Yup: It (the current understanding of the effect of voids on reliability)
doesn't appear as bad as was originally thought when the study I'm talking
about was done.
We had extreme void paranoia. So we weeded out the voided samples. I think
what is likely to have happened if we had tested them is their failure rate
and that of the less or non-voided samples wouldn't have been as different
as our pre-conceived notions expected. Different maybe. But maybe not
dramatically different.
It's my understanding that voids can induce failure depending on where they
occur. But they are not a guarenteed failure initiator.
Maybe some of the rel experts would like to weigh in on this?
-----Original Message-----
From: Peter Barton [mailto:[log in to unmask]]
Sent: Friday, March 12, 2004 6:00 AM
To: [log in to unmask]
Subject: Re: [TN] Reliability of via in pad
Could you please elaborate further on your statement "Given what's coming
out about voids now....." Is there new research showing better/worse
reliability for larger voids?
Looking forward to more information.
Pete Barton
===== Original Message from [log in to unmask] (TechNet E-Mail Forum.) at
11/03/04 19:03
>Joe
>
>I was on the AT&T group that did some VIP for BGAs. We produced what we
>called "lead balloons." Mostly just BIG single voids. (Bob's point about
>height is also well taken.)
>
>They were so dramatic looking we didn't reliability test them.
>
>Given what's coming out about voids now I wish we would have! I think it
was
>a great (and lost) opportunity to look a extreme voids and telecom
>reliability.
>
>Greg
>
>
>-----Original Message-----
>From: Furrow, Robert Gordon (Bob) [mailto:[log in to unmask]]
>Sent: Thursday, March 11, 2004 10:42 AM
>To: [log in to unmask]
>Subject: Re: [TN] Reliability of via in pad
>
>
>Joe,
>
>Fortunately we have no experience with VIP on BGA or CSP pads. Due to
>concerns about solder joint height we never allowed VIPs in those pads.
>
>Thanks,
>Robert Furrow
>Printed Circuit Board Engineer
>Supply Chain Networks
>Lucent Technologies
>978-682-2260 [log in to unmask]
>
>
>-----Original Message-----
>From: Macko, Joe @ IEC [mailto:[log in to unmask]]
>Sent: Thursday, March 11, 2004 1:33 PM
>To: 'TechNet E-Mail Forum.'; 'Furrow, Robert Gordon (Bob)'
>Subject: RE: [TN] Reliability of via in pad
>
>
>Robert,
>
>What has been your experience with VIP for BGA pads? I have seen them
>contribute significantly to voiding. Look forward to your response.
>
>joe
>
>-----Original Message-----
>From: Furrow, Robert Gordon (Bob) [mailto:[log in to unmask]]
>Sent: Thursday, March 11, 2004 10:15 AM
>To: [log in to unmask]
>Subject: Re: [TN] Reliability of via in pad
>
>
>Hi Ioan,
>
>We have designed boards with via in pad (VIP) for well over a decade and
>assuming you have a good solder joint, reliability in Telecom product has
>not been a problem. We did not evaluate for automotive applications. Having
>said that, let me also say that VIP is great for the designer but a royal
>pain for the assembler. It was only intended for designs where absolutely
>necessary, but it quickly got out of hand when designers realized that by
>checking off "yes" to VIP, the computer time required to route a board was
>significantly reduced. It essentially became a defacto standard on many of
>our designs. Some lessons learned were that you need to carefully control
>the finished holes size. If you specify a 10 mil nominal finished hole
there
>is a world of difference between a 13 mil received and one that is truly 10
>mils. Also, as discrete sizes get to 0603 you need to require a smaller
>finished hole. We used enlarged stencil openings as well as step stencils
in
>order to get the n!
> eeded solder paste applied. Another issue is to make sure that the via is
>not shared on both sides of the board with discretes or other surface mount
>pads. I would be glad to discuss further offline if you have additional
>questions or comments. We also did some work with plugging the vias, but
>found it not to be necessary if the surface mount process was optimized, so
>the cost wasn't justified. It is a slippery slope, as once you get
>proficient at one set of pad sizes, the designers are going to want to
>expand the use of VIP to other sizes and feature types.
>
>Thanks,
>Robert Furrow
>Printed Circuit Board Engineer
>Supply Chain Networks
>Lucent Technologies
>978-682-2260 [log in to unmask]
>
>
>-----Original Message-----
>From: Tempea, Ioan [mailto:[log in to unmask]]
>Sent: Thursday, March 11, 2004 8:30 AM
>To: [log in to unmask]
>Subject: [TN] Reliability of via in pad
>
>
>Hi Technos,
>
>I've got an annoying one. I am looking at an assembly for automotive, which
>has 100+ SMT resistor and capacitor pads with vias in them, on both sides
of
>the 9 layer PCB. Now, I know that I will expect solder starvation, since
the
>solder will flow into the via. I could eventually patch this by plugging
the
>vias on the opposite sides of the concerned pads and make slightly bigger
>apertures in the stencil. Or even charge more and touch-up all the opens.
>
>But what does via in pad mean in terms of reliability?
>
>1. There will be voids, which are going to become even more important on
>lead-free (the customer is after the european market). Any reliability
>concerns related to that? Once again, I'm talking automotive.
>
>2. PTH reliability. 100+ vias will have totally random quantities of solder
>in them. I remember one of Werner's contributions (Entschuldigung Herr
>Engelmeier, aber... I lost the e-mail) saying that less than 50% fill
>degrades the reliability. Am I right?
>
>A good fix would be, in case they refuse to re-spin the board and move the
>vias, to fill the holes. What kind of specification should I issue for
>filling, in terms of material and fill percentage?
>
>Any other concerns?
>
>Thanks,
>Ioan
>
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-----------------------------------------------------------------------
Peter Barton
Senior Process Eng
ACW Technology Ltd
Dinas Isaf West
Tonypandy
Mid Glamorgan. CF40 1XX Wales
Tel: 01443 425200
Fax: 023 8048 4882
International Tel : +44 1443 425200
International Fax : +44 23 8048 4882
Website/URL: www.acw.co.uk
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