Hi, again, Alejandro,
I'll wait until Steve has the pictures up on his site before I try to make
much more comment on the problem.
Regarding your thermal profiling, though, I have another string of
questions for you:
What solder are you using? i.e. what is the liquidous temperature? 183
deg C eutectic? Leaded or lead-free?
Can you tell us what the temperatures, ramp rates and dwell times are
for the various zones of the reflow oven?
Where are you placing the thermocouples in relation to your problem QFP?
On the top board surface? Near the QFP leads or further away? On the
component body? On the solder side of the baord?
What temperature(s) are you recording from the thermocouple(s) that
is/are most relevant to the QFP?
Do you use nitrogen or not in the reflow oven to reduce oxidation?
What tests have to carried out to ensure that your profile is suitable
for this component?
Other questions to help me try to help you:
Have your tried hand soldering the affected leads? Do you still have
non-soldering problems?
How do the boards appear - are they still shiny, or do they look dull
with oxide?
What flux are you using and is it water soluble or no-clean?
What other components are close to the QFP?
Are there any large copper planes or fill areas near the QFP, or under
it inside the PCB?
Is there a taller component near the QFP that goes into the reflow oven
ahead of the QFP?
Without seeing the pictures, I think you may have a "shadow" problem,
assuming all the other solder joints on the board are OK and the problem
joints are not soldering properly, or at all. This can sometimes happen,
and putting the board through the reflow oven a different way round (turn
it 90 or 180 degrees from normal) can help. One side of the QFP may be
being sheltered a bit by another device, and is therefore not experiencing
the heating that it should.
I also read your posting another way - that solder joints are being
formed, but that the joints are deformed because of the way the leads are
lying. If that's the case, I would look at the condition of the components
as they arrive in your company, and then how they are handled by your
receiving people, incoming inspection, storemen, progress people and
operators. See if the components are being damaged at any of these stages,
and if so, how, so that you can improve the handling procedures. It may
even be that the placement pressure of the Pick and Place machine is
incorrect and needs to be changed. Maybe I can tell more when I see the
pictures, but hopefully, I've given you some things to think about, or
reject, as appropriate.
Good luck
Peter
Becerra Alejandro <[log in to unmask]> 07/08/2002 10:22 AM
To: DUNCAN Peter/Asst Prin Engr/ST Aero/ST Group@ST Domain, "TechNet E-Mail
Forum." <[log in to unmask]>
cc:
Subject: RE: [TN] Coplanarity in QFP208
Peter,
I am sending some pictures to Steve for the non-soldering.
As you can see in the pictures we are seeing two types of defects:
- One type where the terminal caused a deformation in the solder, but the
terminal is not solder.
- Another type where the terminal did not cause any deformation to the
solder
The profile was checked using a MOLE profiler and attaching the
thermocouples with high temp solder.
The problem occurs always in the same side and pins.
The board finish is HASL.
Regards,
Alejandro
-----Original Message-----
From: [log in to unmask] [mailto:[log in to unmask]]
Sent: Tuesday, August 06, 2002 6:46 PM
To: TechNet E-Mail Forum.; Becerra Alejandro
Cc: [log in to unmask]
Subject: Re: [TN] Coplanarity in QFP208
Alejandro, I think we need a better deescription of your "non-soldering"
phenomenon, and how did you check your thermal profile? It's unlikely that
lack of coplanarity affects solderability, unless leads are so bent that
they don't sit in the solder. Your component data sheet should state the
coplanarity tolerances for the part in question.
Does the problem occur in the same place(s) each time? You could try
turning the board around and reflowing it with a different leading edge and
see if there's a difference. Non-soldering to me, though, means you have a
serious oxidation or contamination problem.
Otherwise:
What is your board finish (HASL, ENIG, Tin, Silver ...?
How old are the boards?
What is the component lead finish?
How old are the components?
What are your storage conditions like?
We need more gen. Any pictures you can post on Steve's site for us to look
at?
Peter
Becerra Alejandro <[log in to unmask]> 06/08/2002 10:46 PM
Sent by: TechNet <[log in to unmask]>
Please respond to "TechNet E-Mail Forum."; Please respond to Becerra
Alejandro
To: [log in to unmask]
cc: (bcc: DUNCAN Peter/Asst Prin Engr/ST Aero/ST Group)
Subject: [TN] Coplanarity in QFP208
Hello to All,
We are having Non Soldering problems in a QFP208 (Pitch is 0.5 mm or 20
mils)
The problem is focused in one area of the component.
We already checked the reflow profile and Solder paste printing and both
are OK.
We realized that the components have coplanarity in the area with failures.
What is the maximum coplanarity accepted for this type of components?
Thanks,
Alejandro Becerra
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