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January 2002

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Subject:
From:
Jeff Ferry <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Thu, 31 Jan 2002 13:59:32 -0600
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Thanks for the replies (see below) to my original posting (see below).

Seems like several of you are having good luck using flux only vs. solder
paste during BGA rework. The thing I wonder about is the reliability of
reworked BGA solder joints. I thought that proper BGA solder joint volume
was based on the original BGA ball combined with the solder added during
the solder paste screen printing process. Thus, what effect does solder
volume and solder joint height have on the reliability of a BGA solder
joints for plastic BGA components?

Thanks again,

Jeff Ferry
CEO
Circuit Technology Center, Inc.


Some Replies to prior posting included:

---------------------------

My "rule of thumb" is plastic BGA's with eutectic balls - I use stick flux
only.  For ceramic BGA's with non-eutectic or "hard" balls, I must use a
microscreen and apply solder paste.
Mark

---------------------------

For our eutectic PBGA's, we only flux (no clean).  Have only done about 50
or so over the past year with very good (97% yield) results.
Have not seen any studies or papers.  Just worked closely with our CM to
create the profile for each type of BGA.  We use Air-Vac.
Kerry

---------------------------

It's the only way to go. I've been designing, placing, reflowing and
reworking BGA's for nearly 8 years now. It took me five minutes to make the
discovery and, as I've said far too often, I'd use flux only on initial
production if feasible.
Regards and respect,
Earl Moon


---------------------------

We have been working and reworking BGA and Micro BGA for quite sometime.
This is a requirement in a prorotye environment. We tried using micro
stencil when we first attempt to replace the BGAs and found out that using
micro stencil was not a good method. We then tried using no-clean tacky
past fux and applied to both the BGA and the PWB substrates. This process
has been adopted in our process and has been working well for us. Here are
some great benefit of using flux paste only.
     - No micro stencil cost.
     - No cleaning is needed (No-clean flux).
     - No aligning equipment is needed, since we can place the BGA into its
footprints without worry about     smearing the solder paste, and if the
hand alignment if off ( no more than 50%), the liquid tension of the
reflowed solder balls will pull it back.
     - Save time and money. ( stencil cost, cleaning, and aligning).

If the solder balls on the BGA are made of non-eutectic, solder paste is
required.

Tuan Bui
Conexant Systems Inc.
Prototype Process Dev. Eng.

---------------------------

It is my opinion that pasting the board enhances wetting and a superior
joint.
Jason Gregory

---------------------------

On Thu, 31 Jan 2002 10:54:24 -0600, Jeff Ferry <[log in to unmask]>
wrote:

>Fellow TechNetters,
>
>We nearly always apply solder paste to the circuit board when we replace
>BGA components during rework. Yet, after speaking with a handfull of BGA
>equipment companies at APEX, seems like they all recommend using flux only
>vs. paste, unless the circuit board is used in a high rel application.
>
>What do ya'all do/recommend for BAG rework? Can you point me to any
>studies/reports on the subject?
>
>Thanks,
>
>Jeff Ferry
>CEO
>Circuit Technology Center, Inc.
>
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