John & Happy,
   Sorry I can't really offer any help, however I think the repair bill
should be sent to the EU. Along with all the bills spent to conform,
etc. Perhaps they can add and keep track of that part, since data
doesn't seem to be something they're interested in?

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of John Burke
Sent: Monday, July 31, 2006 11:49 AM
To: [log in to unmask]
Subject: Re: [TN] SAC-BGAs on ENIG Using SnPb solder paste

Sounds like a combination of issues here, and honestly without a whole
bunch
of photographs and samples I am not sure anyone will work this out by
email.

I will attempt though to highlight a couple of the more interesting
points
you have highlighted.

1       Some pads come off the board - no problem with the soldering
there!!

2       Some solder joints just break ( no problem there either question
is
how much force used and where did the joints break)

3       Some pads are still gold - This is the one that is giving me
indigestion

It looks on the face of it that there may (possibly) be some question on
the
reflow profile.

Without seeing it, it is difficult to form an opinion but are there any
specific patterns to the "still gold" pads, for instance are they all in
the
middle of the BGA field?

Also are the ones that "the pads came off" along the mid - edges of the
BGA?, and the ones that broke situated at the BGA corners?

Kind regards,

John Burke

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Happy Holden
Sent: Monday, July 31, 2006 11:19 AM
To: [log in to unmask]
Subject: [TN] SAC-BGAs on ENIG Using SnPb solder paste

Greetings Assembly Experts,
This is the first time I have asked a question of this robust group of
technologists, but I am way beyond my knowledge of what can happen.

We have many thousands of ENIG multilayers (8 and 10 layer-0.062") that
an
assembler has returned as "Contaminated or Defective BGA pads".  These
boards are smaller (3.0" x 4.25") but they have 3 to 5 fine-pitch BGAs
(0.8mm pitch with 0.3 mm lands) on the Primary side and some have an
additional FP BGA on the Secondary side.
The problem is that after reflow, if the BGAs are pulled, they come
right
off the board.  Some BGA pads are still gold, some pads come off from
the
laminate, some solder joints just break.  They returned the boards
because
they said that the boards exhibited "non-wetting and de-wetting".
We have finally collected all the facts that we can about the assembly
process, and this is where I don't know what to expect, since the
assembly
process seems to be a "Hybrid-RoHS Backward Compatible" assembly.  Here
is
what we know about the assembly process:

1. Components & FP BGAs - SAC Balls with other components fused tin, Imm
Palladium, Ni/Au and Pb-Free solder
2. ENIG PCB Finish (lab, SEM and EDX indicate no 'brittle fracture" of
the
Ni, no C, O, or Br on the Au, a smooth crystalline surface, no unusually
high or low Phosphorous)
3. Assembler had reworked the bare boards by cutting traces and
scratched
off the soldermask to make additional ground connections on the surface
before assembly
4. A tin-lead solder paste was used (R253 from Kester)
5. A higher temperature IR reflow profile was used, 3:30' to heat to
217C,
Peak: 230C, 45 sec above 217C, 120 sec. to cool down from 217C to 98C.
6. The assembly facility is on the West Coast of Mexico near the ocean.
7. The change to ENIG was sudden, same P/Ns were in the facility as
HASL.
8. Some RoHS parts have come in mislabelled, when they were really
Sn-Pb.

They also reported this soldering characteristic when some P/Ns were
soldered with a SAC305 solder paste (Alpha Metals-OM338) and a LF IR
Reflow: 3:00' to heat to 217C, Peak: 255C, 50 sec above 217C, 65 sec to
cool down from 217C to 98C.

What do you experts out there think about this situation?


Happy Holden

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