Thank you Ioan,
The gap between the pads is 0.3mm (if it is 0.023" (0.6mm), the chip whose
length is 0.6mm could not get good wetting in all cases). The size of pad is
0.3x0.3mm. We are using Pb-free solder paste for that PCBA. With the pad
design like this, each electrode of part will sit on pad about 0.15mm in
ideal case. How big is the misalignment which is allowed for this part?
Printing result is registered well, no offsets at placement (I checked with
microscope) and we are doing the aperture 100% as pad size.
What is the ideal time for pre-heating at reflow? Now we don't get any case
of solder ball at these chips with current profile.
I heard that there are some aperture styles which can prevent this problem.
Also, I have never heard about anti-Manhattan/tombstoning solder paste, what
is that?
Thanks and best regards,
L. A. Quoc
----- Original Message -----
From: "Tempea, Ioan" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Thursday, October 14, 2004 7:54 PM
Subject: Re: [TN] Aperture for 0603mm chip
> Quoc,
>
> I don't see you mentioning land pattern design. If the gap between the
pads
> is bigger than 0.023", you start increasing your probability of
tombstoning.
> Then, in case your soldering paste (if no-clean) does not create mid-chip
> balls, you could print 1:1, no homeplating, although we reliably do
> homeplating on 0603s that have a good pad
> design.
>
> After this you just check your process step by step: the printing shall be
> well registered, no offsets at placement and yes, the reflow recipe has an
> influence, if everything else is OK. You will need longer preheating, to
> make sure that the paste on both pads melts at the same time when hitting
> the spike. But a good reflow recipe will not correct poor printing or
> insertion.
>
> Also there are so called anti-tombstoning pastes out there, that are worth
> trying.
>
> Good luck,
> Ioan
>
> > -----Original Message-----
> > From: TechNet [SMTP:[log in to unmask]] On Behalf Of Le Ai Quoc
> > Sent: Wednesday, October 13, 2004 11:32 PM
> > To: [log in to unmask]
> > Subject: [TN] Aperture for 0603mm chip
> >
> > Hi Technetters,
> > Do you know the opening style (aperture) for stencil (metal mask)
applied
> > for printing solder paste on resistance, capacitor chip 0603mmm to
prevent
> > "Tombstone/Manhattan" after reflow. Also, pls. advise about stencil
> > thickness.
> > Last but not least, is the reflow profile important for this defect? Any
> > suggestion?
> > Thanks in advance,
> > Le Ai Quoc
> >
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