Folks,

I may be fooling myself, but this subject is important. As I have reached
the maximum level of the Peter Principle, I really have nothing more to say
on the subject.

However, the following is a response to several off line responses to the
subject:


I agree with all your are saying. All I've been saying, throughout the long
IPC postings on this subject, is that selecting a high Tg material, for its
sake alone, is not the way to go. If needed, certainly use it, if one is
aware of its benefits or detractions. However, all other process
requirements must be met as well.

Certainly, as we have agreed before, Cu plating thickness, though getting
thinner, and ductility (not being assured, in my opinion, adequately with
respect to the former) must be ensured as well - especially in these ever
increasing higher aspect ratio holes. I know Ervin was trying to make this
point as several others said to me offline as well. Today's plating
chemistry and processes still have a way to go, so material alone is not
going to do it.

Also, I have said, Tg only assures more time before hole wall and associated
anomalies, or the reverse, develop. It may take 30% more time for polyimide
to come apart than an high Tg epoxy, but come apart it will over time. We've
all seen TMA and DSC evidence graphically (I will post one on Steve's site
if requested) showing this consistently as the temperature is applied over
time, as expansion takes place, before destruction at or about the rated Tg.
We all know this is because the PPM/C Z-axis expansion rate is about the
same for all materials using reinforced resin systems as epoxies, BT's, and
polyimides. Therefore, hole walls, and associated anomalies, coming apart
must be prevented at the design and process levels. Simply choosing a high
Tg material won't get the job done.

As for the solder floats, and very serious pre-conditioning requirements,
550 for 10 thermal stress, notwithstanding serious thermal shock testing, is
pretty severe even today. This is true though some manual soldering
processes see higher temps, times usually are much shorter. Most certainly
recognize that, even though a soldering iron's tip temperature may be as
high as 800 degrees, it isn't brought to bear on the solder termination
areas for anything approaching 10 seconds. Hardly anything survives these
temps for long durations. As you, and many others, have said before, you
must get on an off in a time consistent with effecting a quality solder
joint - unless you are seeking destruction.

Based on my personal email, and others, we would all appreciate your input,
like this, to be on the TechNet forum. I may be wrong, but it seems very
important stuff to a lot of people seeking this type input.

Also, I'm surprised not to see more of you folks, who have spent so much
time and effort developing all these incredible standards and specifications
(especially the 6010 series), attending this subject. They, unlike some
plated holes, just keep getting better. I, and others, must be missing
something, or it isn't that important after all.

Earl Moon

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