>From the limited information provided, it seems to me that the fact that
this pwba is long AND narrow, perhaps the failure could be due to poor
handling after assembly. If the board is in any way deformed or bent in the
long axis, I would think that you could crack the solder joints on devices.
The poor aspect ratio of length to width would facilitate long axis flexural
mechanical advantage and give the appearance of the boards being 'too
flexible'. 

Dave Rooke
Circo Craft - Pointe Claire

_________________________

>Technet:
>
>	I have a board about 13.5" x 4.5" (PC plug in card), .062" thick,
>8 layer, FR4, 1 oz copper, 2 power planes, with 16  100 pin  TQFP
>packages (0.5mm lead pitch) spread across the board (2 rows of 8), as
>well as many other PLCC and SOIC devices.
>
>	The problem we are having with these prototypes is that some pins
>on the TQFP's pop up durring handling.  The boards seem to be too
>flexable, which probably causes the pins to break off the pads.  Is there
>a way to make the board more rigid besides using board stiffiners?  In
>other words can anything be done as far as changing the board stack up,
>or will using thicker copper help this situation?  Or are there different
>types of FR4 available?  Or is there something I am not looking at?
>
>	Also, what would be a good pad size for the 100 pin TQFP chip? 
>Currently I am using 1.2mm x .25mm, but I think the IPC recommends 1.6mm
>x .35mm, but it doesn't look like it would allow any soldermask between
>pads.  Or does anybody even bother with soldermask between pads at .5mm
>pitch?  What is the middle ground?
>
>Thanks in advance!
>
>Charles Wills
>[log in to unmask]
>
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