hello ernst.
i have the same problem as you,but after using ERSA IR500A bga rework
station.solve all
my BGA warpage problem. because it can use very low temp to rework.
kelvin
wallisch, Ernst wrote:

> Hello TechNet.
>
>         I am looking for information regarding two unsolved mysteries
> I
> have encountered:
>
> 1)  I am able to remove a PBGA388 from a 17 layer (0.125" thick) PWB,
> but cannot place a new device.  The BGA substrate seems to be warping
> and I am getting non-soldered (open) interconnects at the corners of
> the
> BGA.  The rework equipment used is an Air Vac DRS26 (hot gas -
> nitrogen).  If I reduce the temperature or time on the rework profile,
>
> to try and reduce BGA warpage, reflow is not achieved at all
> interconnects.  Has anyone come across a similar problem and found a
> solution?
>
> 2)  After assembly reflow (forced convection system), one to three
> balls
> of a particular BGA, in the same location(s) disappear!  The X-ray
> shows
> no trace of solder on the BGA land pattern of the PWB or BGA
> substrate.
> The surrounding balls are all present and not visibly oversized.  All
> PWB BGA land patterns are NSMD, with dog-bone configuration for vias,
> with soldermask between the land and the via.  The vias are also
> tented.
> Has anyone come across this problem?
>
> Thanks,
>
> Ernst Wallisch
> Manufacturing Engineering
> Computing Devices Canada
> (613) 596-7536
> [log in to unmask]
>
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