Ioan,
We ran a test board long ago which yielded very good results with
round pads.
Very simple: 20-20-20. round 20 mils pads and 20 mil gap. Pay
attention though that
severe copper undercut may change pad size ,and add to this componnets
on the low end
of tolerance and there goes your process. I had also good results
with:
Square pads: x=24mils. gap (x axis) = 20 ;and y=22 . make the corners
round.
Mickey
Mickey Weiner
Sanmina-Sci
Tel: 972-3-9208705
Mobile: 972- 67-467809
>>> [log in to unmask] 10-Apr-02 5:16:31 PM >>>
Hi Dan,
can you give the exact dimensions of the round land pattern?
Thanks,
Ioan
> -----Original Message-----
> From: Dan R. Johnson [SMTP:[log in to unmask]]
> Sent: Wednesday, April 10, 2002 10:22 AM
> To: [log in to unmask]
> Subject: Re: [TN] 0402 tombstone problem
>
> Steve,
> I use round pads to decrease pad size (increase circuit density). A
side
> benefit seems to be less chance of skew, I don't have numbers on
> tombstoning/drawbridging, but product hasn't yelled. I have also
been
> tinkering with the idea of other geometries just haven't come across
the
> right application yet.
> Dan
>
> ----- Original Message -----
> From: [log in to unmask] <mailto:[log in to unmask]>
> To: [log in to unmask] <mailto:[log in to unmask]>
> Sent: Tuesday, April 09, 2002 8:12 PM
> Subject: Re: [TN] 0402 tombstone problem
>
> I just heard something not too long ago, that round pads for
0402's
> are the way to go.
>
> Never heard of that before, but just recently received a board
for
> quote that uses round pads for the 0402 components...anybody else
ever
> heard of this?
>
> Guess I'll find out how it works inna little while, while
pondering
> why a round pad would work better than a square pad....
>
> -Steve Gregory-
>
>
>
>
> Edward,
>
> When we do everything correct on 0402 and 0201 and
still
> have components
> standing-up, we often look to the component
terminations and
> find poor
> plating.
>
> Good luck
> Dave Fish
>
> ----- Original Message -----
> From: "Edward S. Wheeler" <[log in to unmask]>
> To: <[log in to unmask]>
> Sent: Tuesday, April 09, 2002 10:59 AM
> Subject: [TN] 0402 tombstone problem
>
>
> > Hi folks, we are running a new board with 0402 parts
on
> it. It seems that
> > we are having a tombstone problem as well as a
problem
> with parts not
> > staying centered on the pads. We are currently using
20
> mil square pads on
> > the board, with 20 mils of spacing between them. Our
> stencil is 6 mils
> > thick, laser cut and electro polished. The
trapezoidal
> walled apertures
> are
> > slightly reduced, 17 mils square, and centered on
the
> pads. It appears the
> > chip shooter is placing the parts perfectly. We are
using
> eutectic solder
> > paste with an OA flux, and reflowing the parts using
the
> recommended
> profile.
> >
> > Are there any suggestions any of you might have
concerning
> this size of a
> > part? Is there a better stencil design, reflow
profile, or
> pad design that
> > could help us out? I would appreciate any
suggestions.
> >
> > Thanks.
> >
> > Ed
>
>
>
>
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