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December 2001

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Subject:
From:
My Nguyen <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Thu, 13 Dec 2001 10:11:09 -0800
Content-Type:
text/plain
Parts/Attachments:
text/plain (118 lines)
Hello,
Since I cannot get a very clear picture from your
email, I can only provide some hints for your
reference:

1. Verify aspect ratio>=1.5 and area ratio>=0.66: I am
not sure what does that mean?
2. Try type 4 solder paste: We currently use type 3
No-Clean solder from Kester.
3. Make sure PCB have no wicking problem.  The Rambus
PCB are bought from the shell on the market.
4. PCB solder pads have acceptable solderability: They
are gold plated and contaminated free.
5. If PCB is ENIG finish, make sure there is no "Black
Pad" defect: I need more education about the term
"ENIG" and "Black Pad"
6. PCB bow and twist in with specs (>.7 preferred).
They are within spec.
7. If CSP solder ball is 63Sn/37Pb, than I think
solder paste is not a key point for open solder joint
: It is 63Sn/37Pb, no clean solder paste from Kester.
8. Verify your reflow profile is within the specs
(according to solder paste vendor) They are in spec.
9. Cross-section to verify the IMC layer is in
standard thickness: We did cross section them and
found out the in-sufficient solder join or even NO
solder join at all on a few pads.
10. The pads on PCB should be a copper defined instead
of soldermask defined to prevent potential crack: They
are gold-plated.
11. Pay attention to your process to verify NO
excessive tension to your board (e.g. depanel, handle
etc.): We use DEK 265 series to (Horizon and
Infinitive models) print the solder.  Printing at
15-20 mm/s.
12. Try to find where the open have (before wave or
after). If via hole under CSP haven't been plugged,
wave solder sometimes can cause open by remelt the
solder joint: The in-efficient solder firstly found
after screen-printing.
13. Ask your component/PCB vendor to do the failure
analysis, they maybe have much more experience than
you: We are trying.

Hope this helpful. It is helpful.  However, we still
need more information.  Until this moment, we still
think solder paste, stencil apperture, print speed and
pressure, and the stencil thickness could be the
cause.  We are not sure yet.

Best regards,

> -----Original Message-----
> From: My Nguyen [ mailto:[log in to unmask]
> <mailto:[log in to unmask]> ]
> Sent: Wednesday, December 12, 2001 2:43
> To: [log in to unmask]
> Subject: [TN] Inefficient solder on Toshiba micro
> BGA
>
>
> Hello all,
>
> Problem description:
>
> Been happening on Rambus - part number tc59rm81xmb.
> Ball diametter: 0.5 mm; ball pitch: 0.8 mm, ball
> height: 0.4 mm. Pad size: 0.3 mm (11.5 mils)
> 5-10% of the time (we run huge amount of them)
> failure modules came from opening soder join or no
solder join
> at all.  As we inspect the screen printing process
> (we
> use 5 mils stencil - Dek screenprinting, cleaning
> rate: 2 per print, cleaning cycle Wet-Vacuum/Dry),
> we
> found un-event solder deposit.  Some pad even has
> very
> little solder or no solder at all.
>
> Stencil is electro-polish;  Diamond shape aperture,
> 13.5 mils open used trapezoid shape.
>
> We afraid that if we open the apperture bigger, then
> we may have bridging or solder ball.  If we reduce
> the
> stencil to 4 mils to reduce the blockage or
> resistance, then we may have in-efficient solder or
> many other problem relating thin stencil (damage,
> short-life, etc)
>
> What would be your solution?
>
> Thanks,
>
> Stacy
>
>

> ATTACHMENT part 2 image/gif name=std_logo.gif


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