T260 vs T288
Quality & Inspection Standards
PRODUCTS CENTER
Get Custom Quote
PRODUCTS CENTER
T260 vs T288 – What These Thermal Stress Test Times Tell You About Laminate Robustness
T260 passed, T288 failed – and why that mattered
An aerospace PCB supplier qualified a polyimide laminate using T260 testing (260°C, 60 seconds, no delamination). The board passed. However, during lead‑free assembly reflow (peak 260°C), the board showed blistering. After switching to T288 test (288°C, 20 seconds), the same laminate failed within 10 seconds. The lesson: T260 is relevant for tin‑lead assembly (peak 245°C). For lead‑free assembly (peak 260°C, with some processes spiking to 265°C), T288 is more realistic. The supplier switched to a higher‑Tg polyimide that passed T288, and the blistering issue resolved.
What Are T260 and T288? – Not Just Temperatures, But Time to Delamination
T260 and T288 are not simply temperature setpoints. They are time‑to‑delamination measurements performed via Thermomechanical Analysis (TMA) per IPC‑TM‑650 2.4.24.1 (or 2.4.24). The test measures how long a laminate can withstand a fixed temperature before the thickness expands rapidly due to decomposition or delamination.
- T260 – Time (in minutes) to delamination at 260°C. Historically used for tin‑lead assembly (peak reflow ~245°C).
- T288 – Time to delamination at 288°C. Used for lead‑free assembly (peak reflow 260‑265°C) and high‑reliability applications requiring margin.
The test procedure: heat a laminate coupon at 10°C/min to the target temperature (260°C or 288°C) and hold. The TMA probe measures Z‑axis expansion. When delamination occurs, the expansion rate spikes. The time from reaching target temperature to the onset of rapid expansion is recorded as T260 or T288.
Key insight: T260/T288 are indicators of laminate thermal decomposition resistance, not solderability. A high T260/T288 does not guarantee good solderability, but low values guarantee field failures under thermal stress.
Typical Values and Acceptance Criteria – What Is “Good”?
Industry acceptance criteria vary by material grade and application. The table below summarizes typical requirements.
| Material Grade | T260 (min) | T288 (min) | Typical IPC‑4101 Slash Sheet |
|---|---|---|---|
| Standard FR‑4 (low Tg) | ≥10 | Not applicable (fails quickly) | /21, /24 (no T288 requirement) |
| Mid‑Tg FR‑4 (Tg 150‑170°C) | ≥20 | ≥5 (limited) | /26, /98 (some specify T288) |
| High‑Tg FR‑4 (Tg 170‑190°C) | ≥30 | ≥10‑15 | /126, /128 |
| Polyimide / Cyanate Ester | >60 | ≥30 | /42, /43 (space grade) |
| PTFE / Hydrocarbon (RF) | >60 (typically no requirement) | N/A (different failure mode) | Rogers, Taconic (not IPC‑4101) |
For lead‑free assembly (SAC305, peak 260°C), a T288 of ≥10 minutes is considered the minimum for Class 2/3. Aerospace and automotive often require T288 ≥20 minutes.
T260 vs T288 – Which Should You Specify?
The choice depends on your assembly process and reliability requirements. Use the decision matrix below.
| Application / Assembly | Recommended Test | Typical Requirement | Rationale |
|---|---|---|---|
| Tin‑lead assembly (SnPb, peak 245°C) | T260 only | ≥20 min (Class 2), ≥30 min (Class 3) | T288 is unnecessarily stringent; T260 gives margin against process spikes. |
| Lead‑free assembly (SAC305, peak 260°C) | T288 (and optionally T260) | ≥10‑15 min (Class 2), ≥20 min (Class 3) | T288 correlates directly to lead‑free reflow temperature. |
| High‑reliability lead‑free (automotive, medical) | T288 only, high margin | ≥30 min | Longer time ensures multiple reflow passes or rework margin. |
| Aerospace / space (polyimide) | T288 | ≥30 min, often >60 min | Extreme reliability, multiple reflows, potential repair. |
| Legacy / low‑cost consumer (SnPb) | T260 (often waived) | ≥10 min | Basic requirement; T288 not cost‑justified. |
Our internal rule: For any board assembled with lead‑free solder and requiring >2 reflow passes, we require T288 ≥20 minutes. For boards with ≥6 layers or high copper density, increase to ≥30 minutes due to higher thermal mass.
Test Method – IPC‑TM‑650 2.4.24.1 (TMA)
The standard method for T260/T288 measurement is Thermomechanical Analysis (TMA) per IPC‑TM‑650 2.4.24.1. Here's the procedure:
- Cut a small laminate coupon (typically 5×5 mm) from the finished board (after processing).
- Load into TMA with a probe contacting the surface. Apply a small force (typically 5‑10 mN).
- Heat at 10°C/min to the target temperature (260°C or 288°C). Hold isothermally for up to 60 minutes.
- Monitor Z‑axis expansion. Delamination onset is identified as a sharp increase in expansion rate (or a step change in thickness).
- Record the time from reaching target temperature to the onset of rapid expansion = T260 or T288.
Note: Some suppliers use TMA on bare laminate only, but we require testing on finished boards after lamination and copper etching to capture real process effects (e.g., residual stress, moisture absorption).
What Low T260/T288 Values Indicate – Root Causes
If a material fails T260 or T288 (delamination occurs too quickly), the likely root causes are:
- Poor resin system – Low cross‑link density, inadequate thermal stability.
- Moisture absorption – Laminate not dried before testing. Moisture vaporizes at high temperature, causing delamination.
- Incomplete cure – Lamination press cycle insufficient for the resin system.
- Contamination – Ionic residues or foreign material in the prepreg.
We have seen T288 values drop from 30 minutes to 5 minutes after a supplier changed prepreg lots without requalification. The new lot had lower resin content. Regular T288 monitoring caught the drift.
Supplier Audit Checklist – T260/T288 Testing Capability
- Does the supplier have a TMA (thermomechanical analyzer) calibrated and validated for T260/T288 per IPC‑TM‑650 2.4.24.1?
- Do they test finished boards (after lamination and etching) or only bare laminate? (We require finished board testing.)
- What is their historical T260/T288 performance for the laminate you specify? (Ask for SPC charts.)
- Do they perform humidity preconditioning before testing? (IPC‑TM‑650 2.6.1 recommends drying, but we test as‑received to catch moisture issues.)
- Can they provide raw TMA expansion curves, not just a “pass/fail” number?
Related Engineering Resources
Frequently Asked Questions
A> Not necessarily. For tin‑lead assembly (peak 245°C), T260 is sufficient; T288 is over‑specification and may unnecessarily limit material choices. Specify the test that matches your assembly process.
A> Yes. Many mid‑Tg FR‑4 materials have good stability at 260°C but decompose rapidly at 288°C. If you use lead‑free assembly, T288 failure indicates risk of delamination during reflow.
A> Significantly. A dry laminate may have T288 >20 minutes; the same laminate at 0.5% moisture content may drop to <5 minutes. We test as‑received to simulate real‑world storage conditions.
A> IPC‑6012 does not directly mandate T260/T288 values. However, many customers (automotive, aerospace) include them in their procurement specifications. Check your customer's requirements.
A> Td is the temperature at which 5% weight loss occurs (TGA). T260/T288 are time‑based delamination tests at fixed temperatures. Td is a single‑point temperature; T260/T288 measure robustness over time.
Reference standards: IPC‑TM‑650 2.4.24.1 (TMA for delamination time), IPC‑4101 (laminate specifications), IPC‑6012, J‑STD‑020 (reflow profiles).
Specifying T260 or T288 for your PCB laminate?
We help define the right test based on your assembly process (tin‑lead vs lead‑free), board complexity, and reliability targets.
Request a Laminate Thermal Qualification Review →Get Custom Quote
PRODUCTS CENTER
World-class PCB & PCBA manufacturer focused on high-frequency and high-reliability boards for defense, aerospace, automotive and industrial electronics.
You can unsubscribe at any time with a single click.
Copyright © 2025 UltroNiu Electronics Group All Rights reserved.