Hi TN assemblers;
Having followed this thread, I haven't seen any body point a finger at the
board finish as a cause of tombstoneing. I always thought that HASL or
poorly HASSLED boards contributed to tombstoneing. We went to immersion
White Tin years ago in order to make our boards more manufacturable. Is
there a comment from the assembly community about tombstoning and the
topography of the bare board?
Jac Kroeker
Omni Graphics Ltd.
www.omnigraph.com
At 11:16 AM 04/10/2002 -0400, you wrote:
>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
> >
> >
========================================================
Omni Graphics Ltd. 2 - 12760 Bathgate Way, Richmond BC, Canada V6V 1Z4
Tel 604-276-9717 Fax 604-276-2514
[log in to unmask] www.omnigraph.com
========================================================
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