Hi Peter! It is possible to use a soldering iron, using very little to no
additional solder, to reflow the outer row and/or corner solder balls on a
BGA (I highly recommend you don't drink a Diet Coke or Mt. Dew prior to
attempting this action - bad things can happen :) . A skilled operator
using a very fine solder iron tip can accomplish the task consistently.
However, the outer most solder balls on a BGA also see the largest
degradation under thermal cycle conditions so not having that "reflow
solder" geometry/wetting consistency may lead to more reliability problems.
I would recommend against using a manual rework operation except on
prototype assemblies that are not test data critical. Good Luck.
Dave Hillman
Rockwell Collins
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<[log in to unmask]> Subject: [TN] Single BGA ball rework
02/04/2003 10:57
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peter.duncan
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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