Hi, Ted,
Underfilling is historical and because we've conducted all our
qualification tests on this product using it. It stems from the days when
our first BGA-mounted cards were designed and built by a company in the
States. The first time we put them near any (very mild) vibration, they
failed miserably. I was new into this company then, when I was asked to
take a look at why these boards failed, and it became obvious to me that
the workmanship standard was terrible.
I was also new to BGA's then (boy, have I learned a lot about them since!).
I had a couple more cards assembled here in Singapore, working closely with
the assembly house to ensure that the processes were as good as we could
make them. I also came across underfilling as a means of supporting BGA
ball contacts, especially for use in harsh environments. Whatever, I threw
that process into the mix as well, as a sort of insurance policy. It
pleased the bosses to think they had a good, visible solution to the
problem, and certanly none of this model of board have failed since.
Another reason I chose underfilling was to ensure that there could be no
air/moisture/...contaminants (he says with bated breath) trapped
underneath by the later conformal coating.
Maybe next time we design or build a board with BGA's, we'll do away with
the underflling process. I don't like it for many reasons - It's a manual
process for us, potentially messy, certainly time consuming and involves
more elevated temperature exposure for the board while we fill and then
cure.
Peter
Ted Kong <[log in to unmask]> 06/02/2003 06:15 AM
To: "TechNet E-Mail Forum." <[log in to unmask]>, DUNCAN Peter/Asst Prin Engr/ST
Aero/ST Group@ST Domain
cc:
Subject: Re: [TN] Single BGA ball rework
Hi Peter,
What make this BGA so unique that you have to use
underfill? Also interest on what you have decided to
do.
Ted
--- [log in to unmask] wrote:
> Dear All,
>
> Thanks to everyone who responded to my last plea for
> information on
> adhesive for teflon. Tetra-etch is the obvious
> etchant - I must be getting
> old not to have thought of it, though the bigger
> problem is actually to
> separate the still-bonded teflon from its flange in
> order to clean it up,
> re-etch it and bond it back again. Timing is
> everything though. and I was
> shown a memorandum yesterday, announcing that the
> OEM of the component is
> changing the teflon component material to GRP. So
> maybe we'll buy GRP
> replacement bits and bond them on instead of trying
> to recover the teflon
> mouldings.
>
> OK. Today's topic will either bring out amused
> smiles or cries of outrage.
> One of our suppliers designs boards for us
> (functional, schematic diagram
> stuff only - though they do basic testing of built
> boards, once someone
> else has specified the layout design rules the PCB,
> done all the
> manufacturing stuff, etc.). One board is now
> failing, and they have
> diagnosed that one ball on the outside row of a BGA
> is no longer making
> contact with the board. Although only a prototype
> board, it is a Class 3
> type that could ultimately fly.
>
> For various reasons, the supplier is very reluctant
> to reflow the entire
> BGA or to replace it in order to solve the contact
> problem (the BGA is very
> expensive). Instead, they came up with the idea of
> manually soldering the
> defective contact. [ I can now sense incredulous
> reactions from here!].
> They discussed their proposal with a local assembly
> house, who gave them
> the impression that the idea is possible to carry
> out (with suitable but
> unspecified equipment). Since then they have been
> insisting that they be
> allowed to repair the faulty BGA with this method. I
> used my power of veto,
> strongly..
>
> I thought it might be a subject to put before
> learned council here, though,
> in case anyone else has been thinking of trying this
> sort of repair. Has
> anyone out there come across any [successful]
> procedure for - or actually
> tried - manually 'touching up' a single BGA ball? If
> you have, is the
> procedure approved for anything, what is it approved
> for (board class,
> specific incidents/circumstances, etc), and where
> can I get a copy of it?
>
> The BGA in question is a large Xilinx XCV600E FPGA
> (Field Programmable Grid
> Array, not a pin grid array), 40mm (1.6 inches)
> square with 5 rows of balls
> and an open centre portion. The entire top body
> surface is covered with a
> metal plate. Soldered standoff height is about 20
> mils.
>
> Have fun.
>
> Peter
>
> [This e-mail is confidential and may also be
> privileged. If you are not the
> intended recipient, please delete it and notify us
> immediately; you should
> not copy or use it for any purpose, nor disclose its
> contents to any other
> person. Thank you.]
>
> ---------------------------------------------------
> Technet Mail List provided as a free 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/html/forum.htm for additional
> information, or contact Keach Sasamori at
> [log in to unmask] or 847-509-9700 ext.5315
>
-----------------------------------------------------
__________________________________________________
Do you Yahoo!?
Yahoo! Mail Plus - Powerful. Affordable. Sign up now.
http://mailplus.yahoo.com
[This e-mail is confidential and may also be privileged. If you are not the
intended recipient, please delete it and notify us immediately; you should
not copy or use it for any purpose, nor disclose its contents to any other
person. Thank you.]
---------------------------------------------------
Technet Mail List provided as a free 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/html/forum.htm for additional
information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315
-----------------------------------------------------
|
