I can't answer your question directly from a specification point of view. I do not know what the standards may be. From a practicle point of view I would question material with less than a 10-minute time to delamination and even then I would be skeptical.
The problem with T260 is that it has only one thermal cycle. Some poor performing materials can handle one thermal excursion well but are significantly, adversely affected after 3 thermal excursions, which is what most PWBs are exposed to during assembly.
Our company has adopted a "cyclic" T260 (cT260) protocol where a material is thermal cycled to 260 6 times, to simulate assembly (3 cycles) and rework (3 cycles), and then held at 260C until delamination. The cycle we use is a six-step ramp to 260C followed with a 100C/min cool cycle. The total cycle, ambient to ambient is about 6 minutes. Samples from known low reliability boards, where, based on microscopic examination, there are no obvious process problems like low copper etc., fail in less then 10 minutes.
What we have found is that some "high performance" materials degrade with thermal cycling to 260C. A single thermal excursion to 260C is not a very accurate tool for measuring materials reliability.
Even though this is a delamination test, it is important to know that PWBs fabricated with material that have poor cT260 results usually do not fail for delamination. The common failure is barrel cracks in the central zone of the PTH.
Paul Reid
613 596 4244 ext. 229
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Wolfgang Erat
Sent: Friday, October 06, 2006 5:22 PM
To: [log in to unmask]
Subject: [TN] T-260 laminate testing
Good day
What are acceptability minimum results for T-260 testing.
The laminate in question is rather basic FR-4 with a Tg of 140
Doing some searching I come up with numbers anywhere between 5 minutes
and 30 minutes. Any insight is appreciated.
Wolfgang
[log in to unmask]
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