Hi Peter,
Try to get a small piece of the thinnest fluxed solder wire you can
get, and use a thin tweezer or something else to place this piece of
solder as close to the open joint as possible. Then use a hot air gun to
reflow locally.
No approvals, no procedures and a big chance it won't work, but I was
lucky enough to save one or two prototypes using this method.
Daan Terstegge
Thales Communications
Unclassified mail
Personal Website: http://www.smtinfo.net
>>> [log in to unmask] 02/05/03 05:57am >>>
Dear All,
Thanks to everyone who responded to my last plea for information on
adhesive for teflon. Tetra-etch is the obvious etchant - I must be
getting
old not to have thought of it, though the bigger problem is actually
to
separate the still-bonded teflon from its flange in order to clean it
up,
re-etch it and bond it back again. Timing is everything though. and I
was
shown a memorandum yesterday, announcing that the OEM of the component
is
changing the teflon component material to GRP. So maybe we'll buy GRP
replacement bits and bond them on instead of trying to recover the
teflon
mouldings.
OK. Today's topic will either bring out amused smiles or cries of
outrage.
One of our suppliers designs boards for us (functional, schematic
diagram
stuff only - though they do basic testing of built boards, once
someone
else has specified the layout design rules the PCB, done all the
manufacturing stuff, etc.). One board is now failing, and they have
diagnosed that one ball on the outside row of a BGA is no longer
making
contact with the board. Although only a prototype board, it is a Class
3
type that could ultimately fly.
For various reasons, the supplier is very reluctant to reflow the
entire
BGA or to replace it in order to solve the contact problem (the BGA is
very
expensive). Instead, they came up with the idea of manually soldering
the
defective contact. [ I can now sense incredulous reactions from
here!].
They discussed their proposal with a local assembly house, who gave
them
the impression that the idea is possible to carry out (with suitable
but
unspecified equipment). Since then they have been insisting that they
be
allowed to repair the faulty BGA with this method. I used my power of
veto,
strongly..
I thought it might be a subject to put before learned council here,
though,
in case anyone else has been thinking of trying this sort of repair.
Has
anyone out there come across any [successful] procedure for - or
actually
tried - manually 'touching up' a single BGA ball? If you have, is the
procedure approved for anything, what is it approved for (board class,
specific incidents/circumstances, etc), and where can I get a copy of
it?
The BGA in question is a large Xilinx XCV600E FPGA (Field Programmable
Grid
Array, not a pin grid array), 40mm (1.6 inches) square with 5 rows of
balls
and an open centre portion. The entire top body surface is covered with
a
metal plate. Soldered standoff height is about 20 mils.
Have fun.
Peter
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