---|
| Tg | A glass-transition region in the resin system, reported by a particular method | Note the method, such as DSC or DMA. Tg is not a soldering limit or a continuous service rating. |
| Td | A reported decomposition temperature under a stated thermal-analysis criterion | Check the method and criterion, such as the specified weight loss. |
| T260 or T288 | Time associated with a specified test temperature and endpoint in a time-to-delamination test | Check specimen, conditioning, method, endpoint, hold time and whether a result is a minimum, typical value or reporting limit. |
| Z-axis CTE | Expansion behavior through the thickness of the material | Compare the applicable temperature range and whether values are reported below or above Tg. |
A higher Tg alone does not establish a higher T288. Nor does T288 alone describe expansion of a plated hole. Review the values alongside board thickness, layer construction, assembly cycles and the product's reliability requirements. For the broader meaning of Tg, see glass transition temperature; for a guide to thermal and electrical fields in laminate documents, see FR-4 material properties.
How should you read “greater than 30 minutes”?
A greater-than sign changes the meaning of a reported number. In T288 >30 min, the figure is a lower bound for the reported test conditions and endpoint. It does not provide the specimen's exact failure time. The test may have been stopped at a reporting limit or otherwise reported as exceeding that duration; check the source before describing the test termination.
Consider two hypothetical records:
| Record | What can be concluded | What remains unknown |
|---|---|---|
| T288 = 24 min | The reported endpoint occurred at 24 minutes under the documented conditions. | How a different specimen or a finished assembly would behave. |
| T288 >30 min | The reported result exceeded 30 minutes under the documented conditions. | The exact failure time, the results beyond the reporting interval, and suitability for a particular board. |
Do not convert either result into an allowed number of soldering cycles. A reflow profile includes heating, a peak temperature and cooling; a fixed-temperature material test is a different exposure. A finished board introduces additional variables, including copper patterns, interfaces and drilled holes; humidity and prior processing may also affect its response.
Example: identify the source and test conditions
The Isola FR408HR laminate and prepreg data sheet, Revision F dated 24 March 2026, lists T260 of 60 minutes and T288 greater than 30 minutes as typical values. The table identifies TMA, IPC-TM-650 2.4.24.1 and a copper-removed specimen. Those values belong to that supplier's document and its test conditions; they are not guaranteed minimums for all FR-4 materials.
A useful project record would preserve:
- Material supplier, product name and data-sheet revision.
- The specific T260 or T288 value, including
>or other inequality and the reported units. - Test method and revision, specimen type, construction and whether copper was removed.
- Conditioning, thermal ramp, hold time, endpoint and any reporting limit, where available.
- Whether the value is typical, a specification limit, or a measured result for a particular sample.
If the sheet omits a field, mark it as unknown and request the supporting report. Do not infer missing specimen-preparation or tolerance information from a different manufacturer's data sheet. Check the current supplier document before making the result part of a released requirement.
Can T260 and T288 values be compared between materials?
Yes, for initial screening, provided the reported conditions and limitations are understood. Similar labels do not ensure the samples had identical thickness, construction, foil condition or moisture history. Published TMA work has reported specimen-thickness effects, and an IPC-published study has also examined the influence of moisture conditioning.
Use this sequence before ranking candidates:
- Check that the two values refer to the same hold temperature: T260 and T288 are different tests.
- Separate a typical product-sheet value from a contractual minimum or a measured lot result.
- Check specimen type and preparation, including foil, thickness and conditioning.
- Check the method, temperature program and endpoint against the current report.
- Treat
>30as a bound, not as an exact result. Two materials reported>30are not ranked by those numbers alone. - Ask the product owner what finished-board and assembly tests are needed for the intended environment.
A longer time can be useful evidence under comparable test conditions, but it does not establish all aspects of laminate quality. For controlled-impedance boards, the electrical stackup still needs evaluation. For thermal cycling or demanding plated-hole designs, expansion, construction and product validation remain separate questions.
What should the fabricator and product owner confirm?
A material-selection discussion is more productive when the release package states the reason behind the limit. The designer or product owner should define the intended service and assembly exposures, electrical constraints, and the evidence needed to approve the design. The fabrication supplier should identify the proposed laminate and prepreg construction, confirm what material documentation can be supplied and flag feasibility or substitution questions. The assembly team should provide the expected thermal profile and rework exposure.
The product owner decides whether the assembled product has passed its own qualification requirements. A laminate data sheet, a supplier's construction confirmation and a product qualification report are different forms of evidence.
Material and process handoff checklist
- Identify the laminate system, proposed core and prepreg, and any approved alternatives.
- Record the applicable T260 or T288 criterion only when it is relevant to the project, including method and specimen requirements.
- Share the layer count, finished thickness, copper construction and any critical plated-hole or controlled-impedance requirements.
- Provide the intended assembly profile, number of thermal excursions and known storage or moisture conditions.
- Specify which document or test report is required, who reviews any proposed change, and whether new validation is needed.
For the wider material choice, see PCB material selection. A project-specific supplier discussion can clarify which documented material options and test records are available for the proposed build.
Frequently asked questions
Does T288 give the maximum PCB operating temperature?
No. T288 describes a time-to-delamination test at a specified temperature and method. It is not a continuous operating-temperature rating or an approved assembly profile.
Is T288 higher than Tg?
Tg is a transition temperature reported by a particular test method, whereas T288 names a time-to-delamination test at 288 °C. The temperature in the test name and the material's Tg describe different things.
Does a higher T260 guarantee a better finished board?
No. It is one test result for a particular specimen. Finished-board performance also depends on materials, construction, processing, moisture and the product's validation requirements.
Can T260 be converted to T288?
A reliable universal conversion cannot be assumed. Results depend on the material, temperature, specimen and procedure. Obtain the required test value from an applicable source.
What if the data sheet only says “greater than 30 minutes”?
Keep the greater-than sign and the conditions. It establishes a reported lower bound, not an exact failure time or a guaranteed survival time for every finished PCB.
References
- Isola, FR408HR Laminate and Prepreg, Revision F, 24 March 2026, typical values table.
- IPC-TM-650, method 2.4.24.1, Time to Delamination (TMA Method); confirm applicable revision.
- IPC APEX conference paper, Impact of Moisture Content on Printed Circuit Board Laminate Thermal Properties.