No, I would not consider it a defect, given the information you have
provided.
IMHO, it is better to optimize toward excess solder than insufficient.
Solder shorts are obvious and easy to troubleshoot, compared to
troubleshooting an intermittent insufficient solder joint.
Guy
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Ioan Tempea
Sent: Wednesday, August 18, 2010 2:04 PM
To: [log in to unmask]
Subject: Re: [TN] Bulging solder on the sides of QFP leads
Thanks all for your inputs!
And very pertinent questions also! Yes, the footprints are not perfect, the
double soldermask is there indeed (waiting for an answer from fab) and there
obviously are things we can do to reduce the paste volume.
I just wanted to know if the bulging aspect was a defect of any kind and it
seems it isn't. Very interesting point Ian, it went into my knowledge
database. The boards will not see 10 C or lower, though.
I conclude I don't have to change anything for quality/reliability reasons,
so I tend to save the stencil dollars. If the customer will stick to the
cosmetic issue, will order another stencil.
Thanks for your advice,
Ioan Tempea, ing.
Ingénieur Principal de Fabrication / Senior Manufacturing Engineer
T | 450.967.7100 ext.244
E | [log in to unmask]
W | www.digico.cc
N'imprimer que si nécessaire - Print only if you must
-----Message d'origine-----
De : Guy Ramsey [mailto:[log in to unmask]]
Envoyé : August-18-10 1:44 PM
À : [log in to unmask]
Objet : Re: [TN] Bulging solder on the sides of QFP leads
On that line of thought. Remember the paste stencil sits on top of the mask.
You might be putting down more paste than you think
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory
Sent: Wednesday, August 18, 2010 1:35 PM
To: [log in to unmask]
Subject: Re: [TN] Bulging solder on the sides of QFP leads
Hi Ioan,
I don't think it's rejectable. But just an observation, I think the
footprint for the device might be optimized a little more. It looks like
there's a lot of pad extending out from the toe, almost like the footprint
is too wide. The pads could have been a little wider too. How do the heel
fillets look?
Another observation, it kind of looks like the board was double masked, I
wonder why? I say that because you can see a stepped appearance at the mask
edges.
Steve
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Robert Kondner
Sent: Wednesday, August 18, 2010 1:14 PM
To: [log in to unmask]
Subject: Re: [TN] Bulging solder on the sides of QFP leads
Hi,
After seeing the pictures I think back again to the question:
Does Solder Follow The Heat?
As a joint heats, or cools, are there changes in the nature of surface
tension in liquid solder at the interface of the two phases? Lets say the
component cools faster, solder should go to the PCB. If the PCB cools faster
then solder flows to the part, I guess.
What happens at the solid / liquid interface that might explain this
"Solder Follow the Heat" statement? Truth or Myth? (Where are the Myth
Buster guys?)
Inquiring Minds Want to Know! :-)
Bob Kondner
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Ioan Tempea
Sent: Wednesday, August 18, 2010 10:28 AM
To: [log in to unmask]
Subject: [TN] Bulging solder on the sides of QFP leads
Dear Technos,
Please see the gallery http://ipc-technet.groupsite.com/gallery/14996
There seems to be an excess of solder, hence the bulging aspect of the
joints along the pins. Can there be any issue with this? IPC-A-610 does not
seem to be concerned with this situation, as long as the minimal electrical
clearance is not violated, and it's not.
Thanks,
Ioan Tempea, ing.
Ingénieur Principal de Fabrication / Senior Manufacturing Engineer
T | 450.967.7100 ext.244
E | [log in to unmask] <mailto:[log in to unmask]>
W | www.digico.cc <http://www.digico.cc/>
N'imprimer que si nécessaire - Print only if you must
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