I think the technique is to just put the paste on and have it there to facilitate solder flow over the wave. IE it is still just paste when it hits the wave.
I would say that the core issue is wave penetration of the SMT on the bottom. Shadowing and all are hurting the wetting. With the extra solder paste on the pad better results are had. Added cost?
Richard
>>> Miguel Vallejo <[log in to unmask]> 09/25/00 06:13PM >>>
If I understand correctly, you are re-flowing the solder joint a second time
(when it goes through the wave solder). Doesn't that raise a concern
regarding increased intermetalic layer?
> ----------
> From: Jason Gregory[SMTP:[log in to unmask]]
> Sent: Sunday, September 24, 2000 6:45 AM
> To: [log in to unmask]
> Subject: Re: [TN] Bottom Side wave soldering of SMT parts
>
> Mike,
> We print paste and dispense adhesive as a rule. It adds quite a bit of
> insurance to the underside of our boards. We have experimented with no
> pasting, just wave-soldering. Our yields went down at ICT and open
> capacitors went through the roof. We run no-clean for the record. Hope
> this
> helps.
>
> Jason Gregory
> Manufacturing Supervisor
> ACT Manufacturing
> Corinth, MS. 38834
> (662)287-3771 x470
> [log in to unmask]
>
> > -----Original Message-----
> > From: Mike Sewell [SMTP:[log in to unmask]]
> > Sent: Friday, September 22, 2000 3:39 PM
> > To: [log in to unmask]
> > Subject: [TN] Bottom Side wave soldering of SMT parts
> >
> > We build a mixed technology board here with bottom side SMT (SOTs, small
> > chips, all laid out not to solder, ie..90 out from each other) and get
> > very
> > poor yield from wave (chip + lamda) solder. We print the adhesive on,
> > P&P,
> > cure, stuff, wave then TOUCH UP. My question is: what about printing
> > paste,
> > dispensing glue (or vice versa), P&P, reflow/cure, stuff, then wave?
> Will
> > having an existing joint make life easier on wave skips, or will the
> wave
> > disturb the skipped joints to the point of needing touch up?
> >
> > Haven't tried it yet because our dispenser is down,
> > Mike Sewell
> >
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