Hi Jack -
Very capable CM's specializing in prototypes can in som case remove the BGA,
lay down tracks between the pads and put the BGA back on again. I have had
that kind of repair done once, though only with a single track. It may be a
way of connecting one or more GND islands that are now isolated. It can be
tried on a single board to see if it works. Even if does manage to bring the
board alive, the end user must evaluate of this an acceptable strap w.r.t.
reliability, performance etc.  And it will be very expensive.

An almost equally expensive and questionable alternative is to strap (with
tracks) between vias on the back side of the BGA. 

Last suggestion from me: Make the missing connections on a small PCB and
solder it (like a BGA) to the vias on the backside of the board. I know that
approach would violate both design rules and good sense, but if the
situation is desperate enough ...
 
If none of these options are practical, I think your friend is hosed. He
needs to make connections in copper somehow, and I think the only way to
really do that right, is to have new boards manufactured. They can hopefully
salvage the most expensive components and reuse them, though that is not
cheap either. 


________________________________________________
Haldor Husby, Senior Development Engineer
Data Respons Norge AS
Kongsberg Næringspark
P.O. Box 1022
N-3601 Kongsberg, Norway

Tel: +47 32 29 94 00 	Fax: +47 32 29 94 40
Dir: +47 32 29 94 18 	Mob: +47 48 04 83 68
[log in to unmask] 




On Sat, 6 Jan 2007 10:54:33 -0600, Jack Olson <[log in to unmask]> wrote:

>A friend of mine (not on this list) asked me what I would do
>about something, and I didn't know (can you imagine that?)
>
>He is experiencing horrible problems with a product that
>should have worked as designed, only to discover that the
>CAM guy in China went crazy with editing! It took WEEKS
>to discover what he had done.
>The original design was primarily 5/5mil traces/clearances
>and this guy increased the plan clearances under BGAs to
>10 for some reason, claiming "More Manufacturable". He
>also did all kinds of weird pad shaving and stuff which is
>mysterious but probably irrelevent. The poblem was that
>under the BGAs the added clearance took away return path
>for signals and I think even isoalted portions of ground from
>each other, and now the board won't even boot up!
>
>Now, I know many of you are gonna say you don't let vendors
>edit data, and even add notes to the drawing to prevent it.
>
>I'm not one of those people. We use several different vendors
>and if we want 5 mil traces and one vendor knows that their
>process consistently over-etches traces and they want to
>beef them up to 5.5 knowing that the end result will be 5,
>FINE!
>I am very happy when a vendor knows what to do to
>give me what I want. I actually DEPEND on them to edit
>whatever they need to give me my 50 ohm impedance, rather
>than forcing me to specify seperate sets of detailed con-
>structions to suit each of our appoved vendors. Since our
>products last 20 years or more, I don't even know WHO will
>be building them in the year 2020, so I DEPEND on them
>to do what is necessary to make the reliable product.
>
>That said, where do you draw the line between edits to give
>the desired results, and some "wanna be a designer" CAM
>guy making all kinds of "improvements"?
>
>What should I tell my friend to do about these very expensive
>boards that don't work?
>
>Jack
>
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