We going to see plating accept criteria published
for stacked uvias on the next go round? Looking
forward to being standardized that so that it's
not just this <ahem> "unreasonable man" talking with our suppliers.
At 07:59 AM 8/8/2008, Whittaker, Dewey (EHCOE) wrote:
>Bob,
>Thanks for the information. I am on those
>Committees that deal with these issues. We have
>many updates/fixes under way on IPC-A-600,
>IPC-6012, IPC-6011, IPC-2221, as well as several
>other coupon/test task groups. I will see what
>we can do to incorporate what you have presented.
>My attempt at illuminism in this endeavor, just
>like with Deweyisms, does not guarantee they'll see the light.
>Dewey
>
>-----Original Message-----
>From: TechNet [mailto:[log in to unmask]] On Behalf Of Bob Willis
>Sent: Friday, August 08, 2008 5:05 AM
>To: [log in to unmask]
>Subject: Re: [TN] measurement and acceptance of microvias
>
>Like to see any feedback from anyone that has tried the blind via test I
>reported in IPC Review a few months back as a alternative or support to the
>information seen during sectioning or IST due to the recent debate
>
>I hope that the updates to IPC 600 cover via inspection in more detail.
>
>See link to IPC Review Paper www.bobwillis.co.uk/pdf/viatest.pdf
>
>
>Bob Willis
>2 Fourth Ave, Chelmsford, Essex, CM1 4HA England
>Tel: (44) 1245 351502
>Fax: (44) 1245 496123
>Mobile: 07860 775858
>
>www.ASKbobwillis.com
>
>New Bob Willis "Printed Board Inspection & Quality Control Workshop" 3rd
>September www.ASKbobwillis.com/PCBworkshop.pdf
>
>Book your place on Bob's "Step by Step Failure Analysis Workshop" 11th
>September www.ASKbobwillis.com/faworkshops.pdf
>
>
>-----Original Message-----
>From: TechNet [mailto:[log in to unmask]] On Behalf Of Gerald Gagnon
>Sent: 07 August 2008 19:14
>To: [log in to unmask]
>Subject: Re: [TN] measurement and acceptance of microvias
>
>Hi Paul,
>
>Can I have a copy of the Curtis Wright, Coretec and PWB Inc paper to take a
>look at?
>
>You state some interesting results.
>
>Gerry
>
> > Date: Thu, 7 Aug 2008 13:25:19 -0400> From: [log in to unmask]>
>Subject: Re: [TN] measurement and acceptance of microvias> To:
>[log in to unmask]> > Hi Louis,> > We do a lot of microvia reliability testing
>here at PWB Inc. We have tested .002" to .006" microvias; drilled, plasma
>etched (flex circuits) and laser ablated; with and without fill, stacked;
>staggered etc.> > An aspect ratio of 1:1 or less is easier to clean,
>metalize and electro-plate, and, therefore, produces more reliable
>microvias. Many companies are producing reliable microvias with higher
>aspect ratios. You just have to tweak the process using an objective
>measurement like reliability testing to rank methods, processes or
>procedures.> > The shape of the microvia is critical. Flask shaped and
>perpendicular side walls (with right angles at the base) microvias are
>usually less reliable. A "bowl" shape microvia is most reliable but this has
>less surface area at the base than a straight hole wall. Out gassing
>chemistries, surface tension, and the lack of solution movement all conspire
>to inhibit cleaning and plating in corners at the base of the microvia. It
>appears liquid can circulate better in a "bowl" shaped microvia than one
>with straight side walls. So I would say the hole diameter to base surface
>has an inverse relation to reliability until you get below some undefined
>minimum hole or base size. > > Aggressive desmear, desmear that makes the
>hole wall rough, is less reliable. At the same time, any debris on the
>internal pad will induce early failures. The presents of a smooth, slightly
>angled hole wall and a slight microetch in the internal pad is optimal.> >
>Metrology counts in evaluating microvias. Contrary to what you may have
>heard, you must have a slight microetch to evaluate the integrity of the
>microvia in a microsection.> > We feel that you must test microvias at 190°C
>to fail weak microvia within 500 thermal cycles. Tested at 150°C bad
>microvias, ones that will fail in assembly, will survive thousands of
>thermal cycles.> > There is an article available. A joint study was
>undertaken between Curtis Wright, Coretec and PWB Inc. It covers much of
>what I have described.> > Contact me off line for more on microvias.> > By
>the way, I refrain from using the terms target and capture pad. What does
>IPC-T_50 call the external and internal pads in a microvia structure? > >
>Sincerely,> > Paul Reid> > Program Coordinator> > PWB Interconnect Solutions
>Inc.> 235 Stafford Rd., West, Unit 103> Nepean, Ontario> Canada, K2H 9C1> >
>613 596 4244 ext. 229> Skype paul_reid_pwb> [log in to unmask]
><mailto:[log in to unmask]>> > > -----Original Message-----> From:
>TechNet [mailto:[log in to unmask]] On Behalf Of Louis Hart> Sent: Wednesday,
>August 06, 2008 5:12 PM> To: [log in to unmask]> Subject: [TN] measurement and
>acceptance of microvias> > TechNetters, I'm trying to plan a designed
>experiment for optimization of a laser drilling operation, for microvias. I
>need to identify a variable to measure..> > Is the ratio of the diameter of
>the exposed copper at the bottom of a microvia to the diameter of the
>microvia at the surface of the board a suitable measurement? (The jargon may
>be 'ratio of target land diameter to capture land diameter'.)> > What is the
>target value for this ratio? I'm assuming there is one such number - please
>correct me if I am wrong.> > Thanks for any comments or guidance.> > Louis>
> > Louis Hart> Compunetics> Monroeville, PA> USA>
>[log in to unmask]<mailto:[log in to unmask]>> 412-858-1272> > >
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