Patrick Hassell ([log in to unmask]) wrote:

>Mr. Franck, Mr. Paul, and others:
>
>Mr. Paul's last comment on the utility of the existing bow and twist
>measurement guidelines is an important issue.  Mr. Paul noted (in general)
>that the test method should be used as a base line measurement for analyzing
>the effectiveness of process/material improvements.
>
>It is apparent that the existing guidelines and procedures surrounding bow
>and twist have two major shortcomings.

(snip)

>Second, information and know-how on bow and twist does not exist in a readily
>transferable knowledge base.

>It appears that most manufacturers are
>dependent upon certain key individuals with years and years of experience to
>identify causes of excessive warpage and to correct it.  The problem lies in
>the fact that the decisions these key individuals make to solve problems are
>based upon something they have seen or done before.  As effective as they may
>be in solving the problem, once the person is gone it is tough to replace
>them.  A quantifiable knowledge base is not left behind for others to work
>with/from.

Yes, sounds true. That would be me. That would also be what I call "job
security".

>A new technology developed at the Georgia Institute of Technology (Georgia
>Tech), Atlanta, Georgia, may help address the two issues outlined in the
>above paragraphs.  A technique was developed which allows assemblers to
>monitor, in real-time, thermally induced warpage during processing (e.g. IR
>reflow, wave solder, convective reflow, UV cure, etc.).  The technology was
>licensed to a spin-off, start-up company which has commercialized the
>measurement service under the tradename TherMoire.
>
>TherMoire incorporates a well known, and proven technique called shadow
>moire.  Shadow moire is an optical technique which is capable of
>characterizing surfaces in the z-axis dimension.  Basically, it provides a
>topographic map of large area surfaces, much like the contour maps produced
>by the US Geological Survey.

Oh, yeah! the old shadow moire' thing! (Let me look in my desk, here...)

(snip, snip)

>I look forward to meeting and working with many of you in the months ahead.

I apologize if this sounds hypercritical, but groaning...

Warping of boards is a chronic problem, usually largely due to design
characteristics in the original artworks. It is not easy to deal with, even
if you have good data showing just how extensive it is, and defining every
metric with a real time data parametric SVGA color display.

IMO, it also has something to do with weaving cloth out of glass fibers,
soaking several layers with plastic resins, laminating it with metal foil,
smashing it with tons of pressure and heat (repeat that part a couple
times), drilling a few hundred holes in it, plating some metal, etching off
some of the metal in a bizarre pattern, routing it out to some irregular
shape, then immersing it in molten metal. Then we stuff a couple hundred
complex little metal, ceramic, and plastic parts on it, submerge the whole
mess in molten solder or heat it past the glass transition point and back
in a couple minutes, with all that solder re-solidified and those parts
stuck neatly in place.

And then you have some newly revised and official-as-heck specification,
with detailed illustrations (requiring the whole thing to be flatter than a
sheet of plywood at that scale) which can best be interpreted with a
granite tool base and some dial indicators if holding your mouth just
right. Been there, done that.

You got several kinds of metal, plastic, acid, solvent, heat,
polymerization, glass transition, thermal coefficients and mismatches, you
got your basic WARP, man. It's ugly, we've all seen it. Or maybe you
prefer, "the extended process sequence acting on a heterogenous mass tends
to produce a measureable displacement from a geometric plane". Scientific
analysis is bound to solve it someday. I've been waiting...

But if it _somehow_ is not "in spec", then they come over and ask old
non-portable, unquantifiable me: "Jerry, whatta we do now?".

IMO, having a new machine to put that board in would be really cool. You'd
just tell them: "fire up that TherMoire (tm) shadow moire and access the
readily transferable data base, while I go for some coffee". Maybe I'll get
one more level of management outta this.

And I love such high tech tools myself, but let me warn you that if it
costs about 1.5 years of my salary, my Company will likely never own one.
Yes, even if it flouresces X-ray laser beams and has a 133 mHz Pentium; but
especially if that new instrument doesn't give you the first clue as to
what to do next...

But then, maybe you'll have that worked out, too. Guess I better up my 401K
next year...


good luck at Nepcon ;-)


Jerry Cupples
Interphase Corporation
Dallas, TX
http://www.iphase.com

p.s if you got more than one copy of this, it didn't originate here...