> -----Original Message-----
> From: Lee, Scott
> Sent: Tuesday, October 06, 1998 11:08 AM
> To: 'Nüchter Wolfgang (FV/FLT) *'
> Subject: RE: [TN] Via's under BGA's
>
> Wolfgang,
>
> We have been utilizing this land shape since mid 1993. Many of our
> products are used in extreme rugged conditions including deployment in
> a variety of land, air and sea vehicles. These products, obviously,
> go through rigorous qualification testing that includes temperature,
> vibration, and humidity parameters (we base our testing on
> MIL-STD-810E). I am not aware of a land ever being a cause for
> failure.
> We, also, have a pretty fair handle on our component rework process
> and have not experienced land failures due to that mechanism.
>
> As far as your concern of strange pad shapes, we have had success with
> both the teardrop (our preference) and the barbell style pads. But,
> we have not delved into anything particularly exotic.
>
> Best of luck.
>
> Scott E. Lee
> Manufacturing Engineer
> Mercury Computer Systems
>
> -----Original Message-----
> From: Nüchter Wolfgang (FV/FLT) *
> [SMTP:[log in to unmask]]
> Sent: Tuesday, October 06, 1998 10:41 AM
> To: 'TechNet E-Mail Forum.'; 'Lee, Scott'
> Subject: AW: [TN] Via's under BGA's
>
> Scott,
> have you any expirience with lifetime behaviour of your teardrop pads?
> Or temperature cycling, ...
> Does anyone uses other strange pad-shapes and has experience with new
> failure modes?
>
> Wolfgang Nuechter
> Corporate Research
> Robert Bosch GmbH
> Germany
>
>
> > ----------
> > Von: Lee, Scott[SMTP:[log in to unmask]]
> > Antwort an: TechNet E-Mail Forum.;Lee, Scott
> > Gesendet: Montag, 5. Oktober 1998 21:31
> > An: [log in to unmask]
> > Betreff: Re: [TN] Via's under BGA's
> >
> > Romeo,
> >
> > Be very careful of aspect ratios if you go this way, the use of a
> > microvia will generally limit the layer count due to this factor.
> Which
> > in turn, will limit the available surface area for escape routes.
> In a
> > lower I/O count BGA, the impact may be lessened. If not, to
> overcome
> > this, you may need to go to blind segments, this tradeoff is not one
> > that I would accept.
> >
> > We have had much success keeping it simple and utilizing teardropped
> > lands to the via. In this approach, the routing limitations are
> > therefore only felt on the primary layer. In general practice, we
> have
> > found that the more exotic the solution, the lower the yield rates.
> >
> > Scott E. Lee
> > Manufacturing Engineer
> > Mercury Computer Systems
> >
> > > -----Original Message-----
> > > From: Kubes, Romeo (NM75) [SMTP:[log in to unmask]]
> > > Sent: Monday, October 05, 1998 3:03 PM
> > > To: [log in to unmask]
> > > Subject: Re: [TN] Via's under BGA's
> > >
> > > Chad,
> > >
> > > Is using blind Microvias acceptable, since their cavity is so
> small it
> > > would
> > > rob a very small % of the solder? (I know this is expensive, but
> > > besides
> > > this factor).
> > >
> > > R. Kubes
> > > Honeywell DAS Albq
> > >
> > > > ----------
> > > > From: Thibodeau, Chad[SMTP:[log in to unmask]]
> > > > Sent: Monday, October 05, 1998 11:41 AM
> > > > To: [log in to unmask]
> > > > Subject: Re: [TN] Via's under BGA's
> > > >
> > > > Bridget,
> > > >
> > > > There was an excellent paper written by Paul Mescher of Amkor
> Anam
> > > > addressign "...Surface Mount Assembly of Amkor/Anam BGA
> Packages".
> > > In
> > > > this
> > > > paper Paul describes the importance of PTH isolation (via
> isolation)
> > > and
> > > > to
> > > > paraphrase him: "No matter what shape or definition technique is
> > > used for
> > > > the mounting pad, the isolation of the PTH from the mounting pad
> is
> > > an
> > > > important feature. If the PTH is contained within the mounting
> pad,
> > > > solder
> > > > can and will wick down the PTH. The amount of solder that wicks
> > > depends
> > > > on
> > > > many factors, including PTH finish and coating variations.
> Because
> > > of
> > > > this,
> > > > the results are somewhat unpredictable. Some solder joints may
> be
> > > > unaffected, while others will be starved to the point of
> creating
> > > opens.
> > > > The worst result is a partially starved joint with severely
> reduced
> > > cross
> > > > section. This joint can have significantly lower fatigue life
> and
> > > result
> > > > in
> > > > early system failure. Because the quality of the solder joint
> is
> > > > guaranteed
> > > > by control, rather than inspection, designs/processes that
> result in
> > > > random
> > > > distributions are generally considered unacceptable, and the
> > > PTH-in-pad
> > > > design is not recommended."
> > > >
> > > > If you require additional information you may want to talk with
> Paul
> > > > himself. I do not have his number, but he is located in
> Chandler,
> > > AZ.
> > > >
> > > > Chad Thibodeau
> > > > EF Data
> > > > Component Engineer
> > > > 602 333-2138 Phone
> > > > 602 921-9012 Fax
> > > > [log in to unmask]
> > > >
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