Chris
In the paper referred to below I demonstrated that the shear component of
the peel rupture is of the same order of magnitude as the tensile component
and that both stress are dependent upon the local radius of curvature at the
rupture point; which is not controlled. This paper also contained numerous
examples of the inadequacy of the peel test to discriminate between
acceptable and unacceptable bonding of copper foil to substrate. When
failures occur due to thermal expansions etc The rupture stress is entirely
shear ( again see the paper). What is needed is a test that simulates this
condition. The T260 test is a good beginning, but has other issues.
Best regards
Lee
J. Lee Parker, Ph.D.
JLP Consultants LLC
804 779 3389
----- Original Message -----
From: "Chris Mahanna" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Friday, June 02, 2006 11:43 AM
Subject: Re: [IPC-600-6012] Bond Strength -vs- Peel Strength
Of course one could and should separate tensile and shear properties. But,
we as a standard body must think about the cost of testing and the return on
that investment. Essentially, the "bond strength" test (which is supposed
to measure tensile only) is too expensive to be done properly. Too many
uncertainties and non-linearity (probably caused by not truly being able to
separate tensile and shear). That's why Susan called the method
"Provisional". And that's why Russ only does it as a "process indicator",
or whatever you'd like to call it.
The historical "rework/unsupported hole bond strength" testing is pretty
good methodology because it controls many of the uncertainties through
coaxial geometry. This test vehicle could be mimicked on a new board
designs, but I haven't seen it done. Of course, it also incorporates the
rework heat cycles.
I would conjecture that:
1) there are people out there that understand this much better than I, and
2) they would say that while peel strength is a combination of tensile and
shear, it is controlled by defining the bend radius (thickness of foil and
no surface finish)
3) the peel methodology is capable of discriminating "good" foil laminating
from "bad", pass/fail requirements are in place, and testing is already
required.
IMO, to add bond strength testing as a spec. req. one would need to show
that peel methodology is not capable of discriminating "good" foil
laminating from "bad".
Chris
Chris Mahanna
Quality Manager
Robisan Laboratory Inc.
6502 E 21st Street
Indianapolis, Indiana 46219
phone 317.353.6249
fax 317.917.2379
-----Original Message-----
From: IPC-600-6012 [mailto:[log in to unmask]]On Behalf Of Lee parker
Sent: Wednesday, May 31, 2006 10:29 AM
To: [log in to unmask]
Subject: Re: [IPC-600-6012] Bond Strength -vs- Peel Strength
Franklin
At the 2005 Expo I presented a paper that quantified both of these
measurements in terms of the first principals tensile and shear stresses at
the point of rupture. The peel test produces a simultaneous and essentially
uncontrolled combination of both tensile and shear stresses. Ideally you
would prefer only one of these stress to be present an the extent
measurable. The thermal stress test produces only a shear stress between
layers of materials. The drawback here is that the temperature is dynamic
and consequently the stress changes until the entire package reaches thermal
equilibrium. Of the two I prefer the thermal test, but the drawbacks can be
signoficant.
Best regards
Lee
J. Lee Parker, Ph.D.
JLP Consultants LLC
804 779 3389
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