Kishpaugh Geoff wrote:
>
> All,
> I have been watching this discussion with interest and unless I missed some posts have found only 2 answers to the original question. Can I assume that not many companies are using "via in pad"? Is there a reliability issue with this design practice? Any responses are welcome.
>
> Thanks,
>
> Geoff Kishpaugh
> Motorola Inc.
> 1900 Winchester Rd, IL-46
> Libertyville, IL, 60048
> Phone: 847-523-0067
> Fax: 847-523-0078
> email: [log in to unmask]
>
> ------------------------------------------
>
> Hi Leonard,
>
> We typically see blind vias up to .013 drilled size in .030 x .060 pads. You should actually put
> the via towards the end of the pads, rather than the center. Board thickness does make a
> difference and the ratio of board thickness to drilled hole size (aspect ratio) should not
> exceed 10:1 for blind or thru-vias drilled with conventional equipment and 1:1 for controlled
> depth laser drilling, where the drilled via size can go down to .006 inches. The aspect ratios
> mentioned are only for the "blind" portion being drilled and not the thickness of the entire
> board.
>
> You may contact me offline at 817-481-7281 should you have additional questions or wish to
> discuss this further.
>
> Regards,
>
> Keith Larson
> Circuit Technology Inc.
>
> -----Clip------
>
> Leonard;
> The only large company to use via in land on a regular
> basis is Lucent, they have the process down pat.
> The trick is to figure how much solder you going
> to lose to the hole.
> It real helps on high density boards.
> Lou
> -----Clip------
>
> Leonard Toohey wrote:
>
> > What is the state of the industry regarding putting
> > vias in the center of SMT discrete device pads?
> >
> > I am mainly wanting to know about 0603, 0805 and 1206 devices.
> > Is board thickness a factor?
> > What about via hole size?
> >
> > Thanks,
> >
> > Leonard Toohey
> > [log in to unmask]
> > 12303 Technology Blvd.
> > Austin, TX 78727
> > Ph(512) 257-5423
> > Fx(512) 249-7236
> > http://www.netspeed.com
>
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Hello Geoff,
My experience with "via in pad" has been this...during reflow, solder
tends to scavenge into an unfilled via leaving an "insufficient" or
starved solder joint. We had overcome this on older board designs by
filling the PCB vias with solder over a wave solder pot to prepare the
PCB for the SMT process. Now, I'm not very familiar with blind vias and
such, but you might be able to compensate for the solder which will be
lost down the hole by over-printing solder paste. Overprinting can be
accomplished by selectively modifying the stencil apertures for the pads
which contain the via so that you do not put excess solder all over the
board (i.e., by using a thicker stencil.)
That's my 2 cents worth.
Enza
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