Oh, I forgot to also mention that CAF-resistant pre-pregs are REALLY
difficult to laser machine and clean-up! To get CAF resistance you want
something gummy (not brittle!), which can lead to strange sludge to remove
after lasing. MAKE SURE you REALLY need CAF resistant before trying to
qualify for laser vias!
On Sat, Sep 7, 2019 at 5:39 PM Wayne Thayer <[log in to unmask]> wrote:
> 0.5 oz copper on inners, UV laser--don't know specific wavelength. Section
> showed the "landing pad" had a tiny hole and there was a trace of char in
> the dielectric near a tiny plated nugget where the hole was. From then on,
> if possible, I added a desire in layout to eliminate copper on the layer
> beneath the "landing pad". It was quite a number of years ago--perhaps
> 2003. Hopefully processes have improved....
>
> On Sat, Sep 7, 2019 at 11:50 AM Dwight Mattix <[log in to unmask]>
> wrote:
>
>> /Artie Johnson voice: ON/
>> "vewy intewesting"
>>
>> Do tell Wayne.
>>
>> Any more background details on that?
>> Any idea what was copper thickness? I presume to thin side due to thin
>> dielectric flow/fill limitations?
>> How about the laser process used? Any idea if was it UV, IR or a combo
>> laser?
>>
>> -----Original Message-----
>> From: TechNet <[log in to unmask]> On Behalf Of Wayne Thayer
>> Sent: Friday, September 6, 2019 12:00 PM
>> To: [log in to unmask]
>> Subject: [EXT] Re: [TN] CAF in a uVia world
>>
>> Also, don't forget that for non-stacked vias lasers can still damage the
>> dielectric beneath the termination pad you're ablating down to. Not CAF,
>> but bad news nevertheless! I've only seen problems with this on dielectric
>> layers less than 55 microns thick, although that was a 3V system.
>>
>> Wayne Thayer
>>
>> On Thu, Sep 5, 2019 at 7:47 PM Bhanu Sood <[log in to unmask]> wrote:
>>
>> > Voltage is just one factor in a half dozen or so contributors to CAF.
>> >
>> > For example, you’re not out of the CAF woods with laser ablated
>> > microvia holes, a poorly designed or executed siloxane process will
>> > still rear it’s ugly head leading to glass/polymeric separation,
>> > mechanical drilling or not.
>> >
>> > On Thursday, September 5, 2019, Dwight Mattix
>> > <[log in to unmask]>
>> > wrote:
>> >
>> > >
>> > > Anyone here running uVia CAF test vehicles?
>> > >
>> > >
>> > > Bev,
>> > > Thanks for that prompt reply/acknowledgement.
>> > >
>> > > In our uVia area it has mostly been in shorter life, lower voltage
>> > > apps (e.g. high end consumer, engineering ref designs etc) as
>> > > compared to the days when we both played Base Station games (has it
>> > > really been that long?). Those applications allowed room to be
>> > > casual (dismissive?) of
>> > CAF
>> > > concerns in the uVia pwb.
>> > >
>> > > Now these uVia apps are finding their way into critical use case,
>> > > and
>> > long
>> > > term high availability, higher sustained temp/duty cycle
>> > > applications
>> > that
>> > > call for IMHO more attention to CAF now. (Automotive,
>> > > infrastructure)
>> > >
>> > > CAF risks in uVias has the advantage of laser ablated vias vs.
>> > > mechanical drilling disruption of the laminate. But the uvia drill
>> > > edge to drill
>> > edge
>> > > spaces run much tighter than in a mechanically drilled pwb. So… Then
>> > > there's the voltages involved which tend to be lower and lower and
>> > > would it seems work to reduce the CAF risks than in our bad old days
>> > > with PTH only designs for infrastructure on BUTS pwbs (big ugly
>> > > thick
>> > suckers).
>> > >
>> > > re: Certainly for the materials, construction and suppliers used in
>> > > those two projects, stacked microvias were not as robust as staggered.
>> > > Yeah I/we have a bit more experience than the average bear with
>> > > respect
>> > to
>> > > uVia stacking (and uVia stacking on core vias). We were early, very
>> > early,
>> > > adopters -- some would say pioneered even. Living on the leading
>> > > node of pitch and pin count (and frequency/radio complexity) will do
>> that to you.
>> > > :) In any case, have a pretty good understanding of that Z-axis
>> part
>> > of
>> > > it; where to put limits in design; and how to
>> > > test/qualify/demonstrate reliability for our use case.
>> > >
>> > >
>> > > -----Original Message-----
>> > > From: [log in to unmask] <[log in to unmask]>
>> > > Sent: Wednesday, September 4, 2019 3:43 PM
>> > > To: 'TechNet E-Mail Forum' <[log in to unmask]>; Dwight Mattix <
>> > > [log in to unmask]>
>> > > Cc: [log in to unmask]
>> > > Subject: [EXT] RE: [TN] CAF in a uVia world
>> > >
>> > > Dwight,
>> > > Thx.
>> > >
>> > > After BlackBerry ceased making devices and sold off my lab by
>> > > auction ☹,
>> > I
>> > > went to run the CALCE Lab at the University of Maryland, but for a
>> > variety
>> > > of reasons I was not happy there and resigned after four months and
>> > > came home to Canada. The last couple of years I have worked part
>> > > time as a project facilitator for the High Density Packaging User
>> > > Group, an electronics industry research consortium of about 50
>> > > companies. So, I personally or through HDP, have not done any CAF
>> > > testing on what you
>> > label
>> > > ELIC. HDP does have two CAF projects, one looking at developing a
>> > > new standard coupon that will be offered to the industry and another
>> > > project looking to develop a new CAF equation.
>> > >
>> > > With regards to stacked microvias, HDP has completed two other
>> > > projects (presented at SMTAI in 2017), is trying to start a third
>> > > and is keeping a toe in the pool of the microvia turmoil that the IPC
>> is trying to corral.
>> > > Certainly for the materials, construction and suppliers used in
>> > > those two projects, stacked microvias were not as robust as staggered.
>> > >
>> > > Regards,
>> > > Bev Christian
>> > > Project facilitator
>> > > HDPUG
>> > >
>> > >
>> > > -----Original Message-----
>> > > From: TechNet <[log in to unmask]<mailto:[log in to unmask]>> On Behalf Of
>> > > Dwight Mattix
>> > > Sent: September 4, 2019 4:42 PM
>> > > To: [log in to unmask]<mailto:[log in to unmask]>
>> > > Subject: [TN] CAF in a uVia world
>> > >
>> > > Nice to see Bev back in the mix so I admit this post is mostly a bit
>> > > of trolling for his input. :) But I know there are other veterans of
>> > > the CAF wars so...
>> > >
>> > > For those of you working with full stacked uVia designs (aka ELIC:
>> > > Every Layer Interstitial Connection) what have you done in terms of
>> > > CAF
>> > testing?
>> > >
>> > > Use one or more of the standard IPC CAF thru via coupons with the
>> > > hole edge/hole edge spacings down to ~10mils and call it good enough?
>> > > Or do you go to custom CAF test vehicle designs that reflect the
>> > > uVia stack and (tighter) spacing that is typical of uVia designs?
>> > >
>> > >
>> > >
>> >
>> > --
>> > Bhanu Sood
>> > Tel: (202) 468-8449
>> >
>>
>
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