Thanks to everyone for the help and suggestions.
Ben
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Matthew Lamkin
Sent: Thursday, June 09, 2005 3:38 AM
To: [log in to unmask]
Subject: Re: [TN] mystery tombstone cause
What I would say, after seeing the picture is that it should be sent
through the oven left to right not up/down.
They do look to have even pulling forces on their ends as they both have
the same amount of tracks exiting them.
Also, are those caps? those pads are wayyyy too big looking to me, do
you get cracked cap problems too?
We used to have pads as big as those, when we reduced them dramatically
in width placement went a lot better, they did not move around as much,
Tombstoning reduced, no more cracking through pad design & we had more
room on the board.
Matthew Lamkin.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Taheri, Kamran
Sent: Wednesday, June 08, 2005 9:38 PM
To: [log in to unmask]
Subject: Re: [TN] mystery tombstone cause
Ben,
Have you looked inside of your oven for little green monsters
that might be doing this:)? Have you attached TCs to both sides of
these pads to verify the thermal difference? It looks like that the pad
design is reducing your placement accuracy tolerance.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Gumpert, Ben
Sent: Wednesday, June 08, 2005 1:10 PM
To: [log in to unmask]
Subject: Re: [TN] mystery tombstone cause
Bev,
Yes, the direction of the tombstones on a specific board are constant
relative to that board, and are irrespective of board orientation
through the oven.
Ben
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Bev Christian
Sent: Wednesday, June 08, 2005 8:40 AM
To: [log in to unmask]
Subject: Re: [TN] mystery tombstone cause
Ben,
When you say lift in different directions, do you mean in reference to
the board or in reference to the axis of the oven? For instance are you
saying that on a single board you can have tombstones only facing to the
"top" of the board, irrespective of how you put I through the oven?
Hmm, is that clear?
Bev
RIM
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Gumpert, Ben
Sent: June 8, 2005 8:09 AM
To: [log in to unmask]
Subject: [TN] mystery tombstone cause
Technetters,
I have several SMT board styles which give me some trouble with 0306
capacitor tombstones, and through many attempts to reduce the number of
these defects, I have found a condition that I can not seem to attribute
a cause to. I have found that across a board, all the tombstones tend to
lift in the same direction (for components in the same orientation).
I have looked at the build process, but different board styles result in
tombstones in different directions, so I believe the cause to be board
related. I have looked at solder mask registration (misregistration
occurs in various directions), power/ground plane connections by pad
(changes from location to location), and solder bumps due to HASL
(wicked pads have similar results), and nothing has led me to a root
cause.
Any ideas???
Thanks,
Ben Gumpert
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