Perhaps a reverse home base plate design is needed.
I also wonder if you might be dealing with misprinted boards not being
cleaned adequately since it is random.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of
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Sent: Wednesday, February 22, 2012 12:05 AM
To: [log in to unmask]
Subject: Re: [TN] Microballs
Hi Reuven,
Thanks for the answer.
See my comments below
Best regards,
CANTAGALLO Luigi
Technology Engineer
Reuven Rokah <[log in to unmask]>
22/02/2012 07:52
A
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Objet
Re: [TN] Microballs
Hi Luigi,
You have to check:
1. Size of pads (too long under the components body).
On recurrent products, we use the same pads from years without
this problem 2. Size of opening in stencil
Openings are the same with reduction of 20% of opening for R0805
and R1206. No reduction for capacitors 3. P&P accuracy
Checked. It's OK and we have decreased the placing force (To not
crush the paste) without impact on the balls 4. Solder paste temperature
(should be room temperature)
Checked. It's OK. And we have tested the solderability and
coalescence. The "old" paste lots are same quality the news.
5. Oxidation of component / PCB [ads / solder paste particles
The PCB are checked. For the components we are checking if there
is a correlation between defect/PCB/components
Reuven
On Wed, Feb 22, 2012 at 8:33 AM,
<[log in to unmask]>
wrote:
Hello everybody.
Any idea about random presence of microballs (diameter 0.1 to 0.5 mm)
beneath some chips (R and C 0805, 1206,1210, 1812) ?
We use a SnPb process with a vapor phase oven.
We use same types of PCB, same process on same SMT line in a clean room
from years and the balls are randomly present from some months now.
They could be present in one lot of PCB and not the following; beneath a
component on one PCB and not on the same component on other PCB; we have
balls one day and not the day after; the balls disappear for weeks and
re-appear after; ...
I have checked different lots of solder paste, origin of PCB's, all
parameters of printing, P&P and the cleaning (co-solvent station). The
thermal profiles are same.
As it's hi-rel production I cannot change easely products and process.
I suspect a process parameter but which ?
I ask myself if there is not a ghost in the line .. :-)
Best regards.
CANTAGALLO Luigi
Technology Engineer
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