Steve,
The first thing that comes to my mind is -- The parts may be "floating" at reflow.
Did the finish on the component change?
Is it possible it is oxidized a bit?
Did you change pastes or did something change in the flux composition (I'm sure the paste mfr has perfect lot to lot repeatability!)
Did the profile change? Is it hotter? Is there less board mass?
We've seen this occur on some caps that were "old". The date code ranged from 2-4 years. The oxidation was too difficult to see by eye, but, when we placed "new" caps in place, the problem went away. We ran a "controlled" experiment using 1/2 old and 1/2 new caps and only had a problem on the old caps.
-Carrie
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Steve Gregory
Sent: Tuesday, February 24, 2004 5:33 PM
To: [log in to unmask]
Subject: [TN] Skewed Components
Hi All!
Got a little issue here that I need to dig in deeper to, but I thought I'd
post a picture on my web page and ask for your valued opinions. Was building a
board today that we've built before, never had any problems with it. But today
certain 0805 resistors started skewing on their pads during reflow, and I
don't know why. Take a look at:
http://www.stevezeva.homestead.com and look at "skewed components". It's not
really a defect because they're 100% on the pads, and the wetting and fillets
are fine too. They just look funky...and this just started happening. Not so
much as a pimple on the boards before when we built them.
As I said, there's more that I have to dig into, but thought maybe someone
might have had this happen before, and can go; "A-ha Steve! you need to do
this...."
Also, I've posted a pretty awesome picture on my page. Take a look at "F-16
Exit".
A photographer just happened to be at the right place, at the right time,
with the right lense on his camera, the right F-stop, and everything in focus to
take this picture...this truly is a once in a lifetime picture.
The picture was taken from the tower at Mountain Home AFB in September last
year at the air show they have there, the Thunderbirds were demonstrating.
The aircraft was one of the two on the Thunderbird team that flies solo most
of the show, the other 4 aircraft fly in formation.
This aircraft had just done a high performance take-off straight-up, and then
did a split S into a loop, and was just about to round out the loop at the
bottom and pass show center, when the engine started spitting out turbine
blades. There was no power to stop the huge rate of decent of the aircraft, so the
pilot punched out at about 100-feet altitude, and the photographer snapped the
picture.
-Steve Gregory-
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