Status OpenPhoneux / GTA04
Dr. H. Nikolaus Schaller
hns at goldelico.com
Thu Jul 5 09:31:51 CEST 2012
Am 05.07.2012 um 00:13 schrieb Boudewijn:
> On Tuesday 03 July 2012 11:15:16 Dr. H. Nikolaus Schaller wrote:
> > The reason appears that the DM3730CBP gets some warp during
> > the soldering process squeezing the balls in the middle of the BGA
> > grid so that they may touch a neighbor and make a short circuit.
> > And on the corners the balls lift off and this may result in interruptions.
> Can that also be the reason for the AUX button getting stuck? Does the warping of the CPU-PCB also warp the main PCB, or is there no reason to suspect so?
No, the AUX button is a different issue. It is an accumulation of tolerances of the button position and how the whole PCB fits into the plasic case.
And in the meantime I have some doubt that there is really warpage of the CPU. It may be an optical illusion because the image is taken from the top just showing enlarged diameter.
We have been offered our own X-Ray session next week and will try to make an image in 45 or less degrees, i.e. to find out if the balls have the expected volume but are squeezed by warpage and therefore increase the visible diameter or if there is simply too much solder paste involved and therefore the diameter increases without any warpage of the chip (the reason could also be warpage of the stencil).
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