Ioan,
You're explaining a similar problem (on 0805's) we had recently (also on
ENIG boards) - what we noticed was that the applied paste at times was
offset to one end and further exacerbated by the component being placed
off-centre to the other end, hence the apparant randomness. Inspection prior
to reflow indicated fractional or no contact between the solder and the end.
This condition resulted in 2 types of defects after reflow i.e. not soldered
at one end (as you mentioned), as well as the more obvious tombstones when
the tension really gets angry.
Regards
Grant
-----Original Message-----
From: Tempea, Ioan [mailto:[log in to unmask]]
Sent: Thursday, August 30, 2001 4:51 PM
To: [log in to unmask]
Subject: [TN] Component skew after reflow
Hi Technos,
I have an intriguing one.
I find passive components that are not soldered at one end after reflow.
These components show very good joints at one extremity while the other end
is not soldered at all. The not soldered end is usually outside of the pad,
at the mercy of the surface tension, but sometimes it touches the respective
pad, being untouched by the solder, that forms nice bumps on the pad.
We're on no-clean paste, the board finish is ENIG. The assembly has being
running for a long time, we built tenths of thousands without this problem.
But all of a sudden... The problem appears randomly, not always on the same
component, not always at the same place. The frequency is let's say one
occurence every 50 boards. The assembly is not so populated, barely about 50
parts.
I checked the insertion, it is good. I even offset manually some parts
before the reflow, but got good soldering on them. The reflow profile is the
same, I even ran the profiler. The paste is OK, good date code, same
printing conditions, paste height OK. The land patterns are adequate, they
haven't changed.
First, my instinct told me it's the parts, maybe they're too old. I checked
the reels and the manufacturer's date codes (not the broker's) are between
mid 2000 until june 2001. Not that old, are they?
What could it be? The board? What and how to check, since the pads are very
well wet? The parts? Anything else?
Thanks for any input,
Ioan
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