Phil,
I would look at 4 things:
* design of landpattern: as per Werner, the pad shall be not wider than the component; the longer the joint, the more stress on the part
* position of the component: if on bottom side and sees wave soldering, this is your trouble. Never wave these babies. In case the designer does not want to move them, you can manually solder them after, using hot air and not the iron
* position of the component again: should be at at least 0.200" from the edge to minimize stress during depanelizing or to avoid having them bumped in the storing magazines
* touch-up: never with the iron, always with hot air.
Now, the above are general considerations. On a 2x2 you should be very particular with depanelizing. If routed panel, do not place mouse bites where the caps are. If V-groove, you can rout inside the breakaways at the level of these parts. And, of course, use a depanelizer, not the pliers. Also, I would make sure to spec a 16 mil web thickness for the scoring, not more.
Good luck,
Ioan
> -----Original Message-----
> From: TechNet [SMTP:[log in to unmask]] On Behalf Of Phil Nutting
> Sent: Tuesday, January 31, 2006 11:32 AM
> To: [log in to unmask]
> Subject: [TN] Large SMT physical failure prevention
>
> Good morning,
>
> We have some designs that are calling for large, 1825 and 2225
> components. We have seen some mechanical failures where the parts have
> cracked. If we need to use these monster components, how do we ensure
> we reduce or eliminate the mechanical failures.
>
> Our failures were seen on a 16 inch by 17 inch 0.062 thick board. On
> these we have changed our handling methods.
>
> On smaller 2 inch by 2 inch boards is this a don't care? I know that
> rapid temperature ramp up or down in the reflow process could be a
> killer. Something to work out with our CM.
>
> Phil
>
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