Understand you are not happy, despite your forename.
Agree with other guys, not easy to help via email only. However, I just
wonder if your subcontractor is giving you all facts. I suspect (may be
wrong, of course) that they had a primary problem with the wetting, which is
not so unusual. What to do then? Run the boards a second time, maybe in
combination with increased temperature to get better activation and wetting.
The result may be better wetting, but also defective Cu-epoxy joints and
unexpected IMCs, as was mentioned by other Technetters. I have learnt after
many years in the game, not to rely too much on information given by
subcontractors. Not that people mislead on purpose, but rather lack of
disciplin and care. As your situation is also a economical disaster, I would
doublecheck too see if there is some hidden facts before spending days and
nights with sample examinations.
Ingemar Hernefjord
Ericsson Microwave Systems
----- Original Message -----
From: "Happy Holden" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Monday, July 31, 2006 8:18 PM
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
>
> ---------------------------------------------------
> Technet Mail List provided as a service by IPC using LISTSERV 1.8e
> To unsubscribe, send a message to [log in to unmask] with following text in
> the BODY (NOT the subject field): SIGNOFF Technet
> To temporarily halt or (re-start) delivery of Technet send e-mail to
> [log in to unmask]: SET Technet NOMAIL or (MAIL)
> To receive ONE mailing per day of all the posts: send e-mail to
> [log in to unmask]: SET Technet Digest
> Search the archives of previous posts at: http://listserv.ipc.org/archives
> Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16
> for additional information, or contact Keach Sasamori at [log in to unmask] or
> 847-615-7100 ext.2815
> -----------------------------------------------------
> Asian Pacific Materials
---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 1.8e
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL)
To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
Search the archives of previous posts at: http://listserv.ipc.org/archives
Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815
-----------------------------------------------------
|
