Interesting..never seen that before.
Back to basics..
Solder balls are usually from heating to rapidly in the preheat (rapid
solvent evaporation), OR too high temp or too long in soak (allows
re-oxidation of pads), OR too much solder volume.
Tombstoning is usually from unequal wetting on the two terminals, caused by
wrong pad design, unequal solder paste volumes, or thermal variance in the
PCB design between the two pads. Usually the solution is to increase the
soak time.
So to reduce the solder balls decrease the soak time, to reduce the
tombstoning, increase the soak time. Maybe a perfect combo in there
someplace. But how is it that the solder balls are on the bottom of the
oven yet there are no components mixed in? Do you have solder balls on the
PCB too? Do you clean Side 1 before reflowing Side 2?
Kevin Glidden
Manufacturing Engineer
Astronics Luminescent Systems Inc.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory
Sent: Tuesday, October 31, 2006 9:57 AM
To: [log in to unmask]
Subject: [TN] Bizzare Phenomena...
Mornin' All!
This morning I have seen something that I have never, ever have seen before.
It's been a little slow the past week, so we decided to do our maintenance
on our reflow ovens. After we opened the oven up, we found many, many
solderballs laying on the bottom of the oven right around zone 7 - 8, right
at the beginning of the spike zone. Check-out:
http://stevezeva.homestead.com/files/Oven_Solderballs.jpg
http://stevezeva.homestead.com/files/Oven_Solderballs_2.jpg
http://stevezeva.homestead.com/files/Oven_Solderballs_3.jpg
http://stevezeva.homestead.com/files/Oven_Solderballs_4.jpg
We've been having tombstoning problems when we've run the two lead-free jobs
that we have here. I've been working with the paste vendor sending my
profiles and plots, but I haven't been able to solve the problem. The
solderballs in the oven are lead-free solderballs.
We are using a Heller 1809, and my profile set-points are:
120 140 160 180 190 200 230 240 250
120 140 160 180 190 200 230 240 250
Belt speed 26 in per min
The paste is a SAC 305 with a water washable no-clean flux. I think my
profile is pretty reasonable, and the last board we ran is pretty standard,
.062" thick, with no bizzare copper planes. The board finish with both jobs
has been ENIG. The last job I ran we were tombstoning 0805's, the one before
that we were tombstoning 0402's. With both jobs we've had major tombstoning
problems. I've slowed the beltspeed down, sped it up, ramped up slower,
ramped up faster, changed this, changed that, but still haven't resolved my
tombstoning.
Of course, I'm the only one that's having this problem according to my paste
vendor...
I wouldn't have imagined that I would see the solderballs in the oven like
we have...
Have any of you ever seen something like this before?
-Steve Gregory-
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