Bob,
Seems you are reading something into my initial enquiry/response to you
that you shouldn't. I am not upset about anything, simply trying to determine
the veracity of these comments that are being accredited to some Semi App notes.
You seem to have some knowledge that you were willing to share but some
of it seemed like it may be a little out of context. You hadn't worded your
comments in such a manner that I couldn't suspect that you might be talking
about a different case than I was. i.e. "via in pad" (microvias, etc., it is
all in your acceptance of the word's meaning) verses a "via" in a pad.
Your comment about experimenting is bang on, I don't want to become the
experimenter based upon somebody's unfounded theory that flies in the face of
the generally accepted practice. While somewhere there are sources proposing
this 13mil or smaller via in pads, it goes against everything I have previously
been taught and assured was the correct way. At least until you get down below
10 mils and are using laser drills anyway. I am sure the smaller vias would not
cause a problem, it is really the point at which to cross-over that is the real
question. I don't doubt that the statements would be true for a 6 mil via, are
they true for a 13 mil via though?
Sincerely,
Brad Velander
Senior PCB Designer
Northern Airborne Technology
#14 - 1925 Kirschner Road,
Kelowna, BC, V1Y 4N7.
tel (250) 763-2329 ext. 225
fax (250) 762-3374
-----Original Message-----
From: Bob Benjamin [mailto:[EMAIL PROTECTED]
Sent: Friday, December 09, 2005 10:59 AM
To: 'Dennis Saputelli'; 'Protel EDA Discussion List'
Subject: RE: [PEDA] Via size, lead free, etc.
Dennis (and Brad),
I may have opened Pandora's box. In essence I was trying to state that new
technologies are dictating changes in procedures. Some of them are driven
by cost, some by size, some of them by governments. Some issues of
reliability are of great concern, especially with lead-free. This issue
alone could be addressed with reams of paper and days of seminars and still
wouldn't be completely covered.
Regarding vias and hole sizes, that is another topic that can take a lot of
time to completely address. My suggestion is that if you have something
that works now, don't change it. If you don't have to resort to vias in
pads or microvias, don't do it. I regret that in my haste I neglected some
pertinent issues that really can't be addressed in an email....such as
amount of copper content, should you use solder mask and where, stencil
thickness, and in the case of BGA, whether you use paste or just flux.
So let me back up and say that IPC is a good resource of information and
instruction. This is what we know works. If different techniques are
dictated, then you may have to determine how reliable the end result is
until IPC or others complete the work.
I really don't want to belabor the point, but for years we have been told
not to use a tin finish because of whisker growth. Now some lead-free
boards and components are tin plated and solder has a high tin content. We
know this isn't the best approach, but it is being done. The same holds
true for fluxes and chemical cleaning. No-clean flux has it's issues, but
sometimes you have to use second best.
One of the reasons Brad is upset with all of this is reliability. If
somebody's life depends on the working of your product you don't want to be
experimenting with questionable methods. Then again, it may be perfectly ok
to use alternative methods with a cheap throw away consumer item.
And the DAP is Data Acquisition Products...primarily A/D and D/A converters.
Bob Benjamin
DAP - Texas Instruments
Tucson, AZ
(520) 746-7753
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