How about using soldermasking?
Bob
Sent from my iPhone
On Feb 25, 2010, at 10:59 AM, Guy Ramsey <[log in to unmask]> wrote:
> Solder voids that large are not normal. They were normal for some
> solder
> paste formulas. But, the paste companies reformulated the paste and
> minimized the problem.
> So, you will need to have some special paste made or induce the
> voids. I saw
> a video produced by Phoenix X-ray. They induced voids by extending
> the time
> above melt. It took about 10 minutes but the voids were pretty
> spectacular.
>
> Guy
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of David D. Hillman
> Sent: Thursday, February 25, 2010 10:43 AM
> To: [log in to unmask]
> Subject: [TN] Suggestions on Making BGA Voids
>
> Hi gang! Ok, I have a fairly crazy request for suggestions on how to
> make
> BGA voids. First here is the background - Dr. David Bernard (Dage),
> Dave
> Adams (Rockwell Collins) and I are working on a collaborative
> project to
> investigate the thermal cycle solder joint integrity of BGA
> components. We
> are attempting to produce data which the IPC JSTD 001 committee can
> use to
> revise the 25% maximum void criteria. Despite public rumor, this
> current
> IPC JSTD 001 void requirement is based on actual IPC Class 3 field
> equipment results submitted to the committee several years ago.
> However,
> BGAs have changed in both size, pitch and solderball diameter since
> the
> creation of the void criteria thus the reason for collaborative
> project.
> We have a test vehicle which contains BGAs at 0.5mm, 0.8mm and 1.0mm
> pitch
> with each having a corresponding larger solderball diameter. We have
> put
> uvias in the BGA pads to "create" voiding. Great plan, figured we
> had it
> made- however, after running the test vehicles thru a standard reflow
> process (this effort is focused on tin/lead right now) we find that we
> have an average void size in the range of 0-5%! My production process
> folks are very proud of that result but it doesn't do our voiding
> investigation much good (you can imagine the look I got when I told
> them
> they didn't make enough voids greater than 25%). I know that a
> number of
> the Technet community have tried to accomplish this voiding task
> with only
> mild success (i.e. Bev Christian, Martin Wickham, etc.).
>
> My Technet request is - do you have any suggestions on how to
> increase the
> solderball void size without causing a biased negative impact on the
> solder joint quality? I can obviously make some huge solderball voids
> (such as pouring Doug's Diet Mt. Dew on the test vehicles) but the
> overall
> quality of the solder joint would not be representative of the real
> world
> product.
>
> Thanks in advance
>
> Dave Hillman
> Rockwell Collins
> [log in to unmask]
>
>
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