The requirements may include heat transfer
This was a critical specification and drove everything for high current
products.
I have had spec's as tight as 10% or less voiding with a Cpk of better than
1.67.
This results in average voiding less than 5%.

It takes design, equipment, materials and process to achieve this on a 1mm
thick copper and 1.5 mm  Al and Fr4 PCB's.

Digital applications that did not require heat transfer, were 50% and some
application satisfied with a ground connection.

Unfortunately, solder paste selection may be forced on you rather than
selecting one that optimizes low voiding.


On Mon, Jan 8, 2018 at 11:41 AM, David Hillman <
[log in to unmask]> wrote:

> Hi Guy - can you define "excessive"? Currently the IPC-JSTD-001 has no
> requirement for center pad voids. The IPC-7093 specification contains
> guidance that the maximum voiding for the center pad should be 50%. There
> is a IPC-JSTD-001 task group looking at the topic as there has been
> significant discussion on what the maximum void value should be and what
> the current published technical data supports. I can tell you that most of
> the issue isn't solder joint reliability but component functional issues
> which is a design component selection attribute and not a process
> attribute. With that being said, the solder paste formulation has a huge
> impact on the creation of voids provided you have addressed the "open via"
> influences. Take a look at the 2017 SMTAI paper APT5.2 by Richard Coyle, it
> will be very useful in your discussions.
>
> Dave Hillman
> Rockwell Collins
> [log in to unmask]
>
>
> On Mon, Jan 8, 2018 at 10:26 AM, Guy Ramsey <[log in to unmask]> wrote:
>
> > We are having trouble with a lot of boards.
> > We are seeing excessive voids like the ones on page 18 of this
> > presentation.
> >
> > https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=
> > 0ahUKEwj27JnJ38HYAhUF5YMKHWYICvcQFggpMAA&url=https%3A%2F%
> > 2Fwww.eptac.com%2Fwp-content%2Fuploads%2F2012%2F06%2Feptac_
> > 07_18_12.pdf&usg=AOvVaw2OX6J_YRqkuNUNNgDBvmwZ
> >
> >
> > The vias are filled and plated. Anyone seen this, resolved it?
> >
> >
> > Guy
> >
>