Bev - Nortel
   Your reply on the surface tension formula was sent as follows:

> Weight of components (g)                 <30
> Total pad mating area (sq. inches)
>
Would you explain please.

Regards,

Brant McClelland

Design Center,
Solectron Texas
512-425-7095   phone
512-425-7023   fax
[log in to unmask]


> ----------
> From:         Bev Christian[SMTP:[log in to unmask]]
> Reply To:     TechNet E-Mail Forum.;Bev Christian
> Sent:         Monday, March 23, 1998 10:50 AM
> To:   [log in to unmask]
> Subject:      Re: [TN] Double Reflow: Component Weight vs. Pad Contact
> Area Rat io
>
> *       Dave,
> *
> *       Joe Belmonte & Phil Zarrow, "Advanced Surface-Mount Manufacturing
> Methods", Circuits Assembly, September 1996, page 36
> *       Formula for secondary side mounting
> *
> Weight of components (g)                 <30
> Total pad mating area (sq. inches)
>
> Personally I find this too conservative.
>
> Bev Christian
> Nortel
>
>
> > ----------
> > From:         Dave Pick - process engineer[SMTP:[log in to unmask]]
> > Sent:         Monday, March 23, 1998 10:38 AM
> > To:   [log in to unmask]
> > Subject:      [TN] Double Reflow: Component Weight vs. Pad Contact Area
> > Ratio
> >
> > I have read somewhere of a component weight to SMT lead contact area
> ratio
> > rule
> > for double sided reflow. This ratio would be the maximum component
> weight
> > to SMT
> > pad contact area that would allow surface tension to overcome gravity.
> If
> > the
> > weight to surface area ratio is over this number, the part would fall
> off.
> > Does
> > anyone know what this ratio is?
> >
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