Nicolas,
        Are the shorts consistently on two parallel sides closest to the
conveyor rails.  If so, the part and paste are probably sliding to one side
or another on the domed pads that HASL causes.  This usually happens during
the soak zone in the oven when the paste becomes less viscous.  We have
found (like many other have found) that using a flat surface finish will
significantly reduce shorts on fine pitch compared with using HASL.  If you
are at 38 dpmo (I assume for shorts only?) with HASL, I think you are doing
pretty good.  To do better than that, you will have to use a flat surface
finish.

Thanks

Ryan Grant
Advanced Technology Engineer
MCMS
(208) 898-1145
[log in to unmask]




> -----Original Message-----
> From: Nicolas Ortiz [SMTP:[log in to unmask]]
> Sent: Monday, February 05, 2001 1:45 PM
> To:   [log in to unmask]
> Subject:      [TN] QFP144 solder bridging
>
> Currently we are experiencing solder bridging on a 0.5mm pitch,  LQFP,
> 144
> leads. I already reviewed the stencil design, screen printer parameters
> and
> reflow profile. Everything is OK. We have HASL boards. Our current process
> outputs 38 dpmo's. My concern is if I reduce more the apertures, I have
> the
> risk to have solder open or insufficient solder, instead of bridging. Does
> anybody has some input? What dpmo's do you have?
>
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