Thanks Glenn,

I got some feedback from the test guys, they don't want the vias covered, to
be able to use the flying probe on them. So I guess no 1 is not an option.
Can you elaborate on the second option; +2, -10 means the filling will be
higher or lower than the level of the outter copper layers?

Regards,
Ioan

> -----Original Message-----
> From: [log in to unmask] [SMTP:[log in to unmask]]
> Sent: Thursday, March 11, 2004 10:43 AM
> To:   [log in to unmask]; [log in to unmask]
> Subject:      RE: [TN] Reliability of via in pad
>
> Hi Ioan,
>
> There a several things you can do to prevent the solder wicking down the
> hole with the current design, and that's where I would focus.
>
> 1)  Via plug - From opposite of component side, 50~75% of via,
> nonconductive
> epoxy.
> 2)  Via fill - From opposite of component side, +2 mils, -10 mils of
> conductor surface, nonconductive epoxy.
> 3)  Via fill and plate over - Conductive or nonconductive epoxy.  No hole
> in
> via for SMT.
>
> Cost goes up as you go down the list, but you don't need to respin the
> board, reduced to no solder starvation, and little to no rework.
>
> Glenn
>
>
> Disclaimer:  Any ideas or opinions expressed here do not necessarily
> reflect
> the ideas or opinions of my employer.
>
> -----Original Message-----
> From: Tempea, Ioan [mailto:[log in to unmask]]
> Sent: Thursday, March 11, 2004 5:30 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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