Various component locations have different sides connected to ground or power planes. The connections to these planes are made directly by vias from the outside ends of the pads (vias are masked), so there are no traces running from the pads on either side. I have asked Stephen to post an image showing the pad configuration. This image will show a large component right next to a row of 0306 capacitors, but tombstones are in the same direction on other sides of the component, and a board run without any components except the 0306 capacitors shows the same results.
In my reflow process, I am ramping at about 1°C per second to about 165°C, slowing ramp rate (soak period) to increase another 10°C over the next minute, then ramping to peak.
Ben
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Blair K. Hogg
Sent: Wednesday, June 08, 2005 12:12 PM
To: [log in to unmask]
Subject: Re: [TN] mystery tombstone cause
Is one side of the component connected to a voltage or ground plane? It could be that the copper in the plane is taking heat away from the pad. One solution is to separate the pad from the plane by use of a small short trace.
Also, if one pad has a large trace connecting to it, and one has a small trace, the large trace can also take heat away. One way to solve this is to neck down the trace right next to the pad.
Blair
>>> [log in to unmask] 06/08/05 08:09AM >>>
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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